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The incidence of recurrent t(6;9) translocation of the MYB proto‑oncogene to NFIB (the gene that encodes nuclear factor 1 B‑type) in adenoid cystic carcinoma (ACC) tumour tissues is high. However, MYB [the gene that encodes transcriptional activator Myb (MYB)] overexpression is more common, indicating that MYB serves a key role in ACC. The current study aimed to investigate the role of MYB in salivary (S)ACC growth and metastasis. A total of 50 fresh‑frozen SACC tissues and 41 fresh‑frozen normal submandibular gland (SMG) tissues were collected to measure MYB mRNA expression, and to analyse the associations between MYB and epithelial‑mesenchymal transition (EMT) markers. Compared with normal SMG tissue, SACC tissues demonstrated significantly increased MYB expression, with a high expression rate of 90%. Interestingly, MYB tended to be negatively correlated with CDH1 [the gene that encodes cadherin‑1 (E‑cadherin)] and positively correlated with VIM (the gene that encodes vimentin), suggesting that MYB is associated with SACC metastasis. To explore the role of MYB in SACC, the authors stably overexpressed and knocked down MYB in SACC cells. The authors of the current study demonstrated that MYB overexpression promoted SACC cell proliferation, migration and invasion, whereas its knockdown inhibited these activities. Additionally, when MYB was overexpressed, CDH1 expression was downregulated, and CDH2 (the gene that encodes cadherin‑2), VIM and ACTA2 (the gene that encodes actin, aortic smooth muscle) expression was upregulated. Then, the effect of MYB on lung tumour metastasis was investigated in vivo in non‑obese diabetic/severe combined immunodeficiency mice. MYB overexpressing and control cells were injected into the mice through the tail vein. The results revealed that MYB promoted SACC lung metastasis. Collectively, these results demonstrated that MYB is aberrantly overexpressed in SACC tissues, and promotes SACC cell proliferation and metastasis, indicating that MYB may be a novel therapeutic target for SACC.

Surgical and medical treatments usually fail to completely remove the primary lesions of salivary adenoid cystic carcinoma (SACC), resulting in local recurrence due to its strong infiltration, hematogenous metastasis and other unique biological behaviors. Targeted gene therapy, including hypoxia‑inducible factor‑1α (HIF‑1α) therapy, sheds new light on the treatment of salivary gland tumors. However, the mechanisms underlying the downregulation of HIF‑1α expression in SACC have not been well studied. The present study aimed to determine the effects of HIF‑1α downregulation on the proliferation, invasion, apoptosis, cell cycle and angiogenesis of hypoxic SACC‑83 cells, and to elucidate the molecular mechanisms underlying these effects. Western blot analysis was used to evaluate the protein expression levels of HIF‑1α and matrix metalloproteinase‑2 (MMP‑2). Angiogenesis and the protein expression of vascular endothelial growth factor (VEGF) were detected by tube formation assay of human umbilical vein endothelial cells and ELISA, respectively. It was revealed that short hairpin RNA was considerably downregulated following overexpression of HIF‑1α. In addition, downregulation of HIF‑1α inhibited the expression of VEGF and MMP‑2, as well as the proliferation, invasion, migration, and tube formation of hypoxic SACC‑83 cells, while inducing apoptosis in these cells. These results suggest that the downregulation of HIF‑1α may be a novel targeted therapy for SACC.

1,25-Dihydroxyvitamin D3 (1,25D3) is the active form of vitamin D with antineoplastic effects. The glutathione peroxidase-1 (GPX1) gene is associated with tumour progression. The present study aimed to explore the role of GPX1 in 1,25D3-mediated progression of salivary adenoid cystic carcinoma (SACC). Downregulating GPX1 expression inhibited SACC cell proliferation, chemoresistance, motility, and uPA secretion, but promoted apoptosis via the NF-κB pathway. Pre-processing 1,25D3 inhibited expression of NF-κB/GPX1/uPA, which subsequently suppressed cell motility and cisplatin-resistance in ACC-2 cells. In conclusion, 1,25D3 works as a modifier of NF-κB/GPX1/uPA expression, inhibiting cisplatin-resistance and cell invasive ability of SACC cells. The present study comprehensively elucidated the potential mechanism underlying the effects of vitamin D on chemoresistance and invasive potential in SACC.

Perineural invasion (PNI) is a striking biological behavior observed in salivary adenoid cystic carcinoma (SACC). The present study was designed to establish a co-culture model of SACC cells with Schwann cells (SCs), and then study epithelial-mesenchymal transition (EMT) and the Schwann-like differentiation of SACC cells to investigate the likely molecular mechanism of PNI. The co-culture models of SCs with tumor cells (SACC-83, SACC-LM and MEC-1) were established using a Transwell system. An elevated concentration of brain-derived neurotrophic factor (BDNF) was detected by ELISA assay in the co-cultured medium of the SACC-83 group and SACC-LM group rather than the MEC-1 group. The EMT process and Schwann-like differentiation in SACC-83 cells were analyzed by RT-PCR, western blotting, immunofluorescence, photography, and migration and perineural invasion assays. The SACC-83 cells under the co-culture condition with SCs changed to a mesenchymal morphology and had higher migration and invasion capabilities compared with the solely cultured SACC-83 cells, accompanied by the downregulation of E-cadherin and upregulation of N-cadherin and vimentin. The co-cultured SACC-83 cells also developed Schwann-like differentiation with increased expression of SC markers, S100A4 and GFAP. However, inhibition of tropomyosin-related kinase B (TrkB) by K252a markedly blocked these effects. Additionally, the expression and correlation of TrkB, E-cadherin and S100A4 were analyzed by immunohistochemistry in 187 primary SACC cases. The levels of TrkB and S100A4 expression were both positively associated with PNI in the SACC cases, while E-cadherin expression was negatively associated with PNI. Elevated expression of TrkB was significantly correlated with the downregulated expression of E-cadherin and the upregulated expression of S100A4 in the SACC cases. Our results suggest that SCs play a pivotal role in the PNI process by inducing the EMT process and the Schwann-like differentiation of SACC cells via the BDNF/TrkB axis. Interruption of the interreaction between SACC cells and SCs by targeting the BDNF/TrkB axis may be a potential strategy for anti-PNI therapy in SACC.

It is known that the TGF-β superfamily receptors act as master regulators of cancer progression. However, alteration and role of type III TGF-β receptor (TβRIII, or betaglycan) as the most abundant of the TGF-β receptor has not been explored in salivary gland adenoid cystic carcinoma (ACC). Here, we reported that tumor biopsies and matched normal human salivary glands from patients with ACC were examined for the expression of TβRIII. The expression of TβRIII protein is significantly decreased in ACC patients based on immunohistochemistry and western blot analysis. In vitro, a transient overexpression of TβRIII markedly induced apoptosis and cell cycle arrest in the G2/M phase, thereby inhibited cell viability and migration of ACC-M cells. Co-immunoprecipitation revealed that TβRIII, scaffolding protein-arrestin2 (β-arrestin2) and IκBα formed a complex. Transient overexpression of TβRIII decreased p-p65 expression and increased IκBα expression, which was abolished by knockdown of β-arrestin2. The present study defines TβRIII as a biomarker exerting antitumor action on ACC progression.Gene therapy of TβRIII may be a powerful new approach for ACC disease.

Inhibition of histone deacetylases (HDACs) has emerged as a new target for cancer therapies. The present study examined the antitumor effect and molecular mechanism of the HDAC inhibitor apicidin in YD-15 human salivary mucoepidermoid carcinoma (MEC) cells. The cells were treated with apicidin and cell death was quantified using an MTT assay. Apoptosis and autophagy were measured using flow cytometry, immunoblot analysis and cell staining. Regulation of the signaling pathways was monitored using immunoblot analysis and co-treatment with specific inhibitors. Insulin-like growth factor 1 receptor (IGF-1R) was knocked down using specific siRNA. Apicidin significantly inhibited the proliferation of MEC cells. Apicidin also induced apoptosis through the inactivation of extracellular signal-regulated kinase (ERK) and AKT/mTOR signaling and activation of c-Jun NH2-terminal kinase (JNK), whereas apicidin promoted autophagy through inactivation of the AKT/mTOR signaling. These effects may be mediated by the inhibition of IGF-1R, an upstream regulator of MAPK and AKT/mTOR pathways. These results suggested that apicidin is an attractive chemotherapeutic agent against salivary MEC and may be a good candidate for targeting IGF-1R for cancer therapies.

Salivary gland cancer (SGC) has a comparatively poor prognosis and is prone to frequent recurrence and metastases. Therefore, the development of more effective chemotherapy against SGC is desirable. The aim of the present study was to investigate the antitumour effects of valproic acid (VPA) against SGC in vitro and in vivo. Two human SGC cell lines (HSY and HSG cells) were used in the present study. The effects of VPA on the proliferation of SGC cells in vitro were assessed by MTT assay. Cancer cells treated with VPA were subjected to cell cycle analysis by flow cytometry. In addition, the expression levels of p21 and p27 were examined by real-time RT-PCR to identify the mechanisms of the antitumour effect of VPA on SGC. The effects of VPA on cancer growth in vivo were evaluated in a xenograft model. VPA inhibited the proliferation of SGC cells in a dose-dependent manner in vitro. Degenerated cancer cells were observed at high concentrations of VPA. In the cell cycle analysis, VPA induced cell-growth inhibition and G1 arrest of cell cycle progression in both cancer cell lines in a time- and dose-dependent manner. VPA markedly upregulated the mRNA expression levels of both p21 and p27 in both SGC cell lines in a time-dependent manner. In the xenograft model experiment, VPA treatment markedly inhibited the growth of salivary gland tumours when compared with the growth of the untreated controls. VPA may be a valuable drug in the development of better therapeutic regimens for SGC.

Aquaporins (AQPs) are a membrane protein family involved in the selective transport of water across cell membranes. Recent studies have reported the expression of AQP5 in several tumor types such as gastric, pulmonary, ovarian, pancreatic and colorectal cancer. We have previously reported the expression on tumor cells and the important role of AQP3 on cell growth in tongue cancer. However, little is known about the expression and precise role of AQP5 on squamous cell carcinoma (SCC) of the tongue. We investigated the expression of AQP5 and AQP3 in human oral SCC and adenoid cystic carcinoma (ACC). Overexpression of both AQP5 and AQP3 were immunohistochemically observed on tumor cells in SCC, whereas ACC cells were faintly stained with those antibodies against AQPs. Treatment with pan-AQP inhibitor or specific AQP5-siRNA showed inhibition of cell growth in SCC cell lines via the inhibition of integrins and the mitogen-activated protein kinase pathway. AQPs play important roles in cell growth in SCC rather than ACC.

Extracellular matrix metalloproteinase inducer (EMMPRIN) is a transmembrane glycoprotein that is involved in tumor invasion by stimulating matrix metalloproteinase (MMP) expression. Our previous immunohistochemical study found that the expression of EMMPRIN in salivary adenoid cystic carcinoma (SACC) was positively correlated with tumor perineural and perivascular invasion. The present study was designed to further investigate the role of EMMPRIN in the invasion of SACC. Western blot results showed that EMMPRIN was upregulated in the highly metastatic SACC cell line SACC-LM, compared to SACC-83, a SACC cell line with low metastatic ability. Blocking of EMMPRIN by its antibody significantly decreased the adhesion, secretion of MMP-2 and MMP-9, and invasion activity of SACC-LM cells in vitro (P<0.01). Co-cultures of SACC-LM cells with fibroblasts significantly produced elevated levels of MMP-2 and MMP-9, and promoted the in vitro invasion activity of SACC-LM cells, compared with cultures of SACC-LM cells alone (P<0.01). These results indicate that EMMPRIN may play an important role in the invasion of SACC by stimulating the expression of MMP-2 and MMP-9 in tumor and stromal cells.

We analyzed 10 adenoid cystic carcinomas (ACCs) of the salivary glands by array-based comparative genomic hybridization (a-CGH) using DNA chips spotted with 4,030 bacterial artificial chromosome clones. After the data smoothing procedure was applied, a total of 88 DNA copy number aberrations (DCNAs) were detected. The frequent (≥30%) DCNAs were loss of 6q23-27 and 8p23, and gains of 6p, 6q23, 8p23 and 22q13. High-level gains were detected on 12q15, including MDM2 in two cases. These two cases showed an immunohistochemically high-level (>50%) expression of MDM2 and a low-level expression of p53 (<20%). Furthermore, the total number of DCNAs was significantly greater in ACCs with loss of 6q compared to other ACCs, and in ACCs without the loss of 8p23 compared to other ACCs, respectively. Although limitations exist, a-CGH detected several candidate chromosomal imbalances associated with accumulation of DCNAs in ACCs.

To elucidate the potential etiological role of RUNX3 in the development of salivary gland adenoid cystic carcinoma (ACC), we analyzed the methylation status of RUNX3 in a series of 114 ACC tissues and 3 ACC cell lines. Results showed that the methylated rate of RUNX3 was 50.9 and 3.5% in the 114 ACC samples and the corresponding normal salivary glands, respectively, achieving a significant difference (P<0.001). There was a significant correlation between RUNX3 methylation and various clinicopathological parameters of ACCs, such as perineural invasion, lymph node involvement, T-stage and distant metastasis (P<0.001). RUNX3 methylation was a significant predictor of the 5-year disease-free survival in ACC patients after surgery. Partial methylation was found in all 3 ACC cell lines, and the reactivation and more potent expression of RUNX3 was induced by 5-triazole-2-deoxycytidine. Our findings indicate that RUNX3 methylation may occur as a common event in the development of ACC and that methylation may be a major mechanism for inactivation of RUNX3 in ACC.

Cadherins are found in almost all living organisms. In addition to their role in the formation and maintenance of normal tissue architecture, cadherins seem to play a crucial role in the cell-cell interactions of cancer cells in tumorigenesis, invasion and metastasis. The aim of the present study was to identify the role of CDH12 in the invasion and metastasis of salivary adenoid cystic carcinoma (SACC). Real-time PCR results showed that CDH12 is abnormally expressed in the highly metastatic SACC cell line ACC-M, compared to ACC-2, a SACC cell line with low metastatic ability. CDH12 expression was significantly higher in clinical samples with metastasis and recurrence than in those without metastasis and recurrence (P<0.05), as demonstrated by immunohistochemical analysis. Overexpression of the CDH12 protein in ACC-M cells infected with an adenovirus vector containing CDH12 enhanced the invasive and migratory ability of ACC-M cells in vitro compared to ACC-M cells infected with empty vector. Likewise, knockdown of CDH12 by small interfering RNA efficiently inhibited the invasion and migration of ACC-M cells in vitro. These results indicate that CDH12 may play an important role in the invasion and metastasis of SACC.

Bisphosphonates (BPs) inhibit bone resorption by preventing osteoclast maturation and apoptosis induction. Recently, BPs have also been shown to have antitumor effects against various types of carcinomas in vitro and in vivo. In this study, we investigated the antitumor effect of zoledronic acid (ZOL), a third generation bisphosphonate, on proliferation, cell cycle and apoptosis of oral cancer cells. Direct antitumor effects of ZOL against four oral carcinoma cell lines (squamous cell carcinoma, HSC3, HSC4, SCCKN; salivary adenocarcinoma, HSY) were measured by WST assay. Apoptosis-related molecules were analyzed by Western blot analysis and cell cycle was analyzed by flow cytometry. ZOL had a dose-dependent antitumor effect in the four oral cancer cell lines. ZOL activated caspase-3, -8 and -9 and induced cellular apoptosis. Western blot analysis showed that ZOL increased cleaved anti-human poly(ADP-ribose) polymerase expression and decreased Bcl-2 and Bid expression. Treatment with ZOL increased the number of cells in apoptosis, sub G1 phase and S phase, and reduced the number of cells in the G0/G1 and G2/M phase in a concentration-dependent manner. ZOL inhibits cell proliferation and induces apoptosis of oral cancer cells in vitro. These findings suggest that ZOL might be beneficial in the treatment of oral carcinoma patients.

Salivary gland tumours (SGT) constitute a diagnostically challenging group of neoplasms with frequently unpredictable clinical outcome. The proliferation rate facilitates the identification of aggressive SGT. The Chromatin Assembly Factor-1 (CAF-1) is a major epigenetic regulator of nuclear chromatin organization during DNA replication. It plays a critical function in human tumourigenesis and has been proposed as a new proliferation and prognostic marker for some malignancies. This study focused on the role of CAF-1/p60 protein as a marker of clinical value for SGT. The expression of CAF-1/p60 was evaluated by immunohistochemistry on a retrospective series of 362 surgically excised benign and malignant SGT with different histogenesis and, when available, on fine-needle pre-surgical cytological biopsies. The resulting data were compared with traditional prognostic parameters, including the expression of the routine proliferation marker ki67/MIB1. CAF-1/p60 was detectable in all SGT, with highest degree of expression in metastasizing malignant tumours. Moreover, the cases of benign tumours which progressed to carcinoma during the follow-up, showed significantly higher CAF-1/p60 expression than non-progressing benign SGT, both on histological sections and cytological smears of the primary tumour. Cox's multiple regression analysis selected CAF-1/p60 expression as the best independent predictor of cancer development for benign SGT (p<0.0001), and the best independent predictor of metastasis onset for malignant tumours (p<0.0004). Overexpression of CAF-1/p60, on histological and/or cytological samples, characterizes malignant SGT with aggressive behaviour, irrespective of their specific histotype, and allows the early diagnosis of progression toward malignancy of morphologically benign tumours.

The Notch signaling pathway is important for cell-cell communication; it is involved in gene regulation mechanisms that control multiple cell differentiation processes during embryonic and adult life. Notch is present in all metazoans, and vertebrates possess four different Notch receptors: Notch-1, Notch-2, Notch-3, and Notch-4. The aim of the present study was to identify the role of Notch protein in the metastasis of salivary adenoid cystic carcinoma (SACC). Real-time PCR results showed that Notch-1, Notch-2, and Notch-4 were upregulated in the highly metastatic SACC cell line ACC-M, compared to ACC-2, a SACC cell line with low metastatic ability. Knockdown of Notch-4 by small interfering RNA efficiently inhibited the invasion of ACC-M cells. Notch-4 expression was significantly higher in the clinical samples with metastasis and recurrence compared to that in control (p<0.05), shown by immunohistochemistry analysis. These results indicate that Notch-4 may play an important role in SACC metastasis.

Photodynamic therapy has been developed as an alternative therapy of cancer. The aim of this study was to examine whether PDT with hexenyl ester of 5-aminolaevulinic acid (ALA-hx) inhibits the proliferation of the salivary gland adenocarcinoma SGT cells. Cell proliferation was examined by MTT assay. The gene expression of Coproporphyrinogen oxidase (CPO) and ROS production was also examined. Flow cytometry and in vivo Chorioallantoic membrane (CAM) assay was performed. ALA-hx PDT inhibited effectively the proliferation of SGT cells. Treatment of ALA-hx induced CPO mRNA expression and ROS was produced by ALA-hx PDT in SGT cells. Flow cytometry and LDH assay showed that ALA-hx PDT induced necrotic cell death rather than apoptosis in SGT cells. In vivo CAM assay showed that ALA-hx PDT induced tumor destruction by inducing necrosis. These results indicate that ALA-hx PDT effectively inhibits the proliferation of SGT cells by inducing necrosis.

Increasing emphasis has been placed on the role of myoepithelial cells, the contractile components of secretory glands, in the in situ to invasive carcinoma transition. These cells are placed at the interface between luminal epithelial cells and the stromal compartment, which favors their cross-talk with all other cell types comprising the tumor micro-environment. To obtain some clues about this cross-talk and also to better understand our previous immunoprofile study of myoepithelial cells in salivary gland carcinoma ex-pleomorphic adenoma (CXPA), we investigated FGF-2 expression in CXPA in situ structures as well as in cells cultured under conditions attempting to simulate the cellular interactions of this tumor stage. We have observed by immunohistochemistry that myoepithelial cells of CXPA in situ structures overexpress FGF-2. In addition, our results supported by qPCR and Western blotting, demonstrated that the expression of FGF-2 in the benign myoepithelial cells was in fact increased by stimulation with the conditioned medium from malignant cells. Low molecular weight FGF-2, known to be primarily released from the cells to exert its biological activity through receptors, was the predominant FGF-2 form detected in the benign myoepithelial cells. Specific FGF-2 receptors were found in the malignant epithelial but not in the benign myo-epithelial cells of CXPA, indicating a paracrine role for benign myoepithelial cell-derived FGF-2. Abnormal paracrine myo-epithelial/epithelial cell interactions and also myoepithelial/ stromal cell interactions could favor tumor growth, invasion and metastasis.

The aim of the present study was the search of molecular alterations (oncogene amplification or protein overexpression) that could have an impact on the outcome of ACC patients. For this purpose, paraffin-embedded tissue samples of primary ACC of 24 patients were collected. Oncogenic amplification status of six targets previously described to be involved in human carcinogenesis (ERBB1, KIT, PIK3CA, CCND1, MYC and MDM2) were studied by a PCR-based semiquantitative approach. C-Kit, cyclin D1 and EGFR protein levels were immunohistochemically assessed. ERBB1, CCND1 and PIK3CA were frequent targets of oncogene amplification (67, 46 and 38%, respectively). C-Kit and cyclin D1 were overexpressed in 57 and 82%, respectively. CCND1 amplification was associated with advanced tumour stage and ERBB1 amplification to distant metastasis. ERBB1/CCND1/PIK3CA coamplification was the most consistently observed pattern (29%). The cases with this amplification pattern presented a reduced survival. This study points to the importance of ERBB1, CCND1 and PIK3CA oncogenic amplification status in ACC carcinogenesis.

TPX2 is a microtubule-associated protein and is required for microtubule formation at kinetochores in mammalian cells. The purpose of this study was to clarify the expression of TPX2 mRNA and correlation between TPX2 and clinicopathological factors in salivary gland carcinomas. The expression of TPX2 mRNA was investigated in 20 human salivary gland carcinomas (8 mucoepidermoid carcinomas, 7 adenoid cystic carcinomas, 5 acinic cell carcinomas) and 6 normal submandibular glands using real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR). The mean expression level of TPX2 mRNA was higher in mucoepidermoid carcinomas (0.53+/-0.51) than in normal submandibular glands (0.047+/-0.029); a significant association was found (Mann-Whitney U test, P=0.0067). The mean expression levels of TPX2 were also higher in acinic cell carcinomas (0.45+/-0.49) and adenoid cystic carcinomas (0.28+/-0.22) than in normal submandibular glands. Statistical correlations were found (Mann-Whitney U test, P=0.028 and P=0.003, respectively). Correlation between expression of TPX2 and receptor for hyaluronan-mediated motility (RHAMM) was also investigated in this study. A significant association was found between the mRNA expression levels of TPX and RHAMM (Pearson's correlation coefficient by rank test, P=0.020). These results indicate that human TPX2 mRNA is closely linked to increased or abnormal cell proliferation in malignant salivary gland tumors.

Molecular studies of cylindromas, which arise from the eccrine or apocrine cells of the skin, have demonstrated frequent alterations at chromosome 16q12-13, recently found to house the cylindromatosis (CYLD) gene. CYLD, a tumor suppressor gene, has deubiquitinating enzyme activity and inhibits the activation of transcription factor NF-kappaB. Loss of the deubiquitinating activity of CYLD is correlated with tumorigenesis. It has been reported that the expression of CYLD is observed in various organs. We demonstrated previously that human salivary gland tumor (SGT) cell line, HSG spontaneously expresses CYLD and also found that adenoid cystic carcinoma (ACC) arising from the hard palate was distinctly positive for CYLD, immunohistochemically. However, it is unclear whether loss of CYLD is associated with development of SGTs. This study examined CYLD function in SGT cells and attempted to clarify whether CYLD is associated with development of SGTs. The expression of CYLD and NF-kappaB mRNAs in HSG cells was increased by TNF-alpha. Translocation of NF-kappaB protein from the cytoplasm to the nucleus in HSG cells peaked at 30 min after TNF-alpha stimulation, then decreased at 60 min, whereas that of CYLD protein increased gradually in a time-dependent manner. Luciferase reporter assay indicated that TNF-alpha induced a 5-fold increase of NF-kappaB-dependent transcription at 4 h, which was further enhanced by knockdown of CYLD using RNA interference. Taken together, these data demonstrated that the levels of both CYLD and NF-kappaB mRNAs accumulated in HSG cells during 24 h after TNF-alpha stimulation, although the NF-kappaB activity in the cells was at least negatively regulated by CYLD. Immunohistochemical examinations revealed that there are several correlations between the expression of CYLD and NF-kappaB-related factors in 17 cases of ACC tissues. These findings suggest that loss of CYLD is associated with development of SGTs.

Proprotein convertases are serine endoproteases implicated in the proteolytic processing of a large variety of regulatory proteins. An important role of proprotein convertases in tumorigenic processes has been suggested by various studies. In this study, the role of the proprotein convertase furin in PLAG1 proto-oncogene-induced salivary gland tumorigenesis was investigated. PLAG1 overexpression in salivary glands has previously been shown to result in salivary gland tumors in 100% of mice within 5 weeks after birth. MMTV-cre-mediated inactivation of fur without over-expression of PLAG1 caused smaller but histologically normal salivary glands. Moreover, the lymph nodes close to the salivary glands were enlarged, and histology showed that they had activated follicles. When genetic ablation of 1 or 2 alleles of fur and overexpression of the PLAG1 transgene were simultaneously achieved, a significant delay in tumorigenesis was observed. Collectively, these results suggest an important role for furin in PLAG1-induced salivary gland tumorigenesis in mice.

The Pleomorphic adenoma gene 1 (PLAG1) is involved in various human neoplasias, including pleomorphic adenomas of the salivary glands. Moreover, the oncogenic role of PLAG1 was clearly demonstrated in two independent PLAG1 transgenic mouse founders, in which PLAG1 expression could be targeted to different tissues using the Cre/loxP system. MMTV-Cre-mediated targeted overexpression of PLAG1 in the salivary glands of double transgenic offspring mice, referred to as P1-MCre and P2-MCre mice, induced pleomorphic adenomas in this organ. Igf2, a genuine PLAG1 target gene, was highly upregulated in those tumours as well as in human pleomorphic adenomas of the salivary glands. These and previous observations in other PLAG1-induced tumours e.g. breast adenomyoepitheliomas emphasize the importance of Igf upregulation in such tumours. In this study, further evidence for the role of Igf2 in PLAG1-induced tumourigenesis, is reported. Inactivation of Igf2 in P1-MCre mice leads to a significant delay in tumour development. Since tumour development is not fully abrogated by inactivation of Igf2, other signalling pathways are likely to contribute to PLAG1-induced tumourigenesis as well. Further studies revealed that several genes such as H19, Dlk1, Gtl2, Igfbp2, Igfbp3 and genes involved in Wnt signalling, such as Wnt6, Cyclin D1 and beta-catenin are upregulated in P1-MCre mice in which Igf2 is inactivated. In conclusion, we clearly demonstrate upregulation of several genes associated with Igf and Wnt signalling in PLAG1-induced pleomorphic adenomas. Furthermore, inactivation of Igf2 does not affect upregulation of genes associated with Wnt signalling, which might suggest that both signalling pathways are involved.

TGF-beta-stimulated clone-22 (TSC-22) was reported to be a differentiation-inducing factor which negatively regulates the growth of salivary gland cancer cells. In the present study, we examined the expression of TSC-22 in salivary gland tumors by immunohistochemistry. In pleomorphic adenoma (PA), most of the sparse myoepithelial-like tumor cells, which are considered as the differentiated cells because they produce extracellular matrix, expressed TSC-22. However, only a limited number of cases of the solid myoepithelial-like tumor cells in PA, which are considered as the growing cells, expressed TSC-22. In adenoid cystic carcinoma (ACC), inner ductal cells in the tubular structure, strongly expressed TSC-22, though the outer myoepithelial-like tumor cells did not express TSC-22. In the cribriform structure, myoepithelial-like tumor cells did not express TSC-22. However, a small ductal structure in the micro-cyst wall strongly expressed TSC-22. Sparse type myoepithelial-like tumor cells in ACC also expressed TSC-22. In mucoepidermoid carcinoma, epidermoid tumor cells and mucous-producing tumor cells in mucoepidermoid carcinoma frequently expressed TSC-22. Thus, the expression of TSC-22 was frequently observed in the cells with differentiated-phenotypes, although rarely in the cells with growing potentials. These results suggest that TSC-22 may play an important role in maintaining the differentiated phenotype in salivary gland tumors.

The expression of neural cell adhesion molecule (NCAM) was analyzed in immunohistochemical preparations from adenoid cystic carcinoma. The goal was to evaluate whether NCAM expression could be used as a biological marker for the perineural invasion of adenoid cystic carcinoma in the head and neck. The presence of perineural invasion and NCAM expression was evaluated in samples from 49 patients. Perineural invasion was identified in 33 of them (67%). A high incidence of perineural invasion was found in adenoid cystic carcinoma in the parotid, hard palate, maxillary sinus and oral cavity. Positive NCAM staining was observed in 28 of 49 patients (57%). Of the 28 patients with NCAM staining, perineural invasion was identified in 24 (86%). In contrast, only 9 (43%) of the 21 tumors without NCAM staining had perineural invasion. The difference in NCAM expression between cases with and without perineural invasion was statistically significant (p<0.01). When positive NCAM staining was used to estimate the presence of perineural invasion, the sensitivity was 73 and the specificity 75%. Histopathologic nodal involvement was found in 6 of 18 cases in which neck dissection had been performed. All 6 cases displayed positive NCAM staining, and 5 displayed perineural invasion in the primary adenoid cystic carcinoma. In conclusion, NCAM expression can, to a certain extent, be used as a predictor of perineural invasion in adenoid cystic carcinoma. Moreover, lymph node metastases could serve as a clinical indicator for perineural invasion and for NCAM expression.

It has been reported that cimetidine, a histamine type-2 receptor (H2R) antagonist, inhibits the growth of glandular tumors such as colorectal cancer. However, its effects against salivary gland tumors are still unknown. We demonstrated previously that human salivary gland tumor (HSG) cells spontaneously express the neural cell adhesion molecule (NCAM) and also that HSG cell proliferation could be controlled via a homophilic (NCAM-NCAM) binding mechanism and that NCAM may be associated with perineural invasion by malignant salivary gland tumors. In the present study, we investigated the effects of cimetidine via the expression of NCAM on tumor growth and perineural/neural invasion in salivary gland tumor cells. Expression of both NCAM mRNA and protein was found to decrease in a dose-dependent manner upon treatment with cimetidine for 24 h. The MTT assay and confocal laser microscopy clearly showed that HSG cells underwent apoptosis after treatment with cimetidine. Activation of caspases 3, 7, 8 and 9 was observed in HSG cells after cimetidine treatment, thus confirming that the apoptosis was induced by the activated caspases. Apaf-1 activity was also detected in HSG cells in a dose-dependent manner after treatment with cimetidine. We also found that the cimetidine-mediated down-regulation of NCAM expression in HSG cells did not occur via blocking of the histamine receptor, even though H2R expression was observed on HSG cells, as two other H2R antagonists, famotidine and ranitidine, did not show similar effects. We demonstrated for the first time that cimetidine can induce significant apoptosis of salivary gland tumor cells, which express NCAM, at least in part by down-regulation of NCAM expression on the cells. These findings suggest that the growth, development and perineural/neural invasion of salivary gland tumor cells can be blocked by cimetidine administration through down-regulation of NCAM expression, as well as induction of apoptosis.

The aim of the present study was to clarify whether ATP binding cassette transporters are refractory factors in head and neck cancers. For in vitro and in vivo chemotherapeutic studies, we used the following head and neck cancer cell lines: a mouse oral squamous cell carcinoma (SCC) cell line, Sq-1979; a human SCC cell line, SCCHA; a mouse salivary gland adenocarcinoma (SGA) cell line, NR-PG; and a human SGA cell line, HSY. We used a vinca alkaloid anticancer drug, vincristine (VCR), as a chemotherapeutic anticancer drug. To determine the cause of multidrug resistance, Western blot analysis, reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemistry of xenografted tumors in nude mice, drug efflux analysis, and drug efflux inhibitory assays were performed. VCR-treated cell lines, Sq-1979/VCR, SCCHA/VCR, NR-PG/VCR, and HSY/VCR, intensively expressed multidrug resistance (MDR) gene 1 mRNA and multidrug resistance associated protein (MRP) 1 mRNA. MRP7 mRNA and protein were expressed in NR-PG/VCR and HSY/VCR cells, but not in Sq-1979/VCR and SCCHA/VCR cells. In each cell clone of NR-PG/VCR and HSY/VCR, MRP7 mRNA was induced by VCR treatment, suggesting an acquired resistance to VCR in the context of MRP7 expression. In the in vivo chemotherapeutic nude mice model, VCR-treated xenografted SCCHA and HSY cells expressed MDR1 and MRP1. Moreover, MRP7 expression was immunohistochemically found in xenografted HSY cells of VCR-injected tumor-bearing mice, but not in SCCHA cells. Furthermore, doxorubicin accumulation was increased and drug cross-resistance to docetaxel decreased in HSY/VCR in the presence of a competitive MRP7 inhibitor, 17-beta-estradiol-(17-beta-D-glucuronide). These results indicate that MDR1 expression, MRP1 expression, and MRP7 expression are refractory factors in head and neck cancer chemotherapy and suggest that induction of MRP7 expression is involved in drug resistance to natural products, especially to docetaxel in SGA.

The aims of this study were to investigate the expression levels of beta-catenin, Pin1 and cyclin D1 in salivary adenoid cystic carcinomas (SACC ) and to evaluate its clinical importance, furthermore, to elucidate whether beta-catenin expression was aberrant in SACC and whether Pin1 was involved in aberrant beta-catenin and cyclin D1 expression. The expression of Pin1, beta-catenin and cyclin D1 were examined in the specimens of 65 patients with SACC by immunohistochemistry, protein and mRNA expressions were detected by western blotting and RT-PCR in four SACC cell lines. Pin1 was overexpressed in 51 cases of SACC (78%), and high levels of Pin1 expression correlated with cyclin D1 positive expression (p = 0.02). Fourteen (22%) cases showed positive immunoreactivity for beta-catenin protein in the nuclear/cytoplasmic fraction in tumor tissues, which was defined as cytoplasm/nucleus staining, among which quite evident nuclear expression of beta-catenin was detected in six cases (9%), while cyclin D1 positive expression was detected in 41 cases of SACC (63%). Reduced membranous expression of beta-catenin was detected in the cases with metastasis (11/14). Theses results suggest that Pin1 and Wnt signalling pathway are activated in SACC and may play a pivotal role in SACC carcinogenesis and metastasis.

Human Bub1 plays an important role at the spindle assembly check-point to prevent cell cycle progression following spindle damage. We examined the expression of Bub1 mRNA and protein in 21 human salivary gland tumors (7 pleomorphic adenomas, 2 warthin tumors, 5 mucoepidermoid carcinomas, 3 adenoid cystic carcinomas and 4 acinic cell carcinomas) and 3 normal submandibular glands using real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) or western blotting. The mean expression levels of Bub1 mRNA and protein were higher in malignant tumors (0.12+/-0.028/1.75+/-0.53) than normal submandibular glands (0.042+/-0.014/0.19+/-0.044) and benign tumors (0.058+/-0.01/0.97+/-0.44). We found a significant association between the level of Bub1 mRNA/protein expression and clinical stage in malignant tumors (Mann-Whitney U test, p=0.019/p=0.016). We analyzed its relation with the proliferative activity monitored by the Ki-67 labeling index by immunohistochemistry as well as the expression of proliferating cell nuclear antigen (PCNA) by Western blotting. A significant correlation was found between Bub1 mRNA/protein expression and the Ki-67 labeling index in salivary gland tumors (Spearman's correlation coefficient by rank test, p=0.026/p=0.002). These results indicate that increased expression of the human Bub1 gene is closely linked to abnormal cell proliferation in malignant conditions.

CIP/KIP family proteins entitled p21(WAF1/CIP1) and p27(KIP1) have key positions in cell cycle regulation leading to an arrest of cell proliferation. They are supposed to enable a repair process of DNA damage. In several human tumors, a loss of these proteins is associated with poor clinical outcome. The role of these cell cycle regulators in tumors of salivary gland and paranasal sinus origin is still unclear. In this study it was intended to demonstrate and compare the expression of p21, p27, and p53 in benign and malignant tumors of salivary glands and paranasal sinuses. Protein expression was detected by conventional immunohistochemistry (IHC). Additionally, we performed tyramide signal amplified immunohistochemistry (TSA-IHC) for p21 and p53 levels. Nine adenoid cystic carcinomas, 5 adenocarcinomas, 4 cylindrical cell carcinomas, as well as 30 pleomorphic adenomas and 26 inverted papillomas, were studied. In 78% of all adenoid cystic carcinomas a complete loss of p27 expression could be identified, whereas 60% of the adenocarcinomas overexpressed the protein. The majority of cylindrical cell carcinomas showed distinct cytoplasmic accumulation of p27. All malignant tumors turned out to be positive for p21 after performing TSA-IHC, although 72% of those samples had shown weak to negative protein levels in conventional immunostaining. Immunohistochemical results of CIP/KIP proteins were compared to p53 expression as well as to main clinical parameters. The study sheds new light upon the role of CIP/KIP protein family in tumors of salivary glands and paranasal sinuses. Furthermore, it is the first description of p21 and p53 TSA-IHC in these tumor types.

The basic histologic patterns of adenoid cystic carcinoma (ACC) are classified into three types (tubular, cribriform and solid), but clinical significance of the histological type is unclear. We have successfully established a human tumor line derived from ACC that is serially transplantable in nude mice. This tumor showed an increased growth rate as the passage levels proceeded, and the histological type was changed from a cribriform pattern in the initial stage to a solid one. In this study, we investigated the relationship between histological type and biological characteristics by analyzing the serially transplantable ACC tumor model. As a result, the tumor growth rate at the 15th passage level was increased approximately 5-fold compared with that at the initial passage level. In the histological type, approximately 30% of the cribriform pattern in the initial level was changed to a solid one at the 15th passage level, and the PCNA labeling index was elevated 4-fold. Concomitant with this, expression of Ki-67, p53 and bcl-2 proteins was increased, and apoptotic cells were decreased as demonstrated by the TUNEL method. From these findings, it was suggested that cell proliferation and histological change of this ACC tumor are related to the inhibition of apoptosis. This tumor line would provide a useful model for investigating the biological behavior of ACC.

Interactions between hepatocyte growth factor (HGF) and its receptor, c-Met, have been associated with invasion, metastasis and carcinogenesis in in vitro experiments. We investigated the relationship between HGF/c-Met immunoreactivity and the clinical features of 33 patients with high grade salivary gland carcinomas. c-Met and stromal HGF (expression of HGF in fibroblasts adjacent to tumor nests) were found to significantly correlate with regional lymph node and distant metastasis (p<0.05), but not with HGF expression, in tumor cells. Stromal HGF was also found to correlate with tumor size (p<0.05). In addition, a significant correlation between c-Met and stromal HGF expression (p<0.0001) was observed. Overall survival in patients with c-Met and stromal HGF immunoreactivity was significantly worse than in patients without c-Met and stromal HGF immunoreactivity (p=0.0002). The present findings suggest that HGF may bind to c-Met in a paracrine fashion, thereby enabling metastasis of high grade salivary gland carcinomas. Thus, HGF/c-Met immunoreactivity might be associated with a poor prognosis in patients with high grade salivary gland carcinomas.

The aim of this study was to clarify the effects of alpha-N-acetylgalactosaminidase (alpha-NaGalase) produced by human salivary gland adenocarcinoma (SGA) cells on the bioactivity of macrophage-activating factor (GcMAF). High exo-alpha-NaGalase activity was detected in the SGA cell line HSG. HSG alpha-NaGalase had both exo- and endo-enzyme activities, cleaving the Gal-GalNAc and GalNAc residues linked to Thr/Ser but not releasing the [NeuAc2-6]GalNac residue. Furthermore, GcMAF enzymatically prepared from the Gc protein enhanced the superoxide-generation capacity and phagocytic activity of monocytes/macrophages. However, GcMAF treated with purified alpha-NaGalase did not exhibit these effects. Thus, HSG possesses the capacity to produce larger quantities of alpha-NaGalase, which inactivates GcMAF produced from Gc protein, resulting in reduced phagocytic activity and superoxide-generation capacity of monocytes/macrophages. The present data strongly suggest that HSG alpha-NaGalase acts as an immunodeficiency factor in cancer patients.

Several investigators have demonstrated that TGF-beta stimulated clone-22 (TSC-22) regulates cell growth and differentiation, and cell death. TSC-22 is a putative transcriptional regulator containing a leucine zipper-like structure and a nuclear export signal. We previously showed the cytoplasmic localization of TSC-22 and the nuclear translocation of TSC-22 concomitant with induction of apoptosis in salivary gland cancer cells. In the present study, we attempted to identify the active domain of TSC-22 protein that regulated the biological functions of TSC-22. We constructed three mammalian expression vectors, which could produce full length TSC-22 only in cytoplasm, the leucine zipper structure of TSC-22 in both cytoplasm and nucleus, and the leucine zipper structure only in nucleus. Then, we transfected a salivary gland cancer cell line, HSG with these expression vectors, and investigated the growth profile of the transfectants. None of the TSC-22 constructs inhibited the monolayer growth and the anchorage-dependent colony formation of HSG cells. However, the leucine zipper structure of TSC-22 markedly inhibited the anchorage-independent colony formation of HSG cells (p<0.001; one way ANOVA). Full length TSC-22 also suppressed the anchorage-independent colony formation of HSG cells, although the effect of full length TSC-22 was much lower than those of the leucine zipper constructs. These observations suggest that the leucine zipper structure in TSC-22 protein is an active domain that negatively regulates the growth of salivary gland cancer cells.

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a member of the nuclear receptor superfamily of ligand-activated transcription factors. It is expressed in several tissue types, including adipose tissue in which it stimulates adipogenesis. Recent studies have demonstrated that PPARgamma ligands induce cellular differentiation and inhibit cell growth in carcinomas of various organs including the breast, prostate, lung, colon, stomach, bladder, and pancreas. However, whether PPARgamma is expressed in human salivary gland tumors and its function in this tissue is unknown. In the present study, we examined PPARgamma gene expression in human salivary gland cancer cells and tested its ligands for any antitumor effect. PPARgamma mRNA was detected by RT-PCR in both benign and malignant salivary gland tumor tissues. The effect of PPARgamma on cell growth was investigated using four human salivary gland cancer cell lines; HSG, AZA3, HSY and TYS, which were confirmed to express PPARgamma1 mRNA and protein. Retinoid X receptor alpha protein, which forms heterodimers with PPARgamma, was also detected in all the cells tested. Data obtained by luciferase assay indicated that the intrinsic PPARgamma protein was activated by the synthetic ligands, troglitazone and pioglitazone, but not by the natural ligand, 15-deoxy-delta12, 14-prostaglandin J2. The synthetic PPARgamma ligands, particularly troglitazone, caused significant dose-dependent inhibition of cancer cell growth. Furthermore, the overexpression of PPARgamma1 or PPARgamma2 in cancer cells also reduced significantly their growth rate. These results suggest that PPARgamma and its synthetic ligands suppress the growth of human salivary gland cancer cells and it may be a useful molecular target for cancer treatment.

Galectins are a family of non-integrin beta-galactosidase-binding lectins. Altered expression of galectins has been associated with neoplastic transformation and progression in several human tumors. In this study, we examined the distribution patterns of galectin-1 and galectin-3 in normal (n=45), benign (n=16), and malignant (n=49) salivary gland specimens using immunohistochemistry to determine their diagnostic and/or biological implications in salivary gland tumorigenesis. In normal salivary glands, galectin-3 expression was limited to ductal cells, and galectin-1 was usually faintly detected in ductal cells and strongly positive in myoepithelial cells. In benign tumors, galectin-3 maintained the ductal localization, but galectin-1 showed variable expression in ductal and myoepithelial cells. In malignant tumors, most of the polymorphous low-grade adenocarcinomas and carcinoma ex-pleomorphic adenomas expressed both galectins, whereas adenoid cystic and acinic cell carcinomas showed dramatically reduced galectin-3 expression and heterogeneous galactin-1 staining. Our data demonstrated altered localization and expression of galectin-3, and to lesser extent, galectin-1 in salivary gland carcinomas. These findings may assist in the differential diagnosis of some salivary gland malignancies, especially when using small and limited fine-needle aspiration materials.