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Caveolin-1 has a complex role in prostate cancer and has been suggested to be a potential biomarker and therapeutic target. As mature caveolin-1 resides in caveolae, invaginated lipid raft domains at the plasma membrane, caveolae have been suggested as a tumor-promoting signaling platform in prostate cancer. However, caveola formation requires both caveolin-1 and cavin-1 (also known as PTRF; polymerase I and transcript release factor). Here, we examined the expression of cavin-1 in prostate epithelia and stroma using tissue microarray including normal, non-malignant and malignant prostate tissues. We found that caveolin-1 was induced without the presence of cavin-1 in advanced prostate carcinoma, an expression pattern mirrored in the PC-3 cell line. In contrast, normal prostate epithelia expressed neither caveolin-1 nor cavin-1, while prostate stroma highly expressed both caveolin-1 and cavin-1. Utilizing PC-3 cells as a suitable model for caveolin-1-positive advanced prostate cancer, we found that cavin-1 expression in PC-3 cells inhibits anchorage-independent growth, and reduces in vivo tumor growth and metastasis in an orthotopic prostate cancer xenograft mouse model. The expression of α-smooth muscle actin in stroma along with interleukin-6 (IL-6) in cancer cells was also decreased in tumors of mice bearing PC-3-cavin-1 tumor cells. To determine whether cavin-1 acts by neutralizing caveolin-1, we expressed cavin-1 in caveolin-1-negative prostate cancer LNCaP and 22Rv1 cells. Caveolin-1 but not cavin-1 expression increased anchorage-independent growth in LNCaP and 22Rv1 cells. Cavin-1 co-expression reversed caveolin-1 effects in caveolin-1-positive LNCaP cells. Taken together, these results suggest that caveolin-1 in advanced prostate cancer is present outside of caveolae, because of the lack of cavin-1 expression. Cavin-1 expression attenuates the effects of non-caveolar caveolin-1 microdomains partly via reduced IL-6 microenvironmental function. With circulating caveolin-1 as a potential biomarker for advanced prostate cancer, identification of the molecular pathways affected by cavin-1 could provide novel therapeutic targets.

Id-1 (Inhibitor of DNA binding/differential-1) plays a positive role in tumorigenesis through regulation of multiple signaling pathways. Recently, it is suggested that upregulation of Id-1 in cancer cells promotes chromosomal instability. However, the underlying molecular mechanism is not known. In this study, we report a novel function of Id-1 in regulation of mitosis through physical interaction with Cdc20 (cell division cycle protein 20) and Cdh1 (Cdc20 homolog 1). During early mitosis, Id-1 interacts with Cdc20 and RASSF1A (Ras association domain family 1A), leading to enhanced APC(Cdc20) activity, which in turn promotes cyclin B1/securin degradation and premature mitosis. During late mitosis, Id-1 binds to Cdh1 and disrupts the interaction between Cdh1 and APC, resulting in suppression of APC(Cdh1) activity. On the other hand, overexpression of Cdh1 leads to Id-1 protein degradation, suggesting that Id-1 may also act as a substrate of APC(Cdh1). The negative effect of Id-1 on APC(Cdh1) results in suppression of APC(Cdh1)-induced Aurora A and Cdc20 degradation, leading to failure in cytokinesis. As a result, overexpression of Id-1 in human prostate epithelial cells leads to polyploidy in response to microtubule disruption, and this effect is abolished when Id-1 expression is suppressed using antisense technology. These results demonstrate a novel function of Id-1 in promoting chromosomal instability through modification of APC/C activity during mitosis and provide a novel molecular mechanism accounted for the function of Id-1 as an oncogene.

The mitotic arrest deficient 2 (MAD2) is suggested to play a key role in a functional mitotic checkpoint because of its inhibitory effect on anaphase-promoting complex/cyclosome (APC/C) during mitosis. The binding of MAD2 to mitotic checkpoint regulators MAD1 and Cdc20 is thought to be crucial for its function and loss of which leads to functional inactivation of the MAD2 protein. However, little is known about the biological significance of this MAD2 mutant in human cells. In this study, we stably transfected a C-terminal-deleted MAD2 gene (MAD2DeltaC) into a human prostate epithelial cell line, Hpr-1 and studied its effect on chromosomal instability, cell proliferation, mitotic checkpoint control and soft agar colony-forming ability. We found that MAD2DeltaC was able to induce aneuploidy through promoting chromosomal duplication, which was a result of an impaired mitotic checkpoint and cytokinesis, suggesting a crucial role of MAD2-mediated mitotic checkpoint in chromosome stability in human cells. In addition, the MAD2DeltaC-transfected cells displayed anchorage-independent growth in soft agar after challenged by 7,12-dimethylbenz[A]anthracene (DMBA), demonstrating a cancer-promoting effect of a defective mitotic checkpoint in human cells. Furthermore, the DMBA-induced transformation was accompanied by a complete loss of DNA damage-induced p53 response and activation of the MAPK pathway in MAD2DeltaC cells. These results indicate that a defective mitotic checkpoint alone is not a direct cause of tumorigenesis, but it may predispose human cells to carcinogen-induced malignant transformation. The evidence presented here provides a link between MAD2 inactivation and malignant transformation of epithelial cells.

Nasopharyngeal carcinoma is closely associated with Epstein-Barr virus (EBV) infection. The EBV-encoded LMP1 has cell transformation property. It suppresses cellular senescence and enhances cell survival in various cell types. Many of the downstream events of LMP1 expression are mediated through its ability to activate NF-kappaB. In this study, we report a novel function of LMP1 to induce Id1 expression in nasopharyngeal epithelial cells (NP69) and human embryonal kidney cells (HEK293). The Id1 is a basic helix-loop-helix (bHLH) protein and a negative transcriptional regulator of p16(INK4a). Expression of Id1 facilitates cellular immortalization and stimulates cell proliferation. With the combination of both specific chemical inhibitors and genetic inhibitors of cell signaling, we showed that induction of Id1 by LMP1 was dependent on its NF-kappaB activation domain at the carboxy-terminal region, CTAR1 and CTAR2. Induction of Id1 by LMP1 may facilitate clonal expansion of premalignant nasopharyngeal epithelial cells infected with EBV and may promote their malignant transformation.

Taxol is one of the widely used chemotherapeutic drugs against many types of human cancer. While it is considered as one of the most effective anticancer drugs, treatment failure often occurs due to development of acquired resistance. Therefore, it is important to understand the molecular mechanisms responsible for the development of drug resistance. Although it is generally believed that taxol induces cell death through interfering with microtubules leading to mitotic arrest, recent evidence has suggested that taxol-induced cell death also occurs through pathways independent of either microtubule or mitotic arrest. In this study, we report the identification of a novel role for TWIST, a basic helix-loop-helix protein, which plays a central role in cell type determination and differentiation, during generation of acquired resistance to taxol in a nasopharyngeal carcinoma cell line, HNE1-T3, using comparative genome hybridization (CGH) and subsequent RT-PCR and Western blotting. We found that upregulation of TWIST was associated with cellular resistance to taxol but not other drugs with different mechanisms of action. The fact that increased TWIST protein levels were also associated with another microtubule-targeting anticancer drug, vincristine, in four types of human cancer including nasopharyngeal, bladder, ovarian and prostate, indicates that it may play a central role in the resistance to microtubule-disrupting agents. In addition, ectopic expression of TWIST into human cancer cells also led to increased resistance to both taxol and vincristine. Our results indicate a novel mechanism that leads to resistance to microtubule-disrupting anticancer drugs through upregulation of TWIST. Our evidence provides a therapeutic strategy to overcome acquired resistance through inactivation of TWIST expression in human cancer.

The growth-promoting effect of Id-1 (inhibitor of differentiation/DNA binding) has been demonstrated in a number of human cancers. However, the mechanisms responsible for its action are not clear. In this study, we report that in prostate cancer cells, Id-1 promotes cell survival through activation of nuclear factor-kappaB (NF-kappaB) signalling pathway. After stable expression of Id-1 protein in LNCaP cells, we found that the Id-1 transfectants showed increased resistance to apoptosis induced by TNFalpha through inactivation of Bax and caspase 3. In addition, in the LNCaP cells expressing ectopic Id-1 protein, we also observed increased NF-kappaB transactivation activity and nuclear translocation of the p65 and p50 proteins, which was accompanied by upregulation of their downstream effectors Bcl-xL and ICAM-1. These results indicate that the Id-1-induced antiapoptotic effect may be via NF-kappaB signalling transduction pathway in these cells. In addition, inactivation of Id-1 by its antisense oligonucleotide and retroviral construct in DU145 cells resulted in the decrease of nuclear level of p65 and p50 proteins, which was associated with increased sensitivity to TNFalpha-induced apoptosis. Our results strongly suggest that Id-1 may be one of the upstream regulators of NF-kappaB and activation of NF-kappaB signalling pathway may be essential for Id-1 induced cell proliferation through protection against apoptosis. Our findings also suggest a potential therapeutic strategy in which inactivation of Id-1 may lead to sensitization of prostate cancer cells to chemotherapeutic drug-induced apoptosis.

Background Prostate cancer (PCa) frequently relapses after hormone ablation therapy. Unfortunately, once progressed to the castration resistant stage, the disease is regarded as incurable as prostate cancer cells are highly resistant to conventional chemotherapy. Method We recently reported that the two natural compounds polysaccharopeptide (PSP) and Gamma-tocotrienols (γ-T3) possessed potent anti-cancer activities through targeting of CSCs. In the present study, using both prostate cancer cell line and xenograft models, we seek to investigate the therapeutic potential of combining γ-T3 and PSP in the treatment of prostate cancer. Result We showed that in the presence of PSP, γ-T3 treatment induce a drastic activation of AMP-activated protein kinase (AMPK). This was accompanied with inactivation of acetyl-CoA carboxylase (ACC), as evidenced by the increased phosphorylation levels at Ser 79. In addition, PSP treatment also sensitized cancer cells toward γ-T3-induced cytotoxicity. Furthermore, we demonstrated for the first time that combination of PSP and γ-T3 treaments significantly reduced the growth of prostate tumor in vivo. Conclusion Our results indicate that PSP and γ-T3 treaments may have synergistic anti-cancer effect in vitro and in vivo, which warrants further investigation as a potential combination therapy for the treatment of cancer.