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PRRX1 is a homeodomain transcriptional factor, which has two isoforms, PRXX1A and PRRX1B. The PRRX1 isoforms have been demonstrated to be important in pancreatic cancer, especially in the regulation of epithelial-to-mesenchymal transition (EMT) in Pancreatic Ductal Adenocarcinoma (PDAC) and of mesenchymal-to-epithelial transition (MET) in liver metastasis. In order to determine the functional underpinnings of PRRX1 and its isoforms, we have unraveled a new interplay between PRRX1 and the FOXM1 transcriptional factors. Our detailed biochemical analysis reveals the direct physical interaction between PRRX1 and FOXM1 proteins that requires the PRRX1A/B 200-222/217 amino acid (aa) region and the FOXM1 Forkhead domain. Additionally, we demonstrate the cooperation between PRRX1 and FOXM1 in the regulation of FOXM1-dependent transcriptional activity. Moreover, we establish FOXM1 as a critical downstream target of PRRX1 in pancreatic cancer cells. We demonstrate a novel role for PRRX1 in the regulation of genes involved in DNA repair pathways. Indeed, we show that expression of PRRX1 isoforms may limit the induction of DNA damage in pancreatic cancer cells. Finally, we demonstrate that targeting FOXM1 with the small molecule inhibitor FDI6 suppress pancreatic cancer cell proliferation and induces their apoptotic cell death. FDI6 sensitizes pancreatic cancer cells to Etoposide and Gemcitabine induced apoptosis. Our data provide new insights into PRRX1's involvement in regulating DNA damage and provide evidence of a possible PRRX1-FOXM1 axis that is critical for PDAC cells.

High CD44 expression is associated with enhanced malignant potential in esophageal squamous cell carcinoma (ESCC), among the deadliest of all human carcinomas. Although alterations in autophagy and CD44 expression are associated with poor patient outcomes in various cancer types, the relationship between autophagy and cells with high CD44 expression remains incompletely understood. In transformed oesophageal keratinocytes, CD44 Low -CD24 High (CD44L) cells give rise to CD44 High -CD24 -/Low (CD44H) cells via epithelial-mesenchymal transition (EMT) in response to transforming growth factor (TGF)-β. We couple patient samples and xenotransplantation studies with this tractable in vitro system of CD44L to CD44H cell conversion to investigate the functional role of autophagy in generation of cells with high CD44 expression. We report that high expression of the autophagy marker cleaved LC3 expression correlates with poor clinical outcome in ESCC. In ESCC xenograft tumours, pharmacological autophagy inhibition with chloroquine derivatives depletes cells with high CD44 expression while promoting oxidative stress. Autophagic flux impairment during EMT-mediated CD44L to CD44H cell conversion in vitro induces mitochondrial dysfunction, oxidative stress and cell death. During CD44H cell generation, transformed keratinocytes display evidence of mitophagy, including mitochondrial fragmentation, decreased mitochondrial content and mitochondrial translocation of Parkin, essential in mitophagy. RNA interference-mediated Parkin depletion attenuates CD44H cell generation. These data suggest that autophagy facilitates EMT-mediated CD44H generation via modulation of redox homeostasis and Parkin-dependent mitochondrial clearance. This is the first report to implicate mitophagy in regulation of tumour cells with high CD44 expression, representing a potential novel therapeutic avenue in cancers where EMT and CD44H cells have been implicated, including ESCC.

Esophageal cancer is a deadly disease, ranking sixth among all cancers in mortality. Despite incremental advances in diagnostics and therapeutics, esophageal cancer still carries a poor prognosis, and thus, there remains a need to elucidate the molecular mechanisms underlying this disease. There is accumulating evidence that a comprehensive understanding of the molecular composition of esophageal cancer requires attention to not only tumor cells but also the tumor microenvironment (TME), which contains diverse cell populations, signaling factors and structural molecules that interact with tumor cells and support all stages of tumorigenesis. In esophageal cancer, environmental exposures can trigger chronic inflammation, which leads to constitutive activation of pro-inflammatory signaling pathways that promote survival and proliferation. Antitumor immunity is attenuated by cell populations such as myeloid-derived suppressor cells and regulatory T cells, as well as immune checkpoints like programmed death-1. Other immune cells such as tumor-associated macrophages can have other pro-tumorigenic functions, including the induction of angiogenesis and tumor cell invasion. Cancer-associated fibroblasts secrete growth factors and alter the extracellular matrix to create a tumor niche and enhance tumor cell migration and metastasis. Further study of how these TME components relate to the different stages of tumor progression in each esophageal cancer subtype will lead to development of novel and specific TME-targeting therapeutic strategies, which offer considerable potential especially in the setting of combination therapy.

Epidermal growth factor receptor (EGFR) signaling has a critical role in oncogenic Kras-driven pancreatic carcinogenesis. However, the downstream targets of this signaling network are largely unknown. We developed a novel model system utilizing murine primary pancreatic ductal epithelial cells (PDECs), genetically engineered to allow time-specific expression of oncogenic Kras(G12D) from the endogenous promoter. We show that primary PDECs are susceptible to Kras(G12D)-driven transformation and form pancreatic ductal adenocarcinomas in vivo after Cdkn2a inactivation. In addition, we demonstrate that activation of Kras(G12D) induces an EGFR signaling loop to drive proliferation. Interestingly, pharmacological inhibition of EGFR fails to decrease Kras(G12D)-activated ERK or PI3K signaling. Instead our data provide novel evidence that EGFR signaling is needed to activate the oncogenic and pro-proliferative transcription factor c-MYC. EGFR and c-MYC have been shown to be essential for pancreatic carcinogenesis. Importantly, our data link both pathways and thereby explain the crucial role of EGFR for Kras(G12D)-driven carcinogenesis in the pancreas.

Notch activity regulates tumor biology in a context-dependent and complex manner. Notch may act as an oncogene or a tumor-suppressor gene even within the same tumor type. Recently, Notch signaling has been implicated in cellular senescence. Yet, it remains unclear as to how cellular senescence checkpoint functions may interact with Notch-mediated oncogenic and tumor-suppressor activities. Herein, we used genetically engineered human esophageal keratinocytes and esophageal squamous cell carcinoma cells to delineate the functional consequences of Notch activation and inhibition along with pharmacological intervention and RNA interference experiments. When expressed in a tetracycline-inducible manner, the ectopically expressed activated form of Notch1 (ICN1) displayed oncogene-like characteristics inducing cellular senescence corroborated by the induction of G0/G1 cell-cycle arrest, Rb dephosphorylation, flat and enlarged cell morphology and senescence-associated β-galactosidase activity. Notch-induced senescence involves canonical CSL/RBPJ-dependent transcriptional activity and the p16(INK4A)-Rb pathway. Loss of p16(INK4A) or the presence of human papilloma virus (HPV) E6/E7 oncogene products not only prevented ICN1 from inducing senescence but permitted ICN1 to facilitate anchorage-independent colony formation and xenograft tumor growth with increased cell proliferation and reduced squamous-cell differentiation. Moreover, Notch1 appears to mediate replicative senescence as well as transforming growth factor-β-induced cellular senescence in non-transformed cells and that HPV E6/E7 targets Notch1 for inactivation to prevent senescence, revealing a tumor-suppressor attribute of endogenous Notch1. In aggregate, cellular senescence checkpoint functions may influence dichotomous Notch activities in the neoplastic context.

Lin28b is an RNA-binding protein that inhibits biogenesis of let-7 microRNAs. LIN28B is overexpressed in diverse cancers, yet a specific role in the molecular pathogenesis of colon cancer has to be elucidated. We have determined that human colon tumors exhibit decreased levels of mature let-7 isoforms and increased expression of LIN28B. To determine LIN28B's mechanistic role in colon cancer, we expressed LIN28B in immortalized colonic epithelial cells and human colon cancer cell lines. We found that LIN28B promotes cell migration, invasion and transforms immortalized colonic epithelial cells. In addition, constitutive LIN28B expression increases expression of intestinal stem cell markers LGR5 and PROM1 in the presence of let-7 restoration. This may occur as a result of Lin28b protein binding LGR5 and PROM1 mRNA, suggesting that a subset of LIN28B functions is independent of its ability to repress let-7. Our findings establish a new role for LIN28B in human colon cancer pathogenesis, and suggest LIN28B post-transcriptionally regulates LGR5 and PROM1 through a let-7-independent mechanism.

Variable drug responses among malignant cells within individual tumors may represent a barrier to their eradication using chemotherapy. Carcinoma cells expressing mesenchymal markers resist conventional and epidermal growth factor receptor (EGFR)-targeted chemotherapy. In this study, we evaluated whether mesenchymal-like sub-populations within human squamous cell carcinomas (SCCs) with predominantly epithelial features contribute to overall therapy resistance. We identified a mesenchymal-like subset expressing low E-cadherin (Ecad-lo) and high vimentin within the upper aerodigestive tract SCCs. This subset was both isolated from the cell lines and was identified in xenografts and primary clinical specimens. The Ecad-lo subset contained more low-turnover cells, correlating with resistance to the conventional chemotherapeutic paclitaxel in vitro. Epidermal growth factor induced less stimulation of the mitogen-activated protein kinase and phosphatidylinositol-3-kinase pathways in Ecad-lo cells, which was likely due to lower EGFR expression in this subset and correlated with in vivo resistance to the EGFR-targeted antibody, cetuximab. The Ecad-lo and high E-cadherin subsets were dynamic in phenotype, showing the capacity to repopulate each other from single-cell clones. Taken together, these results provide evidence for a low-turnover, mesenchymal-like sub-population in SCCs with diminished EGFR pathway function and intrinsic resistance to conventional and EGFR-targeted chemotherapies.

Epidermal growth factor receptor (EGFR) overexpression and activation is critical in the initiation and progression of cancers, especially those of epithelial origin. EGFR activation is associated with the induction of divergent signal transduction pathways and a gamut of cellular processes; however, the cell-type and tissue-type specificity conferred by certain pathways remains to be elucidated. In the context of the esophageal epithelium, a prototype stratified squamous epithelium, EGFR overexpression is relevant in the earliest events of carcinogenesis as modeled in a three-dimensional organotypic culture system. We demonstrate that the phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway, and not the MEK/MAPK (mitogen-activated protein kinase) pathway, is preferentially activated in EGFR-mediated esophageal epithelial hyperplasia, a premalignant lesion. The hyperplasia was abolished with direct inhibition of PI3K and of AKT but not with inhibition of the MAPK pathway. With the introduction of an inducible AKT vector in both primary and immortalized esophageal epithelial cells, we find that AKT overexpression and activation is permissive for complete epithelial formation in organotypic culture, but imposes a growth constraint in cells grown in monolayer. In organotypic culture, AKT mediates changes related to cell shape and size with an expansion of the differentiated compartment.

We analysed breast tumors and breast cancer cell lines for the expression of beta-parvin (ParvB), an adaptor protein that binds to the integrin-linked kinase (ILK). Quantitative RT-PCR indicated that ParvB mRNA was downregulated, by at least 60%, in four of nine breast tumors, relative to patient-matched normal mammary gland tissue. We also found that ParvB protein levels were reduced by > or =90% in five of seven advanced tumors, relative to matched normal breast tissue. Conversely, ILK protein and kinase activity levels were elevated in these tumors, suggesting that downregulation of ParvB stimulates ILK signaling. Western blot analyses indicated very low levels of ParvB protein in MDA-MB-231 and MCF7 breast cancer cells, facilitating functional studies of the effects of ParvB on ILK signaling. Expression of ParvB in MDA-MB-231 and MCF7 cells increased cell adhesion to collagen. ParvB inhibited ILK kinase activity, anchorage-independent cell growth and in vitro matrigel invasion by MDA-MB-231 cells. EGF-induced phosphorylation of two ILK targets, PKB (Ser473) and glycogen synthase kinase 3beta (Ser9), was also inhibited by ParvB. These results indicated that ParvB inhibits ILK signaling downstream of receptor tyrosine kinases. Our results suggest that loss of ParvB expression is a novel mechanism for upregulating ILK activity in tumors.

The ets family of transcription factors comprises many members which contribute to diverse cellular functions that vary depending upon the cell- and tissue-type context. Recently, different groups have identified a novel member of the ets family that is epithelial-specific. Variably called ESE-1, ERT, jen, ESX, this gene is designated currently as ELF3. In order to understand transcriptional regulatory mechanisms mediated by ELF3, we investigated its effect on the human keratin 4 gene promoter based upon the role of keratin 4 in early differentiation of the esophageal squamous epithelium. Interestingly, ELF3 suppressed basal keratin 4 promoter activity in both esophageal and cervical epithelial cancer cell lines, a novel result, while simultaneously activating the late-differentiation linked SPRR2A promoter. Furthermore, serial deletion constructs of the keratin 4 promoter continued to be suppressed by ELF3, a phenomenon that was only partially rescued by ELF3 ets domain mutants, but completely abrogated by deletion of the ELF3 pointed domain. These results suggest that ELF3 may have dual functions in the transcriptional regulation of genes involved in squamous epithelial differentiation. One of these functions may not be exclusively mediated through DNA binding in the context of transcriptional suppression of the keratin 4 promoter.

We previously described the oral-esophageal tissue-specific expression of cyclin D1 with the Epstein-Barr virus ED-L2 promoter in transgenic mice, and resulting dysplasia. Given the evidence for an interplay between environmental and genetic factors in esophageal squamous carcinogenesis, the aim of this study was to determine the potential cooperation of the nitrosamine compound N-nitrosomethylbenzylamine (NMBA), an esophageal specific carcinogen, in the cyclin D1 transgenic mice. NMBA was first demonstrated to induce dysplasia in two strains of inbred mice, C57BL/6 and FVB/N. Subcutaneous NMBA was then administrated to wild type and transgenic mice beginning at 4 weeks of age. Mice were monitored for the duration of the study for general appearance, activity and weight, and were euthanized at 12 and 15 months. Histopathologic analysis revealed increased severity of dysplasia in cyclin D1 mice treated with NMBA compared with treated age-matched wild-type mice and untreated mice. There was also increased proliferating cell nuclear antigen (PCNA) expression in the esophagi of NMBA treated cyclin D1 mice. Taken together, these findings suggest that a genetic alteration, specifically cyclin D1 overexpression and a chemical carinogen, NMBA, may cooperate to increase the severity of esophageal squamous dysplasia, a prominent precursor to carcinoma.

Cyclin D1 in cooperation with its major catalytic partners, cyclin-dependent kinases cdk4 and cdk6, facilitates progression through the G1 phase of the eukaryotic cell cycle, in part through phosphorylation of the retinoblastoma protein. Cyclin D1's oncogenic properties have been suggested by its cooperation with ras or adenovirus E1a to transform cultured cells, as well its overexpression in transgenic mice that leads to breast cancer. Activated by a number of different mechanisms in human cancers, the cyclin D1 gene is frequently amplified in squamous epithelial cancers derived from the head/neck and esophageal regions. In order to study the functional consequences of cyclin D1 overexpression in these squamous epithelial specific sites, we have linked the Epstein-Barr virus ED-L2 promoter to the human cyclin D1 cDNA and utilized this transgene to generate founder lines. This transgene is transcribed specifically in the tongue, esophagus and forestomach, all sharing a stratified squamous epithelium. The transgene protein product localizes to the basal and suprabasal compartments of these squamous epithelial tissues, and mice from different lines develop dysplasia, a prominent precursor to carcinoma, by 16 months of age in contrast to age-matched wild-type mice. This transgenic model is useful in demonstrating cyclin D1 may be a tumor initiating event in aero-upper digestive squamous epithelial tissues.

The Epstein-Barr virus (EBV), a member of the herpesviruses, is a double stranded 170 kilobase DNA virus important in many human benign and malignant conditions. It has been implicated in the pathogenesis of proliferative diseases of lymphocytes and tumors of epithelial derivation. The etiology and pathogenesis of esophageal squamous cell carcinoma (ESCC) is thought to involve a combination of genetic and environmental events which lead to epithelial cell transformation. The aim of this study was to determine whether an association exists between EBV and ESCC. DNA was extracted from 16 human ESCC cell lines and microdissected tumor specimens from 60 patients. The polymerase chain reaction was used to amplify a 400 base pair fragment corresponding to the BamH1W fragment repeat sequence of EBV. Southern blotting, utilizing an oligonucleotide probe specific for the BamH1W sequence, was used to confirm positive results and increase sensitivity of detection. 5/60 tumor samples and 1/16 ESCC cell lines were positive for the EBV sequence. Positive tumor samples were estimated to contain one copy of EBV per 20 cellular genomes. Given the role of EBV in other tumors of epithelial derivation, it is possible that EBV may contribute to the molecular pathogenesis of ESCC.

We and others have recently shown that p16 can potently and specifically inhibit progression through the G1 phase of the replicative cycle in cells that express the retinoblastoma protein (pRB). However, none of these studies examined cell types in which p16 has been firmly implicated in tumorigenesis. We predicted that such cells would show sensitivity to p16 inhibition, perhaps conferred by proteins in addition to or other than pRB. Intragenic, inactivating mutations of p16 have been found at significant frequency in primary tumors derived from squamous epithelial cells of the esophagus (ESCC). We therefore examined p16 function in ESCC lines and in primary squamous epithelial cells cultured from mouse skin. We find that seven of eight ESCC lines tested are inhibited by p16 and fail to express the protein endogenously. The lone p16-resistant line expresses endogenous p16 but lacks functional pRB. Primary squamous epithelial cells are also inhibited by p16. These data suggest that squamous epithelial cells are generally sensitive to inhibition by a regulatory pathway that involves p16 and pRB, and that, by the time of establishment in culture, there is nearly universal inactivation of this pathway in ESCCs.

MTS-1 is a candidate tumor suppressor gene on chromosome 9p21-22, a region frequently observed to have loss of heterozygosity in esophagus squamous cell carcinomas and pancreatic ductal adenocarcinomas. In order to determine whether MTS-1 sequences are deleted or mutated in cell lines derived from these cancers, we performed PCR amplification of MTS-1 exons 1 and 2. In this fashion, we found that 67% of esophagus squamous cancer cell lines have deletions of both exons 1 and 2, and 50% of pancreatic cancer cell lines have similar deletions. Furthermore, an additional 30% of pancreatic cancer cell lines harbored point mutations or microdeletions based on DNA sequencing. MTS-1 encodes p16, an inhibitor of cyclin-dependent kinase 4 (cdk4) which complexes with cyclin D1. Our data suggest that MTS-1 deletions and mutations may play an important role in the molecular pathogenesis of esophagus squamous cell and pancreatic cancers.