Epithelio-mesenchymal transition in a neoplastic ovarian epithelial hybrid cell line

Purinergic signalling pathway: therapeutic target in ovarian cancer

Background

The lack of early diagnostic tools and the development of chemoresistance have made ovarian cancer (OC) one of the deadliest gynaecological cancers. The tumour microenvironment is characterised by the extracellular release of high levels of ATP, which is followed by the activation of P1 adenosinergic and P2 purinergic signalling systems. The sequential hydrolysis of ATP by the ectonucleotidases CD39 and CD73 generates adenosine, which creates an immune suppressive microenvironment by inhibiting the T and NK cell responses via the A2A adenosine receptor.

Main body of the abstract

In OC, adenosine-induced pAMPK pathway leads to the inhibition of cell growth and proliferation, which offers new treatment options to prevent or overcome chemoresistance. The activation of P2Y12 and P2Y1 purinergic receptors expressed in the platelets promotes epithelial-mesenchymal transition (EMT). The inhibitors of these receptors will be the effective therapeutic targets in managing OC. Furthermore, research on these signalling systems indicates an expanding field of opportunities to specifically target the purinergic receptors for the treatment of OC.

Short conclusion

In this review, we have described the complex purinergic signalling mechanism involved in the development of OC and discussed the merits of targeting the components involved in the purinergic signalling pathway.

Neuronal transcription factor Brn-3a(l) is over expressed in high-grade ovarian carcinomas and tumor cells from ascites of patients with advanced-stage ovarian cancer

Objectives

In view of the recent association of Brn-3 transcription factors with neuroblastomas, cervical, breast, and prostate cancers we examined the expression of Brn-3a(l) in normal ovaries and in different histological grades of ovarian tumors. The expression of Brn-3a(l) was also evaluated in normal ovarian and cancer cell lines and tumor cells isolated from the ascites of advanced-stage ovarian cancer patients.

Methods

Normal ovaries, benign, borderline, grades 1, 2 and 3 ovarian tumors were analyzed by immunohistochemistry for Brn-3a(l) expression. A total of 46 ovarian specimens were included in the study. Immunofluorescence was used to investigate the expression of Brn-3a in normal ovarian and cancer cell lines. Brn-3a(l) expression was also evaluated by Western blot in tumor cells isolated from ascites of advanced-stage ovarian cancer patients and also in ovarian cancer cell lines.

Results

Nearly 12% of normal and benign ovarian tissues and 57% of borderline ovarian tumors were positive for epithelial Brn-3a(l) expression. Stromal staining was higher and it constituted 40% of normal non-cancerous ovaries compared to 50 and 86% in benign and borderline tumors. On the other hand, 85-100% of grades 1, 2 & 3 ovarian tumors demonstrated nuclear and cytoplasmic Brn-3a(l) staining in the epithelium. Stromal staining in grades1, 2 and 3 tumors constituted 71-88% of total staining. Overall, immunoreactive Brn-3a was present in all grades of ovarian tumors. The extent of epithelial and stromal Brn-3a staining was significantly different between the normal and histological grades of tumors (epithelial-χ² = 41.01, df = 20, P = 0.004, stromal-χ² = 24.66. df = 15, P = 0.05). The extent of epithelial staining was significantly higher in grades 1 and 2 ovarian tumors compared to normal ovaries and benign ovarian tumors (p < 0.05). In parallel, stromal staining was significantly higher in grade 3 tumors compared to normal ovaries (p < 0.05). In addition, cytoplasmic and nuclear Brn-3a expression was evident in ovarian cancer cell lines while no such expression was observed in SV40 antigen immortalized normal ovarian cell lines.

Conclusion

These data suggest that like other cancers, Brn-3a(l) expression is enhanced in ovarian tumors and its expression is consistent with its known role in inhibiting apoptosis and enhancing tumorigenesis. Specific targeting of Brn-3a may provide a useful strategy for regulating multiple tumor related genes involved with ovarian carcinomas.

Induction of papillary carcinoma in human ovarian surface epithelial cells using combined genetic elements and peritoneal microenvironment

Papillary differentiation is one of the most common histological features of ovarian cancer, although the underlying mechanism that leads to such differentiation is not known. We hypothesized that human ovarian surface epithelial cells can be transformed into carcinoma with papillary differentiation by overexpressing HER2/neu in these cells. Mice were injected either subcutaneously or intraperitoneally with two immortalized human ovarian surface epithelial cell lines after enforced expression of HER-2/neu. Mice subcutaneously injected with tumor cells from either the T29Nt or T80Nt developed undifferentiated carcinomas. In contrast, mice injected intraperitoneally with T29Nt cells developed papillary carcinoma, and those injected intraperitoneally with T80Nt cells developed undifferentiated carcinoma. Our results demonstrate that ovarian surface epithelial cells can develop into papillary carcinoma in mice, and that the induction of papillary differentiation depends not only on specific genetic modifications but also on the tumor microenvironment and epithelial cell type from ovary from different patients.

Variant HNF1 modulates epithelial plasticity of normal and transformed ovary cells

Ovarian carcinoma arises from the ovarian surface epithelium, which undergoes phenotypic changes characteristic of müllerian epithelium during the first stages of tumorigenesis. The variant isoform of the hepatocyte nuclear factor 1 (vHNF1) is a transcription factor involved in the development of tissues derived from the müllerian duct. Here, we show that vHNF1 knockdown in two ovarian carcinoma cell lines, SKOV3 and IGROV1, leads to reduced E-cadherin (E-cadh) expression and decreased proliferation rate. Accordingly, SKOV3 cells ectopically expressing a dominant-negative (DN) vHNF1 mutant undergo an epithelial-mesenchymal-like transition, acquiring a spindle-like morphology, loss of E-cadh, and disrupted cell-cell contacts. Gene expression profiling of DNvHNF1 cells on the basis of a newly compiled list of epithelial-mesenchymal transition-related genes revealed a correlation between vHNF1 loss-of-function and acquisition of the mesenchymal phenotype. Indeed, phenotypic changes were associated with increased Slug transcription and functionality. Accordingly, vHNF1-transfected immortalized ovarian surface epithelial cells showed down-regulation of Snail and Slug transcripts. In DNvHNF1-transfected SKOV3 cells, growth rate decreased, and in vHNF1-transfected immortalized ovarian surface epithelial cells, growth rate increased. By immunohistochemistry, we found a strong association of vHNF1 with E-cadh in clear cell and in a subset of serous carcinomas, data that could potentially contribute in distinguishing different types of ovarian tumors. Our results may help in understanding the biology of ovarian carcinoma, identifying early detection markers, and opening potential avenues for therapeutic intervention.

Lysophosphatidic acid (LPA) promotes E-cadherin ectodomain shedding and OVCA429 cell invasion in an uPA-dependent manner

OBJECTIVES

To evaluate the role of LPA in regulating E-cadherin cell surface expression, adhesion, and invasion in epithelial ovarian carcinoma (EOC) cells.

METHODS

E-cadherin mRNA expression in OVCA429 and IOSE-29 cells was evaluated by real-time RT-PCR. Immunofluorescence and Western blot analysis were performed to determine cell surface expression and shedding of E-cadherin 80-kDa soluble fragment by LPA. Kinetics of LPA-induced uPA activity was followed with a colorimetric enzymatic assay. Invasion assays were performed in a modified Boyden chamber where cells were allowed to migrate to the bottom compartment through a porous filter coated with collagen. Additionally we measured the 80-kDa form from the ascites of women with stage III/IV EOC.

RESULTS

LPA induces E-cadherin shedding of a soluble 80-kDa fragment. We found that this process is mediated by the uPA proteolytic cascade. High levels of soluble E-cadherin were found in the ascites from women with advanced stage EOC. LPA and a soluble recombinant E-cadherin-Fc chimera promotes invasion of OVCA429 cells.

CONCLUSIONS

LPA induces shedding of an 80-kDa E-cadherin-soluble fragment in an uPA-dependent manner and promotes in vitro invasion. High levels of soluble E-cadherin in malignant ascites may also affect ovarian metastasis.

Serous borderline ovarian tumors in long-term culture: phenotypic and genotypic distinction from invasive ovarian carcinomas

Serous borderline ovarian tumors (SBOTs) are differentiated, slow growing, noninvasive, and have a better prognosis than their invasive counterparts, but recurrence and progression to invasive carcinomas are common, and unlike high-grade serous carcinomas, they tend to be nonresponsive to chemotherapy. However, due to a lack of culture systems and animal models, information about the properties of SBOT and their changes with neoplastic progression is extremely limited. Our objective was to establish a cell culture model for SBOTs and to characterize their phenotype and genotype. We compared cultures derived from two SBOTs, one of which was a short-term culture containing a BRAF mutation but few other cytogenetic changes while the other culture developed into a spontaneously immortalized permanent cell line and had numerical and structural chromosomal abnormalities but lacked RAS/BRAF mutations. Both cultures formed whorl-like epithelial colonies and resembled low-grade invasive carcinomas by their secretion of CA125 and oviduct-specific glycoprotein, production of matrix metalloproteinases, E-cadherin expression, and telomerase activity. Other characteristics associated with neoplastic transformation, including invasiveness, anchorage-independent growth, and tumorigenicity, were not observed. Importantly, cell motility was reduced in both lines, likely contributing to the lack of invasiveness. The results reveal a striking phenotypic similarity between the two cell lines, regardless of their cytogenetic diversity, which suggests that their characteristic phenotype is regulated to a large degree by epigenetic and environmental factors. In conclusion, we have established the first permanent SBOT cell line, which provides a new model to elucidate the undefined relationship of SBOTs to invasive ovarian carcinomas.

The morphogenic function of E-cadherin-mediated adherens junctions in epithelial ovarian carcinoma formation and progression

E-cadherin expression is unusually regulated in epithelial ovarian carcinoma. It is not expressed in poorly cohesive ovarian surface epithelial (OSE) target cells, but is expressed in cohesive pre-malignant lesions and in highly cohesive, well-differentiated tumors where it is membrane associated, presumably in adherens junctions. E-cadherin expression is subsequently suppressed, or its function is disrupted, in late-stage invasive tumors. Here, we observed that increased E-cadherin expression in ovarian carcinoma cells was associated with increased E-cadherin promoter activity, increased adherens junction formation, decreased beta-catenin signaling-dependent LEF-1 activity, and the generation of cohesive spheroids in basement membrane gel culture. Forced expression of wild-type E-cadherin in immortalized OSE cells initiated adherens junction formation, decreased LEF-1 activity, decreased the mesenchymal migration that is a characteristic of OSE cells that have been maintained in monolayer culture, and induced the formation of cohesive spheroids in basement membrane gels. Conversely, forced expression of a dominant-negative E-cadherin mutant in ovarian carcinoma cells disrupted adherens junctions, increased mesenchymal cell migration, and prevented spheroidal morphogenesis without altering LEF-1 signaling. Therefore, in addition to suppressing late-stage tumor progression, E-cadherin-mediated adherens junctions may also contribute to the initial emergence of a cohesive morphogenic phenotype that is a hallmark of differentiated epithelial ovarian carcinoma.

Progressive changes in Met-dependent signaling in a human ovarian surface epithelial model of malignant transformation

We used an experimental in vitro model of human ovarian surface epithelium (OSE), the tissue of origin of >90% of ovarian cancers, to more precisely define the contribution of hepatocyte growth factor (HGF) to various OSE phenotypes at different stages of neoplastic progression. Neoplastic transformation of OSE in cultures was achieved by multiple genetic manipulations, resulting in the nontumorigenic line IOSE-29, the tumorigenic IOSE-Ov29, and the tumor-derived, more highly malignant IOSE-Ov29/T4. We demonstrate here that, compared to IOSE-29, IOSE-Ov29 and IOSE-Ov29/T4 exhibited higher levels of the HGF receptor Met and an increasing duration of ERK1/2 activation with malignant progression, in conjunction with other neoplastic properties. HGF activated Met signaling in all lines but elicited different responses: HGF induced cell dispersion (scattering) and collagen gel invasion in IOSE-Ov29 and IOSE-Ov29/T4 but did not alter the growth pattern of IOSE-29. Inhibition with PD98059 and LY294002 independently prevented HGF-induced invasive growth. Furthermore, our results show that HGF-induced invasion can be mediated through a rapamycin-sensitive p70 S6K cascade, which demonstrates that p70S6K can regulate cell motility in addition to its well-established role in protein synthesis. Taken together, our data correlate specific responses to HGF-mediated signaling with specific signaling pathways and with progressive neoplastic changes.