Loss of integrin alpha3 expression associated with acquisition of invasive potential by ovarian clear cell adenocarcinoma cells

Novel monoclonal antibody against integrin α3 shows therapeutic potential for ovarian cancer

Ovarian cancer has a high recurrence rate after platinum‐based chemotherapy. To improve the treatment of ovarian cancer and identify ovarian cancer‐specific antibodies, we immunized mice with the human ovarian carcinoma cell line, SKOV‐3, and generated hybridoma clones. Several rounds of screening yielded 30 monoclonal antibodies (mAbs) with no cross‐reactivity to normal cells. Among these mAbs, OV‐Ab 30‐7 was found to target integrin α3 and upregulate p53 and p21, while stimulating the apoptosis of cancer cells. We further found that binding of integrin α3 by OV‐Ab 30‐7 impaired laminin‐induced focal adhesion kinase phosphorylation. The mAb alone or in combination with carboplatin and paclitaxel inhibited tumor progression and prolonged survival of tumor‐bearing mice. Moreover, immunohistochemical staining of ovarian patient specimens revealed higher levels of integrin α3 in cancer cells compared with normal cells. By querying online clinical databases, we found that elevated ITGA3 expression in ovarian cancer is associated with poor prognosis. Taken together, our data suggest that the novel mAb, OV‐Ab 30‐7, may be considered as a potential therapeutic for ovarian cancer.

Heterotypic CAF-tumor spheroids promote early peritoneal metastatis of ovarian cancer

The study provides insights in HGSOC by identifying that ascitic CAFs selectively recruit ITGA5^high ascitic tumor cells to form heterotypic spheroids named metastatic units (MUs), which actively engage in peritoneal metastasis, discriminates HGSOC from LGSOC, and act as therapeutic targets in hampering OC metastasis.

High-grade serous ovarian cancer (HGSOC) is hallmarked by early onset of peritoneal dissemination, which distinguishes it from low-grade serous ovarian cancer (LGSOC). Here, we describe the aggressive nature of HGSOC ascitic tumor cells (ATCs) characterized by integrin α5^high (ITGA5^high) ATCs, which are prone to forming heterotypic spheroids with fibroblasts. We term these aggregates as metastatic units (MUs) in HGSOC for their advantageous metastatic capacity and active involvement in early peritoneal dissemination. Intriguingly, fibroblasts inside MUs support ATC survival and guide their peritoneal invasion before becoming essential components of the tumor stroma in newly formed metastases. Cancer-associated fibroblasts (CAFs) recruit ITGA5^high ATCs to form MUs, which further sustain ATC ITGA5 expression by EGF secretion. Notably, LGSOC is largely devoid of CAFs and the resultant MUs, which might explain its metastatic delay. These findings identify a specialized MU architecture that amplifies the tumor–stroma interaction and promotes transcoelomic metastasis in HGSOC, providing the basis for stromal fibroblast-oriented interventions in hampering OC peritoneal propagation.

CD151-α3β1 integrin complexes suppress ovarian tumor growth by repressing slug-mediated EMT and canonical Wnt signaling

Human ovarian cancer is diagnosed in the late, metastatic stages but the underlying mechanisms remain poorly understood. We report a surprising functional link between CD151-α3β1 integrin complexes and the malignancy of serous-type ovarian cancer. Analyses of clinical specimens indicate that CD151 expression is significantly reduced or diminished in 90% of metastatic lesions, while it remains detectable in 58% of primary tumors. These observations suggest a putative tumor-suppressing role of CD151 in ovarian cancer. Indeed, our analyses show that knocking down CD151 or α3 integrin enhances tumor cell proliferation, growth and ascites production in nude mice. These changes are accompanied by impaired cell-cell contacts and aberrant expression of E-cadherin, Mucin 5AC and fibronectin, largely reminiscent of an epithelial to mesenchymal transition (EMT)-like change. Importantly, Slug, a master regulator of EMT, is markedly elevated. Knocking down Slug partially restores CD151-α3β1 integrin complex-dependent suppression of cell proliferation. Moreover, disruption of these adhesion protein complexes is accompanied by a concomitant activation of canonical Wnt signaling, including elevated levels of β-catenin and Axin-2 as well as resistance to the inhibition in β-catenin-dependent transcriptional complexes. Together, our study demonstrates that CD151-α3β1 integrin complexes regulate ovarian tumor growth by repressing Slug-mediated EMT and Wnt signaling.

Expression of integrin α3β1 and cyclooxygenase-2 (COX2) are positively correlated in human breast cancer

BACKGROUND

Expression of integrin α3β1 is associated with tumor progression, metastasis, and poor prognosis in several cancers, including breast cancer. Moreover, preclinical studies have revealed important pro-tumorigenic and pro-metastatic functions for this integrin, including tumor growth, survival, invasion, and paracrine induction of angiogenesis. Our previously published work in a preclinical breast cancer model showed that integrin α3β1 promotes expression of cyclooxygenase-2 (COX2/PTGS2), a known driver of breast cancer progression. However, the clinical significance of this regulation was unknown. The objective of the current study was to assess the clinical relevance of the relationship between integrin α3β1 and COX2 by testing for their correlated expression among various forms of human breast cancer.

METHODS

Immunohistochemistry was performed to assess co-expression of α3 and COX2 in specimens of human invasive ductal carcinoma (IDC), either on a commercial tissue microarray (n = 59 samples) or obtained from Albany Medical Center archives (n = 68 samples). Immunostaining intensity for the integrin α3 subunit or COX2 was scored, and Spearman's rank correlation coefficient analysis was performed to assess their co-expression across and within different tumor subtypes or clinicopathologic criteria.

RESULTS

Although expression of integrin α3 or COX2 varied among clinical IDC samples, a statistically significant, positive correlation was detected between α3 and COX2 in both tissue microarrays (r(s) = 0.49, p < 0.001, n = 59) and archived samples (r(s) = 0.59, p < 0.0001, n = 68). In both sample sets, this correlation was independent of hormone receptor status, histological grade, or disease stage.

CONCLUSIONS

COX2 and α3 are correlated in IDC independently of hormone receptor status or other clinicopathologic features, supporting the hypothesis that integrin α3β1 is a determinant of COX2 expression in human breast cancer. These results support the clinical relevance of α3β1-dependent COX2 gene expression that we reported previously in breast cancer cells. The findings also suggest that COX2-positive breast carcinomas of various subtypes might be vulnerable to therapeutic strategies that target α3β1, and that α3 expression might serve as an independent prognostic biomarker.

Identification of integrin α3 as a molecular marker of cells undergoing epithelial-mesenchymal transition and of cancer cells with aggressive phenotypes

Epithelial-mesenchymal transition (EMT) is a crucial event in wound healing, tissue repair, and cancer progression in adult tissues. Transforming growth factor (TGF)-β induces EMT in mouse epithelial cells. During prolonged treatment, TGF-β successively induces myofibroblastic differentiation with increased expression of myofibroblast marker proteins, including smooth muscle α actin and calponin. We recently showed that fibroblast growth factor-2 prevented myofibroblastic differentiation induced by TGF-β, and transdifferentiated the cells to those with much more aggressive characteristics (enhanced EMT). To identify the molecular markers specifically expressed in cells undergoing enhanced EMT induced by the combination of TGF-β and fibroblast growth factor-2, we carried out a microarray-based analysis and found that integrin α3 (ITGA3) and Ret were upregulated. Intriguingly, ITGA3 was also overexpressed in breast cancer cells with aggressive phenotypes and its expression was correlated with that of δEF-1, a key regulator of EMT. Moreover, the expression of both genes was downregulated by U0126, a MEK 1/2 inhibitor. Therefore, ITGA3 is a potential marker protein for cells undergoing enhanced EMT and for cancer cells with aggressive phenotypes, which is positively regulated by δEF-1 and the MEK-ERK pathway.

Transcription factor POU6F1 is important for proliferation of clear cell adenocarcinoma of the ovary and is a potential new molecular target

OBJECTIVE

Clear cell adenocarcinoma of the ovary often shows resistance to anticancer agents. It accounts for 20% of epithelial ovarian cancer in Japan versus around 5% in other countries. We investigated new molecules to use when developing molecular-targeting therapy for clear cell adenocarcinoma.

METHODS

Reverse transcriptase polymerase chain reaction and Western blot analysis were performed to confirm the expression of POU6F1 in several kinds of cell lines derived from epithelial ovarian carcinoma. Microarray analyses were performed using 2 ovarian cancer microarray data sets available on the Internet. Immunohistochemical staining was also done to confirm both the expression and the localization of POU6F1 using human ovarian epithelial ovarian carcinoma tissue specimens. In addition, the gene cluster located downstream of transcription factor POU6F1 was investigated to analyze its role in the proliferation of clear cell adenocarcinoma of the ovary via the lysophosphatidic acid receptor, a G protein-coupled receptor. Furthermore, RNA interference studies with small interfering RNA (siRNA) were performed to assess the effect of POU6F1 on proliferation of xenograft tumors after injection of clear cell adenocarcinoma cells into nude mice.

RESULTS

Expression of POU6F1 at messenger RNA and protein was confirmed in cell lines derived from epithelial ovarian carcinoma. The microarray analyses performed using the 2 ovarian cancer microarray data sets available on the Internet indicated that POU6F1 expression was significantly greater in clear cell adenocarcinoma. Immunostaining confirmed the nuclear localization of POU6F1 in clear cell adenocarcinoma (100%). Exposure to the siRNA for POU6F1 reduced the expression of lysophosphatidic acid receptors, which are G protein-coupled receptors involved in tumor cell proliferation. POU6F1 siRNA dose-dependently suppressed the proliferation of clear cell adenocarcinoma cell lines, and a similar effect was confirmed for tumors transplanted into nude mice.

CONCLUSIONS

Clear cell adenocarcinoma shows little response to standard therapy. The results of this study suggested that the transcription factor POU6F1 could be a new molecular target for treatment of this cancer.

Expression of integrin α3 in colon cancer and its relationship with invasion and metastasis

AIM: To investigate the expression of integrin α3 in colon cancer and its biological significance.

METHODS: Eighty specimens (male: 47 cases; female: 33 cases) of excised colon cancer, 60 lymph nodes, 40 lymph node metastasis tissues (40 cases) and 20 non-metastatic lymph nodes (20 cases) were selected. All specimens were examined through pathological method. Twelve non-tumorous colon mucosal tissues were chosen as controls. Immunohistochemical assay was used to determine the expression of integrin α3.

RESULTS: The positive rates of integrin α3 expression in the primary lesions of colon cancer and lymph node metastasis tissues were obviously lower than those in the non-tumorous colon mucosa and non-metastatic lymph nodes (52/80 vs 12/12; 24/40 vs 18/20, P < 0.05). The expression of integrin α3 in colon cancer had no correlation with the sex and age of patients, but it was weakened gradually with the increasing of Dukes staging and decreasing of tumor differentiation (P < 0.05). In addition, integrin α3 expression in the primary cases with the metastases of lymph node or liver was significantly weaker than that without metastases (25/49 vs 27/31; 1/16 vs 51/64, P < 0.05).

CONCLUSION: The expression of integrinα3 is correlated with the biological behavior of colon cancer.