Polarization of the alpha 6 beta 4 integrin in ovarian carcinomas

By immunizing a BALB/c mouse with a human ovary-carcinoma cell line (IGROV1), grown intraperitoneally in nude mice, a monoclonal antibody (MAb), designated MAR6, was produced and characterized. Immunofluorescence on the immunizing cell line showed a specific labelling by MAR6 at the cell-to-cell contact points. In addition, MAR6 was found to immunoprecipitate the alpha 6 beta 4 integrin complex. Competition tests with MAbs anti-alpha 6, anti-beta 4, anti-beta 1 sub-units demonstrated that the recognized sub-unit is alpha 6. Indirect immunofluorescence on various cell lines gave MAR6 as positive only on alpha 6-positive lines (IGROV1, OVCAR3, SW626, SKOV3, ME4405, Calu3, N592, MDA468, A431 and HT29). Moreover, on IGROV1 and OVCAR3 ovary-carcinoma cells, which normally grow either adhering to the culture flask or forming clumps in suspension in the medium, MAR6 selectively stained the connection points between the cells in clumps, where, in the same position, the presence of the beta 4 sub-unit, laminin and fibronectin was detected. On the contrary, the beta 1 sub-unit was distributed over the whole cell membrane. The same pattern of labelling by these MAbs was observed in 2 cases of ovarian-carcinoma cells present in ascitic fluids obtained from patients. Immunoperoxidase tests performed on cryosections of various normal tissues showed specific reactivity of MAR6 on basal or basolateral membranes of epithelial cells. On cryosections of ovarian tumors, MAR6 reactivity correlated with the degree of tumor differentiation. Indeed, in benign and well-differentiated tumors, a strong basal or basolateral labelling only of cells surrounding the neoplastic nodules was found. On the contrary, on undifferentiated tumors the inner part of the tumor nodules was also progressively labelled, whereas the staining on the border was weak and discontinuous as a result of the alpha 6 sub-unit dispersion on the tumor cell surface.