LAMININ MEDIATES BASEMENT-MEMBRANE INDUCED-DIFFERENTIATION OF HEC 1B ENDOMETRIAL ADENOCARCINOMA CELLS

In vitro studies on endometrial carcinogenesis have been hampered by l imited differentiation of the cells in culture. Using the endometrial carcinoma cell lines HEC 1B and its subclone HEC 1B(L), we established and characterized cell culture conditions that preserve a more differ entiated state of the tumor cells. Randomly seeded HEC 1B(L) cells, if grown in a serum-free defined medium on top of a reconstituted baseme nt membrane (Matrigel), within a few hours assembled themselves to web like structures. In a thick layer of Matrigel, they showed an even mor e pronounced morphological differentiation. Functionally, two addition al secretory proteins, about 31 and 77 kDa in size, became apparent as a response to matrigel. To further investigate the regulatory role of the extracellular matrix in the process of in vitro differentiation o f endometrial adenocarcinoma cells, we addressed two specific problems . First, we investigated if the capacity of in vitro differentiation i s a specific feature of HEC 1B(L) cells or if it is common to all endo metrial adenocarcinoma cells. Second, we tried to identify the Matrige l component(s) responsible for in vitro differentiation. The assembly of HEC 1B and HEC 1B(L) cells into spatially organized web-like struct ures and the expression of the 77 kDa protein were thereby used as an assay. All endometrial adenocarcinoma cell Lines tested to a variable degree formed web-like structures on Matrigel. Although the pattern of de novo synthesized secretory proteins changed as a response to Matri gel, only HEC 1A, HEC 1B, HEC 1B(L), and Ishikawa cells responded to c ulture on Matrigel by an increased expression of the 77 kDa protein. F unctionally, polyclonal anti-laminin antibodies, but not anti-collagen type IV antibodies, disrupted formation of web-like structures by HEC 1B cells. The laminin-specific peptides YIGSR and SIKVAV but none of the RGD-peptides RODS, GRODSP, or GRADSP affected the three-dimensiona l assembly of these cells in vitro. Both anti-laminin antibodies and l aminin-specific peptides suppressed Matrigel-induced formation of the 77-kDa secretory protein by HEC 1B cells. These findings suggest the i nvolvement of laminin in the in vitro differentiation of the HEC 1B en dometrial adenocarcinoma cell line. In a mechanistic view, laminin app ears to play a crucial role in the regulation of this in vitro differe ntiation process.