Laminin mediates basement membrane induced differentiation of HEC 1B endometrial adenocarcinoma cells.

In vitro studies on endometrial carcinogenesis have been hampered by limited 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 differentiated state of the tumor cells. Randomly seeded HEC 1B(L) cells, if grown in a serum-free defined medium on top of a reconstituted basement membrane (Matrigel), within a few hours assembled themselves to web-like structures. In a thick layer of Matrigel, they showed an even more pronounced morphological differentiation. Functionally, two additional 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 of endometrial adenocarcinoma cells, we addressed two specific problems. First, we investigated if the capacity of in vitro differentiation is a specific feature of HEC 1B(L) cells or if it is common to all endometrial adenocarcinoma cells. Second, we tried to identify the Matrigel component(s) responsible for in vitro differentiation. The assembly of HEC 1B and HEC 1B(L) cells into spatially organized web-like structures 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 Matrigel, only HEC 1A, HEC 1B, HEC 1B(L), and Ishikawa cells responded to culture on Matrigel by an increased expression of the 77 kDa protein. Functionally, 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 RGDS, GRGDSP, or GRADSP affected the three-dimensional assembly of these cells in vitro. Both anti-laminin antibodies and laminin-specific peptides suppressed Matrigel-induced formation of the 77-kDa secretory protein by HEC 1B cells. These findings suggest the involvement of laminin in the in vitro differentiation of the HEC 1B endometrial adenocarcinoma cell line. In a mechanistic view, laminin appears to play a crucial role in the regulation of this in vitro differentiation process.