Tumor cell budding and laminin-5 expression in colorectal carcinoma can bemodulated by the tissue micro-environment

Expression of laminin-5 alpha3, beta3 and gamma2 protein subunits was inves tigated in colorectal adenocarcinomas using immunostaining and confocal mic roscopy. The laminin-5 heterotrimer was found in basement membranes and as extracellular deposits in tumor stroma. In contrast to the alpha3 subunit, which was under-expressed, the gamma2 and beta3 subunits were detected in t he cytoplasm of carcinoma cells dissociating (budding) from neoplastic tubu les, suggestive of focal alterations in laminin-5 assembly and secretion. L aminin-5 gamma2 or beta3 subunit-reactive budding carcinoma cells expressed cytokeratins but not vimentin; they did not proliferate and were not apopt otic. Furthermore, expression of laminin-5 gamma2 and beta3 subunits in bud ding cells was associated with focal underexpression of the E-cadherin-beta -catenin complex. Results from xenograft experiments showed that budding a ctivity in colorectal adenocarcinomas could be suppressed when these tumors grew at ectopic s.c. sites in nude mice. In vitro, cultured colon carcinom a cells, but not adenoma-derived tumor cells, shared the laminin-5 phenotyp e expressed by carcinoma cells in vivo. Using colon carcinoma cell lines im planted orthotopically and invading the cecum of nude mice, the laminin-5-a ssociated budding was restored, indicating that this phenotype is not only determined by tumor cell properties but also dependent on the tissue micro environment. Our results indicate that both laminin-5 alpha3 subunit expres sion and cell-cell cohesiveness are altered in budding carcinoma cells, whi ch we consider to be actively invading. We propose that the local tissue mi cro-environment contributes to these events. (C) 2000 Wiley-Liss, Inc.