ENTEROCYTE DIFFERENTIATION IS COMPATIBLE WITH SV40 LARGE T-EXPRESSIONAND LOSS OF P53 FUNCTION IN HUMAN COLONIC CACO-2 CELLS - STATUS OF THE PRB1 AND PRB2 TUMOR-SUPPRESSOR GENE-PRODUCTS

Transfer of the SV40 large-T (LT) oncogene into isolated human and mur ine intestinal epithelial cells induced alterations of the ultrastruct ural organization and polarization of the resulting immortalized cell lines, We now demonstrate that the functional expression of the SV40 L T antigen in Caco-2 cells did not alter phenotypic markers of differen tiation, including expression of villin, sucrase-isomaltase, brush bor der and dome formation, As compared to parental cells, the transfected Caco-2LT9 cells exhibited similar growth curves and no invasive prope rties in vitro. The major oncogenic function of the SV40 LT antigen in transfected Caco-2 cells is associated with reduced latency times: ne cessary for the manifestation of tumors in athymic nude mice, The Caco -2 cell line contained deleted and mutant p53 alleles (stop codon in p osition 204) and has no detectable truncated p53 protein by Western bl ot, Molecular complexes between the SV40 LT antigen and the retinoblas toma-related proteins pRb1 and Rb2 were clearly identified at the diff erent phases of the growth curve, When compared to normal human coloni c crypts, Caco-2 cell differentiation is related to partial redistribu tion of pRb1 into hypophosphorylated, antiproliferative forms, The pRb 2 protein is found elevated in a subset of human colorectal tumors and their corresponding liver metastases, We conclude that: (1) Caco-2 ce lls exert a dominant control against the oncogenic functions of the LT antigen; (2) loss of p53 function is not restrictive for tile establi shment of polarity and differentiation of the enterocyte lineage; (3) the levels and phosphorylation status of the Rb1 and Rb2 proteins may play important roles in the proliferation and differentiation of norma l and neoplastic human colonic mucosa. (C) 1997 Federation of European Biochemical Societies.