724 Growth and differentiation of human Caco-2 enterocytes after transfer of the SV40LT oncogene: Status of p53 and RB

Our previous investigations clearly indicate that the transfer of SV40LT in human and murine intestinal epithelial cells induced alterations of the ultrastructural organization and polarization of the resulting immortalized cell lines. We now demonstrate that the functional expression of the SV40LT oncogene in Caco-2 cells (C2) did not modify the enterocytic phenotype, including expression of villin, sucrase-isomaltase, brush border and dome formation. As compared to C2 cells, the transfected C2LT9 cells exhibited similar growth curves and no change in invasive properties in vitro, reduced latency times necessary for manifestation of the tumors in vivo, and increased proportion of cells in the S phase of the cell cycle. The LT antigen-RB complexes are clearly identified at the different phases of the growth curve. Differentiation is characterized by the conversion of Rb into hypophosphorylated forms in mature enterocvtes. These results suggest that: (1) C2 cells and Rb exert a dominant control against LT; (2) the enterocytic differentiation is compatible with LT expression when this oncogene is introduced in proliferating cells already engaged in the differentiation process; (3) Rb and its partners may contribute to the genetic and molecular alterations observed during the progression of human colorectal cancer; (4) LT requires p53 for the expression of his oncogenic activity.