A Rho-specific exchange factor Ect2 is induced from S to M phases in regenerating mouse liver

The ect2 oncogene was originally identified as a transforming complementary DNA (cDNA) from mouse epithelial cells in an expression cloning approach a nd encodes a product related to Rho-specific exchange factors and yeast cel l cycle regulators. To explore the potential role of ect2 in the cell cycle , we examined the expression of the ect2 protooncogene in a liver regenerat ion model in mice after partial (two thirds) hepatectomy. We found that the expression of the ect2 transcript and protein were markedly elevated with the onset of DNA synthesis and remained elevated during G2 and M phases. Th e timing of cct2 expression matched that of proliferating cell nuclear anti gen (PCNA) and partially overlapped cell division cycle 2 (Cdc2) expression . In situ hybridization analysis showed that cct2 was expressed at a high l evel in cells undergoing mitosis in regenerating liver. Moreover, expressio n of a dominant negative or an oncogenic mutant of cct2 in cultured mouse h epatocytes resulted in a large increase in the number of binucleated cells. These findings showed that Ect2 is expressed in a cell cycle-dependent man ner during liver regeneration, and suggest that it has an important role in the regulation of cytokinesis.