Role of mgcracgap as a regulator of the small gtpase rho family in differentiation and cytokinesis

Abstract To identify the key molecule which regulats proliferation and differentiation of hematopoietic cells, we carried out retrovirus-mediated functional cDNA screening based on the ability to suppress IL-6 induced differentiation of mouse myeloid leukemic M1 cells, and an antisense cDNA encoding a full-length mouse MgcRacGAP was isolated. We also isolated a full-length of human MgcRacGAP cDNA, which was found to encode additional N terminal 105 amino acid residues compared with the previously published human MgcRacGAP. Overexpression of the full-length form of MgcRacGAP in human HL-60 leukemic cells induced growth suppression and macrophage differentiation. To determine how this protein regulats differentiation and proliferation, an antibody against MgcRacGAP was prepared. Immunohistochemical study revealed MgcRacGAP exhibits nuclear localization in interphase, spreads throughout cytoplasm in prometaphase, and condenses in the central spindle in metaphase to telophase. Overexpression of the N-terminal domain deletion mutant, which lacks the ability to condense into the central spindle, or a GAP-inactive mutant resulted in the formation of multinucleated cells without affecting nuclear division. These results suggest that this GAP regulats differentiation and cytokinesis of hematopoietic cells as a regulator of Rho family of GTPase.