MgcRacGAP Is Involved in Cytokinesis through Associating with Mitotic Spindle and Midbody

Abstract

We have recently cloned a cDNA for a full-length form of MgcRacGAP. Here we show using anti-MgcRacGAP antibodies that, unlike other known GAPs for Rho family, MgcRacGAP localized to the nucleus in interphase, accumulated to the mitotic spindle in metaphase, and was condensed in the midbody during cytokinesis. Overexpression of an N-terminal deletion mutant resulted in the production of multinucleated cells in HeLa cells. This mutant lost the ability to localize in the mitotic spindle and midbody. MgcRacGAP was also found to bind ␣-, ␤-, and ␥-tubulins through its N-terminal myosin-like domain. These results indicate that MgcRacGAP dynamically moves during cell cycle progression probably through binding to tubulins and plays critical roles in cytokinesis. Furthermore, using a GAP-inactive mutant, we have shown that the GAP activity of MgcRac-GAP is required for cytokinesis, suggesting that inactivation of the Rho family of GTPases may be required for normal progression of cytokinesis.

Abr and Bcr, Two Homologous Rac GTPase-Activating Proteins, Control Multiple Cellular Functions of Murine Macrophages

“…Several GAP-defective Rho GAPs act in a dominant negative manner by sequestering substrate GTPases, preventing their inactivation but still allowing their interaction with downstream effectors (23,29,32). We showed that the GAP mutants of Abr and Bcr could still bind to caRac, providing evidence that these act as dominant negative proteins.…”

Implantation of the human embryo requires Rac1-dependent endometrial stromal cell migration

“…RacGAP1 is a GTPase-activating protein that has been implicated in controlling cell growth and differentiation (35) and cytokinesis (25) (24,36), and this may depend on its phosphorylation status (37). In contrast, some studies suggest that RacGAP1 is able to mediate some of its functions independently of its GAP activity (38).…”

“…Immunohistochemistry of hESC monolayers demonstrated that, as seen for other cell types (25,26), RacGAP1 localized to the nucleus and cytosolic structures of hESCs (Fig. 6B).…”

Role of the Midbody Matrix in Cytokinesis: RNAi and Genetic Rescue Analysis of the Mammalian Motor Protein CHO1

“…Interestingly, both NLS sequences are strictly conserved among all vertebrate homologues of CHO1, identified in human, mouse, chicken and zebrafish . Moreover, all three proteins: CHO1/MKLP1, CYK-4/ MgcRacGAP, and Rho GEF ECT2, which appear to exist in a complex (Somers and Saint, 2003), have an NLS and are localized to the nucleus in mammalian cells (Tatsumoto et al, 1999;Hirose et al, 2001;Mishima et al, 2002), suggesting the importance of nuclear localization. Therefore, CHO1 may have to establish interactions with those molecules to become fully active during cytokinesis.…”