Abstract
RhoA, the founding member of mammalian Rho GTPase family, is thought to be essential for actomyosin regulation. To date, the physiologic function of RhoA in mammalian cell regulation has yet to be determined genetically. Here we have created RhoA conditional knock-out mice. Mouse embryonic fibroblasts deleted of RhoA showed no significant change in actin stress fiber or focal adhesion complex formation in response to serum or LPA, nor any detectable change in Rho-kinase signaling activity. Concomitant knock-out or knockdown of RhoB and RhoC in the RhoA(-/-) cells resulted in a loss of actin stress fiber and focal adhesion similar to that of C3 toxin treatment. Proliferation of RhoA(-/-) cells was impaired due to a complete cell cycle block during mitosis, an effect that is associated with defective cytokinesis and chromosome segregation and can be readily rescued by exogenous expression of RhoA. Furthermore, RhoA deletion did not affect the transcriptional activity of Stat3, NFκB, or serum response factor, nor the expression of the cell division kinase inhibitor p21(Cip)1 or p27(Kip1). These genetic results demonstrate that in primary mouse embryonic fibroblasts, RhoA is uniquely required for cell mitosis but is redundant with related RhoB and RhoC GTPases in actomyosin regulation.
Highlights
RhoA is a founding member of the mammalian Rho GTPase family and has been implicated in a variety of roles in cell regulation, mostly by the dominant negative mutant expression approach or applying C3 bacterial toxin that covalently modifies the effector domain of RhoA and other related Rho GTPases (1–3)
We present genetic data to unambiguously demonstrate an essential role of RhoA in regulating cell cytokinesis and a dispensable, redundant role with RhoB and RhoC in regulating the actomyosin and adhesion machineries in primary mouse embryonic fibroblasts (MEFs).[2]
In the present studies, we have presented genetic data to unambiguously demonstrate an essential role of RhoA in regulating cell mitosis, but surprisingly, a dispensable, redundant role in regulating cell actomyosin machineries in MEFs
Summary
RhoA is a founding member of the mammalian Rho GTPase family and has been implicated in a variety of roles in cell regulation, mostly by the dominant negative mutant expression approach or applying C3 bacterial toxin that covalently modifies the effector domain of RhoA and other related Rho GTPases (1–3). Mouse embryonic fibroblasts deleted of RhoA showed no significant change in actin stress fiber or focal adhesion complex formation in response to serum or LPA, nor any detectable change in Rho-kinase signaling activity. These genetic results demonstrate that in primary mouse embryonic fibroblasts, RhoA is uniquely required for cell mitosis but is redundant with related RhoB and RhoC GTPases in actomyosin regulation.
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