RhoA GTPase regulates B cell receptor signaling.
ABSTRACT The RhoA GTPase controls many cellular functions, including gene transcription and actin polymerization. Several lines of evidence suggest that Rho GTPases are required for B cell receptor (BCR) signaling, but whether RhoA is necessary has not been investigated. Here, we show that RhoA is activated, downstream of PI3K, in response to BCR stimulation and is important for BCR-dependent calcium flux and cell proliferation. A RhoA dominant-negative mutant strongly inhibited BCR-dependent calcium mobilization. The RhoA-specific inhibitor, C3 toxin, inhibited both BCR-dependent calcium flux and cell proliferation. RhoA is important for BCR-dependent synthesis of IP(3) by PLCgamma2, but is not required for tyrosine phosphorylation of PLCgamma2. BCR-dependent synthesis of phosphatidylinositol-4,5-bisphosphate (PtdIns-4,5-P(2)) is inhibited in the absence of RhoA function. Providing exogenous PtdIns-4,5-P(2) restores BCR-dependent calcium flux in cells lacking functional RhoA. Our findings support a function for RhoA in BCR-dependent PtdIns-4,5-P(2) synthesis, PLCgamma2 activation, calcium mobilization, and cell proliferation.
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ABSTRACT: The in vivo validation of cancer mutations and genes identified in cancer genomics is resource-intensive because of the low throughput of animal experiments. We describe a mouse model that allows multiple cancer mutations to be validated in each animal line. Animal lines are generated with multiple candidate cancer mutations using transposons. The candidate cancer genes are tagged and randomly expressed in somatic cells, allowing easy identification of the cancer genes involved in the generated tumors. This system presents a useful, generalized and efficient means for animal validation of cancer genes.Genome Biology 09/2014; 15(9):455. DOI:10.1186/PREACCEPT-8659955961236524 · 10.47 Impact Factor
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ABSTRACT: The small Rho GTPase Cdc42, known to interact with Wiskott-Aldrich syndrome (WAS) protein, is an important regulator of actin remodeling. Here, we show that genetic ablation of Cdc42 exclusively in the B cell lineage is sufficient to render mice unable to mount antibody responses. Indeed Cdc42-deficient mice are incapable of forming germinal centers or generating plasma B cells upon either viral infection or immunization. Such severe immune deficiency is caused by multiple and profound B cell abnormalities, including early blocks during B cell development; impaired antigen-driven BCR signaling and actin remodeling; defective antigen presentation and in vivo interaction with T cells; and a severe B cell-intrinsic block in plasma cell differentiation. Thus, our study presents a new perspective on Cdc42 as key regulator of B cell physiology. © 2015 Burbage et al.Journal of Experimental Medicine 01/2015; 212(1):53. DOI:10.1084/jem.20141143 · 13.91 Impact Factor
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ABSTRACT: The Ras-related guanosine triphosphatase RhoA mediates pathological cardiac hypertrophy, but also promotes cell survival and is cardioprotective after ischemia/reperfusion injury. To understand how RhoA mediates these opposing roles in the myocardium, we generated mice with a cardiomyocyte-specific deletion of RhoA. Under normal conditions, the hearts from these mice showed functional, structural, and growth parameters similar to control mice. Additionally, the hearts of the cardiomyocyte-specific, RhoA-deficient mice subjected to transverse aortic constriction (TAC)-a procedure that induces pressure overload and, if prolonged, heart failure-exhibited a similar amount of hypertrophy as those of the wild-type mice subjected to TAC. Thus, neither normal cardiac homeostasis nor the initiation of compensatory hypertrophy required RhoA in cardiomyocytes. However, in response to chronic TAC, hearts from mice with cardiomyocyte-specific deletion of RhoA showed greater dilation, with thinner ventricular walls and larger chamber dimensions, and more impaired contractile function than those from control mice subjected to chronic TAC. These effects were associated with aberrant calcium signaling, as well as decreased activity of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and AKT. In addition, hearts from mice with cardiomyocyte-specific RhoA deficiency also showed less fibrosis in response to chronic TAC, with decreased transcriptional activation of genes involved in fibrosis, including myocardin response transcription factor (MRTF) and serum response factor (SRF), suggesting that the fibrotic response to stress in the heart depends on cardiomyocyte-specific RhoA signaling. Our data indicated that RhoA regulates multiple pathways in cardiomyocytes, mediating both cardioprotective (hypertrophy without dilation) and cardio-deleterious effects (fibrosis).Science Signaling 10/2014; 7(348):ra100. DOI:10.1126/scisignal.2005262 · 7.65 Impact Factor