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GTPase Activating Protein (gtpase + activating_protein)

Distribution by Scientific Domains

Medical Sciences	50%

Selected Abstracts

ROS-inhibitory activity of YopE is required for full virulence of Yersinia in mice

CELLULAR MICROBIOLOGY, Issue 7 2010
Warangkhana Songsungthong
Summary YopE, a type III secreted effector of Yersinia, is a GTPase Activating Protein for Rac1 and RhoA whose catalytic activity is critical for virulence. We found that YopE also inhibited reactive oxygen species (ROS) production and inactivated Rac2. How YopE distinguishes among its targets and which specific targets are critical for Yersinia survival in different tissues are unknown. A screen identifying YopE mutants in Yersinia pseudotuberculosis that interact with different Rho GTPases showed that YopE residues at positions 102, 106, 109 and 156 discern among switch I and II regions of Rac1, Rac2 and RhoA. Two mutants, which expressed YopE alleles with different antiphagocytic, ROS-inhibitory and cell-rounding activities, YptbL109A and YptbESptP, were studied in animal infections. Inhibition of both phagocytosis and ROS production were required for splenic colonization, whereas fewer YopE activities were required for Peyer's patch colonization. This study shows that Y. pseudotuberculosis encounters multiple host defences in different tissues and uses distinct YopE activities to disable them. [source]

Differential actions of p60c-Src and Lck kinases on the Ras regulators p120-GAP and GDP/GTP exchange factor CDC25Mm

FEBS JOURNAL, Issue 11 2001
Carmela Giglione
It is known that the human Ras GTPase activating protein (GAP) p120-GAP can be phosphorylated by different members of the Src kinase family and recently phosphorylation of the GDP/GTP exchange factor (GEF) CDC25Mm/GRF1 by proteins of the Src kinase family has been revealed in vivo[Kiyono, M., Kaziro, Y. & Satoh, T. (2000) J. Biol. Chem.275, 5441,5446]. As it still remains unclear how these phosphorylations can influence the Ras pathway we have analyzed the ability of p60c-Src and Lck to phosphorylate these two Ras regulators and have compared the activity of the phosphorylated and unphosphorylated forms. Both kinases were found to phosphorylate full-length or truncated forms of GAP and GEF. The use of the catalytic domain of p60c-Src showed that its SH3/SH2 domains are not required for the interaction and the phosphorylation of both regulators. Remarkably, the phosphorylations by the two kinases were accompanied by different functional effects. The phosphorylation of p120-GAP by p60c-Src inhibited its ability to stimulate the Ha-Ras-GTPase activity, whereas phosphorylation by Lck did not display any effect. A different picture became evident with CDC25Mm; phosphorylation by Lck increased its capacity to stimulate the GDP/GTP exchange on Ha-Ras, whereas its phosphorylation by p60c-Src was ineffective. Our results suggest that phosphorylation by p60c-Src and Lck is a selective process that can modulate the activity of p120-GAP and CDC25Mm towards Ras proteins. [source]

DLC-1 suppresses non-small cell lung cancer growth and invasion by RhoGAP-dependent and independent mechanisms

MOLECULAR CARCINOGENESIS, Issue 5 2008
Kevin D. Healy
Abstract Expression of the tumor suppressor deleted in liver cancer-1 (DLC-1) is lost in non-small cell lung (NSCLC) and other human carcinomas, and ectopic DLC-1 expression dramatically reduces proliferation and tumorigenicity. DLC-1 is a multi-domain protein that includes a Rho GTPase activating protein (RhoGAP) domain which has been hypothesized to be the basis of its tumor suppressive actions. To address the importance of the RhoGAP function of DLC-1 in tumor suppression, we performed biochemical and biological studies evaluating DLC-1 in NSCLC. Full-length DLC-1 exhibited strong GAP activity for RhoA as well as RhoB and RhoC, but only very limited activity for Cdc42 in vitro. In contrast, the isolated RhoGAP domain showed 5- to 20-fold enhanced activity for RhoA, RhoB, RhoC, and Cdc42. DLC-1 protein expression was absent in six of nine NSCLC cell lines. Restoration of DLC-1 expression in DLC-1-deficient NSCLC cell lines reduced RhoA activity, and experiments with a RhoA biosensor demonstrated that DLC-1 dramatically reduces RhoA activity at the leading edge of cellular protrusions. Furthermore, DLC-1 expression in NSCLC cell lines impaired both anchorage-dependent and -independent growth, as well as invasion in vitro. Surprisingly, we found that the anti-tumor activity of DLC-1 was due to both RhoGAP-dependent and -independent activities. Unlike the rat homologue p122RhoGAP, DLC-1 was not capable of activating the phospholipid hydrolysis activity of phospholipase C-,1. Combined, these studies provide information on the mechanism of DLC-1 function and regulation, and further support the role of DLC-1 tumor suppression in NSCLC. © 2007 Wiley-Liss, Inc. [source]

RGS4 Controls Renal Blood Flow and Inhibits Cyclosporine-Mediated Nephrotoxicity

AMERICAN JOURNAL OF TRANSPLANTATION, Issue 2 2010
A. Siedlecki
Calcineurin inhibitors (CNI) are powerful immunomodulatory agents that produce marked renal dysfunction due in part to endothelin-1-mediated reductions in renal blood flow. Ligand-stimulated Gq protein signaling promotes the contraction of smooth muscle cells via phospholipase C,-mediated stimulation of cytosolic calcium release. RGS4 is a GTPase activating protein that promotes the deactivation of Gq and Gi family members. To investigate the role of G protein-mediated signaling in the pathogenesis of CNI-mediated renal injury, we used mice deficient for RGS4 (rgs4,/,). Compared to congenic wild type control animals, rgs4,/, mice were intolerant of the CNI, cyclosporine (CyA), rapidly developing fatal renal failure. Rgs4,/, mice exhibited markedly reduced renal blood flow after CyA treatment when compared to congenic wild type control mice as measured by magnetic resonance imaging (MRI). Hypoperfusion was reversed by coadministration of CyA with the endothelin antagonist, bosentan. The MAPK/ERK pathway was activated by cyclosporine administration and was inhibited by cotreatment with bosentan. These results show that endothelin-1-mediated Gq protein signaling plays a key role in the pathogenesis of vasoconstrictive renal injury and that RGS4 antagonizes the deleterious effects of excess endothelin receptor activation in the kidney. [source]