Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.5 (thrombin)
 33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A recently identified family of guanine nucleotide exchange factors for Rho that includes PDZ-RhoGEF, LARG, and p115RhoGEF exhibits a unique structural feature consisting in the presence of area of similarity to regulators of G protein signaling (RGS). This RGS-like (RGL) domain provides a structural motif by which heterotrimeric G protein alpha subunits of the Galpha(12) family can bind and regulate the activity of RhoGEFs. Hence, these newly discovered RGL domain-containing RhoGEFs provide a direct link from Galpha(12) and Galpha(13) to Rho. Recently available data suggest, however, that tyrosine kinases can regulate the ability of G protein-coupled receptors (GPCRs) to stimulate Rho, although the underlying molecular mechanisms are still unknown. Here, we found that the activation of thrombin receptors endogenously expressed in HEK-293T cells leads to a remarkable increase in the levels of GTP-bound Rho within 1 min (11-fold) and a more limited but sustained activation (4-fold) thereafter, which lasts even for several hours. Interestingly, tyrosine kinase inhibitors did not affect the early phase of Rho activation, immediately after thrombin addition, but diminished the levels of GTP-bound Rho during the delayed phase. As thrombin receptors stimulate focal adhesion kinase (FAK) potently, we explored whether this non-receptor tyrosine kinase participates in the activation of Rho by GPCRs. We obtained evidence that FAK can be activated by thrombin, Galpha(12), Galpha(13), and Galpha(q) through both Rho-dependent and Rho-independent mechanisms and that PDZ-RhoGEF and LARG can in turn be tyrosine-phosphorylated through FAK in response to thrombin, thereby enhancing the activation of Rho in vivo. These data indicate that FAK may act as a component of a positive feedback loop that results in the sustained activation of Rho by GPCRs, thus providing evidence of the existence of a novel biochemical route by which tyrosine kinases may regulate the activity of Rho through the tyrosine phosphorylation of RGL-containing RhoGEFs.
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PMID:Regulation of G protein-linked guanine nucleotide exchange factors for Rho, PDZ-RhoGEF, and LARG by tyrosine phosphorylation: evidence of a role for focal adhesion kinase. 1179 11

Thrombin and lysophosphatidic acid (LPA) receptors play important roles in vascular biology, development, and cancer. These receptors activate rho via G(12/13) family heterotrimeric G proteins, which are known to directly activate three distinct rho guanine nucleotide exchange factors (rhoGEFs) that contain a regulator of G protein signaling (RGS) domain (RGS-rhoGEFs). However, it is not known which, if any, of these RGS-rhoGEFs (LARG (leukemia-associated rhoGEF), p115rhoGEF, or PDZrhoGEF) plays a role in G protein-coupled receptor-stimulated rho signaling. Using oligonucleotide small interfering RNAs that suppress specific RGS-rhoGEF expression, we show that thrombin receptor stimulation of rho is primarily mediated by LARG in HEK293T and PC-3 prostate cancer cell lines. In contrast, the LPA-stimulated rho response in PC-3 cells is dependent on PDZrhoGEF expression. Suppression of p115rhoGEF had no effect. Thus different rhoGEFs (LARG and PDZrhoGEF) mediate downstream rho signaling by the thrombin and LPA receptors.
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PMID:Thrombin and lysophosphatidic acid receptors utilize distinct rhoGEFs in prostate cancer cells. 1514 72

The strict spatio-temporal control of Rho GTPases is critical for many cellular functions, including cell motility, contractility, and growth. In this regard, the prototypical Rho family GTPases, Rho, Rac, and Cdc42 regulate the activity of each other by a still poorly understood mechanism. Indeed, we found that constitutively active forms of Rac inhibit stress fiber formation and Rho stimulation by thrombin. Surprisingly, a mutant of Rac that is unable to activate Pak1 failed to inhibit thrombin signaling to Rho. To explore the underlying mechanism, we investigated whether Pak1 could regulate guanine nucleotide exchange factors (GEFs) for Rho. We found that Pak1 associates with P115-RhoGEF but not with PDZ-RhoGEF or LARG, and knock down experiments revealed that P115-RhoGEF plays a major role in signaling from thrombin receptors to Rho in HEK293T cells. Pak1 binds the DH-PH domain of P115-RhoGEF, thus suggesting a mechanism by which Rac stimulation of Pak1 may disrupt receptor-dependent Rho signaling. In agreement, expression of a dominant-negative Pak-Inhibitory Domain potentiated the activation of Rho by thrombin, and prevented the inhibition of Rho by Rac. These findings indicate that Rac interferes with receptor-dependent Rho stimulation through Pak1, thus providing a mechanism for cross-talk between these two small-GTPases.
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PMID:Rac inhibits thrombin-induced Rho activation: evidence of a Pak-dependent GTPase crosstalk. 1722 83

To understand the role of epidermal growth factor receptor (EGFR) transactivation in G protein-coupled receptor (GPCR) agonist-induced signaling events, we have studied the capacity of thrombin in the activation of Gab1-SHP2 in vascular smooth muscle cells (VSMCs). Thrombin activated both Gab1 and SHP2 in EGFR-dependent manner. Similarly, thrombin induced Rac1 and Cdc42 activation, and these responses were suppressed when either Gab1 or SHP2 stimulation is blocked. Thrombin also induced PAK1 activation in a time- and EGFR-Gab1-SHP2-Rac1/Cdc42-dependent manner. Inhibition of activation of EGFR, Gab1, SHP2, Rac1, Cdc42, or PAK1 by pharmacological or genetic approaches attenuated thrombin-induced VSMC stress fiber formation and motility. Thrombin activated RhoA in a time-dependent manner in VSMCs. LARG, a RhoA-specific GEF (guanine nucleotide exchange factor), was found to be associated with Gab1 and siRNA-mediated depletion of its levels suppressed RhoA, Rac1 and PAK1 activation. Dominant negative mutant-mediated interference of RhoA activation inhibited thrombin-induced Rac1 and PAK1 stimulation in VSMCs and their stress fiber formation and migration. Balloon injury induced PAK1 activity and interference with its activation led to attenuation of SMC migration from media to intima, resulting in reduced neointima formation and increased lumen size. Inhibition of thrombin signaling by recombinant hirudin also blocked balloon injury-induced EGFR tyrosine phosphorylation and PAK1 activity. These results show that thrombin-mediated PAK1 activation plays a crucial role in vascular wall remodeling and it could be a potential target for drug development against these vascular lesions.
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PMID:A role for Gab1/SHP2 in thrombin activation of PAK1: gene transfer of kinase-dead PAK1 inhibits injury-induced restenosis. 1935 98