A novel role for Gqα in α-thrombin-mediated mitogenic signalling pathways
ABSTRACT α-Thrombin activates several G-proteins including members of the Gq, Gi, and G12/13 families, although the physiological importance of these proteins is still not completely understood. We specifically investigated the role of Gqα in modulating α-thrombin-induced mitogenesis. In Gqa1 cells, a stable cell line expressing reduced amounts of Gqα, concentrations of α-thrombin (1 NIH unit/ml), which induce cell cycle reentry and progression into S phase in wild-type IIC9 cells, do not stimulate phosphatidylinositol (PI) hydrolysis, the rapid early phase of ERK activity, and transit through G1 into S phase as quantified by cyclin-dependent kinase (CDK)4–cyclin D activity and [3H]thymidine incorporation. Interestingly, high concentrations of α-thrombin restore these activities and cell cycle progression into S phase. While, it is well documented that α-thrombin-induced sustained ERK activity mediates important responses for transit through G1 into S phase, the importance of the rapid, Gq-dependent phase as a prerequisite for α-thrombin-mediated mitogenesis has not been appreciated.
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ABSTRACT: Human cytomegalovirus (HCMV) retinitis causing retinal detachment and destruction of the blood-retina barrier is closely related to retinal hemorrhage/coagulation. However, the effects of procoagulants on HCMV (re)activation in retinal cells have not been investigated yet. Therefore, we studied whether thrombin modulates the expression of HCMV immediate early (IE) and late (L) genes in cultured human retinal pigment epithelial cells (RPE). Thrombin specifically stimulated the protease-activated receptor-1 (PAR-1) on RPE and, surprisingly, inhibited basal and 12,0-tetradecanoylphorbol 13-acetate-stimulated HCMV IE gene expression in infected RPE. On the other hand, HCMV strongly induced Sp1 DNA binding activity, which was prevented by thrombin/PAR1-mediated Sp1 hyperphosphorylation. Our data suggest that thrombin/PAR-1 may inhibit Sp1-dependent HCMV replication, which might be an important regulatory mechanism for HCMV persistence and replication in RPE.Medical Microbiology and Immunology 12/2004; 193(4):195-203. · 3.55 Impact Factor