Thrombin Protease-activated Receptor-1 Signals through Gq- and G13-initiated MAPK Cascades Regulating c-Jun Expression to Induce Cell Transformation

Abstract

Although the ability of G protein-coupled receptors to stimulate normal and aberrant cell growth has been intensely investigated, the precise nature of the molecular mechanisms underlying their transforming potential are still not fully understood. In this study, we have taken advantage of the potent mitogenic effect of thrombin and the focus-forming activity of one of its receptors, protease-activated receptor-1, to dissect how this receptor coupled to G␣ i , G␣ q/11 , and G␣ 12/13 transduces signals from the membrane to the nucleus to initiate transcriptional events involved in cell transformation. Using endogenous and transfected thrombin receptors in NIH 3T3 cells, ectopic expression of muscarinic receptors coupled to G␣ q and G␣ i , and chimeric G protein ␣ subunits and murine fibroblasts deficient in G␣ q/11 , and G␣ 12/13 , we show here that, although coupling to G␣ i is sufficient to induce ERK activation, the ability to couple to G␣ q and/or G␣ 13 is necessary to induce c-jun expression and cell transformation. Furthermore, we show that G␣ q and G␣ 13 can initiate the activation of MAPK cascades, including JNK, p38, and ERK5, which in turn regulate the activity of transcription factors controlling expression from the c-jun promoter. We also present evidence that c-Jun and the kinases regulating its expression are integral components of the transforming pathway initiated by protease-activated receptor-1.

Inhibition of Heme Oxygenase-1 Interferes with the Transforming Activity of the Kaposi Sarcoma Herpesvirusencoded G Protein-coupled Receptor

“…Focus-forming Assays-NIH3T3 cells were transfected by the calcium-phosphate precipitation technique with different indicated expression plasmids as described previously (22). The day after transfection, cells were washed three times with DMEM and kept in DMEM supplemented with 5% calf serum alone or with 50 -100 mM SnPP for 2-3 weeks until foci were scored.…”

“…Simian virus 40, large T-antigen-immortalized, murine endothelial cells (SVECs) were maintained in DMEM supplemented with 10% fetal bovine serum. Stable transfections were performed using the calcium phosphate technique (22). NIH3T3 and SVEC cells were plated at 20% confluence in 10-cm plates and transfected with 10 g of pCEFL, pCEFL-vGPCR, or pCEFL-HA-HO-1.…”

Vaso-occlusive and prothrombotic mechanisms associated with tumor hypoxia, necrosis, and accelerated growth in glioblastoma

“…72,73 PAR1 activation can transform cells and is able to enhance tumorigenicity, in large part by signaling through Gaq and Ga13. 74,75 It is also clear that PAR1 activation promotes invasive and metastatic properties of malignant cells. 72,76 Mechanisms of increased invasion include its ability to direct cytoskeletal actin rearrangements, phosphorylation of focal adhesion kinases, and recruitment of avb5 integrin to contact sites.…”

Plasma heparin cofactor II activity is inversely associated with left atrial volume and diastolic dysfunction in humans with cardiovascular risk factors

“…These hypertrophic changes of cardiomyocytes by PAR-1 activation may be partly explained by the mechanism of cleavage of PAR-1 resulting in activation of Gq, G12/ 13 and Gi, as well as downstream signaling pathways, including the MAPK pathways ERK 1/2 and ERK5. 39,40 Therefore, activation of PAR-1 in the heart promotes hypertrophic growth and/or influences the survival of cardiomyocytes. 34 These findings are consistent with the assumption that PAR-1 activation in the heart, including cardiomyocytes and cardiac fibroblasts, accelerates cardiac remodeling, leading to reduced elasticity of the left ventricular wall.…”