PKC isoenzymes differentially modulate the effect of thrombin on MAPK-dependent RPE proliferation.
Thrombin signalling through PAR (protease-activated receptor)-1 is involved in cellular processes, such as proliferation, differentiation and cell survival. Following traumatic injury to the eye, thrombin signalling may participate in disorders, such as PVR (proliferative vitreoretinopathy), a human eye disease characterized by the uncontrolled proliferation, transdifferentiation and migration of otherwise quiescent RPE (retinal pigment epithelium) cells. PARs activate the Ras/Raf/MEK/ERK MAPK pathway (where ERK is extracellular-signal-regulated kinase, MAPK is mitogen-activated protein kinase and MEK is MAPK/ERK kinase) through the activation of G(alpha) and G(betagamma) heterotrimeric G-proteins, and the downstream stimulation of the PLC (phospholipase C)-beta/PKC (protein kinase C) and PI3K (phosphoinositide 3-kinase) signalling axis. In the present study, we examined the molecular signalling involved in thrombin-induced RPE cell proliferation, using rat RPE cells in culture as a model system for PVR pathogenesis. Our results showed that thrombin activation of PAR-1 induces RPE cell proliferation through Ras-independent activation of the Raf/MEK/ERK1/2 MAPK signalling cascade. Pharmacological analysis revealed that the activation of 'conventional' PKC isoforms is essential for proliferation, although thrombin-induced phosphorylation of ERK1/2 requires the activation of atypical PKCzeta by PI3K. Consistently, thrombin-induced ERK1/2 activation and RPE cell proliferation were prevented completely by PI3K or PKCzeta inhibition. These results suggest that thrombin induces RPE cell proliferation by joint activation of PLC-dependent and atypical PKC isoforms and the Ras-independent downstream stimulation of the Raf/MEK/ERK1/2 MAPK cascade. The present study is the first report demonstrating directly thrombin-induced ERK phosphorylation in the RPE, and the involvement of atypical PKCzeta in this process.
Palma-Nicolas
Jose P
JP
Departamento de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México (UNAM), Apartado Postal 70-253, Ciudad Universitaria, C.P. 04510, México, D.F, Mexico.
López
Edith
E
López-Colomé
Ana María
AM
D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D002465:Cell Movement / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects*; D002478:Cells, Cultured; D006490:Hemostatics / Q000378:metabolism / Q000494:pharmacology*; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D007527:Isoenzymes; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D020318:Rats, Long-Evans; D044463:Receptor, PAR-1 / Q000819:agonists / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000378:metabolism*; D013917:Thrombin / Q000378:metabolism / Q000494:pharmacology*; D018630:Vitreoretinopathy, Proliferative / Q000378:metabolism
D006490:Hemostatics; D007527:Isoenzymes; D044463:Receptor, PAR-1; D019869:Phosphatidylinositol 3-Kinases; D011493:Protein Kinase C; D020929:Mitogen-Activated Protein Kinase Kinases; D013917:Thrombin; D020962:Heterotrimeric GTP-Binding Proteins