title: Atypical PKCzeta is involved in RhoA-dependent mitogenic signaling by the P2Y(12) receptor in C6 cells.
abstract: When nucleotide hydrolysis is prevented, agonists of the P2Y(12) receptor enhance the proliferation of C6 glioma cells by RhoA-dependent, protein kinase C (PKC)-dependent activation of the extracellular signal-regulated kinase (ERK) pathway [Claes P, Grobben B, Van Kolen K, Roymans D & Slegers H (2001) Br J Pharmacol134, 402-408; Grobben B, Claes P, Van Kolen K, Roymans D, Fransen P, Sys SU & Slegers H (2001) J Neurochem78, 1325-1338]. In this study, we show that ERK1/2 phosphorylation was not affected by transfection of the cells with the Gbetagamma-subunit-scavenging adrenergic receptor kinase peptide [betaARK1-(495-689)] or with Rap1GAPII, indicating that P2Y(12) receptor stimulation enhances ERK1/2 phosphorylation by G(i)alpha subunit-mediated signaling independently of Rap1 activation. Inhibition of the RhoA downstream effector Rho-associated coiled-coil-containing kinase (ROCK) with Y-27632 did not affect the P2Y(12) receptor-induced increase in ERK1/2 phosphorylation but abrogated the mitogenic response. Involvement of growth factor receptor transactivation in the signaling towards ERK phosphorylation could be ruled out by the lack of an effect of PP2, AG1024, AG1296 or SU1498, inhibitors of Src, insulin-like growth factor receptor, platelet-derived growth factor receptor and vascular endothelial growth factor receptor kinase activity, respectively. Experiments with bisindolylmaleimide I and IX indicated the requirement of PKC activity. Classical and novel PKC isoforms could be excluded by treatment of the cells with Gö6976 and calphostin C, whereas addition of a myristoylated PKCzeta pseudosubstrate inhibitor completely abolished P2Y(12) receptor-induced ERK1/2 activation. Moreover, coimmunoprecipitation experiments revealed PKCzeta/Raf1 and PKCzeta/ERK association, indicating the involvement of PKCzeta. From the data presented, we can conclude that the P2Y(12) receptor enhances cell proliferation by a G(i)alpha-dependent, RhoA-dependent PKCzeta/Raf1/MEK/ERK pathway that requires activation of ROCK, which is not involved in ERK1/2 signaling.
authors.affiliation: Laboratory of Cellular Biochemistry, Department of Biomedical Sciences, University of Antwerp, Belgium.
authors.forename: Kristof
authors.initials: K
authors.lastname: Van Kolen
authors.forename: Herman
authors.initials: H
authors.lastname: Slegers
mesh_terms: D000818:Animals; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000502:physiology; D005910:Glioma / Q000378:metabolism / Q000473:pathology; D047908:Intracellular Signaling Peptides and Proteins; D020935:MAP Kinase Signaling System; D008565:Membrane Proteins / Q000502:physiology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000502:physiology*; D058925:Receptors, Purinergic P2Y12; D015398:Signal Transduction; D014162:Transfection; D014407:Tumor Cells, Cultured; D020744:rac GTP-Binding Proteins / Q000378:metabolism; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*; D000099221:Protein Kinase C zeta
chemical_list: D004791:Enzyme Inhibitors; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D011493:Protein Kinase C; D017346:Protein Serine-Threonine Kinases; D018048:Receptors, Purinergic P2; D058925:Receptors, Purinergic P2Y12; D020744:rac GTP-Binding Proteins; D020827:rap1 GTP-Binding Proteins; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein; D000099221:Protein Kinase C zeta; C553058:P2ry12 protein, rat