title: Intracellular localization and functional effects of P21-activated kinase-1 (Pak1) in cardiac myocytes.
abstract: We investigated intracellular localization and substrate specificity of P21-activated kinase-1 (Pak1) in rat cardiac myocytes. Pak1 is a serine/threonine protein kinase that is activated by Rac1/Cdc42 and important in signaling of stress responses. Yet the localization and in vivo function of Pak1 in heart cells is poorly understood. Studies reported here indicate that Pak1 physically interacts with protein phosphatase 2a and localizes to the Z-disk, cell membrane, intercalated disc, and nuclear membrane of adult rat heart myocytes. We compared levels of phosphorylation of cardiac troponin I (cTnI) in control myocytes with phosphorylation of cTnI and myosin binding protein C (C-protein) in myocytes with increased Pak1 activity. The increase in activity was induced by infection of myocytes with a recombinant adenovirus (AdPak1) containing cDNA for a constitutively active Pak1. Control cells were infected with a virus (AdLacZ) containing LacZ. Basal levels of phosphorylation of cTnI and C-protein were relatively high in the myocytes infected with AdLacZ. However, phosphorylation of cTnI and C-protein in cells expressing constitutively active Pak1 was significantly reduced compared with those expressing LacZ. Measurement of Ca2+ tension relations in single myocytes demonstrated that this reduction in phosphorylation of cTnI and C-protein was associated with the predicted increase in sensitivity to Ca2+. Our data provide evidence for a novel pathway of phosphatase regulation in cardiac myocytes.
authors.affiliation: Department of Physiology and Biophysics, College of Medicine, University of Illinois at Chicago, Chicago, Ill 60612-7342, USA.
authors.forename: Yunbo
authors.initials: Y
authors.lastname: Ke
authors.forename: Lynn
authors.initials: L
authors.lastname: Wang
authors.forename: W Glen
authors.initials: WG
authors.lastname: Pyle
authors.forename: Pieter P
authors.initials: PP
authors.lastname: de Tombe
authors.forename: R John
authors.initials: RJ
authors.lastname: Solaro
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology; D002478:Cells, Cultured; D018076:DNA, Complementary / Q000235:genetics; D007763:Lac Operon; D008297:Male; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D032383:Myocytes, Cardiac / Q000201:enzymology* / Q000502:physiology / Q000648:ultrastructure; D009685:Nuclear Envelope / Q000201:enzymology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D054648:Protein Phosphatase 2; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000502:physiology; D013347:Subcellular Fractions / Q000201:enzymology*; D013379:Substrate Specificity; D019210:Troponin I / Q000378:metabolism; D054462:p21-Activated Kinases; D000099163:Myosin Binding Protein C
chemical_list: D002118:Calcium; D002352:Carrier Proteins; D018076:DNA, Complementary; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D017346:Protein Serine-Threonine Kinases; D011993:Recombinant Fusion Proteins; D019210:Troponin I; D054462:p21-Activated Kinases; D000099163:Myosin Binding Protein C; C515906:Pak1 protein, rat