title: Regulation of LIM-kinase 1 and cofilin in thrombin-stimulated platelets.
abstract: Cofilin is a regulator of actin filament dynamics. We studied whether during platelet activation Rho kinase stimulates LIM kinase (LIMK) leading to subsequent phosphorylation and inactivation of cofilin. Platelet shape change and aggregation/secretion were induced by low and high concentrations of thrombin, respectively. We found that during these platelet responses Rho kinase activation was responsible for mediating rapid Thr508 phosphorylation and activation of LIMK-1 and for the F-actin increase during shape change and, in part, during secretion. Surprisingly, during shape change cofilin phosphorylation was unaltered, and during aggregation/secretion cofilin was first rapidly dephosphorylated by an okadaic acid-insensitive phosphatase and then slowly rephosphorylated by LIMK-1. LIMK-1 phosphorylation and cofilin dephosphorylation and rephosphorylation during aggregation were independent of integrin alpha(IIb)beta(3) engagement. Cofilin phosphorylation did not regulate cofilin association with F-actin and was unrelated to the F-actin increase in thrombin-activated platelets. Our study identifies LIMK-1 as being activated by Rho kinase in thrombin-stimulated platelets. Two counteracting pathways, a cofilin phosphatase and LIMK-1, are activated during platelet aggregation/secretion regulating cofilin phosphorylation sequentially and independently of integrin alpha(IIb)beta(3) engagement. Rho kinase-mediated F-actin increase during platelet shape change and secretion involves a mechanism other than LIMK-1-mediated cofilin phosphorylation, raising the possibility of another LIMK substrate regulating platelet actin assembly.
authors.affiliation: Institute for Prevention of Cardiovascular Diseases, University of Munich, Germany.
authors.forename: Dharmendra
authors.initials: D
authors.lastname: Pandey
authors.forename: Pankaj
authors.initials: P
authors.lastname: Goyal
authors.forename: James R
authors.initials: JR
authors.lastname: Bamburg
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Siess
mesh_terms: D051339:Actin Depolymerizing Factors / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000199:Actins / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D004789:Enzyme Activation; D005786:Gene Expression Regulation; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006490:Hemostatics / Q000494:pharmacology*; D006801:Humans; D054461:Lim Kinases; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D015539:Platelet Activation; D010974:Platelet Aggregation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D013912:Threonine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013917:Thrombin / Q000494:pharmacology*; D016335:Zinc Fingers; D020741:rho GTP-Binding Proteins / Q000378:metabolism
chemical_list: D051339:Actin Depolymerizing Factors; D000199:Actins; D006490:Hemostatics; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D013912:Threonine; D000255:Adenosine Triphosphate; D011494:Protein Kinases; C515892:LIMK1 protein, human; D054461:Lim Kinases; D010749:Phosphoprotein Phosphatases; D013917:Thrombin; D020741:rho GTP-Binding Proteins