Regulation and function of LIM-kinases and cofilin in platelets and endothelial cells

• Applicant: Professor Dr. Wolfgang Siess
• Subject Area: Anatomy and Physiology
• Term: from 2007 to 2012
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 47510382

Platelets and endothelial cells play a central role in the pathogenesis of atherosclerosis andatherothrombosis. One focus of my research group is to understand the signalling mechanismswhich regulate the actin dynamics in these cells. They underlie shape change, spreading andaggregation of platelets, and contraction, migration, bleb formation and apoptosis of endothelialcells. Based on own previous studies which showed that activation of the Rho/Rho-Kinasesignalling pathway plays a central role for platelet shape change and endothelial cell contraction, weconcentrated our studies recently on Rho-kinase mediated activation of LIM-kinases, whichregulate actin dynamics through phosphorylation of the actin-depolymerising protein cofilin. Wefound that the Rho-kinase/LIMK/cofilin pathway is differentially regulated in thrombin-stimulatedplatelets and endothelial cells. Additionally we observed in endothelial cells, that thrombin inducedbleb like structures in LIMK2 but not LIMK1 transfected cells. Furthermore, we found that LIMkinase2 (LIMK2) shuttles between the cytoplasm and nucleus of endothelial cells. We haveidentified in LIMK2 specific nuclear and nucleolar localization sequences, and a PKC-dependentphosphorylation site (Ser-283), which regulate the nuclear import of LIMK2. Since actin, cofilin, andother cytoskeleton proteins are also known to be present in the nucleus, we propose that theLIMK/cofilin pathway functions not only in the cytoplasm, but also in the nucleus. Our main goalsare: (a) to clarify the role of LIMK1/LIMK2 and the cofilin phosphatase slingshot for the regulation ofcofilin phosphorylation and actin in stimulated platelets and endothelial cells; (b) to define theregulation of nucleocytoplasmic shuttling of LIMK2 in endothelial cells, and (c) to understand thenuclear function of LIMK2 and cofilin; (d) to clarify the mechanism and physiological role of LIMK2-dependent bleb formation.

• DFG Programme: Research Grants