American Society for Biochemistry and Molecular Biology
Journal of Biological Chemistry vol:287 issue:12 pages:9473-9483
PMID: 22228765 (JBC nr: M112.339564)
The members of the protein kinase D (PKD) family of serine/threonine kinases are major targets for tumor promoting phorbol esters, G protein-coupled receptors (GPCRs) and activated protein kinase C isoforms (PKCs). The expanding list of cellular processes in which PKDs exert their function via phosphorylation of various substrates include proliferation, apoptosis, migration, angiogenesis and vesicle trafficking. Therefore, identification of novel PKD substrates is necessary to understand the profound role of this kinase family in signal transduction. Here, we show that rhotekin, an effector of RhoA GTPase, is a novel substrate of PKD. We identified Ser435 in rhotekin as the potential site targeted by PKD in vivo. Expression of a phosphomimetic Ser(435)Glu rhotekin mutant resulted in an increase of endogenous active RhoA GTPase levels. Phosphorylation of rhotekin by PKD2 modulates the anchoring of the RhoA in the plasma membrane. Consequently, the Ser(435)Glu rhotekin mutant displayed enhanced stress fiber formation when expressed in serum-starved fibroblasts. Our data thus identify a novel role of PKD as a regulator of RhoA activity and actin stress fiber formation through phosphorylation of rhotekin.