THE PRK2 KINASE IS A POTENTIAL EFFECTOR TARGET OF BOTH RHO AND RAC GTPASES AND REGULATES ACTIN CYTOSKELETAL ORGANIZATION

The Pas-related Rho family GTPases mediate signal transduction pathway s that regulate a variety of cellular processes, Like Ras, the Rho pro teins (which include Rho, Pac, and CDC42) interact directly with prote in kinases, which are likely to serve as downstream effector targets o f the activated GTPase, Activated RhoA has recently been reported to i nteract directly with several protein kinases, p120 PKN, p150 ROK alph a and -beta, p160 ROCK, and p164 Rho kinase, Here, we describe the pur ification of a novel Rho-associated kinase, p140, which appears to be the major Rho-associated kinase activity in most tissues, Peptide micr osequencing revealed that p140 is probably identical to the previously reported PRK2 kinase, a close relative of PKN, However, unlike the pr eviously described Rho-binding kinases, which are Rho specific, p140 a ssociates with Rac as well as Rho, Moreover, the interaction of p140 w ith Rho in vitro is nucleotide independent, whereas the interaction,vi th Pac is completely GTP dependent, The association of p140 with eithe r GTPase promotes kinase activity substantially, and expression of a k inase-deficient form of p140 in microinjected fibroblasts disrupts act in stress fibers, These results indicate that p140 may be a shared kin ase target of both Rho and Rac GTPases that mediates their effects on rearrangements of the actin cytoskeleton.