PRK1 IS TARGETED TO ENDOSOMES BY THE SMALL GTPASE, RHOB

RhoB has been shown to be an endosomal GTPase both by immunocytochemis try and electron microscopy, however, its role in endocytosis is unkno wn. Elucidation of the cellular roles of other members of this superfa mily of signaling proteins has come with the identification of their d ownstream partners. We show here that the recently isolated serine/thr eonine kinase PRK1 is targeted to the endosomal compartment by RhoB. T his is established both through immunofluorescence and cell fractionat ion. PRK1 is shown to interact with activated RhoB in cells and is loc alized to endosomes through its Rho-binding HR1 domain. Translocation of PRK1 to the endosomal compartment by RhoB is accompanied by a shift in the electrophoretic mobility of the kinase indicative of an accomp anying activation.