PHOSPHORYLATION AND ACTIVATION OF P90RSK BY GLYCOGEN SYNTHASE KINASE-3

Abstract Recombinant p90 rsk expressed from baculovirus was found to be phosphorylated and activated by glycogen synthase kinase-3 (GSK-3) in vitro . Phosphorylation of p90 rsk by both GSK-3α and GSK-3β isoforms was predominantly on threonine residues. Activated p90 rsk , resulting from cc-expression in insect cells with the oncogenic protein tyrosine kinase p60 v-src , was able to phosphorylate GSK-3 but was a poor GSK-3 substrate. These results suggest a potentially novel regulatory connection in the signal transduction cascades in which p90 rsk participates.