Serine phosphorylation of the ligand-activated beta-platelet-derived growth factor receptor by casein kinase I-gamma2 inhibits the receptor's autophosphorylating activity.
Platelet-derived growth factor (PDGF) receptors (PDGFRs) are membrane protein-tyrosine kinases that, upon activation, become tyrosine-phosphorylated and associate with numerous SH2 domain-containing molecules involved in mediating signal transduction. In Rat-2 fibroblasts, we have characterized the phosphorylation of the beta-PDGFR following its activation by PDGF. In contrast to tyrosine phosphorylation, which was transient and returned to near basal levels by 30 min, PDGF-stimulated Ser/Thr phosphorylation of the beta-PDGFR was increased by 5 min and remained elevated after 30 min. In vivo, after 5 min of PDGF stimulation, serine phosphorylation of the beta-PDGFR was greatly reduced by CKI-7, a specific inhibitor of casein kinase I (CKI). In vitro, recombinant CKI-gamma2 phosphorylated the ligand-activated beta-PDGFR on serine residues in a CKI-7-sensitive manner and resulted in a marked inhibition of the receptor's autophosphorylating activity. Furthermore, in Rat-2 fibroblasts, expression of hemagglutinin epitope-tagged active CKI-gamma2 resulted in a dramatic decrease in the tyrosine phosphorylation state of the beta-PDGFR in response to PDGF, consistent with receptor inactivation. Our data suggest that upon PDGF stimulation, CKI-gamma2 is activated and/or translocated in proximity to the beta-PDGFR, whereby it phosphorylates the beta-PDGFR on serine residues and negatively regulates its tyrosine kinase activity, leading to receptor inactivation.
Bioukar
E B
EB
Polypeptide Laboratory, Department of Experimental Medicine, McGill University, Montreal, Quebec H3A 2B2, Canada.
Marricco
N C
NC
Zuo
D
D
Larose
L
L
D000818:Animals; D047388:Casein Kinases; D002460:Cell Line; D005347:Fibroblasts / Q000378:metabolism*; D008024:Ligands; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D020797:Receptor, Platelet-Derived Growth Factor beta; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism*; D012694:Serine; D015398:Signal Transduction
D008024:Ligands; D012694:Serine; D011494:Protein Kinases; D020797:Receptor, Platelet-Derived Growth Factor beta; D017479:Receptors, Platelet-Derived Growth Factor; D047388:Casein Kinases