title: Novel phosphorylation of c-ras p21 by protein kinases.
abstract: Novel p21 phosphorylation was found in cells expressing high levels of this product of c-H- and c-K-ras genes. Phorbol 12,13-dibutyrate, a protein kinase C (PKC) activator, and permeable c-AMP derivatives, which activate protein kinase A (PKA), stimulated phosphorylation of K-ras(4B) p21 in 416B cells 3 to 5 fold. By tryptic peptide mapping, it was found that both PKC and PKA phosphorylated in vitro the K-ras p21 at the same site as was found in p21 from cells labeled with [32P]orthophosphate in vivo. A common site of H-ras p21 was also phosphorylated by both PKC and PKA, although phosphopeptides of H-ras p21 were distinct from those of K-ras p21. The construction of a mutant by site-directed mutagenesis allowed the identification of serine-177 as the phosphorylation site of H-ras p21. This novel phosphorylation site lies in the hypervariable region, which links the globular catalytic domain of p21 to the membrane-anchoring site at the C-terminus, a location suggesting that this phosphorylation plays a role in modulating transmembrane signaling.
authors.affiliation: Laboratory of Molecular Oncology, National Cancer Institute, Frederick, Maryland 21701.
authors.forename: P
authors.initials: P
authors.lastname: Saikumar
authors.forename: L S
authors.initials: LS
authors.lastname: Ulsh
authors.forename: D J
authors.initials: DJ
authors.lastname: Clanton
authors.forename: K P
authors.initials: KP
authors.lastname: Huang
authors.forename: T Y
authors.initials: TY
authors.lastname: Shih
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010766:Phosphorylation; D011487:Protein Conformation; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras); D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism
chemical_list: D047428:Protein Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D015240:Phorbol 12,13-Dibutyrate; D000242:Cyclic AMP; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D016283:Proto-Oncogene Proteins p21(ras)