Activation of the phosphatidylinositol-3' kinase pathway and DNA synthesis by a mutant insulin-like growth factor I receptor lacking the NPXY motif.
We have investigated the role of the NPXY motif in the insulin-like growth factor I receptor (IGF-IR) by focusing on the activation of the phosphatidylinositol-3' kinase (PI3-K) pathway and DNA synthesis following IGF-I stimulation. For this purpose, we established stable R-cell lines, which are deficient in endogenous IGF-IR, and express human IGF-IR lacking the whole NPEY(950) sequence (DeltaNPEY). The DeltaNPEY cells showed an apparent autophosphorylation of IGF-IR, albeit with reduced sensitivity to stimulation compared with cells expressing similar levels of wild-type IGF-IR. Activation of insulin receptor substrate (IRS)-1 and IRS-2 was severely impaired in DeltaNPEY cells even at high concentrations of IGF-I. However, recruitment of p85, a regulatory subunit of PI3-K, to activated IRS-2 was similar between the cell lines, but recruitment of p85 to IRS-1 was reduced in DeltaNPEY cells. Essentially similar levels of p85- or phosphotyrosine-associated PI3-K and Akt activities were observed between the cell lines, although the sensitivity to stimulation was reduced in DeltaNPEY cells. Activation of extracellular signal-regulated kinase and DNA synthesis were virtually unaffected by the mutation, in terms of both sensitivity to stimulation and responsiveness. DNA synthesis was completely inhibited by the PI3-K inhibitor, LY294002. These results indicate that the IGF-IR is able to activate the PI3-K pathway and induce DNA synthesis in a normal fashion without the NPXY motif when the receptor is fully activated.
Kataoka
K
K
Molecular Diagnosis and Therapeutics, Department of Oral Restitution, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan.
Yu
D
D
Miura
M
M
D020816:Amino Acid Motifs; D000818:Animals; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D004247:DNA / Q000096:biosynthesis*; D004789:Enzyme Activation; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases / Q000032:analysis / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000235:genetics*
D002867:Chromones; D004247:DNA; D005419:Flavonoids; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I; D047908:Intracellular Signaling Peptides and Proteins; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins; D017526:Receptor, IGF Type 1; C526292:IRS1 protein, human; C526297:IRS2 protein, human; C526295:Irs1 protein, mouse; C526298:Irs2 protein, mouse; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one