Phosphorylation of Irs1 at SER-522 inhibits insulin signaling.
Multisite phosphorylation of Irs1 on serine and threonine residues regulates insulin signaling that can contribute to insulin resistance. We identified by mass spectrometry the phosphorylation of Ser522 in rat Irs1 (S522(Irs1)). The functional effects of this phosphorylation site were investigated in cultured cells using a sequence-specific phosphoserine antibody. Insulin stimulated the phosphorylation of S522(Irs1) in L6 myoblasts and myotubes. S522(Irs1) phosphorylation was inhibited by wortmannin, whereas PD98059, rapamycin, or glucose-starvation had no effect. Reducing Akt expression with small interfering RNA inhibited insulin-stimulated phosphorylation of S522(Irs1), suggesting the involvement of the phosphatidylinositol 3-kinase--> Akt cascade. A S522(Irs1)-->A522(Irs1) substitution increased insulin-stimulated tyrosine phosphorylation of Irs1 and signaling, whereas a S522(Irs1)-->E522(Irs1) substitution reduced insulin-stimulated Irs1 tyrosine phosphorylation. Together, these results suggest the phosphatidylinositol 3-kinase-->Akt cascade can inhibit insulin signaling through the phosphorylation of S522(Irs1).
Giraud
Jodel
J
Howard Hughes Medical Institute, Children's Hospital Boston, Harvard Medical School, Boston, Massachusetts 02115, USA.
Haas
Michael
M
Feener
Edward P
EP
Copps
Kyle D
KD
Dong
Xiaocheng
X
Dunn
Sarah L
SL
White
Morris F
MF
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D007328:Insulin / Q000378:metabolism*; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011817:Rabbits; D012694:Serine / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D013912:Threonine / Q000235:genetics / Q000378:metabolism
D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526296:Irs1 protein, rat; D010750:Phosphoproteins; D013912:Threonine; D012694:Serine