Emanuelli, B

Filloux, C

Hilton, DJ

Peraldi, P

Van Obberghen, E

Suppressor of cytokine signaling (SOCS) proteins were originally described as cytokine-induced molecules involved in negative feedback loops. We have shown that SOCS-3 is also a component of the insulin signaling network (1), Indeed, insulin leads to SOCS-3 expression in 3T3-L1 adipocytes. Once produced, SOCS-3 binds to phosphorylated tyrosine 960 of the insulin receptor and inhibits insulin signaling. Now we show that in 3T3-L1 adipocytes and in transfected COS-7 cells insulin leads to SOCS-3 tyrosine phosphorylation. This phosphorylation takes place on Tyr(204) and is dependent upon a functional SOCS-3 SH2 domain. Purified insulin receptor directly phosphorylates SOCS-3, However, in intact cells, a mutant of the insulin receptor, IRY960F, unable to bind SOCS-3, was as efficient as the wild type insulin receptor to phosphorylate SOCS-3, Importantly, IRY960F is as potent as the wild type insulin receptor to activate janus-activated kinase (Jak) 1 and Jak2, Furthermore, expression of a dominant negative form of Jak2 inhibits insulin-induced SOCS-3 tyrosine phosphorylation, ks transfected Jaks have been shown to cause SOCS-3 phosphorylation, we propose that insulin induces SOCS-3 phosphorylation through Jak activation. Our data indicate that SOCS-3 belongs to a class of tyrosine-phosphorylated insulin signaling molecules, the phosphorylation of which is not dependent upon a direct coupling with the insulin receptor but relies on the Jacks.</p

Insulin induces suppressor of cytokine signaling-3 tyrosine phosphorylation through janus-activated kinase

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