ANALYSIS OF INTERLEUKIN-2 DEPENDENT SIGNAL-TRANSDUCTION THROUGH THE SHC GRB2 ADAPTER PATHWAY - INTERLEUKIN-2-DEPENDENT MITOGENESIS DOES NOTREQUIRE SHC PHOSPHORYLATION OR RECEPTOR ASSOCIATION/

The interleukin (IL)-2 receptor system has previously been shown to si gnal through the association and tyrosine phosphorylation of Shc. This study demonstrates that the IL-2 receptor beta (IL-2R beta) chain is the critical receptor component required to mediate this effect. The u se of IL-2R beta chain deletion mutants transfected into a Ba/F3 murin e cell model describes a requirement for the IL-2R beta ''acid-rich'' domain between amino acids 315 and 384 for Shc tyrosine phosphorylatio n and receptor association. COS cell co-transfection studies of IL-BR beta chain constructs containing point mutations of tyrosine to phenyl alanine along with the tyrosine kinase Jak-1 and a hemagglutinin-tagge d Shc revealed that the motif surrounding phosphorylated tyrosine 338 within the acid-rich domain of the IL-2R beta is a binding site for Sh c. Deletion of this domain has previously been shown to abrogate the a bility of IL-2 to activate Ras but does not affect IL-2-dependent mito genesis in the presence of serum. Proliferation assays of Ba/F3 cells containing IL-2R beta chain deletion mutants in serum-free medium with or without insulin shows that deletion of the acid-rich domain does n ot affect IL-2-driven mitogenesis regardless of the culture conditions . This study thus defines the critical domain within the IL-2R beta ch ain required to mediate Shc binding and Shc tyrosine phosphorylation a nd further shows that Shc binding and phosphorylation are not required for IL-2-dependent mitogenesis. Neither serum nor insulin is required to supplement the loss of induction of the Shc adapter or Ras pathway s, which therefore suggests a novel mechanism for mitogenic signal tra nsduction mediated by this hematopoietin receptor.