Activation of JAK3, but not JAK1, is critical for IL-2-induced proliferation and STAT5 recruitment by a COOH-terminal region of the IL-2 receptor β-chain

Two Discrete Regions of Interleukin-2 (IL2) Receptor β Independently Mediate IL2 Activation of a PD98059/Rapamycin/Wortmannin-insensitive Stat5a/b Serine Kinase

“…The present observation that BD is capable of mediating Stat5a/b phosphorylation (Fig. 3B, lanes i-l) is consistent with the previously proposed roles of Tyr 392 and Tyr 510 of IL2R␤ as essential Stat5 docking sites (9,31,32). However, we have noted an approximately 50% lower efficiency of BD to mediate Stat5a/b tyrosine phosphorylation as compared with FL and AD by antiphosphotyrosine immunoblotting of immunoprecipitated Stat5a/b proteins (not shown).…”

“…The rapid kinetics of Stat5a/b tyrosine phosphorylation were similar to the time response of IL2-induced JAK3 autophosphorylation observed in human T lymphocytes (9). At present, there is no evidence to suggest that JAKs are also serine kinases, and the temporal dissociation of Stat5a/b serine and (lanes a-d), 100 M PD90859 (lanes e-h), 10 nM rapamycin (lanes i-l), or 100 nM wortmannin (lanes m-p).…”

“…On the other hand, a mutant of IL2R␤ (designated SD) that lacks both the acid-rich region and the COOH terminus failed to mediate inducible phosphorylation of Stat5a or Stat5b (not shown). We have previously demonstrated that the SD mutant does not mediate JAK1/JAK3 activation or proliferative signals (9,27). Specific phosphoamino acid analysis of inducibly phosphorylated Stat5a and Stat5b proteins from IL2-stimulated Ba/F3 cells expressing either FL, AD, or BD receptors revealed that each of these biologically active receptor variants were correspondingly competent to mediate IL2-induced serine and tyrosine phosphorylation (Fig.…”

“…3A. Previous analysis had shown that Ba/F3 cells expressing wild-type (FL) receptors or mutant receptor forms devoid of either the acid-rich region (AD) or the COOH terminus (BD) were capable of mediating IL2-induced proliferation and Jak3 activation (9,27). Stable cell clones expressing these forms of IL2R␤ were metabolically labeled with [ 32 P]orthophosphate and incubated with or without IL2 for 10 min.…”

“…In addition to this pair of essential receptor subunits, a third non-conforming protein with a short cytoplasmic domain (TAC or IL2R␣) represents an accessory receptor subunit that can serve as a positive affinity modulator through its regulated expression (5-7). IL2-induced dimerization of IL2R␤ and IL2R␥ results in stimulation of the receptor-associated Janus kinases (JAK) JAK1 and/or JAK3 through intermolecular transphosphorylation (8,9). Activation of JAKs initiates intracellular signaling cascades that include Src tyrosine kinases, phosphatases, serine-threonine kinases, and a family of transcription factors known as signal transducers and activators of transcription (Stats).…”