The region in the common gamma chain between amino acids (aa) 314-323 dictates efficient activation of the insulin receptor substrate (IRS)-2 pathway by interleukin (IL)-4. (134.4)

Abstract

Abstract Previously, we demonstrated that the γC subunit of type I IL-4 receptor was required for robust tyrosine phosphorylation of the downstream adapter protein, IRS-2, and the robust expression of mRNA and protein of a subset of genes characteristic of alternatively-activated macrophages. The type II IL-4 receptor did not have this robust activity. In addition to the unique ability to bind Jak3, the cytoplasmic domain of human γC contains a putative IRS-2 docking motif and other γC-utilizing cytokines also activate IRS-2. Thus, we hypothesized that the γC cytoplasmic domain provides a docking site for IRS-2 cooperating with the site in IL-4Rα. To test this, full-length (FL) and γC truncation mutants were stably co-expressed with wildtype (WT) IL-4Rα in CHO cells; signaling responses to IL-4 were examined. IL-4-induced IRS-2 and STAT6 phosphorylation was observed in CHO expressing FL γC and γC truncated at aa323 but not in cells expressing γC truncated at aa308 or 285. These data suggest robust activation of IRS-2 and STAT6 by IL-4 requires a 15 aa portion of γC between aa314-323. This interval did not contain Tyr325, part of the putative IRS-2 docking motif. Previous studies in other receptor systems suggested that aa323-335 was required for Jak3 engagement. The requirement for IL-4-induced JAK3 recruitment/activation will be examined in these CHO transfectants. Supported by HL096897 (NMH) and AI038985 (ADK).