The role of SHP-1 and SHIP in IL-4 signal pathway

Immunoreceptor tyrosine-based inhibitory motifs (ITIM) have been implicated in the negative regulation of immunoreceptor signal pathway. The IL-4 receptor α chains (IL-4Rα) have a conserved ITIM in the carboxy terminal. Using peptides derived from human IL-4Rα (hIL-4Rα) containing the ITIM, we showed that phosphorylated peptides, but not unphosphorylated peptides, copredpitated SH2-containing tyrosine phophatase 1 (SHP-1) and SH2-containing inositol phosphatase (SHIP). To determine the role of the ITIM and the biological significance of the association of SHP-1 and SHIP with the IL-4Rα in IL-4 signal pathway, we ablated the ITIM of hIL-4Rα by deletion and site-directed mutagenesis and stably expressed these mutant hIL-4Rα in 32D cells. Upon IL-4 treatment, no significant difference in the duration of Stat6 activation was observed. However, 32D cells expressing mutant hIL-4Rα were hyperproliferative in response to hIL-4 when compared to 32D cells expressing wild type (WT) hIL-4Rα. Moreover, 32D cells overexpressing WT SHP-1 had a significant higher level of proliferation than 32D cells overexpressing dominant negative (DN) SHP-1. While no difference in the proliferative response to IL-4 was observed between 32D expressing WT and DN SHIP, both cell lines had lower level of proliferation when compared to parental 32D cells. Further investigation revealed that IL-4 exerted less protection against apoptosis in 32D expressing SHIP (WT or DN). In summary, the results indicate a role for SHP-1 and SHIP in the regulation of proliferation and apoptosis controlled by IL-4.