Interleukin-4 (IL-4) induces phosphatidylinositol 3-kinase (p85) dephosphorylation - Implications for the role of SHP-1 in the IL-4-induced signals in human B cells

Interleukin 4 (IL-4) is a potent cytokine produced by T cells and to a lesser extent by tumor-associated natural killer cells, basophils, and mast cells, IL-4 treatment of T cells and macrophages leads to augmentation of their cytotoxic activity, In human B cells, IL-4 is a potent stimulator of Ig class switching from IgM to IgE, The diverse biological responses induced by IL-4 are mediated through a high affinity receptor complex (IL-4R). Although a wealth of information has accumulated regarding IL-4R, the exact mechanisms of IL-4R-mediated signaling pathways in human B cells are not well defined, In an attempt to characterize the IL-4-induced signals in human B cells, we have found that IL-4 treatment induced rapid dephosphorylation of the 85-kDa regulatory subunit of phosphatidylinositol 3-kinase. To identify the protein-tyrosine phosphatase involved in the IL-4-mediated dephosphorylation, we performed Western blot analysis using monoclonal antibodies specific to protein-tyrosine phosphatases, Upon IL-4 treatment, SHP-1 was specifically translocated to the cellular membrane fraction. Furthermore, immunoprecipitation studies revealed that SHP-1 could be specifically coimmunoprecipitated with the IL-4R as well as with phosphatidylinositol 3-kinase (p85). Collectively, our observations suggest that in addition to protein phosphorylation, protein tyrosine dephosphorylation may play a role in the IL-4-induced signaling pathways.