TNF-{alpha} Induces Tyrosine Phosphorylation and Recruitment of the Src Homology Protein-Tyrosine Phosphatase 2 to the gp130 Signal-Transducing Subunit of the IL-6 Receptor Complex

Recently, it has been demonstrated that TNF-[alpha] and LPS induce the expression of suppressor of cytokine signaling 3 (SOCS3) and inhibit IL-6- induced STAT3 activation in macrophages. Inhibitor studies suggested that both induction of SOCS3 and inhibition of IL-6-induced STAT3 activation depend on the activation of p38 mitogen-activated protein kinase. Since recruitment of the tyrosine phosphatase Src homology protein tyrosine phosphatase 2 (SHP2) to the signal-transducing receptor subunit gp130 attenuates IL-6-mediated STAT- activation, we were interested in whether TNF-[alpha] also induces the association of SHP2 to the gp130 receptor subunit. In this study we demonstrate that stimulation of macrophages and fibroblast cell lines with TNF-[alpha] causes the recruitment of SHP2 to the gp130 signal-transducing subunit and leads to tyrosine phosphorylation of SHP2 and gp130. In this context the cytoplasmic SHP2/SOCS3 recruitment site of gp130 tyrosine 759 is shown to be important for the inhibitory effects of TNF-[alpha], since mutation of this residue completely restores IL-6-stimulated activation of STAT3 and, consequently, of a STAT3-dependent promoter. In this respect murine fibroblasts lacking exon 3 of SHP2 are not sensitive to TNF-[alpha], indicating that functional SHP2 and its recruitment to gp130 are key events in inhibition of IL-6-dependent STAT activation by TNF-[alpha]. Furthermore, activation of p38 mitogen-activated protein kinase is shown to be essential for the inhibitory effect of TNF-[alpha] on IL-6 signaling and TNF-[alpha]-dependent recruitment of SHP2 to gp130.