Shp-2 Tyrosine Phosphatase Functions as a Negative Regulator of the Interferon-Stimulated Jak/STAT Pathway

Abstract

Shp-2 is an SH2 domain-containing protein tyrosine phosphatase. Although the mechanism remains to be defined, substantial experimental data suggest that Shp-2 is primarily a positive regulator in cell growth and development. We present evidence here that Shp-2, while acting to promote mitogenic signals, also functions as a negative effector in interferon (IFN)-induced growth-inhibitory and apoptotic pathways. Treatment of mouse fibroblast cells lacking a functional Shp-2 with IFN-α or IFN-γ resulted in an augmented suppression of cell viability compared to that of wild-type cells. To dissect the molecular mechanism, we examined IFN-induced activation of signal transducers and activators of transcription (STATs) by electrophoretic mobility shift assay, using a specific DNA probe (hSIE). The amounts of STAT proteins bound to hSIE upon IFN-α or IFN-γ stimulation were significantly increased in Shp-2^−/− cells. Consistently, tyrosine phosphorylation levels of Stat1 upon IFN-γ treatment and, to a lesser extent, upon IFN-α stimulation were markedly elevated in mutant cells. Furthermore, IFN-γ induced a higher level of caspase 1 expression in Shp-2^−/− cells than in wild-type cells. Reintroduction of wild-type Shp-2 protein reversed the hypersensitivity of Shp-2^−/− fibroblasts to the cytotoxic effect of IFN-α and IFN-γ. Excessive activation of STATs by IFNs was also diminished in mutant cells in which Shp-2 had been reintroduced. Together, these results establish that Shp-2 functions as a negative regulator of the Jak/STAT pathway. We propose that Shp-2 acts to promote cell growth and survival through two mechanisms, i.e., the stimulation of growth factor-initiated mitogenic pathways and the suppression of cytotoxic effect elicited by cytokines, such as IFNs.

ACKNOWLEDGMENTS

We thank Andrew Larner for antibodies and Mark Kaplan, Lawrence Quilliam, and Rebecca Chan for helpful discussions and for critically reading the manuscript.

This work was supported in part by grants from the National Institutes of Health (R29GM53660) and the Showalter Trust to G.S.F. G.S.F. received a career development award from the American Diabetes Association.