Transforming growth factor β-mediated inhibition of src kinases is regulated by SHP-1

Abstract

Abstract Background Transforming growth factor (TGF) β has been shown to suppress T cell effector functions. Although the mechanisms of such T cell suppression are not known, a disuption of the balance between protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs) has been implicated. The present study investigated the roles of the src-related PTKs, P59fyn and P56lck, and the PTPs SHP-1 and SHP-2 in TGF-β-mediated T cell suppression. Methods Splenic T cells from rats were pretreated with TGF-β 25 ng ml−1 and subsequently stimulated with either anti-CD3 or anti-CD3 plus pervanadate (a PTP inhibitor). After incubation with specific antibodies and immunoprecipitation, the kinase activity of the PTKs was assessed by in vitro kinase assay. Phosphorylation of the PTPs was assessed using antiphosphotyrosine antibodies and immunoblotting. Results Incubation of T cells with TGF-β resulted in decreased activity of P59fyn and P56lck. Although TGF-β treatment resulted in a concomitant increase in SHP-1 activity, no change in SHP-2 activity was observed. When T cells were stimulated with anti-CD3 in the presence of pervanadate, the TGF-β-mediated decrease in P59fyn and P56lck activity was completely prevented. Conclusion These findings show that TGF-β treatment of T cells results in suppression of src kinases, and suggests that such inhibition of kinase activity is mediated by upregulation of SHP-1.