RAPID COMMUNICATION Activation of Stat-3 Is Involved in the Induction of Apoptosis After Ligation of Major Histocompatibility Complex Class I Molecules on Human Jurkat T Cells

Activation of Janus tyrosine kinases (Jak) and Signal transducers and activators of transcription (Stat) after ligation of major histocompatibility complex class I (MHC-I) was explored in Jurkat T cells. Cross-linking of MHC-I mediated tyrosine phosphorylation of Tyk2, but not Jak1, Jak2, and Jak3. In addition, the transcription factor Stat-3 was tyrosine phosphorylated in the cytoplasma and subsequently translocated to the cell nucleus. Data obtained by electrophoretic mobility shift assay suggested that the activated Stat-3 protein associates with the human serum-inducible element (hSIE) DNA-probe derived from the interferon-g activated site (GAS) in the c-fos promoter, a common DNA sequence for Stat protein binding. An association between hSIE and Stat-3 after MHC-I ligation was directly demonstrated by precipitating Stat-3 from nuclear extracts with biotinylated hSIE probe and avidin-coupled agarose. To investigate the function of the activated Stat-3, Jurkat T cells were transiently transfected with a Stat-3 isoform lacking the transactivating domain. This dominant-negative acting Stat-3 isoform significantly inhibited apoptosis induced by ligation of MHC-I. In conclusion, our data suggest the involvement of the Jak/Stat signal pathway in MHC-I–induced signal transduction in T cells. r 1998 by The American Society of Hematology.