Txk, a member of the non‐receptor tyrosine kinase of the Tec family, forms a complex with poly(ADP‐ribose) polymerase 1 and elongation factor 1α and regulates interferon‐γ gene transcription in Th1 cells

Summary We have found previously that Txk, a member of the Tec family tyrosine kinases, is involved importantly in T helper 1 (Th1) cytokine production. However, how Txk regulates interferon (IFN)‐γ gene transcription in human T lymphocytes was not fully elucidated. In this study, we identified poly(ADP‐ribose) polymerase 1 (PARP1) and elongation factor 1α (EF‐1α) as Txk‐associated molecules that bound to the Txk responsive element of the IFN‐γ gene promoter. Txk phosphorylated EF‐1α and PARP1 formed a complex with them, and bound to the IFN‐γ gene promoter in vitro . In particular, the N terminal region containing the DNA binding domain of PARP1 was important for the trimolecular complex formation involving Txk, EF‐1α and PARP1. Several mutant Txk which lacked kinase activity were unable to form the trimolecular complex. A PARP1 inhibitor, PJ34, suppressed IFN‐γ but not interleukin (IL)‐4 production by normal peripheral blood lymphocytes (PBL). Multi‐colour confocal analysis revealed that Txk and EF‐1α located in the cytoplasm in the resting condition. Upon activation, a complex involving Txk, EF‐1α and PARP1 was formed and was located in the nucleus. Collectively, Txk in combination with EF‐1α and PARP1 bound to the IFN‐γ gene promoter, and exerted transcriptional activity on the IFN‐γ gene.