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

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