T-cell protein tyrosine phosphatase (TCPTP) regulates phosphorylation of Txk, a tyrosine kinase of the Tec family

Phosphorylation and dephosphorylation of intracellular enzymes, such as the T-cell-specific Tec family protein kinase Txk, are critically involved in the regulation of a number of cellular functions. Although PTPs located in the nucleus are limited, TCPTP is known to be one such nuclear phosphatase, due to its nuclear localization signal sequences. Here, we investigate the role of TCPTP in the regulation of Txk phosphorylation/dephosphorylation in Txk-transfected Cos7 and Jurkat cells. Nuclear-type TCPTP (TC45) was present in both the nuclear and cytoplasmic compartments of Cos7 cells transfected with TC45. Cytoplasmic-type TCPTP (TC48) was localized in the cytoplasmic compartment of Cos7 cells transfected with TC48. We observed that expression of TC45 dephosphorylated Txk in the nuclei of Cos7 cells. TC48 expression did not dephosphorylate Txk; rather, it enhanced and sustained Txk phosphorylation in the nuclei of Cos7 cells. Phosphorylation of Txk increased 60 minutes after lectin stimulation in Jurkat cells transfected with TCPTP-specific small interfering RNA (siRNA), which efficiently knocked down endogenous TCPTP. TCPTP may play a crucial role in the regulation of Txk phosphorylation status in T-cells after stimulation. Rec./11/5/2014, Acc.11/19/2014, pp240-246