Inhibition of T Cell Antigen Receptor Signaling by VHR-related MKPX (VHX), a New Dual Specificity Phosphatase Related to VH1 Related (VHR)*

A cDNA encoding a novel, human, dual-specific protein phosphatase was identified in the Incyte data base. The open reading frame predicted a protein of 184 amino acids related to theVaccinia virus VH1 and human VH1-related (VHR) phosphatases. Expression VHR-related MKPX (VHX) was highest in thymus, but also detectable in monocytes and lymphocytes. A VHX-specific antiserum detected a protein with an apparent molecular mass of 19 kDa in many cells, including T lymphocytes and monocytes. VHX expression was not induced by T cell activation, but decreased somewhat at later time points. In vitro, VHX dephosphorylated the Erk2 mitogen-activated protein kinase with faster kinetics than did VHR, which is thought to be specific for Erk1 and 2. When expressed in Jurkat T cells, VHX had the capacity to suppress T cell antigen receptor-induced activation of Erk2 and of an NFAT/AP-1 luciferase reporter, but not an NF-κB reporter. Thus, VHX is a new member of the VH1/VHR group of small dual-specific phosphatases that act in mitogen-activated protein kinase signaling pathways.

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