Dual specific phosphatase 14 / MAP-kinase phophatase-6 (DUSP14 / MKP6) is a member of Dual-specificity phosphatases that is a subclass of protein tyrosine phosphatases (PTP) families that can dephosphorylate bothe phosphotyrosine and phosphoserine / phosphothreonine residues in substrates. Unlike many other DUSPs, DUSP14 only contains a catalytic domain within the C-terminal region. In signal transduction, DUSP14 has been considered as negative regulator of the mitogen-activated protein kinase (MAPK) / extracellular signal-regulated kinase 1 / 2 (ERK 1 / 2) pathway. DUSP14 phosphatase activity has been confirmed to be inhibited by PTP inhibitor Ⅳ. PTP inhibitor binds to the catalytic site of DUSP14. PTP inhibitor Ⅳ effectively and specifically inhibited DUSP14-mediated dephosphorylation of JNK, a member of the mitogen-activated protein kinase (MAPK) family through dephosphorylation of both the Ser / Thr and Tyr residues of MAPKs.