Dual specificity phosphatase that dephosphorylates MAPK8/JNK and MAPK14/p38, but not MAPK1/ERK2, in vitro (PubMed:21360282). Exhibits intrinsic phosphatase activity towards both phospho-seryl/threonyl and -tyrosyl residues, with similar specific activities in vitro (PubMed:10585869). H2O + O-phospho-L-tyrosyl-[protein] = L-tyrosyl-[protein] + phosphate H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate Additional isoforms seem to exist. Highly expressed in the testis (at protein level) (PubMed:10585869, PubMed:15252030). Also found in the skeletal muscle (PubMed:15252030). Produced by alternative promoter usage. Produced by alternative promoter usage and alternative splicing. Belongs to the protein-tyrosine phosphatase family. Non-receptor class dual specificity subfamily.