Probable protein tyrosine phosphatase. Has phosphatase activity with synthetic substrates. Has a phosphatase activity-independent regulatory role in MAP3K5/ASK1-mediated apoptosis, preventing MAP3K5/ASK1 inhibition by AKT1. Shows no phosphatase activity on MAPK1/ERK2, MAPK8/JNK, MAPK14/p38 and MAP3K5/ASK1. 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 Monomer. Interacts with MAP3K5/ASK1; may compete with AKT1 preventing MAP3K5/ASK1 phosphorylation by AKT1. Skeletal muscle-specific. Expressed at very low levels in myotubes and early postnatal muscle. Expression markedly increases at approximately the 3rd week after birth and continues to increase gradually into adulthood. Belongs to the protein-tyrosine phosphatase family. Non-receptor class dual specificity subfamily.