Catalytically inactive phosphatase (PubMed:20180778, PubMed:23163895). By binding to G3BP1, inhibits the formation of G3BP1-induced stress granules (PubMed:20180778, PubMed:23163895). Does not act by protecting the dephosphorylation of G3BP1 at 'Ser-149' (PubMed:23163895). Inhibits PTPMT1 phosphatase activity (PubMed:24709986). By inhibiting PTPMT1, positively regulates intrinsic apoptosis (PubMed:21262771). May play a role in the formation of neurites during neuronal development (PubMed:29250526). Interacts with G3BP1 (PubMed:20180778). Interacts with PTPMT1; the interaction inhibits PTPMT1 catalytic activity (PubMed:24709986). Experimental confirmation may be lacking for some isoforms. Belongs to the protein-tyrosine phosphatase family. Non-receptor class subfamily. Lacks the two active site residues His and Cys at position 245 and 246 which are essential for dual-specificity phosphatase activity. Lacks phosphatase activity.