Catalytically inactive phosphatase (PubMed:23847209). Acts as a nuclear anchor for MAPK1/MAPK3 (ERK1/ERK2) (PubMed:23847209). Modulates cell-fate decisions and cell migration by spatiotemporal regulation of MAPK1/MAPK3 (ERK1/ERK2) (PubMed:23847209). By binding to the F-box of FBXW7, prevents the assembly of FBXW7 into the SCF E3 ubiquitin-protein ligase complex, and thereby inhibits degradation of its substrates (PubMed:28007894). Plays a role in spermatogenesis (By similarity). Interacts with MAPK1; independently of MAPK1 phosphorylation status (PubMed:23847209). Interacts with CARHSP1/Crhsp-24 (By similarity). Interacts (via FQQ motif) with FBXW7 isoforms 1 (via F-box domain) and 3 (via F-box domain); the interaction is direct and prevents FBXW7 interaction with SKP1, a component of the SCF(FBXW7) complex (PubMed:28007894). Does not interact with FBXW7 isoform 2 (PubMed:28007894). Predominantly localizes to the nucleus. Belongs to the protein-tyrosine phosphatase family. Non-receptor class subfamily. Contains a Gly residue instead of a conserved Cys residue at position 120 in the dsPTPase catalytic loop which renders it catalytically inactive as a phosphatase. The binding pocket is however sufficiently preserved to bind phosphorylated substrates, and may protect them from phosphatases.