Catalytically inactive phosphatase (PubMed:7592916). Acts as a nuclear anchor for MAPK1/MAPK3 (ERK1/ERK2) (By similarity). Modulates cell-fate decisions and cell migration by spatiotemporal regulation of MAPK1/MAPK3 (ERK1/ERK2) (By similarity). 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 (By similarity). Plays a role in spermatogenesis (PubMed:11842224). Interacts with MAPK1; independently of MAPK1 phosphorylation status (By similarity). Interacts with CARHSP1/Crhsp-24 (PubMed:11842224). Interacts (via FQQ motif) with FBXW7 (via F-box domain); the interaction is direct and prevents FBXW7 interaction with SKP1, a component of the SCF(FBXW7) complex (By similarity). Predominantly localizes to the nucleus. Widely expressed with highest levels in muscle, testis and brain (PubMed:7592916). In testis, expression starts 13-14 days after birth and is limited to the seminiferous tubule and to round and elongating spermatids (PubMed:11842224). Expression is low in condensing spermatids and pachytene spermatocytes, and absent in spermatogonia, spermatozoa and somatic Sertoli cells (PubMed:11842224). Males are infertile due to a disrupted spermatid development, resulting in a >1000-fold decrease in spermatozoa production. 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.