Protein phosphatase that may contribute to contact inhibition of cell growth and motility by mediating the dephosphorylation of focal adhesion-associated substrates and thus negatively regulating integrin-promoted signaling processes. Induces apoptotic cell death by at least two distinct mechanisms: inhibition of cell survival signaling mediated by PI 3-kinase, Akt, and ILK and activation of a caspase-dependent proapoptotic pathway. Inhibits the basal activity of LCK and its activation in response to TCR stimulation and TCR-induced activation of MAP kinase and surface expression of CD69. Inhibits TCR-induced tyrosine phosphorylation of LAT and ZAP70. Inhibits both basal activity of DOK1 and its CD2-induced tyrosine phosphorylation. Induces dephosphorylation of BCAR1, focal adhesion kinase and SRC. Reduces migratory activity of activity of Jurkat cells. Reduces tyrosine phosphorylation of CEACAM20 and thereby contributes to suppress the intestinal immune response CEACAM20 (By similarity). H2O + O-phospho-L-tyrosyl-[protein] = L-tyrosyl-[protein] + phosphate Regulated by reversible dimerization. Dimerization reduces its catalytic activity. Homodimer; disulfide-linked (Probable). Interacts with LCK (PubMed:12837766). Interacts (phosphorylated form) with GRB2 (via SH2 domain) (By similarity). Interacts (phosphorylated form) with FYN (via SH2 domain) (By similarity). Interacts (via extracellular domain) with CEACAM20 (via extracellular domain); the interaction dephosphorylates CEACAM20 (By similarity). Colocalizes with CEACAM20 at the apical brush border of intestinal cells. Expressed at high levels in the brain, spleen and liver and at lower levels in the heart and stomach. Expressed in pancreatic and colorectal cancer cells, but not in normal pancreas or colon. Expression in hepatocellular carcinoma is related to the differentiation status of the tumor and expression is inversely related to tumor aggressiveness. Induced at the early stage of hepatocellular carcinoma and is suppressed at later stages. The extracellular domain mediates homodimerization. One or more cysteines in the extracellular domain is essential for the formation of dimers probably by forming a disulfide bond. The cytoplasmic domain mediates the interaction with LCK. Belongs to the protein-tyrosine phosphatase family. Receptor class 3 subfamily.