PTPRJ (Protein Tyrosine Phosphatase, Receptor Type J): PTPRJ is a member of the protein tyrosine phosphatase (PTP) family, enzymes that regulate cellular activity by removing phosphate groups from tyrosine residues on proteins. It negatively regulates cell proliferation and participates in signaling pathways that control growth and differentiation. Acting as a tumor suppressor in several cancers, PTPRJ helps prevent uncontrolled cell growth, and its loss of function has been associated with enhanced tumor development and progression.