Tyrosine phosphatase enzyme that plays important roles in controlling immune signaling pathways and fundamental physiological processes such as hematopoiesis (PubMed:14739280, PubMed:29925997). Dephosphorylates and negatively regulate several receptor tyrosine kinases (RTKs) such as EGFR, PDGFR and FGFR, thereby modulating their signaling activities (PubMed:21258366, PubMed:9733788). When recruited to immunoreceptor tyrosine-based inhibitory motif (ITIM)-containing receptors such as immunoglobulin-like transcript 2/LILRB1, programmed cell death protein 1/PDCD1, CD3D, CD22, CLEC12A and other receptors involved in immune regulation, initiates their dephosphorylation and subsequently inhibits downstream signaling events (PubMed:11907092, PubMed:14739280, PubMed:37932456, PubMed:38166031). Modulates the signaling of several cytokine receptors including IL-4 receptor (PubMed:9065461). Additionally, targets multiple cytoplasmic signaling molecules including STING1, LCK or STAT1 among others involved in diverse cellular processes including modulation of T-cell activation or cGAS-STING signaling (PubMed:34811497, PubMed:38532423). Within the nucleus, negatively regulates the activity of some transcription factors such as NFAT5 via direct dephosphorylation. Also acts as a key transcriptional regulator of hepatic gluconeogenesis by controlling recruitment of RNA polymerase II to the PCK1 promoter together with STAT5A (PubMed:37595871). {ECO:0000269|PubMed:10574931, ECO:0000269|PubMed:11266449, ECO:0000269|PubMed:11907092, ECO:0000269|PubMed:14739280, ECO:0000269|PubMed:21258366, ECO:0000269|PubMed:29925997, ECO:0000269|PubMed:34811497, ECO:0000269|PubMed:37595871, ECO:0000269|PubMed:37932456, ECO:0000269|PubMed:38166031, ECO:0000269|PubMed:38532423, ECO:0000269|PubMed:9065461, ECO:0000269|PubMed:9733788}. This is the function of PTPN6 (protein tyrosine phosphatase non-receptor type 6, Ensembl gene identifier ENSG00000111679).