Involved in regulation of the actin cytoskeleton. May regulate WAS actin-bundling activity. Bridges the interaction between ABL1 and PTPN18 leading to ABL1 dephosphorylation. May play a role as a scaffold protein between PTPN12 and WAS and allow PTPN12 to dephosphorylate WAS. Has the potential to physically couple CD2 and CD2AP to WAS. Acts downstream of CD2 and CD2AP to recruit WAS to the T-cell:APC contact site so as to promote the actin polymerization required for synapse induction during T-cell activation. Down-regulates CD2-stimulated adhesion through the coupling of PTPN12 to CD2. Also has a role in innate immunity and the inflammatory response. Recruited to inflammasomes by MEFV. Induces formation of pyroptosomes, large supramolecular structures composed of oligomerized PYCARD dimers which form prior to inflammatory apoptosis. Binding to MEFV allows MEFV to bind to PYCARD and facilitates pyroptosome formation. Regulates endocytosis and cell migration in neutrophils. Homodimer. Homotrimer. Interacts (via coiled-coil domain) with CD2AP, PTPN12 and PTPN18. Interacts (via SH3 domain) with ABL1 and WAS. Interacts (via SH3 and coiled-coil domains) with MEFV (via B-box zinc finger); the interaction allows binding of MEFV to PYCARD and facilitates formation of PYCARD pyroptosomes. Interacts with DNM2 and FASLG (By similarity). Interacts with CD2. Colocalized with PTPN12 in the cytoplasm and the perinuclear region (PubMed:11711533). During interphase, colocalizes with F-actin in the cortical cytoskeleton, lamellipodia, and stress fibers (PubMed:9265651). In dividing cells, colocalizes with the F-actin rich cytokinetic cleavage furrow (PubMed:9265651). Colocalized with CD2AP and WAS in the actin cytoskeleton within the cytoplasm (PubMed:12530983, PubMed:9488710). Colocalized with CD2, CD2AP and WAS at the site of T-cell:APC contact (PubMed:12530983). Mainly cytoplasmic in T cells. Colocalizes in cluster with CD2 near the cell surface membrane in activated T-cells. In monocytes, forms a branched filamentous network in the cytoplasm. In transfected cells, forms relatively straight filaments radiating out from the nucleus. Filament formation requires an intact tubulin cytoskeleton. In migrating neutrophils, colocalizes with PIP5K1C and DNM2 to the trailing edge of the uropod in a actin-dependent manner (By similarity). Highly expressed in adult lung and spleen, and weakly expressed in testis, muscle, kidney, brain and heart. Highly expressed in spleen and thymus, moderately in lung, brain and muscle, and weakly expressed in heart and liver (at protein level). Highly expressed in 7 dpc embryos. The F-BAR domain is important for filament formation. The SH3 domain is not required for filament formation or localization to the uropod (By similarity). Dephosphorylated on Tyr-344 by PTPN18, this event negatively regulates the association of PSTPIP1 with SH2 domain-containing proteins as tyrosine kinase. Phosphorylation of Tyr-344 is probably required for subsequent phosphorylation at other tyrosine residues. Phosphorylation is induced by activation of the EGFR and PDGFR in a ABL1 dependent manner. The phosphorylation regulates the interaction with WAS and with MEFV.