Transcriptional coactivator for androgen receptor (AR) and serum response factor (SRF). Contributes to the regulation of cell adhesion, spreading and cell migration and acts as a negative regulator in integrin-mediated cell adhesion events. Suppresses the integrin-induced tyrosine phosphorylation of paxillin (PXN). May play a critical role as an adapter protein in the formation of the adhesion zone in osteoclasts. Negatively regulates B-cell antigen receptor (BCR) signaling. Interacts with PTPN22 (By similarity). Interacts with unphosphorylated ITGA4. Interacts with PTK2B/PYK2, PTPN12, AR and SRF. Interacts (via LD motif 3) with LYN and the interaction is induced upon B-cell antigen receptor (BCR) activation. Interacts (via LD motif 3) with PTK2/FAK. Shuttles between the cytoplasm and nucleus. Recruited to the cell membrane following B-cell antigen receptor (BCR) cross-linking in B-cells. Enhanced focal adhesion kinase activity (PTK2/FAK) attenuates its nuclear accumulation and limits its ability to enhance serum response factor (SRF)-dependent gene transcription. Targeting to focal adhesions is essential for its tyrosine phosphorylation in response to bombesin. Macrophages, monocytes and osteoclasts (at protein level). Strongly expressed in cells and tissues of hematopoietic origin. Highest expression in lymphoid tissues such as spleen, lymph node, thymus and appendix and in the vascular smooth muscle. Lower levels in bone marrow and fetal liver. Also expressed in peripheral blood lymphocytes and a number of hematopoietic cell lines. Very low levels found in epithelial cell lines. Expressed in prostate cancer (PCa) cells and its expression intensity is directly linked to PCa progression. The LIM domain 3 is critical for focal adhesion targeting and the suppression of paxillin (PXN) tyrosine phosphorylation. The LIM domain 3 alone or both LIM domains 3 and 4 can mediate interaction with AR. Phosphorylated on tyrosine residues. Phosphorylation on Tyr-72 is important for its inhibitory function. Bombesin stimulates phosphorylation on Tyr-22, Tyr-62 and Tyr-72. Belongs to the paxillin family.