Calcium-binding protein that plays a role in various cellular processes including motility, angiogenesis, cell differentiation, apoptosis, and autophagy (PubMed:20519440). Increases cell motility and invasiveness by interacting with non-muscle myosin heavy chain (NMMHC) IIA/MYH9 (PubMed:8051043). Mechanistically, promotes filament depolymerization and increases the amount of soluble myosin-IIA, resulting in the formation of stable protrusions facilitating chemotaxis (PubMed:8051043). Modulates also the pro-apoptotic function of TP53 by binding to its C-terminal transactivation domain within the nucleus and reducing its protein levels (By similarity). Within the extracellular space, stimulates cytokine production including granulocyte colony-stimulating factor and CCL24 from T-lymphocytes (PubMed:20103644). In addition, stimulates T-lymphocyte chemotaxis by acting as a chemoattractant complex with PGLYRP1 that promotes lymphocyte migration via CCR5 and CXCR3 receptors (By similarity). Homodimer. Interacts with PPFIBP1 in a calcium-dependent mode. Interacts with PGLYRP1; this complex acts as a chemoattractant that promotes lymphocyte movement. Interacts with MYH9; this interaction increases cell motility. Interacts with Annexin 2/ANXA2. Interacts with TP53; this interaction promotes TP53 degradation. Interacts with CCR5 and CXCR3. Interacts with FCGR3A; this interaction inhibits PKC-dependent phosphorylation of FCGR3A. Specifically expressed in different metastatic cells. The mRNA coding for this protein increases in abundance after serum stimulation of quiescent mouse fibroblasts. Deletion mice are fertile, grow normally and exhibit no overt abnormalities; however loss of S100A4 results in impaired recruitment of macrophages to sites of inflammation in vivo (PubMed:20519440). Mice also show decreased metastatic burden in lungs of PyMT-induced mammary tumors which is associated with reduced vessel density (PubMed:20103644). Belongs to the S-100 family.