| PFN2 (profilin 2) is an actin monomer‑binding protein of the profilin family that links extracellular and intracellular signals to remodeling of the actin cytoskeleton, with particularly high expression in the nervous system and additional expression in other tissues. The protein adopts the conserved profilin fold that presents adjacent binding surfaces for G‑actin, poly‑L‑proline motifs, and phosphoinositides, allowing it to couple actin monomers to proline‑rich nucleation and elongation factors while also sensing membrane lipid signals. PFN2 binds ATP–G‑actin in a 1:1 stoichiometry and at low concentrations promotes actin filament assembly by delivering actin to barbed ends and to formin and Ena/VASP family proteins, whereas at high concentrations it sequesters actin monomers and limits spontaneous nucleation, so its local level and partner availability determine whether it enhances or restrains polymerization. By binding to phosphatidylinositol‑4,5‑bisphosphate (PIP2), PFN2 competes with phospholipase C for this lipid and can reduce the formation of IP3 and diacylglycerol, connecting actin regulation to control of phosphoinositide‑dependent signaling. Interactions with Ena/VASP family members, formins such as FMNL1, and Rho‑GTPase–linked effectors position PFN2 in complexes that drive polarized actin assembly at the leading edge, in growth cones, and at synapses, where changes in profilin–actin–polyproline networks influence spine morphology, vesicle exocytosis, and synaptic plasticity. PFN2 is subject to ubiquitin‑proteasome regulation, including ubiquitination by the E3 ligase cIAP1, and modulation of PFN2 levels by this pathway alters cellular reactive oxygen species, indicating that PFN2 abundance is tuned by ubiquitin signaling and that its actin‑related functions intersect with redox homeostasis. Elevated PFN2 expression has been reported in several cancers, including head and neck and small cell lung cancer, where PFN2 up‑regulation associates with increased proliferation, migration, invasion, and angiogenesis, and experimental manipulation links these effects to activation of PI3K–AKT–GSK3β–β‑catenin and related growth‑promoting pathways. |
