Regulates actin polymerization by stimulating the actin-nucleating activity of the Arp2/3 complex (PubMed:9422512, PubMed:16767080, PubMed:19366662, PubMed:19487689, PubMed:22847007, PubMed:22921828). Involved in various processes, such as mitosis and cytokinesis, via its role in the regulation of actin polymerization (PubMed:9422512, PubMed:19366662, PubMed:19487689, PubMed:22847007, PubMed:22921828). Together with CDC42, involved in the extension and maintenance of the formation of thin, actin-rich surface projections called filopodia (PubMed:9422512). In addition to its role in the cytoplasm, also plays a role in the nucleus by regulating gene transcription, probably by promoting nuclear actin polymerization (PubMed:16767080). Binds to HSF1/HSTF1 and forms a complex on heat shock promoter elements (HSE) that negatively regulates HSP90 expression (By similarity). Plays a role in dendrite spine morphogenesis (By similarity). Decreasing levels of DNMBP (using antisense RNA) alters apical junction morphology in cultured enterocytes, junctions curve instead of being nearly linear (PubMed:19767742). Binds actin and the Arp2/3 complex (PubMed:22847007). Interacts with CDC42 (PubMed:9422512). Interacts with FCHSD1 (By similarity). Interacts with FCHSD2 (PubMed:29887380). Binds to SH3 domains of GRB2. Interacts with the C-terminal SH3 domain of DNMBP (PubMed:19767742, PubMed:24332715, PubMed:17015620). Interacts with SNX9 (By similarity). Interacts with the WW domains of PRPF40A/FBP11 (By similarity). Interacts with PTK2/FAK1 (By similarity). Interacts with PACSIN1, PACSIN2 and PACSIN3 (By similarity). Interacts with NOSTRIN (PubMed:16234328). Binds to TNK2 (PubMed:16257963). Interacts with SNX33 (PubMed:19487689). Interacts with NONO (via second RRM domain); the interaction is direct (PubMed:16767080). Component of a multiprotein complex with NONO and SFPQ; associates with the complex via direct interaction with NONO (PubMed:16767080). (Microbial infection) Interacts with E.coli effector protein EspF(U) (PubMed:19366662, PubMed:22921828). Identified in a complex containing at least WASL, BAIAP2L1 and E.coli EspF(U) (PubMed:22921828). (Microbial infection) Interacts with Shigella flexneri protein IcsA (PubMed:9582270, PubMed:10491394). The interaction with IcsA enhances the affinity of WASL for Arp2/3, thus assembling a tight complex which has maximal activity in actin assembly (PubMed:9582270, PubMed:10491394). Preferentially localized in the cytoplasm when phosphorylated and in the nucleus when unphosphorylated (By similarity). Exported from the nucleus by an nuclear export signal (NES)-dependent mechanism to the cytoplasm (By similarity). Phosphorylation at Ser-242, Tyr-256, Ser-484 and Ser-485 enhances actin polymerization activity.