Binds to WASL/N-WASP and suppresses its translocation from the nucleus to the cytoplasm, thereby inhibiting its cytoplasmic function. Plays a role in the regulation of cell morphology and cytoskeletal organization. Required in the control of cell shape and migration. May play a role in cytokinesis. May be involved in pre-mRNA splicing. Interacts with the N-terminus of HTT and with the phosphorylated C-terminal domain of POLR2A (By similarity). Interacts with AKAP8L, SF1, SRPK1, ENAH, ATBF1 and MECP2. Interacts through the WW domains with formin proline-rich regions and with WASL/N-WASP. Colocalizes with AKAP8L in the nuclear matrix. The WW domains are essential for localization to nuclear speckles. Belongs to the PRPF40 family.