Regulation of RNA-polymerase-II-dependent transcription by N-WASP and its nuclear-binding partners

The presence of actin in the nucleus has been well established, and several studies have implicated nuclear actin in transcriptional regulation(1-3). Neuronal Wiskott-Aldrich syndrome protein ( N-WASP) is a member of the WASP family of proteins; these proteins function in the cytoplasm as key regulators of cortical actin filament(4-6). Interestingly, N-WASP has also been observed in the nucleus(7-11). However, a potential nuclear function for N-WASP has not been established. Here, we report the identification of nuclear N-WASP within a large nuclear-protein complex containing PSF-NonO ( polypyrimidine-tract-binding-protein-associated splicing factor-non-Pou-domain octamer-binding protein/p54nrb), nuclear actin and RNA polymerase II. The PSF-NonO complex is involved in the regulation of many cellular processes(12), such as transcription, RNA processing, DNA unwinding and repair. We demonstrate that the interaction of N-WASP with the PSF-NonO complex can couple N-WASP with RNA polymerase II to regulate transcription. We also provide evidence that the potential function of N-WASP in promoting polymerization of nuclear actins has an important role in this process. Based on these results, we propose a nuclear function for N-WASP in transcriptional regulation.