Cell extracts were prepared in RIPA buffer (Pierce) supplemented with Protease Inhibitor Cocktail (Sigma) and separated on 4–12% gradient sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) gels. Western blotting was performed as described previously (6 (link)). Anti-P54nrb (sc-376865) and anti-PSF (sc-374502) antibodies were purchased from Santa Cruz Biotechnology. Anti-PSPC1 (ab104238), anti-hnRNP K (ab32969), anti-TCP1-β (ab92746) and anti-FUS (ab23439) were purchased from Abcam. Anti-GAPDH (G8795) and anti-γ-Tubulin (T6557) were purchased from Sigma. Anti-phospho-Cyclin D1 (Thr286) (3300) was purchased from Cell Signaling.