Lentiviral shRNA plasmids CCND1-1 (TRCN0000295875) and CCND1-2 (TRCN0000312873) were purchased from Sigma-Aldrich. The lentiviral shRNA vector for shRB1 was obtained from the RPCCC pGIPZ library (Clone ID: V2LHS_139). shRNAs targeting USP27X and ATXN7L3 were previously described (23 (link),28 (link)). Inducible shRNA vectors were generated by subcloning the USP27X targeting oligos (from the constitutive vectors described above) into the pLKO-Tet-On vector as described in (29 (link)). Retroviral vectors were generated by subcloning USP27X and CCND1 into a pBabe-Puro vector (Addgene) and lentiviral USP27X expressing vectors were generated by subcloning USP27X into a pLenti-Puro vector (Addgene).