Supplementary material from "A CDCA2 - MYC positive feedback loop controls cancer cells survival"

MYC transcription factors are encoded by a family of genes which include the prototype member MYC, MYCN and MYCL and most human cancers display expression alterations of MYC genes. MYC is regulated at multiple levels and its stability and activity is modulated by protein phosphorylation; although there is a reasonable knowledge of the kinases required for MYC modifications, the counteracting phosphatases have been understudied. Here we have investigated the role of the chromatin-associated protein phosphatase 1 (PP1) regulatory subunit CDCA2, also known as Repo-Man, in the regulation of MYC proteins in cancer cells. Using RNA interference and degron-mediated degradation of CDCA2, we have demonstrated that the PP1 subunit is required for MYC and MYCN stabilisation and viability of triple negative breast cancer, neuroblastoma and colon cancer cells. Proximity ligation assays indicate that both MYC and MYCN are in close proximity of CDCA2 in vivo. Furthermore, we have shown that CDC2A is a bone-fide MYC target gene in cancer cells, revealing a reciprocal regulatory loop that could be exploited for therapeutic purposes.