RIOK1 and cancer: What is interesting about the shRNA screen conducted in this study using 390 cancer cell lines, is that most of the PRMT5 interacting regulatory subunits, including methylosome protein 50 (MEP50/WDR77), methylosome subunit pICIn, and RIO kinase (RIOK1) were also found to be required for growth of MTAP-deficient cancer cells.