ARRB1 and cancer: Proliferation-related assays, including Cell Counting Kit-8 (CCK-8) and colony formation assays, were performed, and as expected, loss of PRDM2 or gain of the ARRB1-Δexon 13 isoform induced by AEP/tDDX3X-C promoted cancer cell proliferation (Supplemental Figure 9, C–F).