RB1 and cancer: ,8,9 Consistently, we found that genetic RB1 knockout (RB1-KO) via CRISPR-Cas9 indeed increased the abundance of P16 in MGC803 and ECA109 cancer cells (Figures 1A and S2A), whereas transient GFP-RB1 overexpression (RB1-OE) significantly decreased the abundance of P16 (Figure 1B).