POLR2A and neoplasm: When DDB2 was knocked out and cells were treated with PF-3758309, we observed higher protein levels of POLR2A/B/E compared to wild-type cells, providing further evidence that PF-3758309 promotes the degradation of POLR2A/B/E through the DDB2-mediated ubiquitination pathway, thereby inhibiting tumor cell growth (Fig. 5G).