MMP9 and cancer: Remarkably, USP22 knockout had pronounced effects on expression of these important cancer-associated gene sets such as c-Myc, E2F, and selected genes including ALDH1A3, CCNE1/G1, E2F6, HOXA1, MMP9, NFKB2, TP63, TPM4, SET7/9 were validated by qRT–PCR (Fig. 2a).