Because siRNA-mediated suppression of CDK9, performed in the presence or absence of pan-caspase inhibition to exclude a possible impact of CDK9-silencing-induced apoptosis, also resulted in downregulation of cFlip and Mcl-1, we can conclude that CDK9 is required to maintain high expression of these anti-apoptotic proteins in cancer cells (Figure 4c). Here, MCL1 is linked to cancer.