SKP2 and neoplasm: Our study demonstrated that nobiletin inhibited tumor progression by regulating the SKP2-p21/p27-CDK2-RB axis (working model, Figure 8F): SKP2 targets p27 for degradation, CDK2 can be reactivated upon p27 degradation, and phosphorylation of RB is recovered by activated CDK2, which leads to G1/S transition, tumor growth, and progression.