CDK4 and cervical cancer: Among the cell cycle checkpoint proteins that we tested, the expression of cdc25A, CDK2, CDK4, CyclinD1 and CyclinE1 was up-regulated, and the expression of p21 was down-regulated in GDF15-overexpressing cervical cancer cells, which suggests that the cell cycle transition from G0/G1 phase to S phase in cervical cancer cells is regulated by GDF15 through the cdc25A/CDK4-CyclinD1 and p21/CDK2-CyclinE1 complexes.