CDKN1A and hydrops fetalis: By knocking down p21Cip1 and p27Kip1 separately or simultaneously in HCT116 cells and MCF-7 cells, we found that p21Cip1 was required for HF induced G1/G0 arrest, whereas p21Cip1 and p27Kip1 were both required for ATS or HF-ATS combination-mediated cell cycle arrest.