Phospholipase D2 downregulation induces cellular senescence through a reactive oxygen species-p53-p21Cip1/WAF1 pathway

The expression of phospholipase D1 (PLD1) and PLD2 were found to decrease at the transcription level during both replicative and premature senescence in human lung fibroblast IMR-90 cells. Knockdown of PLD2 dramatically induced senescent phenotype in proliferating IMR-90 cells and wild-type HCT116 colon cancer cells, whereas this response was nearly abolished in p53- or p21Cip1/WAF1-null HCT116 cells. PLD2 knockdown increased the intracellular reactive oxygen species (ROS). Antioxidant N-acetyl-l-cysteine, NADPH oxidase inhibitor apocynin, and p22phox small interfering RNA (siRNA) reduced ROS generation and thus suppressed the appearance of senescence markers. Elevated CK2 α subunit (CK2α) expression repressed PLD2 downregulation-mediated senescence. PLD2 overexpression increased protein kinase CK2 (also known as casein kinase 2) (CK2) activity. Taken together, these results show that PLD2 downregulation causes senescence through the p53-p21Cip1/WAF1 pathway by stimulating ROS production, which is induced by CK2 inhibition.