We investigated the impact of protein kinase C (PKC) on cellular senescence. The PKC activity and expression of conventional PKC (cPKC) and atypical PKC (aPKC) isoforms decreased during replicative senescence in IMR-90 cells. Forced inhibition of cPKC or aPKC induced the activation of senescence markers, including senescence-associated beta-galactosidase activity and reactive oxygen species (ROS)-p53-p21(Cip1/WAF1) axis in HCT116 and HEK293 cells. PKC inhibition triggered the nuclear exportation of FoxO3a via stimulation of ART-mediated phosphorylation of FoxO3a, and thereby decreased the transcription of Fox03a target genes. Conversely, ectopic expression of the PKC isoforms led to stimulation of the nuclear import of FoxO3a and expression of the FoxO3a target genes. Ectopic FoxO3a expression attenuated ROS accumulation and senescent phenotypes induced by PKC inhibition. Therefore, this study suggests for the first time that downregulation of PKC induces senescence through the AKT-Fox03a-ROS-p53-p21(Cip1/WAF1) pathway in HCT116 and HEK293 cells. (C) 2017 Elsevier Inc. All rights reserved.