Silencing of the CKIIα and CKIIα′ genes during cellular senescence is mediated by DNA methylation

Previously we reported that down-regulation of CKII activity is tightly associated with cellular senescence and that the mRNA and protein levels of CKII alpha decrease during senescence. The present study demonstrates that the mRNA and protein levels of CKII alpha' also decrease during senescence. Knockdown of CKII alpha' IMR-90 cells by RNA interference induced the senescent phenotype. Treatment of senescent IMR-90 cells with a demethylating agent 5-aza-2'-deoxycytidine induced CKII alpha and CKII alpha' expression, suggesting that DNA hypermethylation might be involved in the silencing of CKII alpha and CKII alpha' genes in senescent cells. However, bisulfite sequencing analysis revealed that the methylation status of the CpG islands within the reported CKII alpha and CKII alpha' promoters was not associated with senescence. Instead, senescence-dependent hypermethylation was observed in the region ranging from position + 1112 to + 1128 of the CKII alpha gene and at positions -527 and +829 of the CKII alpha' gene. In addition, this study indicates that DNA methylation-dependent down-regulation of transcription factors Sp1, Etsl and NF-kappa B might be involved in silencing of the CKII alpha and CKII alpha' genes during cellular senescence. (C) 2008 Elsevier B.V. All rights reserved.