Abstract #3478: Diminution of p53 during cellular senescence and organismal aging in normal human keratinocytes occurs at the post-transcriptional level

Cancer is one of the most prevalent age-associated diseases. Age-dependent cancer occurrence is largely attributed to the enhanced susceptibility to environmental carcinogens and the accumulation of genetic alterations, and the loss of tumor suppressive functions of cells is suggested to play key roles. Although p53 is a well-known potent tumor suppressor, its role during cellular senescence and organismal aging in normal human cells, particularly that of epithelial origins, remains controversial. The current study was undertaken to examine the regulation of p53 during cellular senescence and organismal aging in normal human keratinocytes and epithelium. Normal human oral keratinocytes (NHOKs) undergoing senescence upon serial subcultures exhibited decreases in p53 and p53 target genes, p21 and PUMA, and an increase in cell cycle arrest at G2 phase. Interestingly, p53 mRNA remained constant throughout their replicative lifespan. Screening the rates of depletion or accumulation of p53 upon the treatments of cycloheximide or MG132, respectively, showed no significant differences between young and senescent NHOKs. When newly synthesized p53 was monitored between young and senescent NHOKs using ³⁵S-labled nascent protein synthesis assay, a significant amount of p53 protein synthesis was reduced in senescent NHOKs, suggesting that the post-transcriptional regulation of p53 plays a major role during senescence. Actinomycin D treatment revealed that p53 mRNA decayed more rapidly during senescence. Using luciferase assay with pGL3-p53-3\#8217;UTR chimeric reporter vector, we found that p53 3\#8217;UTR is responsible for the decrease in the protein synthesis during senescence. We further found that RNA-binding protein, HuR, also decreased during senescence, and that the binding of HuR to p53 mRNA decreased during senescence as determined by RNA-immunoprecipitation assay. Finally, the diminution of p53 also occurred in vivo in age-dependent manner as determined by immunohistochemical staining using 20 normal human oral epithelium (NHOEs) from healthy individuals (age range = 28-75, r=0.512). Our study demonstrates that the diminution of p53 during cellular senescence occurs primarily at the post-transcriptional level, and suggests that this diminution of p53 may explain the increased incidence of cancer development during organismal aging. This study was supported by NIDCR/NIH (DE14147 and DE017121).

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 3478.