On the discovery and elucidation of the mechanism via which repression of the Caenorhabditis elegans p53 ortholog cep-1 results in longevity

The objective of this dissertation is to investigate the gerontological phenomenon of a link between p53 and senescence, as a means of illuminating one of the myriad cellular and organismic processes by which aging is regulated. The tumor-suppressor gene p53 has been well documented to regulate the decision of a cell to either repair DNA damage or undergo apoptosis, so as to forestall oncogenesis. Hyperactivation or over-expression of Mus musculus p53 has been shown to result in segmental progeria and a decrease in lifespan. I have investigated the inverse situation in great depth in the nematode Caenorhabditis elegans.; I show that RNAi or genetic knockout of the C. elegans p53 ortholog, cep-1, leads to an increase in lifespan, which is dependent upon functional daf-16. Further, only one other DNA damage-responsive C. elegans mutant, hus-1(op241), exhibits a lifespan increase. The lifespan increase of the cep-1(gk138) knockout mutant is not due to increased resistance to heat, oxidative, or UV stress. Not only is the lifespan of the cep-1(gk138) knockout mutant not due to increased resistance to bacterial proliferation/toxicity, a greater lifespan increase is revealed when bacterial pathogenicity is reduced. The lifespan increase engendered by cep-1 RNAi is additive with that of an age-1(hx546) mutant, suggesting that the two genes regulate lifespan through different mechanisms. cep-1 RNAi did not extend the lifespan of a sir-2.1(geIn3) over-expressing strain. This suggested that SIR-2.1 extends C. elegans lifespan by de-acetylating the histones around the cep-1 gene, as SIR-2.1's yeast homolog SIR2 de-acetylates histones in yeast, or by de-acetylating the CEP-1 protein, as SIR-2.1's mammalian homolog SIRT1 de-acetylates p53 in mammals.; Thus, I show that cep-1 expression is detrimental to the longevity of C. elegans. Although cep-1 suppression's lifespan-extending effect is genetically dependent upon functional daf-16, cep-1 repression does not affect DAF-16 location, does not affect dauer formation, yet does increase the maximal lifespan of a daf-16-dependent long-lived mutant. All of this concurs that CEP-1 does not interact at all biochemically with DAF-16, directly or indirectly; and that the genetic dependence seen is a result of the dependence of an organism with reduced cep-1 function upon the protection of daf-16 for longevity. I also show that the lifespan increase of cep-1-repressed worms is not due to increased stress resistance or increased resistance to bacterial proliferation/toxicity. Furthermore, there does not appear to be any universal applicability of the cep-1 longevity results to the processes of DNA damage-response in general. Finally, there does not appear to be a link between the mode of lifespan increase of cep-1-suppressed worms and that of sir-2.1 over-expressing worms. (Abstract shortened by UMI.)...