ABSTRACT
The SirT1 gene encodes a protein deacetylase that acts on a number of nuclear substrates. p53 was identified as a SirT1 substrate whose transcriptional activity was reported to be negatively regulated by SirT1-dependent deacetylation. We set out to determine whether developmental defects and perinatal lethality observed in SirT1-null mice were caused by p53 hyperactivity by creating mice deficient for both SirT1 and p53. Animals null for both proteins were smaller than normal at birth, had eyelid opening defects and died during the late prenatal and early postnatal periods, a phenotype indistinguishable from mice deficient for SirT1 alone. Upon re-examination of the role of SirT1 in modulating p53 activity, we found that while SirT1 interacts with p53, the SirT1 protein had little effect on p53-dependent transcription of transfected or endogenous genes and did not affect the sensitivity of thymocytes and splenocytes to radiation-induced apoptosis. These findings suggest that SirT1 does not affect many p53-mediated biological activities despite the fact that acetylated p53 has been shown to be a substrate for SirT1.
Subject(s)
Sirtuins/metabolism , Tumor Suppressor Protein p53/metabolism , Animals , Apoptosis , Cells, Cultured , Crosses, Genetic , Dose-Response Relationship, Radiation , Eyelids/anatomy & histology , Mice , Mice, Transgenic , Phenotype , Protein Binding , Sirtuin 1 , Sirtuins/deficiency , Spleen/cytology , Spleen/radiation effects , Survival , T-Lymphocytes, Regulatory/radiation effects , Transcriptional Activation/genetics , Tumor Suppressor Protein p53/geneticsABSTRACT
The NAD-dependent deacetylase SIR2 and the forkhead transcription factor DAF-16 regulate lifespan in model organisms, such as yeast and C. elegans. Here we show that the mammalian SIR2 ortholog SIRT1 deacetylates and represses the activity of the forkhead transcription factor Foxo3a and other mammalian forkhead factors. This regulation appears to be in the opposite direction from the genetic interaction of SIR2 with forkhead in C. elegans. By restraining mammalian forkhead proteins, SIRT1 also reduces forkhead-dependent apoptosis. The inhibition of forkhead activity by SIRT1 parallels the effect of this deacetylase on the tumor suppressor p53. We speculate how down-regulating these two classes of damage-responsive mammalian factors may favor long lifespan under certain environmental conditions, such as calorie restriction.
