ABSTRACT
Following the publication of this article the authors noted that two images were duplicated in Figure 2B. The corrected figure 2B is below. The authors wish to apologize for any inconvenience caused.
ABSTRACT
Long interspersed nuclear elements-1 (L1s) are highly repetitive DNA elements that are capable of altering the human genome through retrotransposition. To protect against L1 retroposition, the cell downregulates the expression of L1 proteins by various mechanisms, including high-density cytosine methylation of L1 promoters and DICER-dependent destruction of L1 mRNAs. In this report, a large number of p53 responsive elements, or p53 DNA binding sites, were detected in L1 elements within the human genome. At least some of these p53 responsive elements are functional and can act to increase the levels of L1 mRNA expression. The p53 protein can directly bind to a short 15-nucleotide sequence within the L1 promoter. This p53 responsive element within L1 is a recent addition to evolution, appearing approximately 20 million years ago. This suggests an interplay between L1 elements, which have a rich history of causing changes in the genome, and the p53 protein, the function of which is to protect against genomic changes. To understand these observations, a model is proposed in which the increased expression of L1 mRNAs by p53 actually increases, rather than decreases, the genomic stability through amplification of p53-dependent processes for genomic protection.
Subject(s)
Evolution, Molecular , Genome, Human/physiology , Genomic Instability/physiology , Long Interspersed Nucleotide Elements/physiology , Response Elements/physiology , Tumor Suppressor Protein p53/metabolism , Cell Line, Tumor , DNA Methylation/physiology , Gene Expression Regulation/physiology , Humans , Models, Genetic , RNA, Messenger/biosynthesis , RNA, Messenger/genetics , Ribonuclease III/genetics , Ribonuclease III/metabolism , Tumor Suppressor Protein p53/geneticsABSTRACT
The p53 tumor suppressor is a nucleocytoplasmic shuttling protein that is found predominantly in the nucleus of cells. In addition to mutation, abnormal p53 cellular localization is one of the mechanisms that inactivate p53 function. To further understand features of p53 that contribute to the regulation of its trafficking within the cell, we analysed the subnuclear localization of wild-type and mutant p53 in human cells that were either permeabilized with detergent or treated with the proteasome inhibitor MG132. We, here, show that either endogenously expressed or exogenously added p53 protein localizes to the nucleolus in detergent-permeabilized cells in a concentration- and ATP hydrolysis-dependent manner. Two discrete regions within the carboxyl terminus of p53 are essential for nucleolar localization in permeabilized cells. Similarly, localization of p53 to the nucleolus after proteasome inhibition in unpermeabilized cells requires sequences within the carboxyl terminus of p53. Interestingly, genotoxic stress markedly decreases the association of p53 with the nucleolus, and phosphorylation of p53 at S392, a site that is modified by such stress, partially impairs its nucleolar localization. The possible significance of these findings is discussed.
Subject(s)
Cell Nucleolus/metabolism , Tumor Suppressor Protein p53/chemistry , Tumor Suppressor Protein p53/metabolism , Adenosine Triphosphate/metabolism , Blotting, Western , Cells, Cultured , Cysteine Proteinase Inhibitors/pharmacology , DNA Damage/drug effects , Detergents/pharmacology , Fluorescent Antibody Technique , Humans , In Vitro Techniques , Leupeptins/pharmacology , Permeability , Proteasome Endopeptidase Complex/drug effects , Proteasome Endopeptidase Complex/metabolism , Protein Structure, Tertiary , Protein Transport/drug effects , Protein Transport/physiology , TransfectionABSTRACT
The p53 protein is a transcription factor that integrates various cellular stress signals. The accumulation of the mutant huntingtin protein with an expanded polyglutamine tract plays a central role in the pathology of human Huntington's disease. We found that the huntingtin gene contains multiple putative p53-responsive elements and p53 binds to these elements both in vivo and in vitro. p53 activation in cultured human cells, either by a temperature-sensitive mutant p53 protein or by gamma-irradiation (gamma-irradiation), increases huntingtin mRNA and protein expression. Similarly, murine huntingtin also contains multiple putative p53-responsive elements and its expression is induced by p53 activation in cultured cells. Moreover, gamma-irradiation, which activates p53, increases huntingtin gene expression in the striatum and cortex of mouse brain, the major pathological sites for Huntington's disease, in p53+/+ but not the isogenic p53-/- mice. These results demonstrate that p53 protein can regulate huntingtin expression at transcriptional level, and suggest that a p53 stress response could be a modulator of the process of Huntington's disease.
