Dissecting the role of p53 phosphorylation in homologous recombination provides new clues for gain-of-function mutants

Regulation of homologous recombination (HR) represents the best-characterized DNA repair function of p53. The role of p53 phosphorylation in DNA repair is largely unknown. Here, we show that wild-type p53 repressed repair of DNA double-strand breaks (DSBs) by HR in a manner partially requiring the ATM/ATR phosphorylation site, serine 15. Cdk-mediated phosphorylation of serine 315 was dispensable for this anti-recombinogenic effect. However, without targeted cleavage of the HR substrate, serine 315 phosphorylation was necessary for the activation of topoisomerase I-dependent HR by p53. Moreover, overexpression of cyclin A1, which mimics the situation in tumors, inappropriately stimulated DSB-induced HR in the presence of oncogenic p53 mutants (not Wtp53). This effect required cyclin A1/cdk-mediated phosphorylation for stable complex formation with topoisomerase I. We conclude that p53 mutants have lost the balance between activation and repression of HR, which results in a net increase of potentially mutagenic DNA rearrangements. Our data provide new insight into the mechanism underlying gain-of-function of mutant p53 in genomic instability

Identification of bZIP interaction partners of viral proteins HBZ, MEQ, BZLF1, and K-bZIP using coiled-coil arrays

Basic-region leucine-zipper transcription factors (bZIPs) contain a segment rich in basic amino acids that can bind DNA, followed by a leucine zipper that can interact with other leucine zippers to form coiled-coil homo- or heterodimers. Several viruses encode proteins containing bZIP domains, including four that encode bZIPs lacking significant homology to any human protein. We investigated the interaction specificity of these four viral bZIPs by using coiled-coil arrays to assess self-associations as well as heterointeractions with 33 representative human bZIPs. The arrays recapitulated reported viral−human interactions and also uncovered new associations. MEQ and HBZ interacted with multiple human partners and had unique interaction profiles compared to any human bZIPs, whereas K-bZIP and BZLF1 displayed homospecificity. New interactions detected included HBZ with MAFB, MAFG, ATF2, CEBPG, and CREBZF and MEQ with NFIL3. These were confirmed in solution using circular dichroism. HBZ can heteroassociate with MAFB and MAFG in the presence of MARE-site DNA, and this interaction is dependent on the basic region of HBZ. NFIL3 and MEQ have different yet overlapping DNA-binding specificities and can form a heterocomplex with DNA. Computational design considering both affinity for MEQ and specificity with respect to other undesired bZIP-type interactions was used to generate a MEQ dimerization inhibitor. This peptide, anti-MEQ, bound MEQ both stably and specifically, as assayed using coiled-coil arrays and circular dichroism in solution. Anti-MEQ also inhibited MEQ binding to DNA. These studies can guide further investigation of the function of viral and human bZIP complexes.National Institutes of Health (U.S.) (NIH Award GM067681)National Science Foundation (U.S.) (NSF Award 0216437

Emerging roles of ATF2 and the dynamic AP1 network in cancer

Cooperation among transcription factors is central for their ability to execute specific transcriptional programmes. The AP1 complex exemplifies a network of transcription factors that function in unison under normal circumstances and during the course of tumour development and progression. This Perspective summarizes our current understanding of the changes in members of the AP1 complex and the role of ATF2 as part of this complex in tumorigenesis.Fil: Lopez Bergami, Pablo Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental (i); Argentina; ArgentinaFil: Lau, Eric . Burnham Institute for Medical Research; Estados UnidosFil: Ronai, Zeev . Burnham Institute for Medical Research; Estados Unido

Histone H3.3 deposition at E2F-regulated genes is linked to transcription

The histone variant H3.3 can be incorporated in chromatin independently of DNA synthesis. By imaging using green fluorescent protein-tagged histones, H3.3 deposition has been found to be linked with transcriptional activation. Here, we investigated H3.3 incorporation during G1 progression on cell-cycle-regulated E2F-dependent genes and on some control loci. We transiently transfected resting cells with an expression vector for tagged H3.3 and we analysed its presence by chromatin immunoprecipitation. We found that replication-independent H3.3 deposition occurred on actively transcribed genes, but not on silent loci, thereby confirming its link with transcription. Interestingly, we observed similar levels of H3.3 occupancy on promoters and on the coding regions of the corresponding genes, indicating that H3.3 deposition is not restricted to promoters. Finally, H3.3 occupancy correlated with the presence of transcription-competent RNA polymerase II. Taken together, our results support the hypothesis that H3.3 is incorporated after disruption of nucleosomes mediated by transcription elongation

New molecular aspects of regulation of mitochondrial activity by fenofibrate and fasting

International audienc

Common haplotypes in five genes influence genetic variance of LDL and HDL cholesterol in the general population

We studied the association between common haplotypes in six relevant lipid metabolism genes with plasma lipid levels. We selected single-nucleotide polymorphisms (SNPs) in the cholesterol ester transfer protein (CETP), lipoprotein lipase (LPL), hepatic triglyceride lipase (HL), low-density lipoprotein cholesterol receptor (LDLR), apolipoprotein E (ApoE) and lecithin-cholesterol acyltransferase (LCAT) genes, and studied 732 individuals from 184 German families. Total cholesterol (TC), low-density lipoprotein cholesterol (LDL) and high-density lipoprotein cholesterol (HDL) were similar to those reported in other European and American populations. Haplotypes derived from SNP combinations resulted in more significance and of a higher degree than did single SNPs in the genotype–phenotype association analysis. Reduction of the polygenic variance attributable to haplotypes was estimated using variance components analysis. Under the biometrical genetic model, allelic association of haplotypes was highly significant for HDL, LDL and the LDL/HDL ratio. The residual kinship correlation was reduced accordingly. The ApoE gene had a strong effect on trait variation; however, the other genes also contributed substantially. An epistatic interaction could not be demonstrated in this sample. The data are consistent with the notion that common genetic variants influence common traits

Identification of functional domains involved in BTG1 cell localization

International audienc

Perceptual memory for highly familiar people's body shape: Manipulation of images of the self and friend

Previous studies have shown that people's ability to detect, from memory, alterations in highly familiar faces is excellent. Indeed, just noticeable differences for the detection of small alterations in a recognition-memory task were not significantly different from the corresponding measures in a perceptual-discrimination task (Brédart and Devue, 2006 Perception 35 101 - 106; Ge et al, 2003 Perception 32 601 - 614). The object of the present study was to evaluate whether people's perceptual memory for body shapes of very familiar persons reaches the high level of precision that was reported for face memory. For one group of participants, the task was to detect body shape alterations (an increase or a decrease of 2% to 10% of the waist-to-hip ratio) on photographs depicting either themselves or a friend. For another group of participants who did not know the target persons, the task was to discriminate whether two photographs presented side by side were the same or not. Results showed that the detection of alterations was significantly better in the perceptual-discrimination task than in the recognition-memory tasks (for the participant's own body as well as for the friend's body). In conclusion, the high fidelity of perceptual memory for very familiar faces does not extend to familiar body shapes