Loss of epigenetic information as a cause of mammalian aging

All living things experience an increase in entropy, manifested as a loss of genetic and epigenetic information. In yeast, epigenetic information is lost over time due to the relocalization of chromatin-modifying proteins to DNA breaks, causing cells to lose their identity, a hallmark of yeast aging. Using a system called "ICE" (inducible changes to the epigenome), we find that the act of faithful DNA repair advances aging at physiological, cognitive, and molecular levels, including erosion of the epigenetic landscape, cellular exdifferentiation, senescence, and advancement of the DNA methylation clock, which can be reversed by OSK-mediated rejuvenation. These data are consistent with the information theory of aging, which states that a loss of epigenetic information is a reversible cause of aging.

Adeno-Associated Virus Technologies and Methods for Targeted Neuronal Manipulation

Cell-type-specific expression of molecular tools and sensors is critical to construct circuit diagrams and to investigate the activity and function of neurons within the nervous system. Strategies for targeted manipulation include combinations of classical genetic tools such as Cre/loxP and Flp/FRT, use of cis-regulatory elements, targeted knock-in transgenic mice, and gene delivery by AAV and other viral vectors. The combination of these complex technologies with the goal of precise neuronal targeting is a challenge in the lab. This report will discuss the theoretical and practical aspects of combining current technologies and establish best practices for achieving targeted manipulation of specific cell types. Novel applications and tools, as well as areas for development, will be envisioned and discussed.

Modulation of the Fanconi anemia pathway via chemically induced changes in chromatin structure

Fanconi anemia (FA) is a rare disease characterized by congenital defects, bone marrow failure, and atypically early-onset cancers. The FA proteins function cooperatively to repair DNA interstrand crosslinks. A major step in the activation of the pathway is the monoubiquitination of the FANCD2 and FANCI proteins, and their recruitment to chromatin-associated nuclear foci. The regulation and function of FANCD2 and FANCI, however, is poorly understood. In addition, how chromatin state impacts pathway activation is also unknown. In this study, we have examined the influence of chromatin state on the activation of the FA pathway. We describe potent activation of FANCD2 and FANCI monoubiquitination and nuclear foci formation following treatment of cells with the histone methyltransferase inhibitor BRD4770. BRD4770-induced activation of the pathway does not occur via the direct induction of DNA damage or via the inhibition of the G9a histone methyltransferase, a mechanism previously proposed for this molecule. Instead, we show that BRD4770-inducible FANCD2 and FANCI monoubiquitination and nuclear foci formation may be a consequence of inhibition of the PRC2/EZH2 chromatin-modifying complex. In addition, we show that inhibition of the class I and II histone deacetylases leads to attenuated FANCD2 and FANCI monoubiquitination and nuclear foci formation. Our studies establish that chromatin state is a major determinant of the activation of the FA pathway and suggest an important role for the PRC2/EZH2 complex in the regulation of this critical tumor suppressor pathway.

Coordinate nuclear targeting of the FANCD2 and FANCI proteins via a FANCD2 nuclear localization signal

Fanconi anemia (FA) is a rare recessive disease, characterized by congenital defects, bone marrow failure, and increased cancer susceptibility. FA is caused by biallelic mutation of any one of sixteen genes. The protein products of these genes function cooperatively in the FA-BRCA pathway to repair DNA interstrand crosslinks (ICLs). A central step in the activation of this pathway is the monoubiquitination of the FANCD2 and FANCI proteins. Monoubiquitinated FANCD2 and FANCI localize to discrete chromatin regions where they function in ICL repair. Despite their critical role in ICL repair, very little is known about the structure, function, and regulation of the FANCD2 and FANCI proteins, or how they are targeted to the nucleus and chromatin. In this study, we describe the functional characterization of an amino-terminal FANCD2 nuclear localization signal (NLS). We demonstrate that the amino terminal 58 amino acids of FANCD2 can promote the nuclear expression of GFP and is necessary for the nuclear localization of FANCD2. Importantly, mutation of this FANCD2 NLS reveals that intact FANCD2 is required for the nuclear localization of a subset of FANCI. In addition, the NLS is necessary for the efficient monoubiquitination of FANCD2 and FANCI and, consequently, for their localization to chromatin. As a result, FANCD2 NLS mutants fail to rescue the ICL sensitivity of FA-D2 patient cells. Our studies yield important insight into the domain structure of the poorly characterized FANCD2 protein, and reveal a previously unknown mechanism for the coordinate nuclear import of a subset of FANCD2 and FANCI, a key early step in the cellular ICL response.

p21 promotes error-free replication-coupled DNA double-strand break repair

p21 is a well-established regulator of cell cycle progression. The role of p21 in DNA repair, however, remains poorly characterized. Here, we describe a critical role of p21 in a replication-coupled DNA double-strand break (DSB) repair that is mechanistically distinct from its cell cycle checkpoint function. We demonstrate that p21-deficient cells exhibit elevated chromatid-type aberrations, including gaps and breaks, dicentrics and radial formations, following exposure to several DSB-inducing agents. p21^−/− cells also exhibit an increased DNA damage-inducible DNA-PK_CS S2056 phosphorylation, indicative of elevated non-homologous DNA end joining. Concomitantly, p21^−/− cells are defective in replication-coupled homologous recombination (HR), exhibiting decreased sister chromatid exchanges and HR-dependent repair as determined using a crosslinked GFP reporter assay. Importantly, we establish that the DSB hypersensitivity of p21^−/− cells is associated with increased cyclin-dependent kinase (CDK)-dependent BRCA2 S3291 phosphorylation and MRE11 nuclear foci formation and can be rescued by inhibition of CDK or MRE11 nuclease activity. Collectively, our results uncover a novel mechanism by which p21 regulates the fidelity of replication-coupled DSB repair and the maintenance of chromosome stability distinct from its role in the G1-S phase checkpoint.

Abstract LB-102: The p21Cip1/Waf1 cyclin-dependent kinase inhibitor is required for the activation of the FA-BRCA pathway

Fanconi anemia (FA) is a rare recessive disorder characterized in part by pronounced cancer susceptibility. The FA proteins, and the protein products of the major breast cancer susceptibility genes BRCA1 and BRCA2, function cooperatively in the FA-BRCA pathway, to repair damaged DNA and to prevent cellular transformation. A major step in the activation of the FA-BRCA pathway is the mono-ubiquitination of the FANCD2 and FANCI proteins, targeting these proteins to discrete chromatin-associated nuclear foci. Importantly, the regulation of FANCD2 (and FANCI) mono-ubiquitination remains poorly understood. To gain further insight into this important post-translational modification step, here we have examined the roles of p53 tumor suppressor as well its downstream target p21Cip1/Waf1 in the regulation of the mono-ubiquitination of FANCD2.

In this study we have used the isogenic HCT116 p53+/+, p53−/−, p21+/+, and p21−/− cell lines, to determine that p21, and not p53, plays a key role in the regulation of the mono-ubiquitination of FANCD2 following exposure to DNA damaging agents. For example, robust FANCD2 mono-ubiquitination is observed in HCT116 p21+/+ cells 2 h following exposure to 20 J/m2 UV irradiation, while this effect is markedly attenuated in p21−/− cells. Using immunofluorescence microscopy we also demonstrate that p21 is necessary for the efficient recruitment of FANCD2 to nuclear foci following exposure to UV irradiation. Furthermore, preliminary protein-protein interaction analyses in COS-7 cells demonstrate that FLAG-p21 and 6xHis/V5-FANCD2 physically interact.

Interestingly, despite a failure to efficiently activate the mono-ubiquitination of FANCD2 following exposure to DNA damaging agents, p21−/− cells are not hypersensitive to the cytotoxic effects of the DNA crosslinking agent mitomycin C (MMC). However, elevated levels of distinct chromosome aberrations, including telomere associations and dicentric chromosomes, are observed in p21−/− cells compared with p21+/+ cells following exposure to MMC. Taken together, our results demonstrate an important upstream role for the p21 cyclin-dependent-kinase inhibitor in the activation of the FA-BRCA pathway. A greater understanding of the regulation of this important tumor suppressor pathway will lead to improved diagnostic and therapeutic approaches to FA and enhance our understanding of the elevated cancer susceptibility of FA patients.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-102.

Functional interaction between the Fanconi Anemia D2 protein and proliferating cell nuclear antigen (PCNA) via a conserved putative PCNA interaction motif

Fanconi Anemia (FA) is a rare recessive disease characterized by congenital abnormalities, bone marrow failure, and cancer susceptibility. The FA proteins and the familial breast cancer susceptibility gene products, BRCA1 and FANCD1/BRCA2, function cooperatively in the FA-BRCA pathway to repair damaged DNA and to prevent cellular transformation. Activation of this pathway occurs via the mono-ubiquitination of the FANCD2 protein, targeting it to nuclear foci where it co-localizes with FANCD1/BRCA2, RAD51, and PCNA. The regulation of the mono-ubiquitination of FANCD2, as well as its function in DNA repair remain poorly understood. In this study, we have further characterized the interaction between the FANCD2 and PCNA proteins. We have identified a highly conserved, putative FANCD2 PCNA interaction motif (PIP-box), and demonstrate that mutation of this motif disrupts FANCD2-PCNA binding and precludes the mono-ubiquitination of FANCD2. Consequently, the FANCD2 PIP-box mutant protein fails to correct the mitomycin C hypersensitivity of FA-D2 patient cells. Our results suggest that PCNA may function as a molecular platform to facilitate the mono-ubiquitination of FANCD2 and activation of the FA-BRCA pathway.

The Fanconi anemia protein interaction network: casting a wide net

It has long been hypothesized that a defect in the repair of damaged DNA is central to the etiology of Fanconi anemia (FA). Indeed, an increased sensitivity of FA patient-derived cells to the lethal effects of various forms of DNA damaging agents was described over three decades ago [A.J. Fornace, Jr., J.B. Little, R.R. Weichselbaum, DNA repair in a Fanconi's anemia fibroblast cell strain, Biochim. Biophys. Acta 561 (1979) 99-109; Y. Fujiwara, M. Tatsumi, Repair of mitomycin C damage to DNA in mammalian cells and its impairment in Fanconi's anemia cells, Biochem. Biophys. Res. Commun. 66 (1975) 592-598; A.J. Rainbow, M. Howes, Defective repair of ultraviolet- and gamma-ray-damaged DNA in Fanconi's anaemia, Int. J. Radiat. Biol. Relat. Stud. Phys. Chem. Med. 31 (1977) 191-195]. Furthermore, the cytological hallmark of FA, the DNA crosslink-induced radial chromosome formation, exemplifies an innate impairment in the repair of these particularly cytotoxic DNA lesions [A.D. Auerbach, Fanconi anemia diagnosis and the diepoxybutane (DEB) test, Exp. Hematol. 21 (1993) 731-733]. Precisely defining the collective role of the FA proteins in DNA repair, however, continues to be one of the most enigmatic and challenging questions in the FA field. The first six identified FA proteins (A, C, E, F, G, and D2) harbored no recognizable enzymatic features, precluding association with a specific metabolic process. Consequently, our knowledge of the role of the FA proteins in the DNA damage response has been gleaned primarily through biochemical association studies with non-FA proteins. Here, we provide a chronological discourse of the major FA protein interaction network discoveries, with particular emphasis on the DNA damage response, that have defined our current understanding of the molecular basis of FA.

[Clinical and laboratorial repercussions of the nasal CPAP in preterm newborns]

OBJECTIVE: Evaluate the efficacy and problems associated with nasal CPAP use. METHODS: 96 preterm newborns needing nasal CPAP either as initial ventilatory support or as weaning from the ventilator were studied prospectively. RESULTS: Nasal CPAP was used in children weighing 480g to 2,450g and corrected gestational age of 24 to 39 weeks. It was indicated in cases of apnea (12.5%), hyaline membrane disease (32.3%), pneumonia (4.2%), transient tachypnea (22%), and weaning from the ventilator (29%). The last indication was more frequent in children with lower weight (p<0.01). The median time in nasal CPAP was 60.3h. After CPAP installation, there was a significant improvement in the respiratory distress that was not shown in the blood gases analysis. The percentage of children with nasal hyperemia, nasal bleeding, abdominal distention and children that could be fed was directly proportional to how long they had been in nasal CPAP. Children weighting </= 1,000g had higher incidence of abdominal distention (p<0.01) and those with weight between 1,500 to 2,500g faced higher difficulty to be maintained on nasal CPAP (p=0.04). Therapeutic success was of 37% for children weighing </=1,000g, 59% for the ones weighing 1,000 to 1,500g, and 83% for those weighing 1,500 to 2,500g. CONCLUSIONS: Nasal CPAP is a good option for ventilatory assistance in preterm babies. It is a safe therapy which in general has only topic complications; it does not prevent patients from being fed during its use. Furthermore, it was successful in 59% of the studied patients. do CPAP nasal.

Analysis of gonadotropin pulsatility in hirsute women with normal menstrual cycles and in women with polycystic ovary syndrome

OBJECTIVE

To study the relation between plasma gonadotropin pulsatility, androgen levels, and estrogen levels in patients with polycystic ovary syndrome (PCOS), in hirsute women with normal menstrual cycles, and in healthy women.

DESIGN

Prospective study.

SETTING

University medical center-based cellular and molecular endocrinology laboratory.

PATIENT(S)

Eight healthy women (group 1), 9 hirsute women with normal menstrual cycles (group 2), and 19 women with PCOS (group 3).

INTERVENTION(S)

Plasma concentrations of LH and FSH were measured by RIA every 15 minutes for 12 hours.

MAIN OUTCOME MEASURE(S)

Rhythmic parameters of 12-hour LH and FSH secretion.

RESULT(S)

Rhythmic parameters of 12-hour LH secretion were significantly higher in patients with PCOS (group 3) than in controls (group 1) or in hirsute women with normal menstrual cycles (group 2). The frequency of LH pulses was statistically higher in patients with PCOS (group 3) than in controls (group 1). Statistically significant correlations were found when the frequency of LH pulses was plotted against basal LH concentrations and rhythmic parameters of 12-hour LH secretion.

CONCLUSION(S)

Luteinizing hormone pulse amplitude was higher in patients with PCOS than in hirsute women with normal menstrual cycles or in healthy women. The LH pulse frequency was increased only in patients with PCOS compared with healthy women and not in hirsute women with normal menstrual cycles.