Rere controls retinoic acid signalling and somite bilateral symmetry.

One of the most notable features of the vertebrate body plan organization is its bilateral symmetry, evident at the level of vertebrae and skeletal muscles. Here we show that a mutation in Rere (also known as atrophin2) leads to the formation of asymmetrical somites in mouse embryos, similar to embryos deprived of retinoic acid. Furthermore, we also demonstrate that Rere controls retinoic acid signalling, which is required to maintain somite symmetry by interacting with Fgf8 in the left-right signalling pathway. Rere forms a complex with Nr2f2, p300 (also known as Ep300) and a retinoic acid receptor, which is recruited to the retinoic acid regulatory element of retinoic acid targets, such as the Rarb promoter. Furthermore, the knockdown of Nr2f2 and/or Rere decreases retinoic acid signalling, suggesting that this complex is required to promote transcriptional activation of retinoic acid targets. The asymmetrical expression of Nr2f2 in the presomitic mesoderm overlaps with the asymmetry of the retinoic acid signalling response, supporting its implication in the control of somitic symmetry. Misregulation of this mechanism could be involved in symmetry defects of the human spine, such as those observed in patients with scoliosis.

Suberoylanilide hydroxamic acid (SAHA)-induced dynamics of a human histone deacetylase protein interaction network.

Histone deacetylases (HDACs) are targets for cancer therapy. Suberoylanilide hydroxamic acid (SAHA) is an HDAC inhibitor approved by the U.S. Food and Drug Administration for the treatment of cutaneous T-cell lymphoma. To obtain a better mechanistic understanding of the Sin3/HDAC complex in cancer, we extended its protein-protein interaction network and identified a mutually exclusive pair within the complex. We then assessed the effects of SAHA on the disruption of the complex network through six homologous baits. SAHA perturbs multiple protein interactions and therefore compromises the composition of large parts of the Sin3/HDAC network. A comparison of the effect of SAHA treatment on gene expression in breast cancer cells to a knockdown of the ING2 subunit indicated that a portion of the anticancer effects of SAHA may be attributed to the disruption of ING2's association with the complex. Our dynamic protein interaction network resource provides novel insights into the molecular mechanism of SAHA action and demonstrates the potential for drugs to rewire networks.

RNA-dependent dynamic histone acetylation regulates MCL1 alternative splicing.

Histone deacetylases (HDACs) and lysine acetyltransferases (KATs) catalyze dynamic histone acetylation at regulatory and coding regions of transcribed genes. Highly phosphorylated HDAC2 is recruited within corepressor complexes to regulatory regions, while the nonphosphorylated form is associated with the gene body. In this study, we characterized the nonphosphorylated HDAC2 complexes recruited to the transcribed gene body and explored the function of HDAC-complex-mediated dynamic histone acetylation. HDAC1 and 2 were coimmunoprecipitated with several splicing factors, including serine/arginine-rich splicing factor 1 (SRSF1) which has roles in alternative splicing. The co-chromatin immunoprecipitation of HDAC1/2 and SRSF1 to the gene body was RNA-dependent. Inhibition of HDAC activity and knockdown of HDAC1, HDAC2 or SRSF1 showed that these proteins were involved in alternative splicing of MCL1. HDAC1/2 and KAT2B were associated with nascent pre-mRNA in general and with MCL1 pre-mRNA specifically. Inhibition of HDAC activity increased the occupancy of KAT2B and acetylation of H3 and H4 of the H3K4 methylated alternative MCL1 exon 2 nucleosome. Thus, nonphosphorylated HDAC1/2 is recruited to pre-mRNA by splicing factors to act at the RNA level with KAT2B and other KATs to catalyze dynamic histone acetylation of the MCL1 alternative exon and alter the splicing of MCL1 pre-mRNA.

Chromatin proteins: key responders to stress.

Environments can be ever-changing and stresses are commonplace. In order for organisms to survive, they need to be able to respond to change and adapt to new conditions. Fortunately, many organisms have systems in place that enable dynamic adaptation to immediate stresses and changes within the environment. Much of this cellular response is coordinated by modulating the structure and accessibility of the genome. In eukaryotic cells, the genome is packaged and rolled up by histone proteins to create a series of DNA/histone core structures known as nucleosomes; these are further condensed into chromatin. The degree and nature of the condensation can in turn determine which genes are transcribed. Histones can be modified chemically by a large number of proteins that are thereby responsible for dynamic changes in gene expression. In this Primer we discuss findings from a study published in this issue of PLoS Biology by Weiner et al. that highlight how chromatin structure and chromatin binding proteins alter transcription in response to environmental changes and stresses. Their study reveals the importance of chromatin in mediating the speed and amplitude of stress responses in cells and suggests that chromatin is a critically important component of the cellular response to stress.

Human family with sequence similarity 60 member A (FAM60A) protein: a new subunit of the Sin3 deacetylase complex.

Here we describe the function of a previously uncharacterized protein, named family with sequence similarity 60 member A (FAM60A) that maps to chromosome 12p11 in humans. We use quantitative proteomics to determine that the main biochemical partners of FAM60A are subunits of the Sin3 deacetylase complex and show that FAM60A resides in active HDAC complexes. In addition, we conduct gene expression pathway analysis and find that FAM60A regulates expression of genes that encode components of the TGF-beta signaling pathway. Moreover, our studies reveal that loss of FAM60A or another component of the Sin3 complex, SDS3, leads to a change in cell morphology and an increase in cell migration. These studies reveal the function of a previously uncharacterized protein and implicate the Sin3 complex in suppressing cell migration.

Association of bradykinin receptor 2 (BDKRB2) variants with physical performance and muscle mass: Findings from the LACE sarcopenia trial.

INTRODUCTION: Understanding genetic contributors to sarcopenia (age-related loss of muscle strength and mass) is key to finding effective therapies. Variants of the bradykinin receptor 2 (BDKRB2) have been linked to athletic and muscle performance. The rs1799722-9 and rs5810761 T alleles have been shown to be overrepresented in endurance athletes, possibly due to increased transcriptional rates of the receptor. These variants have been rarely studied in older people or people with sarcopenia. METHODS: We performed a post hoc sub-study of the Leucine and ACE (LACE) inhibitor trial, which enrolled 145 participants aged ≥70 years with low grip strength and low gait speed. Participants' blood samples were genotyped for rs179972 using TaqMan and rs5810761 by amplification through Hotstar Taq. Genotypes were compared with outcomes of physical performance and body composition measures. RESULTS: Data from 136 individuals were included in the analysis. For rs1799722 the genotype frequency (TT: 17, CC: 48, CT: 71) remained in Hardy-Weinberg Equilibrium (HWE p = 0.248). There was no difference between the genotypes for six-Minute Walk Distance (6MWD) or Short Physical Performance Battery (SPPB). Men with the TT genotype had a significantly greater 6MWD than other genotypes (TT 400m vs CT 310m vs CC 314m, p = 0.027), and greater leg muscle mass (TT 17.59kg vs CT 15.04kg vs CC 15.65kg, p = 0.007). For rs5810761, the genotype frequency (-9-9: 31, +9+9: 43, -9+9: 60) remained in HWE (p = 0.269). The +9+9 genotype was associated with a significant change in SPPB score at 12 months (-9-9 0 vs -9+9 0 vs +9+9-1, p<0.001), suggesting an improvement. In men, the -9-9 genotype was associated with lower arm fat (-9-9 2.39kg vs -9+9 2.72kg vs +9+9 2.76kg, p = 0.019). CONCLUSION: In men, the rs1799722 TT genotype was associated with longer 6MWD and greater leg muscle mass, while the rs5810761 -9-9 genotype was associated with lower arm fat mass.

ACE I/D genotype associates with strength in sarcopenic men but not with response to ACE inhibitor therapy in older adults with sarcopenia: Results from the LACE trial.

BACKGROUND: Angiotensin II (AII), has been suggested to promote muscle loss. Reducing AII synthesis, by inhibiting angiotensin converting enzyme (ACE) activity has been proposed as a method to inhibit muscle loss. The LACE clinical trial was designed to determine whether ACE inhibition would reduce further muscle loss in individuals with sarcopenia but suffered from low recruitment and returned a negative result. Polymorphic variation in the ACE promoter (I/D alleles) has been associated with differences in ACE activity and muscle physiology in a range of clinical conditions. This aim of this analysis was to determine whether I/D polymorphic variation is associated with muscle mass, strength, in sarcopenia or contributed to the lack of response to treatment in the LACE study. METHODS: Sarcopenic individuals were recruited into a 2x2 factorial multicentre double-blind study of the effects of perindopril and/or leucine versus placebo on physical performance and muscle mass. DNA extracted from blood samples (n = 130 72 women and 58 men) was genotyped by PCR for the ACE I/D polymorphism. Genotypes were then compared with body composition measured by DXA, hand grip and quadriceps strength before and after 12 months' treatment with leucine and/or perindopril in a cross-sectional analysis of the influence of genotype on these variables. RESULTS: Allele frequencies for the normal UK population were extracted from 13 previous studies (I = 0.473, D = 0.527). In the LACE cohort the D allele was over-represented (I = 0.412, D = 0.588, p = 0.046). This over-representation was present in men (I = 0.353, D = 0.647, p = 0.010) but not women (I = 0.458, D = 0.532, p = 0.708). In men but not women, individuals with the I allele had greater leg strength (II/ID = 18.00 kg (14.50, 21.60) vs DD = 13.20 kg (10.50, 15.90), p = 0.028). Over the 12 months individuals with the DD genotype increased in quadriceps strength but those with the II or ID genotype did not. Perindopril did not increase muscle strength or mass in any polymorphism group relative to placebo. CONCLUSION: Our results suggest that although ACE genotype was not associated with response to ACE inhibitor therapy in the LACE trial population, sarcopenic men with the ACE DD genotype may be weaker than those with the ACE I/D or II genotype.

Activin type I receptor polymorphisms and body composition in older individuals with sarcopenia-Analyses from the LACE randomised controlled trial.

BACKGROUND: Ageing is associated with changes in body composition including an overall reduction in muscle mass and a proportionate increase in fat mass. Sarcopenia is characterised by losses in both muscle mass and strength. Body composition and muscle strength are at least in part genetically determined, consequently polymorphisms in pathways important in muscle biology (e.g., the activin/myostatin signalling pathway) are hypothesised to contribute to the development of sarcopenia. METHODS: We compared regional body composition measured by DXA with genotypes for two polymorphisms (rs10783486, minor allele frequency (MAF) = 0.26 and rs2854464, MAF = 0.26) in the activin 1B receptor (ACVR1B) determined by PCR in a cross-sectional analysis of DNA from 110 older individuals with sarcopenia from the LACE trial. RESULTS: Neither muscle mass nor strength showed any significant associations with either genotype in this cohort. Initial analysis of rs10783486 showed that males with the AA/AG genotype were taller than GG males (174±7cm vs 170±5cm, p = 0.023) and had higher arm fat mass, (median higher by 15%, p = 0.008), and leg fat mass (median higher by 14%, p = 0.042). After correcting for height, arm fat mass remained significantly higher (median higher by 4% padj = 0.024). No associations (adjusted or unadjusted) were seen in females. Similar analysis of the rs2854464 allele showed a similar pattern with the presence of the minor allele (GG/AG) being associated with greater height (GG/AG = 174±7 cm vs AA = 170 ±5cm, p = 0.017) and greater arm fat mass (median higher by 16%, p = 0.023). Again, the difference in arm fat remained after correction for height. No similar associations were seen in females analysed alone. CONCLUSION: These data suggest that polymorphic variation in the ACVR1B locus could be associated with body composition in older males. The activin/myostatin pathway might offer a novel potential target to prevent fat accumulation in older individuals.

Effect of perindopril or leucine on physical performance in older people with sarcopenia: the LACE randomized controlled trial.

BACKGROUND: This trial aimed to determine the efficacy of leucine and/or perindopril in improving physical function in older people with sarcopenia. METHODS: Placebo-controlled, parallel group, double-blind, randomized two-by-two factorial trial. We recruited adults aged ≥ 70 years with sarcopenia, defined as low gait speed (<0.8 m/s on 4 m walk) and/or low handgrip strength (women < 20 kg, men < 30 kg) plus low muscle mass (using sex and body mass index category-specific thresholds derived from normative UK BioBank data) from 14 UK centres. Eligible participants were randomized to perindopril 4 mg or placebo, and to oral leucine powder 2.5 g or placebo thrice daily. The primary outcome was the between-group difference in the short physical performance battery (SPPB) score over 12-month follow-up by repeated-measures mixed models. Results were combined with existing systematic reviews using random-effects meta-analysis to derive summary estimates of treatment efficacy. RESULTS: We screened 320 people and randomized 145 participants compared with an original target of 440 participants. For perindopril [n = 73, mean age 79 (SD 6), female sex 39 (53%), mean SPPB 7.1 (SD 2.3)] versus no perindopril [n = 72, mean age 79 (SD 6), female sex 39 (54%), mean SPPB 6.9 (SD 2.4)], median adherence to perindopril was lower (76% vs. 96%; P < 0.001). Perindopril did not improve the primary outcome [adjusted treatment effect -0.1 points (95%CI -1.2 to 1.0), P = 0.89]. No significant treatment benefit was seen for any secondary outcome including muscle mass [adjusted treatment effect -0.4 kg (95%CI -1.1 to 0.3), P = 0.27]. More adverse events occurred in the perindopril group (218 vs. 165), but falls rates were similar. For leucine [n = 72, mean age 78 (SD 6), female sex 38 (53%), mean SPPB 7.0 (SD 2.1)] versus no leucine [n = 72, mean age 79 (SD 6), female sex 40 (55%), mean SPPB 7.0 (SD 2.5)], median adherence was the same in both groups (76% vs. 76%; P = 0.99). Leucine did not improve the primary outcome [adjusted treatment effect 0.1 point (95%CI -1.0 to 1.1), P = 0.90]. No significant treatment benefit was seen for any secondary outcome including muscle mass [adjusted treatment effect -0.3 kg (95%CI -1.0 to 0.4), P = 0.47]. Meta-analysis of angiotensin converting enzyme inhibitor/angiotensin receptor blocker trials showed no clinically important treatment effect for the SPPB [between-group difference -0.1 points (95%CI -0.4 to 0.2)]. CONCLUSIONS: Neither perindopril nor leucine improved physical performance or muscle mass in this trial; meta-analysis did not find evidence of efficacy of either ACE inhibitors or leucine as treatments to improve physical performance.

Transcription, translation and fragile X syndrome.

The fragile X mental retardation protein (FMRP) plays a role in the control of local protein synthesis in the dendrites. Loss of its production in fragile X syndrome is associated with transcriptional dysregulation of the gene. Recent work demonstrates that Sp1 and NRF1 transcriptionally control this gene. Other studies reveal how the microRNA pathway and signaling are related to FMRP function through the metabotropic glutamate receptor. These studies provide new insights through which we can better understand the inactivation of the FMR1 gene and, in turn, the consequence of FMRP loss.

Histone deacetylase inhibitors: anticancer compounds.

The reversible acetylation of proteins is mediated by histone acetyltransferases which acetylate proteins and histone deacetylases that remove the acetyl groups. High levels of histone acetylation are correlated with active genes, while hypoacetylation of histones corresponds with gene repression. Importantly, acetylation also occurs on non-histone proteins and this can affect the activity and stability of these proteins. Aberrant epigenetic changes are a common hallmark of tumors and imbalances in the activities of deacetylases have been associated with cancers. Accordingly, inhibitors to the histone deacetylases are in clinical trials for the treatment of several cancer types. These drugs mediate a number of molecular changes and in turn can induce cell cycle arrest, apoptosis or differentiation of cancer cells while displaying limited toxicity in normal cells.

The gene encoding the fragile X RNA-binding protein is controlled by nuclear respiratory factor 2 and the CREB family of transcription factors.

FMR1 encodes an RNA-binding protein whose absence results in fragile X mental retardation. In most patients, the FMR1 gene is cytosine-methylated and transcriptionally inactive. NRF-1 and Sp1 are known to bind and stimulate the active, but not the methylated/silenced, FMR1 promoter. Prior analysis has implicated a CRE site in regulation of FMR1 in neural cells but the role of this site is controversial. We now show that a phospho-CREB/ATF family member is bound to this site in vivo. We also find that the histone acetyltransferases CBP and p300 are associated with active FMR1 but are lost at the hypoacetylated fragile X allele. Surprisingly, FMR1 is not cAMP-inducible and resides in a newly recognized subclass of CREB-regulated genes. We have also elucidated a role for NRF-2 as a regulator of FMR1 in vivo through a previously unrecognized and highly conserved recognition site in FMR1. NRF-1 and NRF-2 act additively while NRF-2 synergizes with CREB/ATF at FMR1's promoter. These data add FMR1 to the collection of genes controlled by both NRF-1 and NRF-2 and disfavor its membership in the immediate early response group of genes.

Leucine and ACE inhibitors as therapies for sarcopenia (LACE trial): study protocol for a randomised controlled trial.

BACKGROUND: Sarcopenia (the age-related loss of muscle mass and function) is a major contributor to loss of mobility, falls, loss of independence, morbidity and mortality in older people. Although resistance training is effective in preventing and reversing sarcopenia, many older people are sedentary and either cannot or do not want to exercise. This trial examines the efficacy of supplementation with the amino acid leucine and/or angiotensin converting enzyme inhibition to potentially improve muscle mass and function in people with sarcopenia. Promising preliminary data exist from small studies for both interventions, but neither has yet been tested in adequately powered randomised trials in patients with sarcopenia. METHODS: Leucine and ACE inhibitors in sarcopenia (LACE) is a multicentre, masked, placebo-controlled, 2 × 2 factorial randomised trial evaluating the efficacy of leucine and perindopril (angiotensin converting enzyme inhibitor (ACEi)) in patients with sarcopenia. The trial will recruit 440 patients from primary and secondary care services across the UK. Male and female patients aged 70 years and over with sarcopenia as defined by the European Working Group on Sarcopenia (based on low total skeletal muscle mass on bioimpedance analysis and either low gait speed or low handgrip strength) will be eligible for participation. Participants will be excluded if they have a contraindication to, or are already taking, an ACEi, angiotensin receptor blocker or leucine. The primary clinical outcome for the trial is the between-group difference in the Short Physical Performance Battery score at all points between baseline and 12 months. Secondary outcomes include appendicular muscle mass measured using dual-energy X-ray absorptiometry, muscle strength, activities of daily living, quality of life, activity using pedometer step counts and falls. Participants, clinical teams, outcomes assessors and trial analysts are masked to treatment allocation. A panel of biomarkers including microRNAs, neurohormones, genetic polymorphisms and markers of inflammation relevant to muscle pathophysiology will be measured to explore predictors of response and further elucidate mechanisms underlying sarcopenia. Participants will receive a total of 12 months of either perindopril or placebo and either leucine or placebo. DISCUSSION: The results will provide the first robust test of the overall clinical and cost-effectiveness of these novel therapies for older patients with sarcopenia. TRIAL REGISTRATION: ISRCTN, ISRCTN90094835 . Registered on 18 February 2015.

Cisplatin and carboplatin-based chemotherapy in the first-line treatment of non-small cell lung cancer: Analysis from the European FRAME study.

OBJECTIVES: To explore patient and disease factors, and reasons behind the physician's choice of platinum backbone for the first-line treatment of non-small cell lung cancer (NSCLC), as observed in a European prospective observational study of patients receiving platinum-based chemotherapy as first-line treatment for advanced or metastatic NSCLC (the FRAME study). Additionally, overall survival (OS) for patients who received cisplatin or carboplatin was evaluated. MATERIALS AND METHODS: A post-hoc analysis of the prospective study population was conducted. Baseline characteristics of patients receiving cisplatin versus carboplatin were compared and summarized by propensity score. Survival for matched patients was summarized using the Kaplan-Meier approach. RESULTS: Of the 1564 patients who were included in the prospective study, 1520 received either cisplatin (54%) or carboplatin (46%) in combination with pemetrexed, gemcitabine, taxanes or vinorelbine. Patients treated with carboplatin were older than patients receiving cisplatin (mean age 67 versus 61 years; p<0.001), had poorer performance status (p<0.001), and more comorbidities (p<0.001). Cisplatin was most frequently combined with pemetrexed (47%), and carboplatin most frequently with taxanes (31%). Unadjusted median OS estimates for patients from the total prospective study sample were 11.5 months (95% confidence interval [CI] 10.1-12.9) for cisplatin recipients and 9.0 months (95% CI 8.1-10.6) for carboplatin recipients. Median (95% CI) overall survival for the matched cohorts was 10.8 months (8.8-14.3) for cisplatin versus 9.5 months (8.2-11.3) for carboplatin; p=0.086. CONCLUSION: This post-hoc analysis illustrated real-life differences in patients with NSCLC prescribed platinum-based first-line treatment, and suggested that baseline patient and disease characteristics were associated with physician's choice of platinum agent, with cisplatin being more frequently prescribed to younger and fitter patients.

Non-small cell lung cancer patients with brain metastases treated with first-line platinum-doublet chemotherapy: Analysis from the European FRAME study.

OBJECTIVES: We report on a post-hoc analysis of patients with brain metastases from a large prospective observational study of first-line treatment of non-small cell lung cancer (NSCLC). The aim was to describe baseline characteristics of NSCLC patients with brain metastases, understand their first-line treatment and report outcomes attained in real-world settings. MATERIALS AND METHODS: This post-hoc analysis included all patients in the European observational FRAME study who had brain metastases at initiation of first-line treatment. Descriptive statistics were used for continuous and categorical variables and survival outcomes were assessed using the Kaplan-Meier approach. RESULTS: Our data showed that 17% of patients (263/1564) had spread of the disease to the brain at initiation of first-line treatment. Patients with brain metastases were slightly younger, and more likely to have NSCLC of non-squamous histology than the overall study sample. 34% had received prior palliative radiotherapy to the brain. Our analysis showed a median overall survival (OS) of 7.2 months [95% confidence interval (CI) 6.1-8.2] for all patients with brain metastases treated with first-line platinum-based chemotherapy, ranging from 5.6 months for those treated with gemcitabine plus platinum up to 9.3 months for those treated with pemetrexed plus platinum. Further analysis showed that patients with brain metastases were more frequently treated with pemetrexed platinum-doublet therapy than with any other regimen. CONCLUSIONS: Our analysis provides a unique set of real-world data which adds to current understanding about treatment decisions and outcomes for NSCLC patients with brain metastases for whom there is little clinical trial data available.

Outcomes and resource use of non-small cell lung cancer (NSCLC) patients treated with first-line platinum-based chemotherapy across Europe: FRAME prospective observational study.

INTRODUCTION: FRAME was a prospective observational study that captured real-world data on patients with advanced or metastatic non-small cell lung cancer (NSCLC) receiving platinum-based chemotherapies as first-line treatment (FLT) across Europe. As previously reported, most patients observed in the study had initiated FLT with either pemetrexed, gemcitabine, vinorelbine or taxanes in combination with a platinum. Baseline patient and disease characteristics including age, performance status, and histology varied (all p<0.01) across cohorts. METHODS: Consenting adult patients initiating FLT for advanced or metastatic NSCLC with platinum-based chemotherapy, with or without a targeted agent, entered the study between April 2009 and February 2011. The choice of FLT was left to physicians' discretion per routine clinical practice. The primary objective was to evaluate overall survival (OS) across platinum-based doublet chemotherapy cohorts and key secondary objectives included the evaluation of OS in patients with different histological subtypes of NSCLC. Survival outcomes were assessed using Kaplan-Meier analysis, and unadjusted estimates are presented. RESULTS: Median OS in months was 10.3 across cohorts (n=1524), 10.7 for pemetrexed (n=569), 10.0 for gemcitabine (n=360), 9.1 for taxanes (n=295), and 10.7 for vinorelbine (n=300). For patients with non-squamous NSCLC who received cisplatin (n=616, 40% of total), median OS in months was 10.6 across the cohorts, 11.6 for pemetrexed, 8.4 for gemcitabine, 9.6 for taxanes, and 9.9 for vinorelbine. CONCLUSIONS: FRAME describes real-world treatment patterns and survival for patients initiating FLT for advanced or metastatic NSCLC between 2009 and 2011 across Europe.

Deacetylase inhibitors dissociate the histone-targeting ING2 subunit from the Sin3 complex.

Histone deacetylase (HDAC) inhibitors are in clinical development for several diseases, including cancers and neurodegenerative disorders. HDACs 1 and 2 are among the targets of these inhibitors and are part of multisubunit protein complexes. HDAC inhibitors (HDACis) block the activity of HDACs by chelating a zinc molecule in their catalytic sites. It is not known if the inhibitors have any additional functional effects on the multisubunit HDAC complexes. Here, we find that suberoylanilide hydroxamic acid (SAHA), the first FDA-approved HDACi for cancer, causes the dissociation of the PHD-finger-containing ING2 subunit from the Sin3 deacetylase complex. Loss of ING2 disrupts the in vivo binding of the Sin3 complex to the p21 promoter, an important target gene for cell growth inhibition by SAHA. Our findings reveal a molecular mechanism by which HDAC inhibitors disrupt deacetylase function.

Occupancy and synergistic activation of the FMR1 promoter by Nrf-1 and Sp1 in vivo.

Fragile X syndrome is due to mutation of the FMR1 gene. The most common mutation is an expansion of a CGG repeat in the 5' UTR that triggers dense DNA methylation and formation of a heterochromatin-like structure which lead to transcriptional silencing. In vitro experiments have identified several transcription factors, including Sp1, Nrf-1 and USF1/2, as potential regulators of normal FMR1 promoter activity. Using CpG methylation-deficient Drosophila cells, we demonstrate in vivo that Nrf-1 and Sp1 are strong, synergistic activators of an unmethylated human FMR1-driven reporter, while USF1/2 and Max repress this activation. In addition, analyses of transcription factor activity upon DNA methylation of the reporter show that Sp1 activity was largely intact when the promoter was densely methylated, but Nrf-1 transactivation was very sensitive to dense methylation. Notably, Nrf-1 transactivation was relatively insensitive to methylation of cytosines only at its binding site. FMR1 reporter activity is also reduced in HeLa cells after expression of a short interfering RNA directed against endogenous Nrf-1. Using chromatin immunoprecipitation, we demonstrate directly that Sp1 and Nrf-1 occupy the human FMR1 promoter in vivo and these interactions are disrupted in fragile X patient cells. In addition, we discover that Max resides at the FMR1 promoter and show that USF1/2 but not c-Myc are present at endogenous FMR1. These findings provide the first direct in vivo evidence identifying the specific transcription factors that regulate FMR1.