Summary Circadian clocks are encoded by a transcription-translation feedback loop that aligns energetic processes with the solar cycle. Here we show that genetic disruption of the clock activator BMAL1 in skeletal myotubes and fibroblasts increased levels of the hypoxia-inducible factor 1α (HIF1α) under hypoxic conditions. Bmal1−/− myotubes displayed reduced anaerobic glycolysis, mitochondrial respiration with glycolytic fuel, and transcription of HIF1α targets Phd3, Vegfa, Mct4, Pk-m, and Ldha, whereas abrogation of the clock repressors CRY1/2 stabilized HIF1α in response to hypoxia. HIF1α bound directly to core clock gene promoters and, when co-expressed with BMAL1, led to transactivation of PER2-LUC and HRE-LUC reporters. Further, genetic stabilization of HIF1α in Vhl−/− cells altered circadian transcription. Finally, induction of clock- and HIF1α-target genes in response to strenuous exercise varied according to the time-of-day in wild-type mice. Collectively, our results reveal bi-directional interactions between circadian and HIF pathways that influence metabolic adaptation to hypoxia.

Purpose Identification of predictive biomarkers is critically needed to improve selection of patients who derive the most benefit from platinum-based chemotherapy. We hypothesized that decreased expression of SMARCA4/BRG1, a known regulator of transcription and DNA repair, is a novel predictive biomarker of increased sensitivity to adjuvant platinum-based therapies in NSCLC. Experimental Design The prognostic value was tested using a gene expression microarray from the Director’s Challenge Lung Study (n=440). The predictive significance of SMARCA4 was determined using a gene expression microarray (n=133) from control and treatment arms of the JBR.10 trial of adjuvant cisplatin/vinorelbine. Kaplan-Meier method and log-rank tests were used to estimate and test the differences of probabilities in overall survival (OS) and disease-specific survival (DSS) between expression groups and treatment arms. Multivariate Cox regression models were used while adjusting for other clinical covariates. Results In the Director’s Challenge Study, reduced expression of SMARCA4 was associated with poor OS compared to high and intermediate expression (P<0.001 and P=0.009, respectively). In multivariate analysis, compared to low, high SMARCA4 expression predicted a decrease in risk of death (HR=0.6, 95% CI: 0.4–0.8, P=0.002). In the JBR.10 trial, improved five-year DSS was noted only in patients with low SMARCA4 expression when treated with adjuvant cisplatin/vinorelbine (HR=0.1, 95% CI: 0.0–0.5, P=0.002 [low]; HR 1.0, 95% CI: 0.5–2.3, P=0.92 [high]). An interaction test was highly significant (P=0.01). Conclusions Low expression of SMARCA4/BRG1 is significantly associated with worse prognosis; however, it is a novel significant predictive biomarker for increased sensitivity to platinum-based chemotherapy in NSCLC.

Acute myelogenous leukemia (AML) is a high-risk hematopoietic malignancy caused by a variety of mutations, including genes encoding the cohesin complex. Recent studies have demonstrated that reduction in cohesin complex levels leads to enhanced self-renewal in hematopoietic stem and progenitors (HSPCs). We sought to delineate the molecular mechanisms by which cohesin mutations promote enhanced HSPC self-renewal since this represents a critical initial step during leukemic transformation. We verified that RNAi against the cohesin subunit Rad21 causes enhanced self-renewal of HSPCs in vitro through derepression of Polycomb Repressive Complex 2 (PRC2) target genes, including Hoxa7 and Hoxa9. Importantly, knockdown of either Hoxa7 or Hoxa9 suppressed self-renewal, implying both are critical downstream effectors of reduced cohesin levels. We further demonstrate that the cohesin and PRC2 complexes interact and are bound in close proximity to Hoxa7 and Hoxa9. Rad21 depletion resulted in decreased levels of H3K27me3 at the Hoxa7 and Hoxa9 promoters, consistent with Rad21 being critical to proper gene silencing by recruiting the PRC2 complex. Our data demonstrates that the cohesin complex regulates PRC2 targeting to silence Hoxa7 and Hoxa9 and negatively regulate self-renewal. Our studies identify a novel epigenetic mechanism underlying leukemogenesis in AML patients with cohesin mutations.

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Key Points miR-486-5p, a GATA1 regulated miR, is expressed in ML-DS and enhances their aberrant erythroid phenotype. miR-486-5p cooperates with GATA1s to promote the survival of pre-leukemic and leukemic cells.