No abstract

SUMMARY SNPs affecting disease risk often reside in non-coding genomic regions. Here we show that SNPs are highly enriched at mouse strain-selective adipose tissue binding sites for PPARγ, a nuclear receptor for antidiabetic drugs. Many such SNPs alter binding motifs for PPARγ or cooperating factors, and functionally regulate nearby genes whose expression is strain-selective and imbalanced in heterozygous F1 mice. Moreover, genetically-determined binding of PPARγ accounts for mouse strain-specific transcriptional effects of TZD drugs, providing proof-of-concept for personalized medicine related to nuclear receptor genomic occupancy. In human fat, motif-altering SNPs cause differential PPARγ binding, provide a molecular mechanism for some expression quantitative trait loci, and are risk factors for dysmetabolic traits in genome-wide association studies. One PPARγ motif-altering SNP is associated with HDL levels and other metabolic syndrome parameters. Thus, natural genetic variation in PPARγ genomic occupancy determines individual disease risk and drug response.

RES and MAL conceived all studies, with help from DJS and SEM. Most of the experiments were designed by RES and performed by ERC, YHF, and KKB. Additional experiments were conducted by JRD (macrophage and 3T3-L1 ChIP-seq); DJS (H3K27ac and Pol2 ChIP-seq); MJE (cold exposure); MK and PS (primary adipocyte culture); CJM and JFJ (some Ucp1 studies); and ERB, LCP, and RKD (animal husbandry and other assays). Computational analyses of RNA-seq were done by ZL and ChIP-seq by RES, with help from SRR, MD, HWL, and KJW. The manuscript was drafted by RES and MAL and revised and approved by all authors.

Lysine specific demethylase 1 (LSD1) is a histone modifying enzyme that suppresses gene expression through demethylation of lysine 4 on histone H3. The anti-tumor activity of GSK2879552 and GSK-LSD1, potent, selective irreversible inactivators of LSD1, has previously been described. Inhibition of LSD1 results in a cytostatic growth inhibitory effect in a range of acute myeloid leukemia cell lines. To enhance the therapeutic potential of LSD1 inhibition in this disease setting, a combination of LSD1 inhibition and all- trans retinoic acid was explored. All- trans retinoic acid is currently approved for use in acute promyelocytic leukemia in which it promotes differentiation of abnormal blast cells into normal white blood cells. Combined treatment with all- trans retinoic acid and GSK2879552 results in synergistic effects on cell proliferation, markers of differentiation, and, most importantly, cytotoxicity. Ultimately the combination potential for LSD1 inhibition and ATRA will require validation in acute myeloid leukemia patients, and clinical studies to assess this are currently underway.

BET inhibitors exhibit broad activity in cancer models, making predictive biomarkers challenging to define. Here we investigate the biomarkers of activity of the clinical BET inhibitor GSK525762 (I-BET; I-BET762) across cancer cell lines and demonstrate that KRAS mutations are novel resistance biomarkers. This finding led us to combine BET with RAS pathway inhibition using MEK inhibitors to overcome resistance, which resulted in synergistic effects on growth and survival in RAS pathway mutant models as well as a subset of cell lines lacking RAS pathway mutations. GSK525762 treatment up-regulated p-ERK1/2 levels in both RAS pathway wild-type and mutant cell lines, suggesting that MEK/ERK pathway activation may also be a mechanism of adaptive BET inhibitor resistance. Importantly, gene expression studies demonstrated that the BET/MEK combination uniquely sustains down-regulation of genes associated with mitosis, leading to prolonged growth arrest that is not observed with either single agent therapy. These studies highlight a potential to enhance the clinical benefit of BET and MEK inhibitors and provide a strong rationale for clinical evaluation of BET/MEK combination therapies in cancer.