PPARß/δ recruits NCOR and regulates transcription reinitiation of ANGPTL4.

In the absence of ligands, the nuclear receptor PPARß/δ recruits the NCOR and SMRT corepressors, which form complexes with HDAC3, to canonical target genes. Agonistic ligands cause dissociation of corepressors and enable enhanced transcription. Vice versa, synthetic inverse agonists augment corepressor recruitment and repression. Both basal repression of the target gene ANGPTL4 and reinforced repression elicited by inverse agonists are partially insensitive to HDAC inhibition. This raises the question how PPARß/δ represses transcription mechanistically. We show that the PPARß/δ inverse agonist PT-S264 impairs transcription initiation by decreasing recruitment of activating Mediator subunits, RNA polymerase II, and TFIIB, but not of TFIIA, to the ANGPTL4 promoter. Mass spectrometry identifies NCOR as the main PT-S264-dependent interactor of PPARß/δ. Reconstitution of knockout cells with PPARß/δ mutants deficient in basal repression results in diminished recruitment of NCOR, SMRT, and HDAC3 to PPAR target genes, while occupancy by RNA polymerase II is increased. PT-S264 restores binding of NCOR, SMRT, and HDAC3 to the mutants, resulting in reduced polymerase II occupancy. Our findings corroborate deacetylase-dependent and -independent repressive functions of HDAC3-containing complexes, which act in parallel to downregulate transcription.

Overexpression of MicroRNA miR-7-5p Is a Potential Biomarker in Neuroendocrine Neoplasms of the Small Intestine.

BACKGROUND/AIMS: Neuroendocrine neoplasms of the small intestine (SI-NENs) constitute 25-30% of all gastroenteropancreatic NEN. These tumors arise from enterochromaffin cells, and little is known about their microRNA (miRNA) expression. The purpose of this study was to characterize the expression of miRNAs in SI-NEN and to determine the potential of miRNAs as noninvasive blood-based biomarkers. METHODS: miRNA was purified from 15 tumor and 7 control tissue samples, converted to cDNA, and applied to a miScript miRNA PCR. The small nucleolar RNA, SNORD95, was used as an endogenous control. RESULTS: Microarray analysis revealed 7 miRNAs that showed a promising distinction between tumorous and healthy tissue. The miRNAs miR-7-5p and miR-96-5p were clearly upregulated in the tumor compared to the healthy tissue. In contrast, miRNAs miR-9-5p, miR-122-5p, miR-124-3p, miR-143-3p, and miR-144-3p showed a distinct downregulation in the tumor compared to the healthy tissue. These results were validated on a further 15 tumor samples, and the findings held true. As the miR-7-5p was significantly upregulated and revealed a low range across tumor samples, its presence was tested in the sera of 32 tumor patients and 25 healthy controls. Sera from all patients with SI-NENs had significantly higher levels of miR-7-5p than those from the 25 healthy controls (p = 0.0002), whereas there was no correlation with age, gender, or T-stage or UICC stage. CONCLUSION: The miRNA miR-7-5p may be a promising biomarker test for SI-NEN, which should be validated in a large-scale prospective study.

Deregulation of PPARß/δ target genes in tumor-associated macrophages by fatty acid ligands in the ovarian cancer microenvironment.

The nuclear receptor peroxisome proliferator-activated receptor ß/δ (PPARß/δ) is a lipid ligand-inducible transcription factor associated with macrophage polarization. However, its function in tumor-associated macrophages (TAMs) has not been investigated to date. Here, we report the PPARß/δ-regulated transcriptome and cistrome for TAMs from ovarian carcinoma patients. Comparison with monocyte-derived macrophages shows that the vast majority of direct PPARß/δ target genes are upregulated in TAMs and largely refractory to synthetic agonists, but repressible by inverse agonists. Besides genes with metabolic functions, these include cell type-selective genes associated with immune regulation and tumor progression, e.g., LRP5, CD300A, MAP3K8 and ANGPTL4. This deregulation is not due to increased expression of PPARß/δ or its enhanced recruitment to target genes. Instead, lipidomic analysis of malignancy-associated ascites revealed high concentrations of polyunsaturated fatty acids, in particular linoleic acid, acting as potent PPARß/δ agonists in macrophages. These fatty acid ligands accumulate in lipid droplets in TAMs, thereby providing a reservoir of PPARß/δ ligands. These observations suggest that the deregulation of PPARß/δ target genes by ligands of the tumor microenvironment contributes to the pro-tumorigenic polarization of ovarian carcinoma TAMs. This conclusion is supported by the association of high ANGPTL4 expression with a shorter relapse-free survival in serous ovarian carcinoma.

Possible Role of the Iron Coordination Sphere in Hemoprotein Electron Transfer Self-Exchange: (1)H NMR Study of the Cytochrome c-PMe(3) Complex.

The rates of self-exchange electron transfer in the trimethylphosphine complex of cytochrome c have been measured by an NMR technique over a large range of ionic strengths. The rate constant is 1.56 x 10(4) M(-)(1) s(-)(1) at 23 degrees C (&mgr; = 0.34 M) at pH 6.9. Dependence on ionic strength of the rate constant is treated by van Leeuwen theory. Extrapolation of the rate constant to infinite ionic strength gives a rate constant of 3.9 x 10(5) M(-)(1) s(-)(1). This rate constant is compared with others reported for myoglobin and cytochrome b(5)(). The values for these systems range over 2 orders of magnitude with myoglobin-PMe(3) << cytochrome b(5)() < cytochrome c-PMe(3) < cytochrome c. Analysis of the data in terms of Marcus theory gives a reorganization energy, lambda, for self-exchange of 0.75 eV mol(-)(1) for cytochrome c-PMe(3). Substitution of Met-80 by PMe(3) appears to influence only weakly the rearrangement barrier to electron transfer.