Transcriptional regulation of the resistin gene

Resistin expression in human monocytes is controlled by two linked promoter SNPs mediating NFKB p50/p50 binding and C-methylation

Resistin is a key cytokine associated with metabolic and inflammatory diseases. Especially in East Asian populations, the expression levels are strongly influenced by genetic polymorphisms. Mechanisms and functional implications of this genetic control are still unknown. By employing reporter assays, EMSA, inhibition studies, bisulphite sequencing, ChIP-Seq and gene-editing we show that the p50/p50 homodimer known to act as repressor for a number of pro-inflammatory genes plays a central role in the genetic regulation of resistin in monocytes along with promoter methylation. In the common RETN haplotype p50/p50 constitutively dampens the expression by binding to the promoter. In an Asian haplotype variant however this interaction is disrupted by the A allele of rs3219175. The SNP is in very close linkage to rs34861192, a CpG SNP, located 280 bp upstream which provides an allele-specific C-methylation site. rs34861192 is located in a 100 bp region found to be methylated in the common but not in the Asian haplotype, resulting in the latter having a higher basal expression, which also associates with elevated histone acetylation (H3K27ac). Genotype associations within cohort data of 200 East Asian individuals revealed significant associations between this haplotype and the plasma levels of factors such as TGF-b, S100B, sRAGE and IL-8 as well as with myeloid DC counts. Thus, the common RETN haplotype is tightly regulated by the epigenetic mechanism linked to p50/p50-binding. This control is lost in the Asian haplotype, which may have evolved to balance the antagonistic RETN effects on pathogen protection vs. metabolic and inflammatory disease induction.

In vitro interaction between resistin and peroxisome proliferator-activated receptor γ in porcine ovarian follicles

In the present study, using real-time polymerase chain reaction and immunoblotting methods, we quantified the expression of peroxisome proliferator-activated receptor (PPAR) γ, PPARα and PPARβ in different sized ovarian follicles (small (SF), medium (MF) and large (LF) follicles) in prepubertal and adult pigs. In prepubertal pigs, PPARγ and PPARα expression was highest in LF; however, PPARβ expression did not differ among SF, MF and LF. In mature pigs, only protein expression of PPARγ and PPARα increased during ovarian follicle development. Following identification of very high levels of PPARγ expression in LF in prepubertal and adult pigs, using in vitro culture of ovarian follicles, we determined the effect of resistin at 0.1, 1 and 10 ng mL–1 on PPARγ mRNA and protein expression and the effect of rosiglitazone at 25 and 50 µM (a PPARγ agonist) on resistin mRNA and protein expression. Resistin increased PPARγ expression in ovarian follicles in both prepubertal and adult pigs, whereas rosiglitazone had an inhibitory effect on resistin expression. The role of PPARγ in regulating the effects of resistin on ovarian steroidogenesis was investigated using GW9662 (a PPARγ antagonist at dose of 1 μM). In these studies, GW9662 reversed the effect of resistin on steroid hormone secretion. The data suggest that there is local cooperation between resistin and PPARγ expression in the porcine ovary. Resistin significantly increased the expression of PPARγ, whereas PPARγ decreased resistin expression; thus, PPARγ is a new key regulator of resistin expression and function.

C/EBPα promotes transcription of the porcine perilipin5 gene

PERILIPIN5 (PLIN5) is a newly discovered member of the PAT family that regulates cellular neutral lipid stores and use. It is expressed in highly oxidative tissues and is induced during fasting. Like other members of the PAT family, PERILIPIN5 expression is also regulated by PPARα. However, its induction by fasting is PPARα-independent. So far, the transcriptional regulation of perilipin5, apart from PPARα, remains unclear. In the present study, we investigated the transcriptional regulation of pig perilipin5 and revealed that its promoter activity was up-regulated by C/EBPα. By constructing various progressive deletions and mutants, the binding region of C/EBPα was discovered. Furthermore, the binding site was identified by chromatin immunoprecipitation and luciferase reporter assays. Moreover, over-expression of C/EBPα induced endogenous perilipin5 expression in the pig kidney cell line IBRS2. Data from arrays showed that C/EBPα expression was induced during fasting. Taken together, our results indicate that C/EBPα is an essential regulatory factor for perilipin5 transcription and suggest that fasting stimulates perilipin5 transcription through influencing C/EBPα expression.

Transcription of human resistin gene involves an interaction of Sp1 with peroxisome proliferator-activating receptor gamma (PPARgamma)

BACKGROUND

Resistin is a cysteine rich protein, mainly expressed and secreted by circulating human mononuclear cells. While several factors responsible for transcription of mouse resistin gene have been identified, not much is known about the factors responsible for the differential expression of human resistin.

METHODOLOGY/PRINCIPAL FINDING

We show that the minimal promoter of human resistin lies within approximately 80 bp sequence upstream of the transcriptional start site (-240) whereas binding sites for cRel, CCAAT enhancer binding protein alpha (C/EBP-alpha), activating transcription factor 2 (ATF-2) and activator protein 1 (AP-1) transcription factors, important for induced expression, are present within sequences up to -619. Specificity Protein 1(Sp1) binding site (-276 to -295) is also present and an interaction of Sp1 with peroxisome proliferator activating receptor gamma (PPARgamma) is necessary for constitutive expression in U937 cells. Indeed co-immunoprecipitation assay demonstrated a direct physical interaction of Sp1 with PPARgamma in whole cell extracts of U937 cells. Phorbol myristate acetate (PMA) upregulated the expression of resistin mRNA in U937 cells by increasing the recruitment of Sp1, ATF-2 and PPARgamma on the resistin gene promoter. Furthermore, PMA stimulation of U937 cells resulted in the disruption of Sp1 and PPARgamma interaction. Chromatin immunoprecipitation (ChIP) assay confirmed the recruitment of transcription factors phospho ATF-2, Sp1, Sp3, PPARgamma, chromatin modifier histone deacetylase 1 (HDAC1) and the acetylated form of histone H3 but not cRel, C/EBP-alpha and phospho c-Jun during resistin gene transcription.

CONCLUSION

Our findings suggest a complex interplay of Sp1 and PPARgamma along with other transcription factors that drives the expression of resistin in human monocytic U937 cells.

Clenbuterol inhibits SREBP-1c expression by activating CREB1

As a beta(2)-adrenergic agonist, clenbuterol decreases body fat, but the molecular mechanism underlying this process is unclear. In the present study, we treated 293T and L-02 cells with clenbuterol and found that clenbuterol downregulates SREBP-1c expression and upregulates CREB1 expression. Considering SREBP-1c has the function of regulating the transcription of several lipogenic enzymes, we considered that the downregulation of SREBP-1c is responsible for body fat reduction by clenbuterol. Many previous studies have found that clenbuterol markedly increases intracellular cAMP levels, therefore, we also investigated whether CREB1 is involved in this process. The data from our experiments indicate that CREB1 overexpression inhibits SREBP-1c transcription, and that this action is antagonized by CREB2, a competitive inhibitor of CREB1. Furthermore, since PPARs are able to repress SREBP-1c transcription, we investigated whether clenbuterol and CREB1 function via a pathway involving PPAR activation. However, our results showed that clenbuterol or CREB1 overexpression suppressed PPARs transcription in 293T and L-02 cells, which suggested that they impair SREBP-1c expression in other ways.