FoxO-dependent and -independent mechanisms mediate SirT1 effects on IGFBP-1 gene expression.
ABSTRACT Sirtuin 1 (SirT1), an NAD-dependent deacetylase that is important for promoting longevity during caloric restriction, can deacetylate and enhance the function of forkhead box transcription factors, O subfamily (FoxO). We examined the effect of SirT1 on the regulation of insulin-like growth factor-binding protein 1 (IGFBP-1), a known target of FoxO proteins that is increased in fasting. Co-transfection with a SirT1 expression vector dose-dependently stimulated IGFBP-1 promoter activity and a heterologous reporter gene construct containing three FoxO-binding sites linked to a minimal promoter. This effect is mimicked by 20muM resveratrol, a potent SirT1 activator, and immunoprecipitation and Western blotting confirm that SirT1 and FoxO1 interact in cells. Interestingly, mutation of FoxO-binding sites in the IGFBP-1 promoter reduces, but does not completely disrupt, the stimulatory effect of SirT1 on promoter activity. We found that overexpression of SirT1 is accompanied by enhanced mitogen-activated protein kinase (MAPK) activation. Treatment of SirT1-cotransfected cells with PD98059, which inhibits MAPK activation, decreased IGFBP-1 promoter activity by approximately 50%, in a FoxO-binding site-independent manner, and disrupts the residual effect of SirT1. These results indicate that SirT1 stimulates IGFBP-1 promoter activity through FoxO-dependent and -independent mechanisms, and provides the first evidence that activation of MAPK contributes to effects of SirT1 on gene expression.
SourceAvailable from: Galia Yablonski[Show abstract] [Hide abstract]
ABSTRACT: Malnutrition is considered a leading cause of growth attenuation in children. When food is replenished, spontaneous catch-up (CU) growth usually occurs, bringing the child back to its original growth trajectory. However, in some cases, the CU growth is not complete, leading to a permanent growth deficit. This review summarizes our current knowledge regarding the mechanism regulating nutrition and growth, including systemic factors, such as insulin, growth hormone, insulin- like growth factor-1, vitamin D, fibroblast growth factor-21, etc., and local mechanisms, including autophagy, as well as regulators of transcription, protein synthesis, miRNAs and epigenetics. Studying the molecular mechanisms regulating CU growth may lead to the establishment of better nutritional and therapeutic regimens for more effective CU growth in children with malnutrition and growth abnormalities. It will be fascinating to follow this research in the coming years and to translate the knowledge gained to clinical benefit.Nutrients 01/2015; 7(1):517-551. DOI:10.3390/nu7010517 · 3.15 Impact Factor
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ABSTRACT: Our previous studies have shown that multidrug resistance protein 2 (MRP2) is overexpressed in tamoxifen-resistant MCF-7 breast cancer cells (TAMR-MCF-7 cells) and forkhead box-containing protein, O subfamily1 (FoxO1), functions as a key regulator of multidrug resistance 1 (MDR1) gene transcription. This study aimed to investigate the role of FoxO1 in regulating MRP2 gene expression in TAMR-MCF-7 cells. The proximal promoter region of the human MRP2 gene contains four putative FoxO binding sites, and MRP2 gene transcription was stimulated by FoxO1 overexpression in MCF-7 cells. Subcellular fractionation and immunoblot analyses revealed that basal MRP2 expression and nuclear levels of FoxO1 were enhanced in TAMR-MCF-7 cells compared to MCF-7 cells and the enhanced MRP2 gene transcription was suppressed by FoxO1 siRNA. Because nuclear localization of FoxO1 is regulated by SIRT1 deacetylase, we were further interested in whether SIRT1 is involved in MRP2 expression. Overexpression of SIRT1 with FoxO1 potentiated the gene transcriptional activity of MRP2, and the basal activity and expression of SIRT1 was increased in TAMR-MCF-7 cells. In addition, SIRT1 inhibition reduced both the nuclear FoxO1 levels and MRP2 expression and enhanced cytotoxic effects of paclitaxel and doxorubicin in TAMR-MCF-7 cells. These results suggest that FoxO1 activation via SIRT1-mediated deacetylation is closely related with up-regulation of MRP2 in TAMR-MCF-7 cells.Molecular Pharmaceutics 06/2013; 10(7). DOI:10.1021/mp400287p · 4.57 Impact Factor
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ABSTRACT: Clinically relevant prostate cancer is more frequent in Westernised societies and increasingly men have co-morbidities associated with a Western lifestyle primarily diabetes, characterised by hyperinsulinemia and hyperglycaemia. Insulin-like growth factors and their binding proteins are important mediators of the effects of nutrition on growth and play a key role in the development of prostate caner. We used DU145, PC3 and LNCaP prostate cancer cell lines to examine how hyperglycaemia altered their response to docetaxel. Trypan blue dye-exclusion assay was used to determine the percentage cell death. Protein abundance was determined using Western immunoblotting. Levels of insulin-like growth factor binding protein-2 (IGFBP-2) were measured using an Enzyme-linked Immunoassay. IGFBP-2 gene silencing was achieved using siRNA technology. DNA methylation was assessed using combined bisulfite restriction analysis (COBRA). Acetylation status of histones H3 and H4 associated with IGFBP-2 gene was assessed using Chromatin Immunoprecipitation assay (ChIP). Hyperglycemia reduced Docetaxel-induced apoptosis by 40% for DU145 cells and by 88% for LNCaP cells. This reduced cell death was mediated by a glucose-induced up-regulation of IGFBP-2, as silencing IGFBP-2 negated the survival effect of high glucose. Glucose increased IGFBP-2 via increasing the acetylation of histones associated with the IGFBP-2 gene promoter. This finding could have important implications in relation to therapeutic strategies as epigenetic modulation could be reversible.Endocrine Related Cancer 08/2013; 20(5). DOI:10.1530/ERC-13-0077 · 5.26 Impact Factor