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.
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ABSTRACT: Evidence is accumulating regarding the importance of circadian core oscillators, several associated factors, and melatonin signaling in the maintenance of health. Dysfunction of endogenous clocks, melatonin receptor polymorphisms, age- and disease-associated declines of melatonin likely contribute to numerous diseases including cancer, metabolic syndrome, diabetes type 2, hypertension, and several mood and cognitive disorders. Consequences of gene silencing, overexpression, gene polymorphisms, and deviant expression levels in diseases are summarized. The circadian system is a complex network of central and peripheral oscillators, some of them being relatively independent of the pacemaker, the suprachiasmatic nucleus. Actions of melatonin on peripheral oscillators are poorly understood. Various lines of evidence indicate that these clocks are also influenced or phase-reset by melatonin. This includes phase differences of core oscillator gene expression under impaired melatonin signaling, effects of melatonin and melatonin receptor knockouts on oscillator mRNAs or proteins. Cross-connections between melatonin signaling pathways and oscillator proteins, including associated factors, are discussed in this review. The high complexity of the multioscillator system comprises alternate or parallel oscillators based on orthologs and paralogs of the core components and a high number of associated factors with varying tissue-specific importance, which offers numerous possibilities for interactions with melatonin. It is an aim of this review to stimulate research on melatonin signaling in peripheral tissues. This should not be restricted to primary signal molecules but rather include various secondarily connected pathways and discriminate between direct effects of the pineal indoleamine at the target organ and others mediated by modulation of oscillators.Journal of Pineal Research 03/2012; 52(2):139-66. · 7.30 Impact Factor
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ABSTRACT: The Intracellular levels of nicotinamide adenine dinucleotide (NAD(+)) are rhythmic and controlled by the circadian clock. However, whether NAD(+) oscillation in turn contributes to circadian physiology is not fully understood. To address this question we analyzed mice mutated for the NAD(+) hydrolase CD38. We found that rhythmicity of NAD(+) was altered in the CD38-deficient mice. The high, chronic levels of NAD(+) results in several anomalies in circadian behavior and metabolism. CD38-null mice display a shortened period length of locomotor activity and alteration in the rest-activity rhythm. Several clock genes and, interestingly, genes involved in amino acid metabolism were deregulated in CD38-null livers. Metabolomic analysis identified alterations in the circadian levels of several amino acids, specifically tryptophan levels were reduced in the CD38-null mice at a circadian time paralleling with elevated NAD(+) levels. Thus, CD38 contributes to behavioral and metabolic circadian rhythms and altered NAD(+) levels influence the circadian clock.Aging 08/2011; 3(8):794-802. · 4.70 Impact Factor
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ABSTRACT: Acne in adolescents of developed countries is an epidemic skin disease and has currently been linked to the Western diet (WD). It is the intention of this viewpoint to discuss the possible impact of WD-mediated nutrient signalling in the pathogenesis of acne. High glycaemic load and dairy protein consumption both increase insulin/insulin-like growth factor-1 (IGF-1) signalling (IIS) that is superimposed on elevated IGF-1 signalling of puberty. The cell's nutritional status is primarily sensed by the forkhead box transcription factor O1 (FoxO1) and the serine/threonine kinase mammalian target of rapamycin complex 1 (mTORC1). Increased IIS extrudes FoxO1 into the cytoplasm, whereas nuclear FoxO1 suppresses hepatic IGF-1 synthesis and thus impairs somatic growth. FoxO1 attenuates androgen signalling, interacts with regulatory proteins important for sebaceous lipogenesis, regulates the activity of innate and adaptive immunity, antagonizes oxidative stress and most importantly functions as a rheostat of mTORC1, the master regulator of cell growth, proliferation and metabolic homoeostasis. Thus, FoxO1 links nutrient availability to mTORC1-driven processes: increased protein and lipid synthesis, cell proliferation, cell differentiation including hyperproliferation of acroinfundibular keratinocytes, sebaceous gland hyperplasia, increased sebaceous lipogenesis, insulin resistance and increased body mass index. Enhanced androgen, TNF-α and IGF-1 signalling due to genetic polymorphisms promoting the risk of acne all converge in mTORC1 activation, which is further enhanced by nutrient signalling of WD. Deeper insights into the molecular interplay of FoxO1/mTORC1-mediated nutrient signalling are thus of critical importance to understand the impact of WD on the promotion of epidemic acne and more serious mTORC1-driven diseases of civilization.Experimental Dermatology 05/2013; 22(5):311-5. · 3.58 Impact Factor