Leptin decreases BC cell susceptibility to NK lysis via PGC1A pathway.

Large prospective studies established a link between obesity and breast cancer (BC) development. Yet, the mechanisms underlying this association are not fully understood. Among the diverse adipocytokine secreted by hypertrophic adipose tissue, leptin is emerging as a key candidate molecule linking obesity and cancer, since it promotes proliferation and invasiveness of tumors. However, the potential implication of leptin on tumor escape mechanisms remains unknown. This study aims to explore the effect of leptin on tumor resistance to NK lysis and the underlying mechanism. We found that leptin promotes both BC resistance to NK92-mediated lysis and ß oxidation on MCF-7, by the up-regulation of a master regulator of mitochondrial biogenesis, the peroxisome proliferator activated receptor coactivator-1 α (PGC1A). Using adenoviral approaches, we show that acute elevation of PGC1A enhances the fatty acid oxidation pathway and decreases the susceptibility of BC cells to NK92-mediated lysis. Importantly, we identified the involvement of PGC1A and leptin in the regulation of hypoxia inducible factor-1 alpha (HIF1A) expression by tumor cells. We further demonstrate that basal BC cells MDA-MB-231 and BT-20 exhibit an increased PGC1A mRNA level and an enhanced oxidative phosphorylation activity; in comparison with luminal BC cells MCF7 and MDA-361, which are associated with more resistance NK92 lysis. Altogether, our results demonstrate for the first time how leptin could promote tumor resistance to immune attacks. Reagents blocking leptin or PGC1A activity might aid in developing new therapeutic strategies to limit tumor development in obese BC patients.

Hepatic SRC-1 activity orchestrates transcriptional circuitries of amino acid pathways with potential relevance for human metabolic pathogenesis.

Disturbances in amino acid metabolism are increasingly recognized as being associated with, and serving as prognostic markers for chronic human diseases, such as cancer or type 2 diabetes. In the current study, a quantitative metabolomics profiling strategy revealed global impairment in amino acid metabolism in mice deleted for the transcriptional coactivator steroid receptor coactivator (SRC)-1. Aberrations were hepatic in origin, because selective reexpression of SRC-1 in the liver of SRC-1 null mice largely restored amino acids concentrations to normal levels. Cistromic analysis of SRC-1 binding sites in hepatic tissues confirmed a prominent influence of this coregulator on transcriptional programs regulating amino acid metabolism. More specifically, SRC-1 markedly impacted tyrosine levels and was found to regulate the transcriptional activity of the tyrosine aminotransferase (TAT) gene, which encodes the rate-limiting enzyme of tyrosine catabolism. Consequently, SRC-1 null mice displayed low TAT expression and presented with hypertyrosinemia and corneal alterations, 2 clinical features observed in the human syndrome of TAT deficiency. A heterozygous missense variant of SRC-1 (p.P1272S) that is known to alter its coactivation potential, was found in patients harboring idiopathic tyrosinemia-like disorders and may therefore represent one risk factor for their clinical symptoms. Hence, we reinforce the concept that SRC-1 is a central factor in the fine orchestration of multiple pathways of intermediary metabolism, suggesting it as a potential therapeutic target that may be exploitable in human metabolic diseases and cancer.

Increased gene copy number of VAMP7 disrupts human male urogenital development through altered estrogen action.

Despite the fact that genitourinary defects are among the most common birth defects in newborns, little is known about their etiology. Here we analyzed children born with congenital genitourinary tract masculinization disorders by array-comparative genomic hybridization, which revealed in 1.35% of cases the presence of de novo copy number gains at Xq28 encompassing the VAMP7 gene, which encodes a vesicle-trafficking protein that is part of the SNARE complex. Transgenic mice carrying a bacterial artificial chromosome encoding human VAMP7 mimicked the defective urogenital traits observed in boys with masculinization disorders such as cryptorchidism, urethral defects and hypospadias. Transgenic mice also exhibited reduced penile length, focal spermatogenic anomalies, diminished sperm motility and subfertility. VAMP7 colocalized with estrogen receptor α (ESR1) in the presence of its cognate ligand, 17ß-estradiol. Elevated levels of VAMP7 markedly intensified ESR1-potentiated transcriptional activity by increasing ESR1 protein cellular content upon ligand stimulation and upregulated the expression of estrogen-responsive genes including ATF3, CYR61 and CTGF, all of which have been implicated in human hypospadias. Hence, increased gene dosage of VAMP7, and thus higher expression levels of its protein product, enhances estrogen receptor action in male genitourinary tissues, affects the virilization of the reproductive tract and results in genitourinary birth defects in humans.

Increased expression of CYP24A1 correlates with advanced stages of prostate cancer and can cause resistance to vitamin D3-based therapies.

A major limitation of exogenous vitamin D3 administration for the treatment of prostate cancer is the marginal, if any, clinical efficacy. We dissected the basis for the resistance to the vitamin D3 antitumor properties and specifically examined the effect of its major catabolic enzyme, CYP24A1, in prostate cancer. Local CYP24A1 expression levels and the effect of selective modulation were analyzed using tissue microarrays from needle core biopsy specimens and xenograft-bearing mouse models. CYP24A1 mRNA was elevated in malignant human prostate tissues compared to benign lesions. High CYP24A1 protein levels were seen in poorly differentiated and highly advanced stages of prostate cancer and correlated with parallel increase in the tumor proliferation rate. The use of CYP24A1 RNAi enhanced the cytostatic effects of vitamin D3 in human prostate cancer cells. Remarkably, subcutaneous and orthotopic xenografts of prostate cancer cells harboring CYP24A1 shRNA resulted in a drastic reduction in tumor volume when mice were subjected to vitamin D3 supplementation. CYP24A1 may be a predictive marker of vitamin D3 clinical efficacy in patients with advanced prostate cancer. For those with up-regulated CYP24A1, combination therapy with RNAi targeting CYP24A1 could be considered to improve clinical responsiveness to vitamin D3.

Ablation of steroid receptor coactivator-3 resembles the human CACT metabolic myopathy.

Oxidation of lipid substrates is essential for survival in fasting and other catabolic conditions, sparing glucose for the brain and other glucose-dependent tissues. Here we show Steroid Receptor Coactivator-3 (SRC-3) plays a central role in long chain fatty acid metabolism by directly regulating carnitine/acyl-carnitine translocase (CACT) gene expression. Genetic deficiency of CACT in humans is accompanied by a constellation of metabolic and toxicity phenotypes including hypoketonemia, hypoglycemia, hyperammonemia, and impaired neurologic, cardiac and skeletal muscle performance, each of which is apparent in mice lacking SRC-3 expression. Consistent with human cases of CACT deficiency, dietary rescue with short chain fatty acids drastically attenuates the clinical hallmarks of the disease in mice devoid of SRC-3. Collectively, our results position SRC-3 as a key regulator of ß-oxidation. Moreover, these findings allow us to consider platform coactivators such as the SRCs as potential contributors to syndromes such as CACT deficiency, previously considered as monogenic.

Cellular energy depletion resets whole-body energy by promoting coactivator-mediated dietary fuel absorption.

All organisms have devised strategies to counteract energy depletion and promote fitness for survival. We show here that cellular energy depletion puts into play a surprising strategy that leads to absorption of exogenous fuel for energy repletion. The energy-depletion-sensing kinase AMPK binds, phosphorylates, and activates the transcriptional coactivator SRC-2, which in a liver-specific manner promotes absorption of dietary fat from the gut. Hepatocyte-specific deletion of SRC-2 results in intestinal fat malabsorption and attenuated entry of fat into the blood stream. This defect can be attributed to AMPK- and SRC-2-mediated transcriptional regulation of hepatic bile acid (BA) secretion into the gut, as it can be completely rescued by replenishing intestinal BA or by genetically restoring the levels of hepatic bile salt export pump (BSEP). Our results position the hepatic AMPK-SRC-2 axis as an energy rheostat, which upon cellular energy depletion resets whole-body energy by promoting absorption of dietary fuel.

Identification of de novo copy number variants associated with human disorders of sexual development.

Disorders of sexual development (DSD), ranging in severity from genital abnormalities to complete sex reversal, are among the most common human birth defects with incidence rates reaching almost 3%. Although causative alterations in key genes controlling gonad development have been identified, the majority of DSD cases remain unexplained. To improve the diagnosis, we screened 116 children born with idiopathic DSD using a clinically validated array-based comparative genomic hybridization platform. 8951 controls without urogenital defects were used to compare with our cohort of affected patients. Clinically relevant imbalances were found in 21.5% of the analyzed patients. Most anomalies (74.2%) evaded detection by the routinely ordered karyotype and were scattered across the genome in gene-enriched subtelomeric loci. Among these defects, confirmed de novo duplication and deletion events were noted on 1p36.33, 9p24.3 and 19q12-q13.11 for ambiguous genitalia, 10p14 and Xq28 for cryptorchidism and 12p13 and 16p11.2 for hypospadias. These variants were significantly associated with genitourinary defects (P = 6.08×10(-12)). The causality of defects observed in 5p15.3, 9p24.3, 22q12.1 and Xq28 was supported by the presence of overlapping chromosomal rearrangements in several unrelated patients. In addition to known gonad determining genes including SRY and DMRT1, novel candidate genes such as FGFR2, KANK1, ADCY2 and ZEB2 were encompassed. The identification of risk germline rearrangements for urogenital birth defects may impact diagnosis and genetic counseling and contribute to the elucidation of the molecular mechanisms underlying the pathogenesis of human sexual development.

The coactivator SRC-1 is an essential coordinator of hepatic glucose production.

Gluconeogenesis makes a major contribution to hepatic glucose production, a process critical for survival in mammals. In this study, we identify the p160 family member, SRC-1, as a key coordinator of the hepatic gluconeogenic program in vivo. SRC-1-null mice displayed hypoglycemia secondary to a deficit in hepatic glucose production. Selective re-expression of SRC-1 in the liver restored blood glucose levels to a normal range. SRC-1 was found induced upon fasting to coordinate in a cell-autonomous manner, the gene expression of rate-limiting enzymes of the gluconeogenic pathway. At the molecular level, the main role of SRC-1 was to modulate the expression and the activity of C/EBPα through a feed-forward loop in which SRC-1 used C/EBPα to transactivate pyruvate carboxylase, a crucial gene for initiation of the gluconeogenic program. We propose that SRC-1 acts as a critical mediator of glucose homeostasis in the liver by adjusting the transcriptional activity of key genes involved in the hepatic glucose production machinery.

Absence of the SRC-2 coactivator results in a glycogenopathy resembling Von Gierke's disease.

Hepatic glucose production is critical for basal brain function and survival when dietary glucose is unavailable. Glucose-6-phosphatase (G6Pase) is an essential, rate-limiting enzyme that serves as a terminal gatekeeper for hepatic glucose release into the plasma. Mutations in G6Pase result in Von Gierke's disease (glycogen storage disease-1a), a potentially fatal genetic disorder. We have identified the transcriptional coactivator SRC-2 as a regulator of fasting hepatic glucose release, a function that SRC-2 performs by controlling the expression of hepatic G6Pase. SRC-2 modulates G6Pase expression directly by acting as a coactivator with the orphan nuclear receptor RORalpha. In addition, SRC-2 ablation, in both a whole-body and liver-specific manner, resulted in a Von Gierke's disease phenotype in mice. Our results position SRC-2 as a critical regulator of mammalian glucose production.

The genetic ablation of SRC-3 protects against obesity and improves insulin sensitivity by reducing the acetylation of PGC-1{alpha}.

Transcriptional control of metabolic circuits requires coordination between specific transcription factors and coregulators and is often deregulated in metabolic diseases. We characterized here the mechanisms through which the coactivator SRC-3 controls energy homeostasis. SRC-3 knock-out mice present a more favorable metabolic profile relative to their wild-type littermates. This metabolic improvement in SRC-3(-/-) mice is caused by an increase in mitochondrial function and in energy expenditure as a consequence of activation of PGC-1alpha. By controlling the expression of the only characterized PGC-1alpha acetyltransferase GCN5, SRC-3 induces PGC-1alpha acetylation and consequently inhibits its activity. Interestingly, SRC-3 expression is induced by caloric excess, resulting in the inhibition of PGC-1alpha activity and energy expenditure, whereas caloric restriction reduces SRC-3 levels leading to enhanced PGC-1alpha activity and energy expenditure. Collectively, these data suggest that SRC-3 is a critical link in a cofactor network that uses PGC-1alpha as an effector to control mitochondrial function and energy homeostasis.

Coregulators in adipogenesis: what could we learn from the SRC (p160) coactivator family?

Strong epidemiological studies clearly show that reduction in body fat content decreases the risk for many clinical conditions including diabetes, hypertension, coronary atherosclerotic heart disease and some forms of cancer. Therefore, detailed understanding of the mechanisms underlying how fat pads expand appears crucial. Extensive studies already identified a cohort of transcription factors involved in adipocyte differentiation but the fine interrelationship between the myriads of cellular and molecular events occurring during this complex biological process is far from being completely understood. Since the cloning of the first coregulator, the impact of those molecules has dramatically increased. In this review, we will summarize the emerging impact of coregulators on energy balance with a specific interest for fat formation. Emphasis will be given to the coactivators of the SRC (p160) family.

Oncogenic steroid receptor coactivator-3 is a key regulator of the white adipogenic program.

The white adipocyte is at the center of dysfunctional regulatory pathways in various pathophysiological processes, including obesity, diabetes, inflammation, and cancer. Here, we show that the oncogenic steroid receptor coactivator-3 (SRC-3) is a critical regulator of white adipocyte development. Indeed, in SRC-3(-/-) mouse embryonic fibroblasts, adipocyte differentiation was severely impaired, and reexpression of SRC-3 was able to restore it. The early stages of adipocyte differentiation are accompanied by an increase in nuclear levels of SRC-3, which accumulates to high levels specifically in the nucleus of differentiated fat cells. Moreover, SRC-3(-/-) animals showed reduced body weight and adipose tissue mass with a significant decrease of the expression of peroxisome proliferator-activated receptor gamma2 (PPARgamma2), a master gene required for adipogenesis. At the molecular level, SRC-3 acts synergistically with the transcription factor CAAT/enhancer-binding protein to control the gene expression of PPARgamma2. Collectively, these data suggest a crucial role for SRC-3 as an integrator of the complex transcriptional network controlling adipogenesis.

Antidiabetic actions of estrogen: insight from human and genetic mouse models.

There is increasing evidence both in humans and rodents linking the endogenous estrogen 17b-estradiol (E2) to the maintenance of glucose homeostasis. Postmenopausal women develop visceral obesity and insulin resistance and are at increased risk for type 2 diabetes mellitus, but hormone replacement therapy leads to a reduction in the incidence of diabetes. In various spontaneous rodent models of type 2 diabetes, female rodents are protected against hyperglycemia unless they are ovariectomized, and E2 perfusion reverses diabetes in male rodents. Finally, the study of transgenic mice and mice with genetic alteration of E2 secretion or E2 action has shed light on the antidiabetic properties of E2 at a tissue-specific level. Thus, E2 secretion and action in rodents seems to be implicated 1) in adipose tissue biology and the prevention of obesity, 2) in the stimulation of liver fatty acid metabolism and suppression of hepatic glucose production, and 3) in the protection of pancreatic b-cell function/survival and insulin secretion in conditions of oxidative stress.

The coactivator PGC-1 is involved in the regulation of the liver carnitine palmitoyltransferase I gene expression by cAMP in combination with HNF4 alpha and cAMP-response element-binding protein (CREB).

Liver carnitine palmitoyltransferase I catalyzes the transfer of long-chain fatty acids into mitochondria. L-CPT I is considered the rate-controlling enzyme in fatty acid oxidation. Expression of the L-CPT I gene is induced by starvation in response to glucagon secretion from the pancreas, an effect mediated by cAMP. Here, the molecular mechanisms underlying the induction of L-CPT I gene expression by cAMP were characterized. We demonstrate that the cAMP response unit of the L-CPT I gene is composed of a cAMP-response element motif and a DR1 sequence located 3 kb upstream of the transcription start site. Our data strongly suggest that the coactivator PGC-1 is involved in the regulation of this gene expression by cAMP in combination with HNF4 alpha and cAMP-response element-binding protein (CREB). Indeed, (i) cotransfection of CREB or HNF4 alpha dominant negative mutants completely abolishes the effect of cAMP on the L-CPT I promoter, and (ii) the cAMP-responsive unit binds HNF4 alpha and CREB through the DR1 and the cAMP-response element sequences, respectively. Moreover, cotransfection of PGC-1 strongly activates the L-CPT I promoter through HNF4 alpha bound at the DR1 element. Finally, we show that the transcriptional induction of the PGC-1 gene by glucagon through cAMP in hepatocytes precedes that of L-CPT-1. In addition to the key role that PGC-1 plays in glucose homeostasis, it may also be critical for lipid homeostasis. Taken together these observations suggest that PGC-1 acts to coordinate the process of metabolic adaptation in the liver.