Metformin: From Diabetes to Cancer-Unveiling Molecular Mechanisms and Therapeutic Strategies.

Metformin, a widely used anti-diabetic drug, has garnered attention for its potential in cancer management, particularly in breast and colorectal cancer. It is established that metformin reduces mitochondrial respiration, but its specific molecular targets within mitochondria vary. Proposed mechanisms include inhibiting mitochondrial respiratory chain Complex I and/or Complex IV, and mitochondrial glycerophosphate dehydrogenase, among others. These actions lead to cellular energy deficits, redox state changes, and several molecular changes that reduce hyperglycemia in type 2 diabetic patients. Clinical evidence supports metformin's role in cancer prevention in type 2 diabetes mellitus patients. Moreover, in these patients with breast and colorectal cancer, metformin consumption leads to an improvement in survival outcomes and prognosis. The synergistic effects of metformin with chemotherapy and immunotherapy highlights its potential as an adjunctive therapy for breast and colorectal cancer. However, nuanced findings underscore the need for further research and stratification by molecular subtype, particularly for breast cancer. This comprehensive review integrates metformin-related findings from epidemiological, clinical, and preclinical studies in breast and colorectal cancer. Here, we discuss current research addressed to define metformin's bioavailability and efficacy, exploring novel metformin-based compounds and drug delivery systems, including derivatives targeting mitochondria, combination therapies, and novel nanoformulations, showing enhanced anticancer effects.

A new FRDA mouse model [Fxn null:YG8s(GAA) > 800] with more than 800 GAA repeats.

Introduction: Friedreich's ataxia (FRDA) is an inherited recessive neurodegenerative disorder caused by a homozygous guanine-adenine-adenine (GAA) repeat expansion within intron 1 of the FXN gene, which encodes the essential mitochondrial protein frataxin. There is still no effective therapy for FRDA, therefore the development of optimal cell and animal models of the disease is one of the priorities for preclinical therapeutic testing. Methods: We obtained the latest FRDA humanized mouse model that was generated on the basis of our previous YG8sR, by Jackson laboratory [YG8JR, Fxn null:YG8s(GAA) > 800]. We characterized the behavioral, cellular, molecular and epigenetics properties of the YG8JR model, which has the largest GAA repeat sizes compared to all the current FRDA mouse models. Results: We found statistically significant behavioral deficits, together with reduced levels of frataxin mRNA and protein, and aconitase activity in YG8JR mice compared with control Y47JR mice. YG8JR mice exhibit intergenerational GAA repeat instability by the analysis of parent and offspring tissue samples. Somatic GAA repeat instability was also detected in individual brain and cerebellum tissue samples. In addition, increased DNA methylation of CpG U13 was identified in FXN GAA repeat region in the brain, cerebellum, and heart tissues. Furthermore, we show decreased histone H3K9 acetylation and increased H3K9 methylation of YG8JR cerebellum tissues within the FXN gene, upstream and downstream of the GAA repeat region compared to Y47JR controls. Discussion: These studies provide a detailed characterization of the GAA repeat expansion-based YG8JR transgenic mouse models that will help investigations of FRDA disease mechanisms and therapy.

Estrogen Impairs Adipose Tissue Expansion and Cardiometabolic Profile in Obese-Diabetic Female Rats.

It has been reported that 17ß-estradiol (E2) can exert beneficial effects against the development of obesity, providing women with a healthier metabolic profile and conferring cardiovascular protection. However, a growing body of evidence questions this role in the context of obesity and diabetes. We focus on the adipose tissue-heart axis to address the question of whether E2 can have metabolically detrimental effects in an obese-diabetic rat model. Female Zucker Diabetic Fatty rats were used: LEAN, fa/+; SHAM, sham-operated fa/fa; OVA, ovariectomized fa/fa, and OVA+E2, ovariectomized and E2 treated fa/fa. The secretory expression profile, tissue expansion parameters and composition of visceral adipose tissue, as well as systemic and cardiac parameters related to insulin resistance, fibrosis, and inflammation were analyzed. Ovariectomy induced an attenuation of both diabetic condition and metabolic dysfunction of adipose tissue and cardiac muscle in fa/fa rats, suggesting that E2, in the context of diabetes and obesity, loses its cardioprotective role and could even contribute to greater metabolic alterations. Adipose tissue from OVA rats showed a healthier hyperplastic expansion pattern, which could help maintain tissue function, increase adiponectin expression, and decrease pro-inflammatory adipokines. These findings should be taken into account when considering hormone replacement therapy for obese-diabetic women.

Sex Differences in Nonalcoholic Fatty Liver Disease: Estrogen Influence on the Liver-Adipose Tissue Crosstalk.

Significance: Nonalcoholic fatty liver disease (NAFLD) is a hepatic and systemic disorder with a complex multifactorial pathogenesis. Owing to the rising incidence of obesity and diabetes mellitus, the prevalence of NAFLD and its impact on global health care are expected to increase in the future. Differences in NAFLD exist between males and females, and among females depending on their reproductive status. Clinical and preclinical data show that females in the fertile age are more protected against NAFLD, and studies in postmenopausal women and ovariectomized animal models support a protective role for estrogens. Recent Advances: An efficient crosstalk between the liver and adipose tissue is necessary to regulate lipid and glucose metabolism, protecting the liver from steatosis and insulin resistance contributing to NALFD. New advances in the knowledge of sexual dimorphism in liver and adipose tissue are providing interesting clues about the sex differences in NAFLD pathogenesis that could inspire new therapeutic strategies. Critical Issues: Sex hormones influence key master regulators of lipid metabolism and oxidative stress in liver and adipose tissue. All these sex-biased metabolic adjustments shape the crosstalk between liver and adipose tissue, contributing to the higher protection of females to NAFLD. Future Directions: The development of novel drugs based on the protective action of estrogens, but without its feminizing or undesired side effects, might provide new therapeutic strategies for the management of NAFLD. Antioxid. Redox Signal. 35, 753-774.

HMTase Inhibitors as a Potential Epigenetic-Based Therapeutic Approach for Friedreich's Ataxia.

Friedreich's ataxia (FRDA) is a progressive neurodegenerative disorder caused by a homozygous GAA repeat expansion mutation in intron 1 of the frataxin gene (FXN), which instigates reduced transcription. As a consequence, reduced levels of frataxin protein lead to mitochondrial iron accumulation, oxidative stress, and ultimately cell death; particularly in dorsal root ganglia (DRG) sensory neurons and the dentate nucleus of the cerebellum. In addition to neurological disability, FRDA is associated with cardiomyopathy, diabetes mellitus, and skeletal deformities. Currently there is no effective treatment for FRDA and patients die prematurely. Recent findings suggest that abnormal GAA expansion plays a role in histone modification, subjecting the FXN gene to heterochromatin silencing. Therefore, as an epigenetic-based therapy, we investigated the efficacy and tolerability of two histone methyltransferase (HMTase) inhibitor compounds, BIX0194 (G9a-inhibitor) and GSK126 (EZH2-inhibitor), to specifically target and reduce H3K9me2/3 and H3K27me3 levels, respectively, in FRDA fibroblasts. We show that a combination treatment of BIX0194 and GSK126, significantly increased FXN gene expression levels and reduced the repressive histone marks. However, no increase in frataxin protein levels was observed. Nevertheless, our results are still promising and may encourage to investigate HMTase inhibitors with other synergistic epigenetic-based therapies for further preliminary studies.

Metabolic Fingerprinting Links Oncogenic PIK3CA with Enhanced Arachidonic Acid-Derived Eicosanoids.

Oncogenic transformation is associated with profound changes in cellular metabolism, but whether tracking these can improve disease stratification or influence therapy decision-making is largely unknown. Using the iKnife to sample the aerosol of cauterized specimens, we demonstrate a new mode of real-time diagnosis, coupling metabolic phenotype to mutant PIK3CA genotype. Oncogenic PIK3CA results in an increase in arachidonic acid and a concomitant overproduction of eicosanoids, acting to promote cell proliferation beyond a cell-autonomous manner. Mechanistically, mutant PIK3CA drives a multimodal signaling network involving mTORC2-PKCζ-mediated activation of the calcium-dependent phospholipase A2 (cPLA2). Notably, inhibiting cPLA2 synergizes with fatty acid-free diet to restore immunogenicity and selectively reduce mutant PIK3CA-induced tumorigenicity. Besides highlighting the potential for metabolic phenotyping in stratified medicine, this study reveals an important role for activated PI3K signaling in regulating arachidonic acid metabolism, uncovering a targetable metabolic vulnerability that largely depends on dietary fat restriction. VIDEO ABSTRACT.

17ß-estradiol ameliorates lipotoxicity-induced hepatic mitochondrial oxidative stress and insulin resistance.

The prevalence and severity of nonalcoholic fatty liver disease (NAFLD) is higher in men and postmenopausal women compared to premenopausal women, suggesting a protective role for ovarian hormones. Diet-induced obesity and fatty acids surplus promote mitochondrial dysfunction in liver, triggering oxidative stress and activation of c-Jun N-terminal kinase (JNK) which has been related to the development of insulin resistance and steatosis, the main hallmarks of NAFLD. Considering that estrogen, in particular 17ß-estradiol (E2), have been reported to improve mitochondrial biogenesis and function in liver, our aim was to elucidate the role of E2 in preventing fatty acid-induced insulin resistance in hepatocytes through modulation of mitochondrial function, oxidative stress and JNK activation. An in vivo study was conducted in Wistar rats of both sexes (n = 7) fed control diet and high-fat diet (HFD), and in vitro studies were carried out in HepG2 cells treated with palmitate (PA) and E2 for 24 h. Our HFD-fed male rats showed a prediabetic state characterized by greater systemic and hepatic insulin resistance, as well as higher lipid content in liver, compared to females. JNK activation rose markedly in males in response to HFD feeding, in parallel with mitochondrial dysfunction and oxidative stress. Consistently, in PA-exposed HepG2 cells, E2 treatment prevented JNK activation, insulin resistance and fatty acid accumulation. Altogether, our data highlights the importance of E2 as a mitigating factor of fatty acid-insulin resistance in hepatocytes through downregulation of JNK activation, by means of mitochondrial function improvement.

PARK2 Depletion Connects Energy and Oxidative Stress to PI3K/Akt Activation via PTEN S-Nitrosylation.

PARK2 is a gene implicated in disease states with opposing responses in cell fate determination, yet its contribution in pro-survival signaling is largely unknown. Here we show that PARK2 is altered in over a third of all human cancers, and its depletion results in enhanced phosphatidylinositol 3-kinase/Akt (PI3K/Akt) activation and increased vulnerability to PI3K/Akt/mTOR inhibitors. PARK2 depletion contributes to AMPK-mediated activation of endothelial nitric oxide synthase (eNOS), enhanced levels of reactive oxygen species, and a concomitant increase in oxidized nitric oxide levels, thereby promoting the inhibition of PTEN by S-nitrosylation and ubiquitination. Notably, AMPK activation alone is sufficient to induce PTEN S-nitrosylation in the absence of PARK2 depletion. Park2 loss and Pten loss also display striking cooperativity to promote tumorigenesis in vivo. Together, our findings reveal an important missing mechanism that might account for PTEN suppression in PARK2-deficient tumors, and they highlight the importance of PTEN S-nitrosylation in supporting cell survival and proliferation under conditions of energy deprivation.

Resveratrol induces mitochondrial respiration and apoptosis in SW620 colon cancer cells.

BACKGROUND: The polyphenol resveratrol (RSV) is found in the skin of red grapes and has been reported to exhibit anticancer properties. The antitumor effects of RSV in the gastrointestinal tract have gained considerable interest due to the high exposure of this tissue to this dietary compound. One of the hallmarks of cancer cells is their particular metabolism mainly relying on glycolysis for ATP production rather than mitochondrial oxidative phosphorylation. Although RSV has been described to act as a calorie-restriction mimetic, modulating energy metabolism in normal tissues, little efforts have been done to study the effects of this polyphenol in the metabolism of cancer cells. Taking this into account, the aim of this study was to explore metabolic effects of this polyphenol in colon cancer. METHODS: Oxygen consumption, ATP levels, Western blotting and other molecular biology techniques were carried out to characterize the metabolic signature of RSV in SW620 colon cancer cells. RESULTS: Paradoxically, the cytotoxic effects of RSV were associated with an increase in oxygen consumption supported by mitochondrial biogenesis and increased fatty acid oxidation. This partial reversion of the Warburg effect was followed by hyperpolarization of mitochondrial membrane and ROS production, leading to an increased apoptosis. CONCLUSIONS: Our results propose that the anticancer mechanisms of RSV could reside in targeting cancer cell metabolism, promoting mitochondrial electron transport chain overload and, ultimately, increasing ROS production. GENERAL SIGNIFICANCE: These results shed new light into the anticancer mechanism of RSV supporting the ability of this compound in potentiating the effects of chemotherapy.

Leptin regulates energy metabolism in MCF-7 breast cancer cells.

Obesity is known to be a poorer prognosis factor for breast cancer in postmenopausal women. Among the diverse endocrine factors associated to obesity, leptin has received special attention since it promotes breast cancer cell growth and invasiveness, processes which force cells to adapt their metabolism to satisfy the increased demands of energy and biosynthetic intermediates. Taking this into account, our aim was to explore the effects of leptin in the metabolism of MCF-7 breast cancer cells. Polarographic analysis revealed that leptin increased oxygen consumption rate and cellular ATP levels were more dependent on mitochondrial oxidative metabolism in leptin-treated cells compared to the more glycolytic control cells. Experiments with selective inhibitors of glycolysis (2-DG), fatty acid oxidation (etomoxir) or aminoacid deprivation showed that ATP levels were more reliant on fatty acid oxidation. In agreement, levels of key proteins involved in lipid catabolism (FAT/CD36, CPT1, PPARα) and phosphorylation of the energy sensor AMPK were increased by leptin. Regarding glucose, cellular uptake was not affected by leptin, but lactate release was deeply repressed. Analysis of pyruvate dehydrogenase (PDH), lactate dehydrogenase (LDH) and pyruvate carboxylase (PC) together with the pentose-phosphate pathway enzyme glucose-6 phosphate dehydrogenase (G6PDH) revealed that leptin favors the use of glucose for biosynthesis. These results point towards a role of leptin in metabolic reprogramming, consisting of an enhanced use of glucose for biosynthesis and lipids for energy production. This metabolic adaptations induced by leptin may provide benefits for MCF-7 growth and give support to the reverse Warburg effect described in breast cancer.

UCP2 inhibition sensitizes breast cancer cells to therapeutic agents by increasing oxidative stress.

Modulation of oxidative stress in cancer cells plays an important role in the study of the resistance to anticancer therapies. Uncoupling protein 2 (UCP2) may play a dual role in cancer, acting as a protective mechanism in normal cells, while its overexpression in cancer cells could confer resistance to chemotherapy and a higher survival through downregulation of ROS production. Thus, our aim was to check whether the inhibition of UCP2 expression and function increases oxidative stress and could render breast cancer cells more sensitive to cisplatin (CDDP) or tamoxifen (TAM). For this purpose, we studied clonogenicity, mitochondrial membrane potential (ΔΨm), cell viability, ROS production, apoptosis, and autophagy in MCF-7 and T47D (only the last four determinations) breast cancer cells treated with CDDP or TAM, in combination or without a UCP2 knockdown (siRNA or genipin). Furthermore, survival curves were performed in order to check the impact of UCP2 expression in breast cancer patients. UCP2 inhibition and cytotoxic treatments produced a decrease in cell viability and clonogenicity, in addition to an increase in ΔΨm, ROS production, apoptosis, and autophagy. It is important to note that CDDP decreased UCP2 protein levels, so that the greatest effects produced by the UCP2 inhibition in combination with a cytotoxic treatment, with regard to treatment alone, were observed in TAM+UCP2siRNA-treated cells. Moreover, this UCP2 inhibition caused autophagic cell death, since apoptosis parameters barely increased after UCP2 knockdown. Finally, survival curves revealed that higher UCP2 expression corresponded with a poorer prognosis. In conclusion, UCP2 could be a therapeutic target in breast cancer, especially in those patients treated with tamoxifen.

Chronic-leptin attenuates Cisplatin cytotoxicity in MCF-7 breast cancer cell line.

BACKGROUND/AIMS: Large-scale epidemiological studies support a correlation between obesity and breast cancer in postmenopausal women. Circulating leptin levels are increased in obese and it has been suggested to play a significant role in mammary tumor formation and progression. Moreover, regulation of oxidative stress is another important factor in both tumor development and responses to anticancer therapies. The aim of this study was to examine the relationship between oxidative stress and chronic leptin exposure. METHODS: We treated MCF-7 breast cancer cells with 100 ng/mL leptin for 10 days and analyzed cell growth, ROS production and oxidative damage, as well as, some of the main antioxidant systems. Furthermore, since the hyperleptinemia has been associated with a worse pathology prognosis, we decided to test the influence of leptin in response to cisplatin anticancer treatment. RESULTS: Leptin signalling increased cell proliferation but reduced ROS production, as well as, oxidative damage. We observed an upregulation of SIRT1 after leptin exposure, a key regulator of stress response and metabolism. Additionally, leptin counteracted cisplatin-induced cytotoxicity in tumor cells, showing a decrease in cell death. CONCLUSION: Chronic leptin could contribute to the effective regulation of endogenous and treatment-induced oxidative stress, and it contributes to explain in part its proliferative effects.

Leptin Modulates Mitochondrial Function, Dynamics and Biogenesis in MCF-7 Cells.

The adipokine leptin, known for its key role in the control of energy metabolism, has been shown to be involved in both normal and tumoral mammary growth. One of the hallmarks of cancer is an alteration of tumor metabolism since cancerous cells must rewire metabolism to satisfy the demands of growth and proliferation. Considering the sensibility of breast cancer cells to leptin, the objective of this study was to explore the effects of this adipokine on their metabolism. To this aim, we treated the MCF-7 breast cancer cell line with 50 ng/mL leptin and analyzed several features related to cellular and mitochondrial metabolism. As a result, leptin increased cell proliferation, shifted ATP production from glycolysis to mitochondria and decreased the levels of the glycolytic end-product lactate. We observed an improvement in ADP-dependent oxygen consumption and an amelioration of oxidative stress without changes in total mitochondrial mass or specific oxidative phosphorylation (OXPHOS) complexes. Furthermore, RT-PCR and western blot showed an up-regulation for genes and proteins related to biogenesis and mitochondrial dynamics. This expression signature, together with an increased mitophagy observed by confocal microscopy suggests that leptin may improve mitochondrial quality and function. Taken together, our results propose that leptin may improve bioenergetic efficiency by avoiding the production of reactive oxygen species (ROS) and conferring benefits for growth and survival of MCF-7 breast cancer cells.

Effect of xanthohumol and 8-prenylnaringenin on MCF-7 breast cancer cells oxidative stress and mitochondrial complexes expression.

Xanthohumol (XN) and 8-prenylnaringenin (8PN) are hop (Humulus lupulus L.) polyphenols studied for their chemopreventive effects on certain cancer types. The breast cancer line MCF-7 was treated with doses ranging from 0.001 to 20 µM of XN or 8PN in order to assess the effects on cell viability and oxidative stress. Hoechst 33342 was used to measure cell viability and reactive oxygen species (ROS) production was determined by 2',7'-dichlorofluorescein diacetate. Catalase, superoxide dismutase, and glutathione reductase enzymatic activities were determined and protein expression of sirtuin1, sirtuin3, and oxidative phosphorylation system (OXPHOS) were done by Western blot. Treatments XN 0.01, 8PN 0.01, and 8PN 1 µM led to a decrease in ROS production along with an increase of OXPHOS and sirtuin expression; in contrast, XN 5 µM gave rise to an increase of ROS production accompanied by a decrease in OXPHOS and sirtuin expression. These results suggest that XN in low dose (0.01 µM) and 8PN at all assayed doses (0.001-20 µM) presumably improve mitochondrial function, whereas a high dose of XN (5 µM) worsens the functionality of this organelle.

The oxidative stress in breast tumors of postmenopausal women is ERα/ERß ratio dependent.

Estrogen receptor status is a diagnostic parameter in breast cancer treatment. Estrogen receptor presence is related to a better prognosis because the principal treatments attacking breast cancer tumors have their action site directed at the estrogen receptor. However, the two different subtypes of estrogen receptor, ERα and ERß, have different functions. In this work an alternative point of view focusing on oxidative stress is shown, given that estrogen receptors regulate several proteins related to this oxidative stress, such as antioxidant enzymes, sirtuins, and uncoupling proteins. Postmenopausal human breast tumors with different ERα/ERß ratios were analyzed to characterize the amount of oxidative stress, mitochondrial function, and proliferation-related and oxidative stress-activated signaling pathways. Results showed that tumors with a low ERα/ERß ratio have greater oxidative damage and higher antioxidant enzyme protein levels, as well as uncoupling protein (UCP) and sirtuin 3 (SIRT3), and have high studied signaling pathway activation. Glutathione peroxidase, Complex V, Complex III, Complex II, Complex IV, AKT, SAPK, and ERα were significantly and positively correlated with ERα/ERß ratio. However, carbonyl groups, catalase, CuZn-superoxide dismutase, UCP5, SIRT3, and ERß were significantly and negatively correlated with ERα/ERß ratio. From the independent variables included in the step-by-step stepwise multiple linear regression analysis, only the ERα/ERß ratio was independently associated with carbonyl groups. Surprisingly, these low ERα/ERß ratio tumors have poor prognosis for the patient, and these results and those of other authors suggest that these tumors are adapted to conditions of increased oxidative stress.

The effects of 17ß-estradiol on mitochondrial biogenesis and function in breast cancer cell lines are dependent on the ERα/ERß ratio.

BACKGROUND/AIMS: 17ß-estradiol (E2) is a risk factor for the development of breast cancer, and cause tumorigenesis in epithelial breast cells. Moreover, E2 has distinct effects on different tissues that are attributed to the presence of two estrogen receptor isoforms, ERα and ERß. METHODS: The effect of E2 on mitochondrial biogenesis and function was investigated in two breast cancer cell lines with different estrogen receptor ratios, MCF-7 (high ERα/ERß ratio) and T47D (low ERα/ERß ratio) cell lines treated with physiological concentrations of E2 (1 nM). RESULTS: Mitochondria of the MCF-7 cell line showed an increase in proliferation but a decrease in functionality, while the T47D cell line, with low ERα/ERß ratio, maintained functionality with fewer mitochondria. CONCLUSION: Our results suggest that ERs endowment and its subtypes relation have an effect on treatment response and could contribute new ideas about mitochondria and ERs in breast cancer, as well as new indicators to the disease progression.

Identification of liver proteins altered by type 2 diabetes mellitus in obese subjects.

BACKGROUND: Type 2 diabetes mellitus (T2DM) is a well-known factor risk for non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) in obese patients. AIMS: To better understand the association between T2DM and NAFLD, global changes in protein expression in diabetic and non-diabetic obese subjects were assessed by a proteomic approach. METHODS: Liver samples were obtained from diabetic and non-diabetic morbid obese subjects (BMI>40 kg/m(2) ). Histological analysis was used to evaluate hepatic steatosis and the degree of anatomopathological alteration. Changes in protein expression were analysed by two-dimentional electrophoresis combined with MALDI-TOF mass spectrometry. Levels of glutathione, carbonyl and 4-HNE protein adducts were used to assess oxidative stress status. RESULTS: Of 850 proteins analysed, 33 were differentially expressed in T2DM obese subjects. Of these, 27 were unequivocally identified by mass spectrometry. Analysis of protein sets revealed patterns of decreased abundance in mitochondrial enzymes, proteins involved in methione metabolism, and oxidative stress response. Accordingly, T2DM subjects showed decreased levels of glutathione, the antioxidant byproduct of methionine metabolism via the transsulfuration pathway, and higher levels of protein and lipid oxidative damage. Changes in detoxyfing enzymes, carbohydrate metabolism, proteasome subunits and retinoic acid synthesis were also found. CONCLUSIONS: The results suggest alterations in mitochondrial function and methionine metabolism as potential contributing factors to increased oxidative stress in liver of obese diabetic patients which may be influencing the development of NAFLD and NASH.

Chronic leptin treatment sensitizes MCF-7 breast cancer cells to estrogen.

BACKGROUND/AIMS: Obesity is associated with an increased risk of estrogen-dependent breast cancer. The adipokine leptin, whose levels are chronically increased in obese people, has been shown to stimulate ER positive cancer cell growth. Considering previous evidence of a crosstalk between leptin and estrogen signaling, the objective of this study was to establish the influence of chronic leptin treatment on estrogen-dependent cell growth. METHODS: To this aim, we use the estrogen receptor (ER) positive MCF-7 breast cancer cell line treated chronically with leptin and analyzed estrogen-dependent cell growth, ERs (ERα and ERß) expression, ER-dependent transcriptional activity as well as cell survival to the antiestrogenic agents tamoxifen and ICI 182,780. RESULTS: Leptin signaling pathway kept activated after chronic stimulation (7 days) with leptin showing significant phosphorylation of JAK2 and STAT3 and higher cell proliferation rate. Chronic leptin at 100 ng/mL dose increased ERα to ERß ratio and consistently enhanced estrogen-dependent transcriptional activity, increasing E2-dependent cell growth and resistance to antiestrogen agents. CONCLUSION: This study supports the existence of a crosstalk between leptin and estrogen, in which leptin might play an important role potentiating the mitogenic action of estrogen, probably by alteration of ERα to ERß ratio.

Resveratrol potentiates the cytotoxic oxidative stress induced by chemotherapy in human colon cancer cells.

The treatment of advanced colorectal cancer with 5-fluorouracil has two major problems: development of tumor resistance and toxicity toward normal tissues. The aim of this study was to investigate the possible advantages of combining 5-fluorouracil (5-FU) with resveratrol (trans-3, 4', 5-trihydroxystilbene) for treating HT-29 and SW-620 colorectal carcinoma cell lines. Since combined treatment using 5-FU with resveratrol resulted in a significant decrease in long-term cell survival, we investigated the possible basis of this synergistic interaction at a molecular level, focusing on oxidative stress as a possible mediator of cell death. Resveratrol established interactions with the mitochondria of cancer cells and induced an imbalance in cellular antioxidant activities, leading to a significant increase in the levels of both intracellular reactive oxygen species (ROS) and lipid peroxides. Combined treatment with resveratrol sensitized colon cancer cells to 5-fluorouracil, inducing a further increase in oxidative stress, which was linked to the inhibition of AKT and STAT3 proteins, which are known to have oncogenic potential in colorectal carcinomas.

Stabilization of Suv39H1 by SirT1 is part of oxidative stress response and ensures genome protection.

Sirtuins are NAD-dependent deacetylases that sense oxidative stress conditions and promote a protective cellular response. The Sirtuin SirT1 is involved in facultative heterochromatin formation through an intimate functional relationship with the H3K9me3 methyltransferase Suv39h1, a chromatin organization protein. However, SirT1 also regulates Suv39h1-dependent constitutive heterochromatin (CH) through an unknown mechanism; interestingly, SirT1 does not significantly localize in these regions. Herein, we report that SirT1 controls global levels of Suv39h1 by increasing its half-life through inhibition of Suv39h1 lysine 87 polyubiquitination by the E3-ubiquitin ligase MDM2. This in turn increases Suv39h1 turnover in CH and ensures genome integrity. Stress conditions that lead to SirT1 upregulation, such as calorie restriction, also induce higher levels of Suv39h1 in a SirT1-dependent manner in vivo. These observations reflect a direct link between oxidative stress response and Suv39h1 and support a dynamic view of heterochromatin, in which its structure adapts to cell physiology.