SIRT1 positively regulates breast cancer associated human aromatase (CYP19A1) expression

SIRT1 mediates breast cancer development and tumorigenesis controlled by estrogen-related receptor β

Silent mating type information regulation 2 homolog 1 (SIRT1) is a class III histone deacetylase (HDAC) that is NAD + dependent and essential for metabolism, senescence, and cell survival. SIRT1 is overexpressed in several cancers, including breast cancer. SIRT1 is a well-known target gene of the estrogen receptor alpha (ER alpha) and is closely related to ER alpha deacetylation. Transcription factor Estrogen-related receptors (ERRs) share sequence homology with ERs in the DNA-binding domain, therefore, the possibility of sharing target genes between them is high. Our current research aims to gain insight into the function of ERRβ in regulating the activity of SIRT1 during the progression of breast cancer. ER-positive (ER + ve) breast cancer cells and tissues had considerably enhanced SIRT1 expression. Six potential ERRE sites were identified by analysis of the 5' upstream region of SIRT1, and both in vitro and in vivo experiments supported their presence. We found SIRT1 to be up-regulated in ERRβ overexpressed ER + ve breast cancer cells. Furthermore, our findings suggested that ectopic production of ERR and PCAF would increase SIRT1 activity. Our findings also indicated that ectopic production of ERRβ and PCAF increased SIRT1 activity. With sufficient evidence demonstrating the substantial involvement of SIRT1 in cell proliferation, migration, and colony formation capability, we were also able to illustrate the tumorigenic role of SIRT1. Overall, our findings highlight SIRT1's tumorigenic influence on breast cancer and suggest that SIRT1 inhibitors might serve as potential therapeutic drugs for the treatment of breast cancer.

Estradiol as the Trigger of Sirtuin-1-Dependent Cell Signaling with a Potential Utility in Anti-Aging Therapies

Aging entails the inevitable loss of the structural and functional integrity of cells and tissues during the lifetime. It is a highly hormone-dependent process; although, the exact mechanism of hormone involvement, including sex hormones, is unclear. The marked suppression of estradiol synthesis during menopause suggests that the hormone may be crucial in maintaining cell lifespan and viability in women. Recent studies also indicate that the same may be true for men. Similar anti-aging features are attributed to sirtuin 1 (SIRT1), which may possibly be linked at the molecular level with estradiol. This finding may be valuable for understanding the aging process, its regulation, and possible prevention against unhealthy aging. The following article summarizes the initial studies published in this field with a focus on age-associated diseases, like cancer, cardiovascular disease and atherogenic metabolic shift, osteoarthritis, osteoporosis, and muscle damage, as well as neurodegenerative and neuropsychiatric diseases.

Sirtuin 1 Expression in Canine Mammary Tumors: A Pilot Study

Sirtuin 1 (SIRT1) is a protein involved in aging, cell protection, and energy metabolism in mammals. Recently, SIRT1 has been intensively studied in medical oncology, but the role of SIRT1 is still controversial, as it has been proposed as both an oncogene and a tumor suppressor. The aim of this study is to investigate the expression of SIRT1 by immunohistochemistry in canine mammary tissues, and by Western blot and immunofluorescence analysis in different canine mammary cell lines. Our results showed a decrease in SIRT1 expression from normal mammary gland tissue, and from benign and well-differentiated malignant tumors (G1) to less differentiated ones (G2-G3). Furthermore, a shift in the subcellular localization of SIRT1 from the nucleus to the cytoplasm was observed in less differentiated malignant tumors. However, further studies are needed to investigate the subcellular localization of SIRT1 in canine cancer cells and the role it may play in oncogenesis in animals.

Expression and Function of StAR in Cancerous and Non-Cancerous Human and Mouse Breast Tissues: New Insights into Diagnosis and Treatment of Hormone-Sensitive Breast Cancer

Breast cancer (BC) is primarily triggered by estrogens, especially 17β-estradiol (E2), which are synthesized by the aromatase enzyme. While all steroid hormones are derived from cholesterol, the rate-limiting step in steroid biosynthesis is mediated by the steroidogenic acute regulatory (StAR) protein. Herein, we demonstrate that StAR mRNA expression was aberrantly high in human hormone-dependent BC (MCF7, MDA-MB-361, and T-47D), modest in hormone-independent triple negative BC (TNBC; MDA-MB-468, BT-549, and MDA-MB-231), and had little to none in non-cancerous mammary epithelial (HMEC, MCF10A, and MCF12F) cells. In contrast, these cell lines showed abundant expression of aromatase (CYP19A1) mRNA. Immunofluorescence displayed qualitatively similar patterns of both StAR and aromatase expression in various breast cells. Additionally, three different transgenic (Tg) mouse models of spontaneous breast tumors, i.e., MMTV-Neu, MMTV-HRAS, and MMTV-PyMT, demonstrated markedly higher expression of StAR mRNA/protein in breast tumors than in normal mammary tissue. While breast tumors in these mouse models exhibited higher expression of ERα, ERβ, and PR mRNAs, their levels were undetected in TNBC tumors. Accumulation of E2 in plasma and breast tissues, from MMTV-PyMT and non-cancerous Tg mice, correlated with StAR, but not with aromatase, signifying the importance of StAR in governing E2 biosynthesis in mammary tissue. Treatment with a variety of histone deacetylase inhibitors (HDACIs) in primary cultures of enriched breast tumor epithelial cells, from MMTV-PyMT mice, resulted in suppression of StAR and E2 levels. Importantly, inhibition of StAR, concomitant with E2 synthesis, by various HDACIs, at clinical and preclinical doses, in MCF7 cells, indicated therapeutic relevance of StAR in hormone-dependent BCs. These findings provide insights into the molecular events underlying the differential expression of StAR in human and mouse cancerous and non-cancerous breast cells/tissues, highlighting StAR could serve not only as a novel diagnostic maker but also as a therapeutic target for the most prevalent hormone-sensitive BCs.

The Mechanistic Roles of Sirtuins in Breast and Prostate Cancer

Simple Summary

There are diverse reports of the dual role of sirtuin genes and proteins in breast and prostate cancers. This review discusses the current information on the tumor promotion or suppression roles of SIRT1–7 in breast and prostate cancers. Precisely, we highlight that sirtuins regulate various proteins implicated in proliferation, apoptosis, autophagy, chemoresistance, invasion, migration, and metastasis of both breast and prostate cancer. We also provide evidence of the direct regulation of sirtuins by miRNAs, highlighting the consequences of this regulation in breast and prostate cancer. Overall, this review reveals the potential value of sirtuins as biomarkers and/or targets for improved treatment of breast and prostate cancers.

Abstract

Mammalian sirtuins (SIRT1–7) are involved in a myriad of cellular processes, including apoptosis, proliferation, differentiation, epithelial-mesenchymal transition, aging, DNA repair, senescence, viability, survival, and stress response. In this review, we discuss the current information on the mechanistic roles of SIRT1–7 and their downstream effects (tumor promotion or suppression) in cancers of the breast and prostate. Specifically, we highlight the involvement of sirtuins in the regulation of various proteins implicated in proliferation, apoptosis, autophagy, chemoresistance, invasion, migration, and metastasis of breast and prostate cancer. Additionally, we highlight the available information regarding SIRT1–7 regulation by miRNAs, laying much emphasis on the consequences in the progression of breast and prostate cancer.

Virtual Screening in the Identification of Sirtuins’ Activity Modulators

Sirtuins are NAD⁺-dependent deac(et)ylases with different subcellular localization. The sirtuins’ family is composed of seven members, named SIRT-1 to SIRT-7. Their substrates include histones and also an increasing number of different proteins. Sirtuins regulate a wide range of different processes, ranging from transcription to metabolism to genome stability. Thus, their dysregulation has been related to the pathogenesis of different diseases. In this review, we discussed the pharmacological approaches based on sirtuins’ modulators (both inhibitors and activators) that have been attempted in in vitro and/or in in vivo experimental settings, to highlight the therapeutic potential of targeting one/more specific sirtuin isoform(s) in cancer, neurodegenerative disorders and type 2 diabetes. Extensive research has already been performed to identify SIRT-1 and -2 modulators, while compounds targeting the other sirtuins have been less studied so far. Beside sections dedicated to each sirtuin, in the present review we also included sections dedicated to pan-sirtuins’ and to parasitic sirtuins’ modulators. A special focus is dedicated to the sirtuins’ modulators identified by the use of virtual screening.

Additive pharmacological interaction between sirtuin inhibitor cambinol and paclitaxel in MCF7 luminal and MDA-MB-231 triple-negative breast cancer cells

Background

Breast cancer (BC) is the most common malignancy and the leading cause of cancer-related death in women worldwide. Sirtuin inhibitors (SIRTi), belonging to the histone deacetylase inhibitors group (HDIs), are potent epigenetic drugs that have been investigated for therapeutic use in different clinical disorders, including hematological malignancies and solid tumors.

Methods

The influence of cambinol (CAM; SIRTi) used individually or in combination with standard chemotherapeutic paclitaxel (PAX) on viability (MTT assay), proliferation (BrdU assay), induction of apoptosis and cell cycle arrest (FACS analysis) was determined in MCF7 luminal and MDA-MB-231 triple-negative breast cancer (TNBC) cells. The types of pharmacological drug–drug interaction between CAM and PAX were determined by an exact and rigorous pharmacodynamic method—an isobolography, to determine the presence of synergism, addition or antagonism between analyzed drugs using a variety of fixed-dose ratios.

Results

The combination of CAM and PAX at a fixed ratio of 1:1 exerted additive interaction in the viability of MCF7 and MDA-MB-231 BC cells. Both active agents used separately reduced viability and proliferation of BC cells as well as induced apoptosis and cell cycle arrest. These effects were much more evident in MCF7 than in MDA-MB-231 BC cells. Additionally, CAM combined with PAX increased anti-cancer activity compared to PAX used alone.

Conclusion

CAM might be considered a potential therapeutic agent individually or in combined therapy with PAX against luminal or TNBC.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s43440-022-00393-w.

Hormonal and Genetic Regulatory Events in Breast Cancer and Its Therapeutics: Importance of the Steroidogenic Acute Regulatory Protein

Estrogen promotes the development and survival of the majority of breast cancers (BCs). Aromatase is the rate-limiting enzyme in estrogen biosynthesis, and it is immensely expressed in both cancerous and non-cancerous breast tissues. Endocrine therapy based on estrogen blockade, by aromatase inhibitors, has been the mainstay of BC treatment in post-menopausal women; however, resistance to hormone therapy is the leading cause of cancer death. An improved understanding of the molecular underpinnings is the key to develop therapeutic strategies for countering the most prevalent hormone receptor positive BCs. Of note, cholesterol is the precursor of all steroid hormones that are synthesized in a variety of tissues and play crucial roles in diverse processes, ranging from organogenesis to homeostasis to carcinogenesis. The rate-limiting step in steroid biosynthesis is the transport of cholesterol from the outer to the inner mitochondrial membrane, a process that is primarily mediated by the steroidogenic acute regulatory (StAR) protein. Advances in genomic and proteomic technologies have revealed a dynamic link between histone deacetylases (HDACs) and StAR, aromatase, and estrogen regulation. We were the first to report that StAR is abundantly expressed, along with large amounts of 17β-estradiol (E2), in hormone-dependent, but not hormone-independent, BCs, in which StAR was also identified as a novel acetylated protein. Our in-silico analyses of The Cancer Genome Atlas (TCGA) datasets, for StAR and steroidogenic enzyme genes, revealed an inverse correlation between the amplification of the StAR gene and the poor survival of BC patients. Additionally, we reported that a number of HDAC inhibitors, by altering StAR acetylation patterns, repress E2 synthesis in hormone-sensitive BC cells. This review highlights the current understanding of molecular pathogenesis of BCs, especially for luminal subtypes, and their therapeutics, underlining that StAR could serve not only as a prognostic marker, but also as a therapeutic candidate, in the prevention and treatment of this life-threatening disease.

Type I IFN stimulates IFI16-mediated aromatase expression in adipocytes that promotes E2-dependent growth of ER-positive breast cancer

Although type I interferons (IFNs) play multifaceted roles during tumorigenesis and cancer treatment, the interplay between type I IFNs and estrogen signaling in breast cancer (BC) microenvironment is not well understood. Here, we report a novel function of type I IFNs in inducing aromatase expression in adipose tissues surrounding BC, which potentiates the E₂-dependent growth of estrogen receptor (ER)-positive BC. First, we found that expression levels of type I IFNs correlate negatively with clinical outcome but positively with tumor grade in patients with ER-positive BC. Levels of type I IFNs were elevated in cocultured media of immune cells and BC cells, which increased aromatase expression and E₂ production in Simpson-Golabi-Behmel syndrome preadipocytes. The type I IFN-induced aromatase expression was dependent on IFN-γ-inducible protein 16 (IFI16), which is encoded by an interferon-stimulated gene. At the molecular level, type I IFNs led to recruitment of HIF1α-IFI16-PRMT2 complex to the hypoxia-response element located in the aromatase PI.3/PII promoter. Next, we generated an adipocyte-specific Ifi204, which is a mouse ortholog of human IFI16, knockout mouse (Ifi204-AKO). IFNβ induced E₂ production in the preadipocytes isolated from the control mice, but such E₂ production was far lower in the Ifi204-AKO preadipocytes. Importantly, the growth of orthotopically inoculated E0771 ER-positive mammary tumors was reduced significantly in the Ifi204-AKO mice. Taken together, our findings provide novel insights into the crosstalk between type I IFNs and estrogen signaling in the progression of ER-positive BC.

Flavonoids as Sirtuin Modulators

Sirtuins (SIRTs) are described as NAD+-dependent deacetylases, also known as class III histone deacetylases. So far, seven sirtuin genes (SIRTS 1-7) have been identified and characterized in mammals and also known to occur in bacteria and eukaryotes. SIRTs are involved in various biological processes including endocrine system, apoptosis, aging and longevity, diabetes, rheumatoid arthritis, obesity, inflammation, etc. Among them, the best characterized one is SIRT1. Actually, small molecules seem to be the most effective SIRT modulators. Flavonoids have been reported to possess many positive effects favrable for human health, while a relatively less research has been reported so far on their funcions as SIRT modulation mechanisms. In this regard, we herein aimed to focus on modulatory effects of flavonoids on SIRTs as the most common secondary metabolites in natural products. Our literature survey covering the years of 2006-2021 pointed out that flavonoids frequently interact with SIRT1 and SIRT3 followed by SIRT6. It can be also concluded that some popular flavonoid derivatives, e.g. resveratrol, quercetin, and catechin derivatives came forward in terms of SIRT modulation.

Photoperiodic modulation of ovarian metabolic, survival, proliferation and gap junction markers in adult golden hamster, Mesocricetus auratus

Female reproductive physiology is greatly dependent on tight regulation of metabolic and survival factors. Photoperiod regulates female reproductive rhythms but very less information exists explaining whether photoperiod could modulate thyroid hormone homeostasis, metabolic/energy parameters along with survival, proliferation and gap junction proteins in the ovary of a long-day breeder, Mesocricetus auratus. Adult female hamsters were exposed to different photoperiodic regimes i.e., critical photoperiod (CP; 12.5L:11.5D), short photoperiod (SP; 8L:16D) and long photoperiod (LP; 16L:8D) for 12 weeks. LP upregulated thyroidal and gonadal activity as apparent by histoarchitecture, thyroid hormone profile [triiodothyronine (T3), thyroxin (T4) and thyroid stimulating hormone (TSH)], luteinizing hormone (LH), follicle stimulating hormone (FSH), estradiol (E2) and progesterone (P4) levels when compared with SP exposed hamsters. Further, LP increased thyroid hormone receptor-α/deiodinase-2 (TRα/Dio-2), estrogen receptor-α (ERα)/aromatase and insulin receptor/glucose transporter-4 (IR/GLUT-4) expressions in ovary. Interestingly, ovarian sirtuin-1 (SIRT-1) expression was also upregulated under LP condition along with cell proliferation (proliferating cell nuclear antigen or PCNA), survival (B cell lymphoma-2 or Bcl-2) and gap junction (connexin-43) markers when compared to SP exposed hamsters. We also noted elevated levels of circulatory leptin, insulin along with melatonin and its receptor (MT-1) in ovary under SP condition. Thus, we suggest that photoperiod plays a vital role in regulation of thyroid and reproductive hormone homeostasis along with key metabolic and survival markers in the ovary of adult golden hamsters, M. auratus providing further insight into the regulation of female reproductive seasonality in a long-day breeder.

Mechanisms of endocrine therapy resistance in breast cancer

The most commonly diagnosed breast cancer (BC) subtype is characterized by estrogen receptor (ER) expression. Treatment of this BC subtype typically involves modalities that either suppress the production of estrogen or impede the binding of estrgen to its receptors, constituting the basis for endocrine therapy. While many patients have benefitted from endocrine therapy with clear reduction in mortality and cancer recurrence, one of the clinical hurdles that remain involves overcoming intrinsic (de novo) or acquired resistance to endocrine therapy driven by diverse and complex changes occurring in the tumor microenvironment. Moreover, such resistance may persist even after progression through additional antiestrogen therapies thus demonstrating the importance of further investigation of mechanisms of ER modulation. Here, we discuss a number of advances that provide a better understanding of the complex mechanistic basis for resistance to endocrine therapy as well as future therapeutic maneuvers that may break this resistance.

Regulation of aromatase expression: Potential therapeutic insight into breast cancer treatment

Estrogen signaling has been implicated in hormone-dependent breast cancer which constitutes >75% of breast cancer diagnosis and other malignancies. Aromatase, the key enzyme involved in the synthesis of estrogen, is often dysregulated in breast cancers. This has led to the administration of aromatase-inhibitors (AIs), commonly used for hormone-dependent breast cancers. Unfortunately, the increasing development of acquired resistance to the current AIs and modulators of estrogen receptors, following initial disease steadiness, has posed a serious clinical challenge in breast cancer treatment. In this review we highlight historical and recent advances on the transcriptional and post-translational regulation of aromatase in both physiological and pathological contexts. We also discuss the different drug combinations targeting various tumor promoting cell signaling pathways currently being developed and tested both in laboratory settings and in the clinic.

SIRT1 and gynecological malignancies (Review)

Sirtuin 1 (SIRT1), a member of the sirtuin protein family, is a nicotinamide adenine dinucleotide (NAD⁺)-dependent type III histone deacetylase and mono-ADP-ribosyltransferase. SIRT1 can deacetylate histones (H1, H3, and H4) and non-histone proteins, and it is widely involved in various physiological and pathological processes in the body, including metabolism, aging, transcription, DNA damage and repair, apoptosis, cell cycle regulation, inflammation and cancer. Research has shown that SIRT1 is involved in tumorigenesis, tumor metastasis and chemotherapy resistance, but it exerts opposing effects and plays different roles in different pathogenic processes. Recent studies have demonstrated that SIRT1 may be implicated in the pathogenesis, development, treatment and prognosis of tumors; however, its role in gynecological tumors remains elusive. The aim of the present review was to summarize the pathogenic roles of SIRT1 in cancer, and to provide what is, to the best of our knowledge, the first review of recent advances involving SIRT1 in cervical cancer, endometrial cancer (EC) and ovarian cancer (OC). In addition, the critical research gaps regarding SIRT1, particularly its potential involvement in the concurrence of EC and cervical cancer and its antagonistic effect against poly(ADP-ribose) polymerase inhibitors in OC, were highlighted.

Effects of Adiposity and Exercise on Breast Tissue and Systemic Metabo-Inflammatory Factors in Women at High Risk or Diagnosed with Breast Cancer

Excess body fat and sedentary behavior are associated with increased breast cancer risk and mortality, including in normal weight women. To investigate underlying mechanisms, we examined whether adiposity and exercise impact the breast microenvironment (e.g., inflammation and aromatase expression) and circulating metabo-inflammatory factors. In a cross-sectional cohort study, breast white adipose tissue (WAT) and blood were collected from 100 women undergoing mastectomy for breast cancer risk reduction or treatment. Self-reported exercise behavior, body composition measured by dual-energy x-ray absorptiometry (DXA), and waist:hip ratio were obtained prior to surgery. Breast WAT inflammation (B-WATi) was assessed by IHC and aromatase expression was assessed by quantitative PCR. Metabolic and inflammatory blood biomarkers that are predictive of breast cancer risk and progression were measured. B-WATi was present in 56 of 100 patients and was associated with older age, elevated BMI, postmenopausal status, decreased exercise, hypertension and dyslipidemia (Ps < 0.001). Total body fat and trunk fat correlated with B-WATi and breast aromatase levels (Ps < 0.001). Circulating C-reactive protein, IL6, insulin, and leptin positively correlated with body fat and breast aromatase levels, while negative correlations were observed for adiponectin and sex hormone binding globulin (P < 0.001). Inverse relationships were observed with exercise (Ps < 0.05). In a subgroup of 39 women with normal BMI, body fat levels positively correlated with B-WATi and aromatase expression (Ps < 0.05). In conclusion, elevated body fat levels and decreased exercise are associated with protumorigenic micro- and host environments in normal, overweight, and obese individuals. These findings support the development of BMI-agnostic lifestyle interventions that target adiposity. PREVENTION RELEVANCE: We report that individuals with high body fat and low exercise levels have breast inflammation, higher breast aromatase expression, and levels of circulating metabo-inflammatory factors that have been associated with increased breast cancer risk. These findings support interventions to lower adiposity, even among normal weight individuals, to prevent tumor growth.

Targeting SIRT1 to inhibit the proliferation of multiple myeloma cells

Multiple myeloma (MM) is the second most common hematopoietic malignancy and remains an incurable disease. Thus, novel drugs and therapeutic methods are required for patients with MM. The present study aimed to investigate the effect of sirtuin 1 (SIRT1) inhibitor cambinol on the proliferation and apoptosis of myeloma cell lines, RPMI8226 and U266. Moreover, the present study evaluated the underlying molecular mechanisms of proliferation inhibition and apoptosis induced by cambinol. A Cell Counting Kit-8 assay was used to measure the viability of RPMI8226 and U266 cells treated with cambinol. Apoptosis and the cell cycle were analyzed via flow cytometry. The expression levels of caspase-3, poly(ADP-ribose) polymerase 1 (PARP), p53, acetylated p53 (Ac-p53), Bcl-2, cyclin D1 and p21 were detected in cells treated with cambinol using western blot analysis. The results demonstrated that cambinol inhibited the proliferation of RPMI8226 and U266 cells in a time- and dose-dependent manner. Increased apoptosis and G₁ cell cycle arrest, together with enhanced procaspase-3 degradation and PARP cleavage were identified in cambinol-treated cells compared with controls. Western blotting results also revealed the upregulation of p53 acetylation and p21, as well as the downregulation of Bcl-2 and cyclin D1 in cells treated with cambinol. In conclusion, the present results suggest that cambinol inhibits the proliferation and induces apoptosis in RPMI8226 and U266 cells by regulating acetylation of p53 via the targeting of SIRT1.

Regulation of aromatase in cancer

The regulation of aromatase, an enzyme involved in the biosynthesis of estrogen in normal and cancer cells, has been associated with growth factor signaling and immune response modulation. The tissue-specific regulatory roles of these factors are of particular importance as local aromatase expression is strongly linked to cancer development/progression and disease outcomes in patients. Therefore, aromatase has become a chemotherapeutic target and aromatase inhibitors (AIs) are used in the clinic for treating hormone-dependent cancers. Although AIs have shown promising results in the treatment of cancers, the emerging increase in AI-resistance necessitates the development of new and improved targeted therapies. This review discusses the role of tumor and stromal-derived growth factors and immune cell modulators in regulating aromatase. Current single-agent and combination therapies with or without AIs targeting growth factors and immune checkpoints are also discussed. This review highlights recent studies that show new connections between growth factors, mediators of immune response, and aromatase regulation.

Sirtuins-The New Important Players in Women's Gynecological Health

The participation of sirtuins in the regulation of oxidative stress and inflammation lies at the basis of their possible modes of action and is related to their expression in various cell structures; their location in the mitochondria and blood plasma has been indicated as of primary importance. Despite many existing studies, research on sirtuins continues to present an opportunity to discover new functions and dependencies, especially when it comes to women's gynecological health. Sirtuins have a significant role in both the formation and the course of many gynecological diseases. Their role is particularly important and well documented in the course of the development of cancer within the female reproductive organs; however, disturbances observed in the ovary and oocyte as well as in follicular fluid are also widely investigated. Additionally, sirtuins take part in some gynecological disturbances as regulative factors in pathways associated with insulin resistance, glucose and lipids metabolism disorders. In this review, we would like to summarize the existing knowledge about sirtuins in the manner outlined above.

Sirtuins as Important Factors in Pathological States and the Role of Their Molecular Activity Modulators

Sirtuins (SIRTs), enzymes from the family of NAD⁺-dependent histone deacetylases, play an important role in the functioning of the body at the cellular level and participate in many biochemical processes. The multi-directionality of SIRTs encourages scientists to undertake research aimed at understanding the mechanisms of their action and the influence that SIRTs have on the organism. At the same time, new substances are constantly being sought that can modulate the action of SIRTs. Extensive research on the expression of SIRTs in various pathological conditions suggests that regulation of their activity may have positive results in supporting the treatment of certain metabolic, neurodegenerative or cancer diseases or this connected with oxidative stress. Due to such a wide spectrum of activity, SIRTs may also be a prognostic markers of selected pathological conditions and prove helpful in assessing their progression, especially by modulating their activity. The article presents and discusses the activating or inhibiting impact of individual SIRTs modulators. The review also gathered selected currently available information on the expression of SIRTs in individual disease cases as well as the biological role that SIRTs play in the human organism, also in connection with oxidative stress condition, taking into account the progress of knowledge about SIRTs over the years, with particular reference to the latest research results.

Influence of CYP19A1 gene expression levels in women with breast cancer: a systematic review of the literature

Breast cancer is the most frequently diagnosed malignant neoplasm in women and is considered a multifactorial disease of unknown etiology. One of the major risk factors is genetic alteration. Changes in CYP19A1 gene expression levels have been associated with increased risk and increased aggressiveness of breast cancer. Increased CYP19A1 gene expression and/or aromatase activity are among the major regulatory events for intratumoral production of estrogens in breast malignant tissues. This systematic review aimed to investigate the influence of CYP19A1 gene expression levels in women with breast cancer. The research was carried out using the PubMed, Scopus, and Web of Science databases. Searches were conducted between February 2 and May 15, 2019. Inclusion criteria were studies published between 2009 and 2019, English language publications, and human studies addressing the gene expression of CYP19A1 in breast cancer. A total of 6.068 studies were identified through PubMed (n=773), Scopus (n=2,927), and the Web of Science (n=2,368). After selecting and applying the inclusion and exclusion criteria, six articles were included in this systematic review. This systematic review provides evidence that increased or decreased levels of CYP19A1 gene expression may be related to pathological clinical factors of disease, MFS, OS, DFS, WATi, markers of metabolic function, concentrations of E1, FSH, and in the use of multiple exons 1 of the CYP19A1 gene in breast cancer.

Identification of Novel MeCP2 Cancer-Associated Target Genes and Post-Translational Modifications

Abnormal regulation of DNA methylation and its readers has been associated with a wide range of cellular dysfunction. Disruption of the normal function of DNA methylation readers contributes to cancer progression, neurodevelopmental disorders, autoimmune disease and other pathologies. One reader of DNA methylation known to be especially important is MeCP2. It acts a bridge and connects DNA methylation with histone modifications and regulates many gene targets contributing to various diseases; however, much remains unknown about how it contributes to cancer malignancy. We and others previously described novel MeCP2 post-translational regulation. We set out to test the hypothesis that MeCP2 would regulate novel genes linked with tumorigenesis and that MeCP2 is subject to additional post-translational regulation not previously identified. Herein we report novel genes bound and regulated by MeCP2 through MeCP2 ChIP-seq and RNA-seq analyses in two breast cancer cell lines representing different breast cancer subtypes. Through genomics analyses, we localize MeCP2 to novel gene targets and further define the full range of gene targets within breast cancer cell lines. We also further examine the scope of clinical and pre-clinical lysine deacetylase inhibitors (KDACi) that regulate MeCP2 post-translationally. Through proteomics analyses, we identify many additional novel acetylation sites, nine of which are mutated in Rett Syndrome. Our study provides important new insight into downstream targets of MeCP2 and provide the first comprehensive map of novel sites of acetylation associated with both pre-clinical and FDA-approved KDACi used in the clinic. This report examines a critical reader of DNA methylation and has important implications for understanding MeCP2 regulation in cancer models and identifying novel molecular targets associated with epigenetic therapies.

The Versatility of Sirtuin-1 in Endocrinology and Immunology

Sirtuins belong to the class III family of NAD-dependent histone deacetylases (HDAC) and are involved in diverse physiological processes that range from regulation of metabolism and endocrine function to coordination of immunity and cellular responses to stress. Sirtuin-1 (SIRT1) is the most well-studied family member and has been shown to be critically involved in epigenetics, immunology, and endocrinology. The versatile roles of SIRT1 include regulation of energy sensing metabolic homeostasis, deacetylation of histone and non-histone proteins in numerous tissues, neuro-endocrine regulation via stimulation of hypothalamus-pituitary axes, synthesis and maintenance of reproductive hormones via steroidogenesis, maintenance of innate and adaptive immune system via regulation of T- and B-cell maturation, chronic inflammation and autoimmune diseases. Moreover, SIRT1 is an appealing target in various disease contexts due to the promise of pharmacological and/or natural modulators of SIRT1 activity within the context of endocrine and immune-related disease models. In this review we aim to provide a broad overview on the role of SIRT1 particularly within the context of endocrinology and immunology.

Natural Products as Modulators of Sirtuins

Natural products have been used for the treatment of human diseases since ancient history. Over time, due to the lack of precise tools and techniques for the separation, purification, and structural elucidation of active constituents in natural resources there has been a decline in financial support and efforts in characterization of natural products. Advances in the design of chemical compounds and the understanding of their functions is of pharmacological importance for the biomedical field. However, natural products regained attention as sources of novel drug candidates upon recent developments and progress in technology. Natural compounds were shown to bear an inherent ability to bind to biomacromolecules and cover an unparalleled chemical space in comparison to most libraries used for high-throughput screening. Thus, natural products hold a great potential for the drug discovery of new scaffolds for therapeutic targets such as sirtuins. Sirtuins are Class III histone deacetylases that have been linked to many diseases such as Parkinson`s disease, Alzheimer’s disease, type II diabetes, and cancer linked to aging. In this review, we examine the revitalization of interest in natural products for drug discovery and discuss natural product modulators of sirtuins that could serve as a starting point for the development of isoform selective and highly potent drug-like compounds, as well as the potential application of naturally occurring sirtuin inhibitors in human health and those in clinical trials.

Emerging role of sirtuins in breast cancer metastasis and multidrug resistance: Implication for novel therapeutic strategies targeting sirtuins

Sirtuins (SIRTs), a class III histone deacetylases (HDACs) that require NAD⁺ as a cofactor and include SIRT1-7 proteins in mammals. Accumulative evidence has established that every sirtuin possesses exclusive and poised biology, implicating their role in the regulation of multifaceted biological functions leading to breast cancer initiation, progression, and metastasis. This article provides an outline of recent developments in the role of sirtuins in breast cancer metastasis and development of multidrug resistance (MDR). In addition, we have also highlighted the impending prospects of targeting SIRTs to overcome MDR to bring advancement in breast cancer management. Further, this review will focus on strategies for improving the activity and efficacy of existing cancer therapeutics by combining (adjuvant treatment/therapy) them with sirtuin inhibitors/modulators. All available as well as newly discovered synthetic and dietary sirtuin inhibitors, activators/modulators have been extensively reviewed and compiled to provide a rationale for targeting sirtuins. Further, we discuss their potential in developing future therapeutics against sirtuins proposing their use along with conventional chemotherapeutics to overcome the problem of breast cancer metastasis and MDR.

SIRT1: a potential tumour biomarker and therapeutic target

SIRT1, which is highly homologous to yeast silent information regulator 2, has recently garnered tremendous attention because of its various regulatory effects in several pathological conditions. Numerous studies have found that SIRT1 is highly expressed in a broad range of tumours compared with the paracancerous tissue. However, the role of SIRT1 in malignancies has yet to be systematically elucidated, and its use as a promising biomarker or therapeutic target for tumours has not been well-reported. Herein, we focus on the roles of SIRT1 in cancers and summarise the potential use of SIRT1 as a promising tumour biomarker or therapeutic target.

The effect of adipocyte-macrophage crosstalk in obesity-related breast cancer

Adipose tissue is the primary source of many pro-inflammatory cytokines in obesity. Macrophage numbers and pro-inflammatory gene expression are positively associated with adipocyte size. Free fatty acid and tumor necrosis factor-α involve in a vicious cycle between adipocytes and macrophages aggravating inflammatory changes. Thereby, M1 macrophages form a characteristic 'crown-like structure (CLS)' around necrotic adipocytes in obese adipose tissue. In obese women, CLSs of breast adipose tissue are responsible for both increase in local aromatase activity and aggressive behavior of breast cancer cells. Interlinked molecular mechanisms between adipocyte-macrophage-breast cancer cells in obesity involve seven consecutive processes: Excessive release of adipocyte- and macrophage-derived inflammatory cytokines, TSC1-TSC2 complex-mTOR crosstalk, insulin resistance, endoplasmic reticulum (ER) stress and excessive oxidative stress generation, uncoupled respiration and hypoxia, SIRT1 controversy, the increased levels of aromatase activity and estrogen production. Considering elevated risks of estrogen receptor (E2R)-positive postmenopausal breast cancer growth in obesity, adipocyte-macrophage crosstalk is important in the aforementioned issues. Increased mTORC1 signaling in obesity ensures the strong activation of oncogenic signaling in E2Rα-positive breast cancer cells. Since insulin and insulin-like growth factors have been identified as tumor promoters, hyperinsulinemia is an independent risk factor for poor prognosis in breast cancer despite peripheral insulin resistance. The unpredictable effects of adipocyte-derived leptin-estrogen-macrophage axis, and sirtuin 1 (SIRT1)-adipose-resident macrophage axis in obese postmenopausal patients with breast cancer are unresolved mechanistic gaps in the molecular links between the tumor growth and adipocytokines.

Noscapine Inhibiting the Growth and Angiogenesis of Human Eutopic Endometrium of Endometriosis Patients through Expression of Apoptotic Genes and Nitric Oxide Reduction in Three-Dimensional Culture Model

Noscapine is a natural alkaloid with anti-angiogenesis activities. The aim of the present study was to examine the effect of noscapine on eutopic endometrium of endometriosis patients (EEE) and normal endometrium (NE) in a three-dimensional (3D) culture model. In this experimental in-vitro study, EEE (n = 8) and NE (n = 8) biopsies were taken from 16 reproductive aged women. The biopsies were cleared from blood and mucus. Each biopsy was cut into small fragments (1 × 1 mm) in a sterile condition. For 3D culture, the endometrial fragments were put between two layers of fibrin jell made of fibrinogen solution [3 mg/mL in Medium199 (M199) + thrombin]. Twenty-four wells of culture dish was divided into 5 groups for each biopsy: the control wells were treated with M199 containing 5% fetal bovine serum (FBS) while, the test wells were exposed to the same media containing one of the noscapine doses (10, 50, 100, and 200 μM). The expression of apoptotic genes, growth score, angiogenesis, and nitric oxide (NO) secretion were evaluated. The mean of growth score of groups exposed to 0, 10, 50, 100, and 200 μM were 2.2 ± 0.55, 1.7 ± 0.45, 1.44 ± 0.27, 0.29 ± 0.1, and 0.1 ± 0.08 in EEE, and also, 2.11 ± 0.6, 1.65 ± 0.5, 0.79 ± 0.41, 0.18 ± 0.1, and 0.1 ± 0.1 in NE, respectively, and the difference between the groups was significant (P < 0.05). The expression of apoptotic genes significantly increased while, the levels of Bcl-2 and Sirt1 reduced (P = 0.004). NO secretion reduced significantly (P < 0.05) in both EEE and NE groups. In conclusion, higher doses of noscapine showed inhibitory effect on growth and angiogenesis of EEE and NE.

Overexpression of the steroidogenic acute regulatory protein in breast cancer: Regulation by histone deacetylase inhibition

Dysregulation of steroid biosynthesis has been implicated in the pathophysiology of a variety of cancers. One such common malignancy in women is breast cancer that is frequently promoted by estrogen overproduction. All steroid hormones are made from cholesterol, and the rate-limiting step in steroid biosynthesis is primarily mediated by the steroidogenic acute regulatory (StAR) protein. Whereas the involvement of StAR in the regulation steroid hormone biosynthesis is well established, its association to breast cancer remains obscure. Herein, we report that estrogen receptor positive breast cancer cell lines (MCF7, MDA-MB-361, and T-47D) displayed aberrant high expression of the StAR protein, concomitant with 17β-estradiol (E2) synthesis, when compared their levels with normal mammary epithelial (MCF10A and MCF12F) and triple negative breast cancer (MDA-MB-468, MDA-MB-231, and BT-549) cells. StAR was identified as a novel acetylated protein in MCF7 cells, in which liquid chromatography-tandem mass spectrometry analysis identified seven StAR acetyl lysine residues under basal and in response to histone deacetylase (HDAC) inhibition. A number of HDAC inhibitors were capable of diminishing StAR expression and E2 synthesis in MCF7 cells. The validity of StAR protein acetylation and its correlation to HDAC inhibition mediated steroid synthesis was demonstrated in adrenocortical tumor H295R cells. These findings provide novel insights that StAR protein is abundantly expressed in the most prevalent hormone sensitive breast cancer subtype, wherein inhibition of HDACs altered StAR acetylation patterns and decreased E2 levels, which may have important therapeutic implications in the prevention and treatment of this devastating disease.

Prostaglandin E2 down-regulates sirtuin 1 (SIRT1), leading to elevated levels of aromatase, providing insights into the obesity-breast cancer connection

Obesity increases the risk of hormone receptor-positive breast cancer in postmenopausal women. Levels of aromatase, the rate-limiting enzyme in estrogen biosynthesis, are increased in the breast tissue of obese women. Both prostaglandin E₂ (PGE₂) and hypoxia-inducible factor 1α (HIF-1α) contribute to the induction of aromatase in adipose stromal cells (ASCs). Sirtuin 1 (SIRT1) binds, deacetylates, and thereby inactivates HIF-1α. Here, we sought to determine whether SIRT1 also plays a role in regulating aromatase expression. We demonstrate that reduced SIRT1 levels are associated with elevated levels of acetyl-HIF-1α, HIF-1α, and aromatase in breast tissue of obese compared with lean women. To determine whether these changes were functionally linked, ASCs were utilized. In ASCs, treatment with PGE₂, which is increased in obese individuals, down-regulated SIRT1 levels, leading to elevated acetyl-HIF-1α and HIF-1α levels and enhanced aromatase gene transcription. Chemical SIRT1 activators (SIRT1720 and resveratrol) suppressed the PGE₂-mediated induction of acetyl-HIF-1α, HIF-1α, and aromatase. Silencing of p300/CBP-associated factor (PCAF), which acetylates HIF-1α, blocked PGE₂-mediated increases in acetyl-HIF-1α, HIF-1α, and aromatase. SIRT1 overexpression or PCAF silencing inhibited the interaction between HIF-1α and p300, a coactivator of aromatase expression, and suppressed p300 binding to the aromatase promoter. PGE₂ acted via prostaglandin E2 receptor 2 (EP₂) and EP₄ to induce activating transcription factor 3 (ATF3), a repressive transcription factor, which bound to a CREB site within the SIRT1 promoter and reduced SIRT1 levels. These findings suggest that reduced SIRT1-mediated deacetylation of HIF-1α contributes to the elevated levels of aromatase in breast tissues of obese women.

DVL1 and DVL3 differentially localize to CYP19A1 promoters and regulate aromatase mRNA in breast cancer cells

The CYP19A1 gene encodes aromatase, an enzyme that converts androgens into estrogens and consequently directly contributes to both the depletion of androgens and the synthesis of estrogens in several organs. Aromatase is critical for diverse biological processes such as proliferation, regulation of fat metabolism and hormone signaling. Additionally, it is also overexpressed in diverse cancers and drives hormone-dependent tumor progression and increases 17-β-estradiol (E₂) within tumors and the tumor microenvironment. Although the inhibition of E₂ production via aromatase inhibitors represents a major therapeutic paradigm in clinical oncology, fundamental questions regarding how cancer cells gain the capacity to overexpress aromatase remain unanswered. Multiple tissue-specific CYP19A1 promoters are known to be aberrantly active in tumors, yet how this occurs is unclear. Here, for the first time, we report that Dishevelled (DVL) proteins, which are key mediators of Wnt signaling, regulate aromatase expression in multiple breast cancer cell lines. We also report that DVL enters the nucleus and localizes to at least two different CYP19A1 promoters (pII and I.4) previously reported to drive overexpression in breast tumors and to a very distal CYP19A1 placental promoter (I.1) that remains poorly characterized. We go on to demonstrate that DVL-1 and DVL-3 loss of function leads to differential changes in various aromatase transcripts and in E₂ production. The report, herein, uncovers a new regulator of CYP19A1 transcription and for the first time demonstrates that DVL, a critical mediator of WNT signaling, contributes to aberrant breast cancer-associated estrogen production.

Aromatase Acetylation Patterns and Altered Activity in Response to Sirtuin Inhibition

Aromatase, a cytochrome P450 member, is a key enzyme involved in estrogen biosynthesis and is dysregulated in the majority of breast cancers. Studies have shown that lysine deacetylase inhibitors (KDI) decrease aromatase expression in cancer cells, yet many unknowns remain regarding the mechanism by which this occurs. However, advances have been made to clarify factors involved in the transcriptional regulation of the aromatase gene (CYP19A1). Yet, despite aromatase being a primary target for breast cancer therapy, its posttranslational regulation has been virtually unexplored. Acetylation is a posttranslational modification (PTM) known to alter the activity and stability of many oncoproteins, and given the role of KDIs in regulating aromatase expression, we postulate that aromatase acetylation acts as a novel posttranslational regulatory mechanism that impacts aromatase expression and/or activity in breast cancer. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis revealed that aromatase is basally acetylated on several lysine residues (108, 169, 242, 262, 334, 352, and 354) in MCF-7 cells, and treatment with a SIRT-1 inhibitor induced additional acetylation (376, 390, 440, and 448). These acetylated lysine residues are in regions critical for aromatase activity. Site-directed mutagenesis and overexpression studies demonstrated that K108R/Q or K440R/Q mutations significantly altered aromatase activity in breast cancer cells without altering its subcellular localization.Implications: These findings demonstrate a novel posttranslational regulation of aromatase and uncover novel anticancer effects of deacetylase inhibitors, thus providing new insight for ongoing development of deacetylase inhibitors as cancer therapeutics. Mol Cancer Res; 16(10); 1530-42. ©2018 AACR.

SIRT7 depletion inhibits cell proliferation, migration, and increases drug sensitivity by activating p38MAPK in breast cancer cells

SIRT7 is a member of the sirtuin family of proteins that are known to be associated with tumor development. However, the functional roles and molecular mechanisms underlying the function of SIRT7 in breast cancer cell survival and tumor development remain unclear. Recent studies demonstrated that SIRT7 is upregulated in breast cancer cells and tissues. In the present study, we systematically explored the roles of SIRT7 in the growth of breast cancer cells and tumors both in vitro and in vivo. Our results showed that SIRT7 plays a major role in facilitating cell survival by promoting cell proliferation and inhibiting apoptosis. SIRT7 depletion significantly inhibited cell invasion and wound healing by blocking cell cycle progression and inducing cell apoptosis. Meanwhile, SIRT7 depletion can increase the sensitivity of breast cancer cells to doxorubicin (DOX). Xenograft model studies showed that stable silencing of SIRT7 inhibited tumor growth and enhanced tumor sensitivity to DOX. Further research revealed that p38MAPK is involved in SIRT7-mediated regulation of breast cancer cell proliferation and tumor growth. Taken together, our results showed that SIRT7 plays a critical role in breast cancer cell survival, migration, and tumor growth, and increased the efficiency of DOX treatment both in vitro and in vivo. Therefore, SIRT7 is a promising therapeutic target in breast cancer treatment.

SIRT1 and Estrogen Signaling Cooperation for Breast Cancer Onset and Progression

Breast cancer remains a significant female mortality cause. It constitutes a multifactorial disease for which research on environmental factors offers little help in predicting onset or progression. The pursuit for its foundations by analyzing hormonal changes as a motive for disease development, indicates that increased exposure to estrogens associates with increased risk. A prevalent number of breast cancer cases show dependence on the increased activity of the classic nuclear estrogen receptor (ER) for cell proliferation and survival. SIRT1 is a Type III histone deacetylase which is receiving increasing attention due to its ability to perform activities over relevant non-histone proteins and transcription factors. Interestingly, concomitant SIRT1 overexpression is commonly found in ER-positive breast cancer cases. Both proteins had been shown to directly interact, in a process related to altered intracellular signaling and aberrant transcription, then promoting tumor progression. Moreover, SIRT1 activities had been also linked to estrogenic effects through interaction with the G-protein coupled membrane bound estrogen receptor (GPER). This work aims to summarize present knowledge on the interplay between SIRT1 and ER/GPER for breast cancer onset and progression. Lastly, evidences on the ability of SIRT1 to interact with TGFß signaling, a concurrent pathway significantly involved in breast cancer progression, are reported. The potential of this research field for the development of innovative strategies in the assessment of orphan breast cancer subtypes, such as triple negative breast cancer (TNBC), is discussed.

Dysregulation of Aromatase in Breast, Endometrial, and Ovarian Cancers: An Overview of Therapeutic Strategies

Aromatase is the rate-limiting enzyme in the biosynthesis of estrogens, which play crucial roles on a spectrum of developmental and physiological processes. The biological actions of estrogens are classically mediated by binding to two estrogen receptors (ERs), ERα and ERβ. Encoded by the cytochrome P450, family 19, subfamily A, polypeptide 1 (CYP19A1) gene, aromatase is expressed in a wide variety of tissues, as well as benign and malignant tumors, and is regulated in a pathway- and tissue-specific manner. Overexpression of aromatase, leading to elevated systemic levels of estrogen, is unequivocally linked to the pathogenesis and growth of a number malignancies, including breast, endometrium, and ovarian cancers. Aromatase inhibitors (AIs) are routinely used to treat estrogen-dependent breast cancers in postmenopausal women; however, their roles in endometrial and ovarian cancers remain obscure. While AI therapy is effective in hormone sensitive cancers, they diminish estrogen production throughout the body and, thus, generate undesirable side effects. Despite the effectiveness of AI therapy, resistance to endocrine therapy remains a major concern and is the leading cause of cancer death. Considerable advances, toward mitigating these issues, have evolved in conjunction with a number of histone deacetylase (HDAC) inhibitors for countering an assortment of diseases and cancers, including the aforesaid malignancies. HDACs are a family of enzymes that are frequently dysregulated in human tumors. This chapter will discuss the current understanding of aberrant regulation and expression of aromatase in breast, endometrial, and ovarian cancers, and potential therapeutic strategies for prevention and treatment of these life-threatening diseases.

Molecular and Cellular Changes During Cancer Progression Resulting From Genetic and Epigenetic Alterations

Tumorigenesis is a complex process that involves a persistent dismantling of cellular safeguards and checkpoints. These molecular and cellular changes that accumulate over months or decades lead to a change in the fundamental identity of a cell as it transitions from normal to malignant. In this chapter, we will examine some of the molecular changes in the evolving relationship between the genome and epigenome and highlight some of the key changes that occur as normal cells progress to tumor cells. For many years tumorigenesis was almost exclusively attributed to mutations in protein-coding genes. This notion that mutations in protein-coding genes were a fundamental driver of tumorigenesis enabled the development of several novel therapeutics that targeted the mutant protein or overactive pathway responsible for driving a significant portion of the tumor growth. However, because many therapeutic challenges remained in the face of these advances, it was clear that other pieces to the puzzle had yet to be discovered. Advances in molecular and genomics techniques continued and the study of epigenetics began to expand and helped reshape the view that drivers of tumorigenesis extended beyond mutations in protein-coding genes. Studies in the field of epigenetics began to identify aberrant epigenetic marks which created altered chromatin structures and enabled protein expression in tissues that defied rules governing tissue-specificity. Not only were epigenetic alterations found to enable overexpression of proto-oncogenes, they also led to the silencing of tumor suppressor genes. With these discoveries, it became clear that tumor growth could be stimulated by much more than mutations in protein-coding genes. In fact, it became increasingly clear that much of the human genome, while transcribed, did not lead to proteins. This discovery further led to studies that began to uncover the role of noncoding RNAs in regulating chromatin structure, gene transcription, and tumor biology. In this chapter, some of the key alterations in the genome and epigenome will be explored, and some of the cancer therapies that were developed as a result of these discoveries will be discussed.

Effects of BMAL1-SIRT1-positive cycle on estrogen synthesis in human ovarian granulosa cells: an implicative role of BMAL1 in PCOS

Brain and muscle ARNT-like protein 1 (BMAL1) is necessary for fertility and has been found to be essential to follicle growth and steroidogenesis. Sirtuin1 (SIRT1) has been reported to interact with BMAL1 and function in a circadian manner. Evidence has shown that SIRT1 regulates aromatase expression in estrogen-producing cells. We aimed to ascertain if there is a relationship between polycystic ovary syndrome (PCOS) and BMAL1, and whether and how BMAL1 takes part in estrogen synthesis in human granulosa cells (hGCs). Twenty-four women diagnosed with PCOS and 24 healthy individuals undergoing assisted reproduction were studied. BMAL1 expression in their granulosa cells (GCs) was observed by quantitative real-time polymerase chain reaction (qRT-PCR). The level of expression in the PCOS group was lower than that of the group without PCOS (p < 0.05). We also analyzed estrogen synthesis and aromatase expression in KGN cell lines. Both were downregulated after BMAL1 and SIRT1 knock-down and, conversely, upregulated after overexpression treatments of these two genes in KGN cells. Both BMAL1 and SIRT1 had a mutually positive regulation, as did the phosphorylation of JNK. Furthermore, JNK overexpression increased estrogen synthesis activity and the expression levels of aromatase, BMAL1, and SIRT1. In KGN and hGCs, estrogen synthesis and aromatase expression were downregulated after treatment with JNK and SIRT1 inhibitors. In addition, BMAL1, SIRT1, and JNK expression levels were all downregulated. Our results demonstrate the effects of BMAL1 on estrogen synthesis in hGCs and suggest a BMAL1-SIRT1-JNK positive feedback cycle in this process, which points out an important role of BMAL1 in the development of PCOS.

High-throughput screening of Sirtuin family of genes in breast cancer

Mammalian Sirtuins have been shown to perform distinct cellular functions and deregulated expression of these genes was reported to be involved in the development of various malignancies including breast cancer. An increasing number of evidence indicates that Sirtuins have both tumor promoter and tumor suppressor functions. However, the roles of Sirtuins have not been well-reported in breast cancer. In the present study, quantitative expression levels of Sirtuins (SIRT1-7) in breast cancer patients and breast cancer cell lines (MCF-7 and SKBR3) and control cell line (CRL-4010) were assessed by using a high-throughput real-time PCR method. As a result, Sirtuins were found to be differentially expressed in breast cancer tissues and cancer cell lines. Particularly, expressions of SIRT1 and SIRT4 were found to be significantly down-regulated in breast cancer tissues and SKBR3 breast cancer cells. In contrast, SIRT2, SIRT3, and SIRT5 genes were shown to be up-regulated in our study. Although SIRT6 and SIRT7 were also up-regulated in breast cancer tissues, these expression changes were statistically insignificant. Additionally, SIRT2, SIRT3, SIRT5, SIRT6 and SIRT7 were found to be differentially expressed in breast cancer cell lines. Yet, these changes were not well-correlated with tissue expression levels. In conclusion, Sirtuin family of genes shows differential expressions in breast cancer tissues and cells and SIRT1 and SIRT4 seem to play key tumor suppressor roles in breast cancer development. Herein, we report expression levels of Sirtuin family of genes in both breast cancer tissues and cancer cell lines simultaneously.

Role of the steroidogenic acute regulatory protein in health and disease

Steroid hormones are an important class of regulatory molecules that are synthesized in steroidogenic cells of the adrenal, ovary, testis, placenta, brain, and skin, and influence a spectrum of developmental and physiological processes. The steroidogenic acute regulatory protein (STAR) predominantly mediates the rate-limiting step in steroid biosynthesis, i.e., the transport of the substrate of all steroid hormones, cholesterol, from the outer to the inner mitochondrial membrane. At the inner membrane, cytochrome P450 cholesterol side chain cleavage enzyme cleaves the cholesterol side chain to form the first steroid, pregnenolone, which is converted by a series of enzymes to various steroid hormones in specific tissues. Both basic and clinical evidence have demonstrated the crucial involvement of the STAR protein in the regulation of steroid biosynthesis. Multiple levels of regulation impinge on STAR action. Recent findings demonstrate that hormone-sensitive lipase, through its action on the hydrolysis of cholesteryl esters, plays an important role in regulating STAR expression and steroidogenesis which involve the liver X receptor pathway. Activation of the latter influences macrophage cholesterol efflux that is a key process in the prevention of atherosclerotic cardiovascular disease. Appropriate regulation of steroid hormones is vital for proper functioning of many important biological activities, which are also paramount for geriatric populations to live longer and healthier. This review summarizes the current level of understanding on tissue-specific and hormone-induced regulation of STAR expression and steroidogenesis, and provides insights into a number of cholesterol and/or steroid coupled physiological and pathophysiological consequences.

A novel MeCP2 acetylation site regulates interaction with ATRX and HDAC1

Methyl-CpG-binding protein-2 (MeCP2) regulates gene expression by recruiting SWI/SNF DNA helicase/ATPase (ATRX) and Histone Deacetylase-1 (HDAC1) to methylated gene regions and modulates heterochromatin association by interacting with Heterochromatin protein-1. As MeCP2 contributes to tumor suppressor gene silencing and its mutation causes Rett Syndrome, we investigated how novel post-translational-modification contributes to its function. Herein we report that upon pharmacological inhibition of SIRT1 in RKO colon and MCF-7 breast cancer cells, endogenous MeCP2 is acetylated at sites critical for binding to DNA and transcriptional regulators. We created an acetylation mimetic mutation in MeCP2 and found it to possess decreased binding to ATRX and HDAC1. Conditions inducing MeCP2 acetylation do not alter its promoter occupancy at a subset of target genes analyzed, but do cause decreased binding to ATRX and HDAC1. We also report here that a specific inhibitor of SIRT1, IV, can be used to selectively decrease H3K27me3 repressive marks on a subset of repressed target gene promoters analyzed. Lastly, we show that RKO cells over-expressing MeCP2 mutant show reduced proliferation compared to those over-expressing MeCP2-wildtype. Our study demonstrates the importance of acetylated lysine residues and suggests their key role in regulating MeCP2 function and its ability to bind transcriptional regulators.

Transcriptomic characterization of fibrolamellar hepatocellular carcinoma

Fibrolamellar hepatocellular carcinoma (FLHCC) tumors all carry a deletion of ∼ 400 kb in chromosome 19, resulting in a fusion of the genes for the heat shock protein, DNAJ (Hsp40) homolog, subfamily B, member 1, DNAJB1, and the catalytic subunit of protein kinase A, PRKACA. The resulting chimeric transcript produces a fusion protein that retains kinase activity. No other recurrent genomic alterations have been identified. Here we characterize the molecular pathogenesis of FLHCC with transcriptome sequencing (RNA sequencing). Differential expression (tumor vs. adjacent normal tissue) was detected for more than 3,500 genes (log2 fold change ≥ 1, false discovery rate ≤ 0.01), many of which were distinct from those found in hepatocellular carcinoma. Expression of several known oncogenes, such as ErbB2 and Aurora Kinase A, was increased in tumor samples. These and other dysregulated genes may serve as potential targets for therapeutic intervention.

Expression of sirtuin 1 and 2 is associated with poor prognosis in non-small cell lung cancer patients

Background

Sirtuin 1 (SIRT1) and sirtuin 2 (SIRT2) are NAD+-dependent protein deacetylases involved in the regulation of key cancer-associated genes. In this study we evaluated the relevance of these deacetylases in lung cancer biology.

Material and Methods

Protein levels of SIRT1 and SIRT2 were determined in non-small cell lung cancer (NSCLC) cell lines and primary tumors from 105 patients. Changes in proliferation were assessed after SIRT1 and SIRT2 downregulation in lung cancer cell lines using siRNA-mediated technology or tenovin-1, a SIRT1 and SIRT2 inhibitor.

Results

High SIRT1 and SIRT2 protein levels were found in NSCLC cell lines compared with non-tumor lung epithelial cells. The expression of SIRT1 and SIRT2 proteins was also significantly higher in lung primary tumors than in normal tissue (P<0.001 for both sirtuins). Stronger nuclear SIRT1 staining was observed in adenocarcinomas than in squamous cell carcinomas (P=0.033). Interestingly, in NSCLC patients, high SIRT1 and SIRT2 expression levels were associated with shorter recurrence-free survival (P=0.04 and P=0.007, respectively). Moreover, the combination of high SIRT1 and SIRT2 expression was an independent prognostic factor for shorter recurrence-free survival (P=0.002) and overall survival (P=0.022). In vitro studies showed that SIRT1 and/or SIRT2 downregulation significantly decreased proliferation of NSCLC.

Conclusions

Our results support the hypothesis that SIRT1 and SIRT2 have a protumorigenic role in lung cancer, promoting cell proliferation. Moreover, the expression of these proteins is associated with poor prognosis in NSCLC patients and may help to identify those NSCLC patients with high risk of recurrence that could benefit from adjuvant therapy after resection.

Sirtuin inhibitors as anticancer agents

Sirtuins are a class of enzymes with nicotinamide adenine dinucleotide (NAD)-dependent protein lysine deacylase function. By deacylating various substrate proteins, including histones, transcription factors, and metabolic enzymes, sirtuins regulate various biological processes, such as transcription, cell survival, DNA damage and repair, and longevity. Small molecules that can inhibit sirtuins have been developed and many of them have shown anticancer activity. Here, we summarize the major biological findings that connect sirtuins to cancer and the different types of sirtuin inhibitors developed. Interestingly, biological data suggest that sirtuins have both tumor-suppressing and tumor-promoting roles. However, most pharmacological studies with small-molecule inhibitors suggest that inhibiting sirtuins has anticancer effects. We discuss possible explanations for this discrepancy and suggest possible future directions to further establish sirtuin inhibitors as anticancer agents.

Diverse roles of SIRT1 in cancer biology and lipid metabolism

SIRT1, an NAD⁺-dependent deacetylase, has been described in the literature as a major player in the regulation of cellular stress responses. Its expression has been shown to be altered in cancer cells, and it targets both histone and non-histone proteins for deacetylation and thereby alters metabolic programs in response to diverse physiological stress. Interestingly, many of the metabolic pathways that are influenced by SIRT1 are also altered in tumor development. Not only does SIRT1 have the potential to regulate oncogenic factors, it also orchestrates many aspects of metabolism and lipid regulation and recent reports are beginning to connect these areas. SIRT1 influences pathways that provide an alternative means of deriving energy (such as fatty acid oxidation and gluconeogenesis) when a cell encounters nutritive stress, and can therefore lead to altered lipid metabolism in various pathophysiological contexts. This review helps to show the various connections between SIRT1 and major pathways in cellular metabolism and the consequence of SIRT1 deregulation on carcinogenesis and lipid metabolism.

Transcriptional control of local estrogen formation by aromatase in the breast

Aromatase is the critical enzyme that converts androgens to estrogens. It is frequently highly expressed in the tumour bearing breast of women diagnosed with estrogen receptor positive tumours, resulting in dramatically increased local estrogen production to drive tumour progression. Expression of aromatase is regulated primarily at the transcriptional level of its encoding gene CYP19A1, located on chromosome 15 of the human genome. A characteristic feature of CYP19A1 expression is its use of alternative promoters to regulate transcription in a tissue-specific manner. In breast cancer, the increase in aromatase expression is mediated via higher expression of the distal adipose-specific promoter I.4 and a switch to the preferential use of proximal promoters I.3 and II. This results in a net increase of CYP19A1 transcripts in tumour-bearing breast up to 3-4-fold higher than normal breast. Current aromatase inhibitors - whilst efficacious - exhibit significant side effects that reduce patient compliance. Understanding the transcription factors and signalling pathways that control aromatase expression will lead to opportunities to develop breast-specific inhibitors with an improved side-effects profile. This article is part of a Special Issue entitled 'Essential role of DHEA'.

Frizzled 7 expression is positively regulated by SIRT1 and β-catenin in breast cancer cells

The Wnt signaling pathway is often chronically activated in diverse human tumors, and the Frizzled (FZD) family of receptors for Wnt ligands, are central to propagating oncogenic signals in a β-catenin-dependent and independent manner. SIRT1 is a class III histone deacetylase (HDAC) that deacetylates histone and non-histone proteins to regulate gene transcription and protein function. We previously demonstrated that SIRT1 loss of function led to a significant decrease in the levels of Dishevelled (Dvl) proteins. To further explore this connection between the sirtuins and components of the Wnt pathway, we analyzed sirtuin-mediated regulation of FZD proteins. Here we explore the contribution of sirtuin deacetylases in promoting constitutive Wnt pathway activation in breast cancer cells. We demonstrate that the use of small molecule inhibitors of SIRT1 and SIRT2, and siRNA specific to SIRT1, all reduce the levels of FZD7 mRNA. We further demonstrate that pharmacologic inhibition of SIRT1/2 causes a marked reduction in FZD7 protein levels. Additionally, we show that β-catenin and c-Jun occupy the 7 kb region upstream of the transcription start site of the FZD7 gene, and SIRT1 inhibition leads to a reduction in the occupancy of both β-catenin and c-Jun at points along this region. This work uncovers a new mechanism for the regulation of FZD7 and provides a critical new link between the sirtuins and FZD7, one of the earliest nodal points from which oncogenic Wnt signaling emanates. This study shows that inhibition of specific sirtuins may provide a unique strategy for inhibiting the constitutively active Wnt pathway at the level of the receptor.

Inhibition of SIRT1 signaling sensitizes the antitumor activity of silybin against human lung adenocarcinoma cells in vitro and in vivo

Although silybin, a natural flavonolignan, has been shown to exhibit potent antitumor activities against various types of cancers, including lung cancer, the molecular mechanisms behind these activities remain unclear. Silent information regulator 1 (SIRT1) is a conserved NAD(+)-dependent deacetylase that has been implicated in the modulation of transcriptional silencing and cell survival. Furthermore, it plays a key role in carcinogenesis through the deacetylation of important regulatory proteins, including p53. In this study, we investigated the antitumor activity of silybin towards human lung adenocarcinoma cells in vitro and in vivo and explored the role of the SIRT1 signaling pathway in this process. Silybin treatment resulted in a dose- and time-dependent decrease in lung adenocarcinoma A549 cell viability. In addition, silybin exhibited strong antitumor activity illustrated by reductions in tumor cell adhesion, migratory capability, and glutathione levels and by increased apoptotic indices and reactive oxygen species levels. Silybin treatment also downregulated SIRT1 and upregulated p53 acetylation. SIRT1 siRNA (in vitro) or cambinol (a known SIRT1 inhibitor used for in vivo studies) further enhanced the antitumor activity of silybin. In summary, silybin is a potent inhibitor of lung adenocarcinoma cell growth that interferes with SIRT1 signaling, and this inhibition is a novel mechanism of silybin action that may be used for therapeutic intervention in lung adenocarcinoma treatment.

The sirtuins promote Dishevelled-1 scaffolding of TIAM1, Rac activation and cell migration

Rac1-GTPases serve as intermediary cellular switches which conduct transient and constitutive signals from upstream cues, including those from Ras oncoproteins. While the sirtuin1 (SIRT1) deacetylase is overexpressed in several human cancers and has recently been linked to cancer cell motility as a context-dependent regulator of multiple pathways, its role in Rac1 activation has not been reported. Likewise, SIRT2 has been demonstrated to be upregulated in some cancers; however, studies have also reported its role in tumor suppression. Here, we demonstrate that SIRT1 and SIRT2 positively regulate the levels of Rac1-GTP and the activity of T-cell lymphoma invasion and metastasis 1 (TIAM1), a Rac guanine nucleotide exchange factor (GEF). Transient inhibition of SIRT1 and SIRT2 resulted in increased acetylation of TIAM1 whereas chronic SIRT2 knockdown resulted in enhanced acetylation of TIAM1. SIRT1 regulates Dishevelled (DVL) protein levels in cancer cells and DVL along with TIAM1 are known to augment Rac activation; however, SIRT1 or 2 have not been previously linked with TIAM1. We found that diminished sirtuin activity led to the disruption of the DVL1-TIAM1 interaction. We hence propose a model for Rac activation where SIRT1/2 positively modulate the DVL/TIAM1/Rac axis and promote sustained pathway activation.

Elevated microRNA-34a in obesity reduces NAD+ levels and SIRT1 activity by directly targeting NAMPT

SIRT1 is an NAD(+)-dependent deacetylase that is implicated in prevention of many age-related diseases including metabolic disorders. As SIRT1 deacetylase activity is dependent on NAD(+) levels and the development of compounds that directly activate SIRT1 has been controversial, indirectly activating SIRT1 through enhancing NAD(+) bioavailability has received increasing attention. NAD(+) levels are reduced in obesity and the aged, but the underlying mechanisms remain unclear. We recently showed that hepatic microRNA-34a (miR-34a), which is elevated in obesity, directly targets and decreases SIRT1 expression. Here, we further show that miR-34a reduces NAD(+) levels and SIRT1 activity by targeting NAMPT, the rate-limiting enzyme for NAD(+) biosynthesis. A functional binding site for miR-34a is present in the 3' UTR of NAMPT mRNA. Hepatic overexpression of miR-34a reduced NAMPT/NAD(+) levels, increased acetylation of the SIRT1 target transcriptional regulators, PGC-1α, SREBP-1c, FXR, and NF-κB, and resulted in obesity-mimetic outcomes. The decreased NAMPT/NAD(+) levels were independent of miR-34a effects on SIRT1 levels as they were also observed in SIRT1 liver-specific knockout mice. Further, the miR-34a-mediated decreases were reversed by treatment with the NAD(+) intermediate, nicotinamide mononucleotide. Conversely, antagonism of miR-34a in diet-induced obese mice restored NAMPT/NAD(+) levels and alleviated steatosis, inflammation, and glucose intolerance. Anti-miR-34a-mediated increases in NAD(+) levels were attenuated when NAMPT was downregulated. Our findings reveal a novel function of miR-34a in reducing both SIRT1 expression and activity in obesity. The miR-34a/NAMPT axis presents a potential target for treating obesity- and aging-related diseases involving SIRT1 dysfunction like steatosis and type 2 diabetes.