An estrogen receptor-selective coregulator that potentiates the effectiveness of antiestrogens and represses the activity of estrogens

The role of estrogen receptors in intracellular estrogen signaling pathways, an overview

To date five members of estrogen receptors (ESRs) have been reported. They are grouped into two classes, the nuclear estrogen receptors are members of the nuclear receptor family which found at nuclear, cytoplasm and plasma membrane, and the membrane estrogen receptors, such as G protein-coupled estrogen receptor 1, ESR-X and Gq-coupled membrane estrogen receptor. The structure and function of estrogen receptors, and interaction between ESR and coregulators were reviewed. In canonical pathway ESRs can translocate to the nucleus, bind to the target gene promotor with or without estrogen responsive element and regulate transcription, mediating the genomic effects of estrogen. Coactivators and corepressors are recruited to activate or inhibit transcription by activated ESRs. Many coactivators and corepressors are recruited to activate or inhibit ESR mediated gene transcription via different mechanisms. ESRs also indirectly bind to the promoter via interaction with other transcription factors, tethering the transcription factors. ESRs can be phosphorylated by several kinases such as p38, extracellular-signal-regulated kinase, and activated protein kinase B, and which activates transcription without ligand binding. Non-genomic estrogen action can be manifested by the increases of cytoplasmic NO and Ca2+ through the activation of membrane ESRs. In female, ESRs signaling is crucial for folliculogenesis, oocyte growth, ovulation, oviduct and uterus. In male, ESRs signaling modulates libido, erectile function, leydig cell steroidogenesis, sertoli cell's function, and epididymal fluid homeostatsis, supporting spermatogenesis and sperm maturation. The abnormal ESRs signaling is believed to be closely related to reproductive diseases and cancer.

Exosome-delivered NR2F1-AS1 and NR2F1 drive phenotypic transition from dormancy to proliferation in treatment-resistant prostate cancer via stabilizing hormonal receptors

Cancer cells acquire the ability to reprogram their phenotype in response to targeted therapies, yet the transition from dormancy to proliferation in drug-resistant cancers remains poorly understood. In prostate cancer, we utilized high-plasticity mouse models and enzalutamide-resistant (ENZ-R) cellular models to elucidate NR2F1 as a key factor in lineage transition and ENZ resistance. Depletion of NR2F1 drives ENZ-R cells into a relative dormancy state, characterized by reduced proliferation and heightened drug resistance, while NR2F1 overexpression yields contrasting outcomes. Transcriptional sequencing analysis of NR2F1-silenced prostate cancer cells and tissues from the Cancer Genome Atlas-prostate cancer and SU2C cohorts indicated exosomes as the most enriched cell component, with pathways implicated in steroid hormone biosynthesis and drug metabolism. Moreover, NR2F1-AS1 forms a complex with SRSF1 to upregulate NR2F1 expression, facilitating its binding with ESR1 to sustain hormonal receptor expression and enhance proliferation in ENZ-R cells. Furthermore, HnRNPA2B1 interacts with NR2F1 and NR2F1-AS1, assisting their packaging into exosomes, wherein exosomal NR2F1 and NR2F1-AS1 promote the proliferation of dormant ENZ-R cells. Our works offer novel insights into the reawaking of dormant drug-resistant cancer cells governed by NR2F1 upregulation triggered by exosome-derived NR2F1-AS1 and NR2F1, suggesting therapeutic potential for phenotype reversal.

Essential Protein PHB2 and Its Regulatory Mechanisms in Cancer

Prohibitins (PHBs) are a highly conserved class of proteins and have an essential role in transcription, epigenetic regulation, nuclear signaling, mitochondrial structural integrity, cell division, and cellular membrane metabolism. Prohibitins form a heterodimeric complex, consisting of two proteins, prohibitin 1 (PHB1) and prohibitin 2 (PHB2). They have been discovered to have crucial roles in regulating cancer and other metabolic diseases, functioning both together and independently. As there have been many previously published reviews on PHB1, this review focuses on the lesser studied prohibitin, PHB2. The role of PHB2 in cancer is controversial. In most human cancers, overexpressed PHB2 enhances tumor progression, while in some cancers, it suppresses tumor progression. In this review, we focus on (1) the history, family, and structure of prohibitins, (2) the essential location-dependent functions of PHB2, (3) dysfunction in cancer, and (4) the promising modulators to target PHB2. At the end, we discuss future directions and the clinical significance of this common essential gene in cancer.

Inhibition of Prolyl Oligopeptidase Restores Prohibitin 2 Levels in Psychosis Models: Relationship to Cognitive Deficits in Schizophrenia

Cognitive impairment represents one of the core features of schizophrenia. Prolyl Oligopeptidase (POP) inhibition is an emerging strategy for compensating cognitive deficits in hypoglutamatergic states such as schizophrenia, although little is known about how POP inhibitors exert their pharmacological activity. The mitochondrial and nuclear protein Prohibitin 2 (PHB2) could be dysregulated in schizophrenia. However, altered PHB2 levels in schizophrenia linked to N-methyl-D-aspartate receptor (NMDAR) activity and cognitive deficits are still unknown. To shed light on this, we measured the PHB2 levels by immunoblot in a postmortem dorsolateral prefrontal cortex (DLPFC) of schizophrenia subjects, in the frontal pole of mice treated with the NMDAR antagonists phencyclidine and dizocilpine, and in rat cortical astrocytes and neurons treated with dizocilpine. Mice and cells were treated in combination with the POP inhibitor IPR19. The PHB2 levels were also analyzed by immunocytochemistry in rat neurons. The PHB2 levels increased in DLPFC in cases of chronic schizophrenia and were associated with cognitive impairments. NMDAR antagonists increased PHB2 levels in the frontal pole of mice and in rat astrocytes and neurons. High levels of PHB2 were found in the nucleus and cytoplasm of neurons upon NMDAR inhibition. IPR19 restored PHB2 levels in the acute NMDAR inhibition. These results show that IPR19 restores the upregulation of PHB2 in an acute NMDAR hypoactivity stage suggesting that the modulation of PHB2 could compensate NMDAR-dependent cognitive impairments in schizophrenia.

PHB2 Maintains the Contractile Phenotype of VSMCs by Counteracting PKM2 Splicing

BACKGROUND

Phenotypic transition of vascular smooth muscle cells (VSMCs) accounts for the pathogenesis of a variety of vascular diseases during the early stage. Recent studies indicate the metabolic reprogramming may be involved in VSMC phenotypic transition. However, the definite molecules that link energy metabolism to distinct VSMC phenotype remain elusive.

METHODS

A carotid artery injury model was used to study postinjury neointima formation as well as VSMC phenotypic transition in vivo. RNA-seq analysis, cell migration assay, collagen gel contraction assay, wire myography assay, immunoblotting, protein interactome analysis, co-immunoprecipitation, and mammalian 2-hybrid assay were performed to clarify the phenotype and elucidate the molecular mechanisms.

RESULTS

We collected cell energy-regulating genes by using Gene Ontology annotation and applied RNA-Seq analysis of transforming growth factor-β or platelet-derived growth factor BB stimulated VSMCs. Six candidate genes were overlapped from energy metabolism-related genes and genes reciprocally upregulated by transforming growth factor-β and downregulated by platelet-derived growth factor BB. Among them, prohibitin 2 has been reported to regulate mitochondrial oxidative phosphorylation. Indeed, prohibitin 2-deficient VSMCs lost the contractile phenotype as evidenced by reduced contractile proteins. Consistently, Phb2^SMCKO mice were more susceptible to postinjury VSMC proliferation and neointima formation compared with Phb2^flox/flox mice. Further protein interactome analysis, co-immunoprecipitation, and mammalian 2-hybrid assay revealed that prohibitin 2, through its C-terminus, directly interacts with hnRNPA1, a key modulator of pyruvate kinase M1/2 (PKM) mRNA splicing that promotes PKM2 expression and glycolysis. Prohibitin 2 deficiency facilitated PKM1/2 mRNA splicing and reversion from PKM1 to PKM2, and enhanced glycolysis in VSMCs. Blocking prohibitin 2-hnRNPA1 interaction resulted in increased PKM2 expression, enhanced glycolysis, repressed contractile marker genes expression in VSMCs, as well as aggravated postinjury neointima formation in vivo.

CONCLUSIONS

Prohibitin 2 maintains VSMC contractile phenotype by interacting with hnRNPA1 to counteract hnRNPA1-mediated PKM alternative splicing and glucose metabolic reprogramming.

Insights Into the Role of Epigenetic Factors Determining the Estrogen Response in Estrogen-Positive Ovarian Cancer and Prospects of Combining Epi-Drugs With Endocrine Therapy

Ovarian cancer is one of the most lethal malignancies. The population at the risk is continually on the rise due to the acquired drug resistance, high relapse rate, incomplete knowledge of the etiology, cross-talk with other gynecological malignancies, and diagnosis at an advanced stage. Most ovarian tumors are thought to arise in surface epithelium somehow in response to changes in the hormonal environment. Prolonged treatment with hormone replacement therapy (HRT) is also considered a contributing factor. Estrogens influence the etiology and progression of the endocrine/hormone-responsive cancers in a patient-specific manner. The concept of hormonal manipulations got attention during the last half of the 20th century when tamoxifen was approved by the FDA as the first selective estrogen receptor modulator (SERM). Endocrine therapy that has been found to be effective against breast cancer can be an option for ovarian cancer. It is now established that global changes in the epigenetic landscape are not only the hallmark of tumor development but also contribute to the development of resistance to hormone therapy. A set of functionally related genes involved in epigenetic reprogramming are controlled by specific transcription factors (TFs). Thus, the activities of TFs mediate important mechanisms through which epigenetic enzymes and co-factors modify chromatin for the worst outcome in a site-specific manner. Furthermore, the role of epigenetic aberrations involving histone modifications is established in ovarian cancer pathogenesis. This review aims to provide insights on the role of key epigenetic determinants of response as well as resistance to the hormone therapy, the current status of research along with its limitations, and future prospects of epigenetic agents as biomarkers in early diagnosis, prognosis, and personalized treatment strategies. Finally, the possibility of small phytoestrogenic molecules in combination with immunotherapy and epi-drugs targeting ovarian cancer has been discussed.

Identification of a novel ER-NFĸB-driven stem-like cell population associated with relapse of ER+ breast tumors

BACKGROUND

Up to 40% of patients with estrogen receptor-positive (ER+) breast cancer experience relapse. This can be attributed to breast cancer stem cells (BCSCs), which are known to be involved in therapy resistance, relapse, and metastasis. Therefore, there is an urgent need to identify genes/pathways that drive stem-like cell properties in ER+ breast tumors.

METHODS

Using single-cell RNA sequencing and various bioinformatics approaches, we identified a unique stem-like population and established its clinical relevance. With follow-up studies, we validated our bioinformatics findings and confirmed the role of ER and NFĸB in the promotion of stem-like properties in breast cancer cell lines and patient-derived models.

RESULTS

We identified a novel quiescent stem-like cell population that is driven by ER and NFĸB in multiple ER+ breast cancer models. Moreover, we found that a gene signature derived from this stem-like population is expressed in primary ER+ breast tumors, endocrine therapy-resistant and metastatic cell populations and predictive of poor patient outcome.

CONCLUSIONS

These findings indicate a novel role for ER and NFĸB crosstalk in BCSCs biology and understanding the mechanism by which these pathways promote stem properties can be exploited to improve outcomes for ER+ breast cancer patients at risk of relapse.

The Identification of Prohibitin in the Rat Heart Mitochondria in Heart Failure

Mitochondria are considered the main organelles in the cell. They play an important role in both normal and abnormal heart function. There is a supramolecular organization between the complexes of the respiratory chain (supercomplexes (SCs)), which are involved in mitochondrial respiration. Prohibitins (PHBs) participate in the regulation of oxidative phosphorylation (OXPHOS) activity and interact with some subunits of the OXPHOS complexes. In this study, we identified a protein whose level was decreased in the mitochondria of the heart in rats with heart failure. This protein was PHB. Isoproterenol (ISO) has been used as a compound to induce heart failure in rats. We observed that astaxanthin (AX) increased the content of PHB in rat heart mitochondria isolated from ISO-injected rats. Since it is known that PHB forms complexes with some mitochondrial proteins and proteins that are part of the complexes of the respiratory chain, the change in the levels of these proteins was investigated under our experimental conditions. We hypothesized that PHB may be a target for the protective action of AX.

PGRMC1 Promotes Progestin-Dependent Proliferation of Breast Cancer Cells by Binding Prohibitins Resulting in Activation of ERα Signaling

Simple Summary

Combined menopausal hormone therapy is associated with increased breast cancer risk in postmenopausal women. In our previous studies, progesterone receptor membrane component 1 (PGRMC1) was shown to play a role in progestins’ elicitation of enhanced proliferation of breast cancer cells. Here we describe a potential mechanism by which PGRMC1 contributes to breast cancer progression via interaction with prohibitins, inhibiting their function as transcriptional repressors. This facilitates estrogen receptor alpha (ERα) transcriptional activity and enhances oncogenic signaling upon treatment with certain progestins, including norethisterone and dydrogesterone. Our data underline the contribution of PGRMC1 to especially hormone receptor positive breast cancer pathogenesis and demonstrate the need for further studies to understand its role in cancer.

Abstract

In previous studies, we reported that progesterone receptor membrane component 1 (PGRMC1) is implicated in progestin signaling and possibly associated with increased breast cancer risk upon combined hormone replacement therapy. To gain mechanistic insight, we searched for potential PGRMC1 interaction partners upon progestin treatment by co-immunoprecipitation and mass spectrometry. The interactions with the identified partners were further characterized with respect to PGRMC1 phosphorylation status and with emphasis on the crosstalk between PGRMC1 and estrogen receptor α (ERα). We report that PGRMC1 overexpression resulted in increased proliferation of hormone receptor positive breast cancer cell lines upon treatment with a subgroup of progestins including norethisterone and dydrogesterone that promote PGRMC1-phosphorylation on S181. The ERα modulators prohibitin-1 (PHB1) and prohibitin-2 (PHB2) interact with PGRMC1 in dependency on S181-phosphorylation upon treatment with the same progestins. Moreover, increased interaction between PGRMC1 and PHBs correlated with decreased binding of PHBs to ERα and subsequent ERα activation. Inhibition of either PGRMC1 or ERα abolished this effect. In summary, we provide strong evidence that activated PGRMC1 associates with PHBs, competitively removing them from ERα, which then can develop its transcriptional activities on target genes. This study emphasizes the role of PGRMC1 in a key breast cancer signaling pathway which may provide a new avenue to target hormone-dependent breast cancer.

Functional genomics for breast cancer drug target discovery

Breast cancer is a heterogeneous disease that develops through a multistep process via the accumulation of genetic/epigenetic alterations in various cancer-related genes. Current treatment options for breast cancer patients include surgery, radiotherapy, and chemotherapy including conventional cytotoxic and molecular-targeted anticancer drugs for each intrinsic subtype, such as endocrine therapy and antihuman epidermal growth factor receptor 2 (HER2) therapy. However, these therapies often fail to prevent recurrence and metastasis due to resistance. Overall, understanding the molecular mechanisms of breast carcinogenesis and progression will help to establish therapeutic modalities to improve treatment. The recent development of comprehensive omics technologies has led to the discovery of driver genes, including oncogenes and tumor-suppressor genes, contributing to the development of molecular-targeted anticancer drugs. Here, we review the development of anticancer drugs targeting cancer-specific functional therapeutic targets, namely, MELK (maternal embryonic leucine zipper kinase), TOPK (T-lymphokine-activated killer cell-originated protein kinase), and BIG3 (brefeldin A-inhibited guanine nucleotide-exchange protein 3), as identified through comprehensive breast cancer transcriptomics.

Oncogenic role of PinX1 in prostate cancer cells through androgen receptor dependent and independent mechanisms

Coregulators play an important role in prostate cancer (PCa), modulating androgen receptor (AR) action and representing a possible cause of androgen deprivation therapy failure. Pin2-interacting protein X1 (PinX1) is a nucleolar protein described as a steroid hormone receptor coregulator in breast cancer cell lines. In this work, we studied the effect of PinX1 on AR action in PCa. Our results demonstrate that PinX1 acts as an AR coactivator, increasing its transcriptional activity and target gene expression, as well as proliferation, migration and colony formation in PCa cell lines. These effects are observed in the presence and absence of AR agonist and antagonists, suggesting a possible androgen independent pathway for PinX1. We present the first oncogenic roles described for PinX1, acting as a coactivator of the AR.

Mitophagy Receptors in Tumor Biology

Mitochondria are multifunctional organelles that regulate cancer biology by synthesizing macromolecules, producing energy, and regulating cell death. The understanding of mitochondrial morphology, function, biogenesis, fission and fusion kinetics, and degradation is important for the development of new anticancer strategies. Mitophagy is a type of selective autophagy that can degrade damaged mitochondria under various environmental stresses, especially oxidative damage and hypoxia. The key regulator of mitophagy is the autophagy receptor, which recognizes damaged mitochondria and allows them to enter autophagosomes by binding to MAP1LC3 or GABARAP, and then undergo lysosomal-dependent degradation. Many components of mitochondria, including mitochondrial membrane proteins (e.g., PINK1, BNIP3L, BNIP3, FUNDC1, NIPSNAP1, NIPSNAP2, BCL2L13, PHB2, and FKBP8) and lipids (e.g., cardiolipin and ceramides), act as mitophagy receptors in a context-dependent manner. Dysfunctional mitophagy not only inhibits, but also promotes, tumorigenesis. Similarly, mitophagy plays a dual role in chemotherapy, radiotherapy, and immunotherapy. In this review, we summarize the latest advances in the mechanisms of mitophagy and highlight the pathological role of mitophagy receptors in tumorigenesis and treatment.

Physiological and genomic insight into neuroendocrine regulation of puberty in gilts

The timing of pubertal attainment in gilts is a critical factor for pork production and is an early indicator of future reproductive potential. Puberty, defined as age at first standing estrus in the presence of a boar, is brought about by an escape from estrogen inhibition of the GnRH pulse generator, which allows for increasing LH pulses leading to the onset of cyclicity. The biological mechanisms that control the timing of these events is related to decreasing inhibitory signals with a concomitant increase in stimulatory signals within the hypothalamus. The roles of gamma-aminobutyric acid, endogenous opioid peptides, and gonadotropin-inhibitory hormone in negatively regulating gonadotropin secretion in gilts is explored. Developmental changes in stimulatory mechanisms of glutamatergic and kisspeptin neurons are important for increased LH pulsatility required for the occurrence of puberty in pigs. Age at first estrus of gilts is metabolically gated, and numerous metabolites, metabolic hormones, and appetite-regulating neurotransmitters have been implicated in the nutritional regulation of gonadotropin secretion. Leptin is an important metabolic signal linking body energy reserves with age at puberty in gilts. Leptin acting through neuropeptide Y and proopiomelanocortin neurons in the hypothalamus has important impacts on the function of the reproductive neurosecretory axis of gilts. Age at puberty in swine is heritable, and genomic analyses reveal it to be a polygenic trait. Genome-wide association studies for pubertal age in gilts have revealed several genomic regions in common with those identified for age at menarche in humans. Candidate genes have been identified that have important functions in growth and adiposity. Numerous genes regulating hypothalamic neuronal function, gonadotropes in the adenohypophysis, and ovarian follicular development have been identified and illustrate the complex maturational changes occurring in the hypothalamic-pituitary-ovarian axis during puberty in gilts.

A conserved mechanism of sirtuin signalling through steroid hormone receptors

SIRT1 and orthologous sirtuins regulate a universal mechanism of ageing and thus determine lifespan across taxa; however, the precise mechanism remains vexingly polemical. They also protect against many metabolic and ageing-related diseases by dynamically integrating several processes including autophagy, proteostasis, calorie restriction, circadian rhythmicity and metabolism. These sirtuins are therefore important drug targets particularly because they also transduce allosteric signals from sirtuin-activating compounds such as resveratrol into increased healthspan in evolutionarily diverse organisms. While many of these functions are apparently regulated by deacetylation, that mechanism may not be all-encompassing. Since gonadal signals have been shown to regulate ageing/lifespan in worms and flies, the present study hypothesized that these sirtuins may act as intermediary factors for steroid hormone signal transduction. Accordingly, SIRT1 and its orthologues, Sir2 and Sir-2.1, are shown to be veritable nuclear receptor coregulators that classically coactivate the oestrogen receptor in the absence of ligand; coactivation was further increased by 17β-oestradiol. Remarkably in response to the worm steroid hormone dafachronic acid, SIRT1 reciprocally coactivates DAF-12, the steroid receptor that regulates nematode lifespan. These results suggest that steroid hormones may co-opt and modulate a phyletically conserved mechanism of sirtuin signalling through steroid receptors. Hence, it is interesting to speculate that certain sirtuin functions including prolongevity and metabolic regulation may be mechanistically linked to this endocrine signalling pathway; this may also have implications for understanding the determinative role of gonadal steroids such as oestradiol in human ageing. At its simplest, this report shows evidence for a hitherto unknown deacetylation-independent mechanism of sirtuin signalling.

Prohibitin ligands: a growing armamentarium to tackle cancers, osteoporosis, inflammatory, cardiac and neurological diseases

Over the last three decades, the scaffold proteins prohibitins-1 and -2 (PHB1/2) have emerged as key signaling proteins regulating a myriad of signaling pathways in health and diseases. Small molecules targeting PHBs display promising effects against cancers, osteoporosis, inflammatory, cardiac and neurodegenerative diseases. This review provides an updated overview of the various classes of PHB ligands, with an emphasis on their mechanism of action and therapeutic potential. We also describe how these ligands have been used to explore PHB signaling in different physiological and pathological settings.

Cytoplasmic sequestration of the RhoA effector mDiaphanous1 by Prohibitin2 promotes muscle differentiation

Muscle differentiation is controlled by adhesion and growth factor-dependent signalling through common effectors that regulate muscle-specific transcriptional programs. Here we report that mDiaphanous1, an effector of adhesion-dependent RhoA-signalling, negatively regulates myogenesis at the level of Myogenin expression. In myotubes, over-expression of mDia1ΔN3, a RhoA-independent mutant, suppresses Myogenin promoter activity and expression. We investigated mDia1-interacting proteins that may counteract mDia1 to permit Myogenin expression and timely differentiation. Using yeast two-hybrid and mass-spectrometric analysis, we report that mDia1 has a stage-specific interactome, including Prohibitin2, MyoD, Akt2, and β-Catenin, along with a number of proteosomal and mitochondrial components. Of these interacting partners, Prohibitin2 colocalises with mDia1 in cytoplasmic punctae in myotubes. We mapped the interacting domains of mDia1 and Phb2, and used interacting (mDia1ΔN3/Phb2 FL or mDia1ΔN3/Phb2-Carboxy) and non-interacting pairs (mDia1H + P/Phb2 FL or mDia1ΔN3/Phb2-Amino) to dissect the functional consequences of this partnership on Myogenin promoter activity. Co-expression of full-length as well as mDia1-interacting domains of Prohibitin2 reverse the anti-myogenic effects of mDia1ΔN3, while non-interacting regions do not. Our results suggest that Prohibitin2 sequesters mDia1, dampens its anti-myogenic activity and fine-tunes RhoA-mDia1 signalling to promote differentiation. Overall, we report that mDia1 is multi-functional signalling effector whose anti-myogenic activity is modulated by a differentiation-dependent interactome. The data have been deposited to the ProteomeXchange with identifier PXD012257.

Prohibitin: a prime candidate for a pleiotropic effector that mediates sex differences in obesity, insulin resistance, and metabolic dysregulation

Adipocytes and macrophages, the two major constituents of adipose tissue, exhibit sex differences and work in synergy in adipose tissue physiology and pathophysiology, including obesity-linked insulin resistance and metabolic dysregulation. Sex steroid hormones play a major role in sex differences in adipose tissue biology. However, our knowledge of the molecules that mediate these effects in adipose tissue remains limited. Consequently, it remains unclear whether these effector molecules in different adipose and immune cell types are distinct or if there are also pleiotropic effectors. Recently, a protein named prohibitin (PHB) with cell compartment- and tissue-specific functions has been found to play a role in sex differences in adipose and immune functions. Transgenic (Tg) mouse models overexpressing PHB (PHB-Tg) and a phospho-mutant PHB (mPHB-Tg) from the fatty acid binding protein-4 (Fabp-4) gene promoter display sex-neutral obesity; however, obesity-related insulin resistance and metabolic dysregulation are male-specific. Intriguingly, with aging, the male PHB-Tg mice developed hepatic steatosis and subsequently liver tumors whereas the male mPHB-Tg mice developed lymph node tumors and splenomegaly. Unlike the male transgenic mice, the female PHB-Tg and mPHB-Tg mice remain protected from obesity-related metabolic dysregulation and tumor development. In conclusion, the sex-dimorphic metabolic and immune phenotypes of PHB-Tg and mPHB-Tg mice have revealed PHB as a pleiotropic effector of sex differences in adipose and immune functions. In this mini-review, we will discuss the pleiotropic attributes of PHB and potential mechanisms that may have contributed to the sex-dimorphic metabolic phenotypes in PHB-Tg and mPHB-Tg mice, which warrant future research. We propose that PHB is a prime candidate for a pleiotropic mediator of sex differences in adipose and immune functions in both physiology and pathophysiology, including obesity, insulin resistance, and metabolic dysregulation.

Estrogen signaling: An emanating therapeutic target for breast cancer treatment

Breast cancer, a most common malignancy in women, was known to be associated with steroid hormone estrogen. The discovery of estrogen receptor (ER) gave us not only a powerful predictive and prognostic marker, but also an efficient target for the treatment of hormone-dependent breast cancer with various estrogen ligands. ER consists of two subtypes i.e. ERα and ERβ, that are mostly G-protein-coupled receptors and activated by estrogen, specially 17β-estradiol. The activation is followed by translocation into the nucleus and binding with DNA to modulate activities of different genes. ERs can manage synthesis of RNA through genomic actions without directly binding to DNA. Receptors are tethered by protein-protein interactions to a transcription factor complex to communicate with DNA. Estrogens also exhibit nongenomic actions, a characteristic feature of steroid hormones, which are so rapid to be considered by the activation of RNA and translation. These are habitually related to stimulation of different protein kinase cascades. Majority of post-menopausal breast cancer is estrogen dependent, mostly potent biological estrogen (E2) for continuous growth and proliferation. Estrogen helps in regulating the differentiation and proliferation of normal breast epithelial cells. In this review we have investigated the important role of ER in development and progression of breast cancer, which is complicated by receptor's interaction with co-regulatory proteins, cross-talk with other signal transduction pathways and development of treatment strategies viz. selective estrogen receptor modulators (SERMs), selective estrogen receptor down regulators (SERDs), aromatase and sulphatase inhibitors.

Natural Products Mediated Targeting of Virally Infected Cancer

The role of viral infection in developing cancer was determined in the start of 20th century. Until now, 8 different virus-associated cancers have been discovered and most of them progressed in immunosuppressed individuals. The aim of the present study is to look into the benefits of natural products in treating virally infected cancers. The study focuses on bioactive compounds derived from natural sources. Numerous pharmaceutical agents have been identified from plants (vincristine, vinblastine, stilbenes, combretastatin, and silymarin), marine organisms (bryostatins, cephalostatin, ecteinascidins, didemnin, and dolastatin), insects (cantharidin, mastoparan, parectadial, and cecropins), and microorganisms (vancomycin, rhizoxin, ansamitocins, mitomycin, and rapamycin). Beside these, various compounds have been observed from fruits and vegetables which can be utilized in anticancer therapy. These include curcumin in turmeric, resveratrol in red grapes, S-allyl cysteine in allium, allicin in garlic, catechins in green tea, and β-carotene in carrots. The present study addresses various types of virally infected cancers, their mechanism of action, and the role of different cell surface molecules elicited during viral binding and entry into the target cell along with the anticancer drugs derived from natural products by targeting screening of bioactive compounds from natural sources.

Short and Long Noncoding RNAs Regulate the Epigenetic Status of Cells

SIGNIFICANCE

The concepts of junk DNA and transcriptional noise are long gone as the existence of noncoding RNAs (ncRNAs) has been tested extensively in recent years. Given that the epigenetic status of cells affects many biological processes, how ncRNAs mechanistically contribute to these processes is of great interest. Recent Advances: Recent studies show that various ncRNAs interact with epigenetic and/or transcription factors to modulate the epigenetic status of cells directly and/or indirectly. There exists growing interest in the field of cardiovascular research to understand the roles of ncRNAs. Due to the large number of ncRNAs in the mammalian genome, only a handful of ncRNAs have been functionally elucidated, which makes it difficult to understand how ncRNAs interact with protein-coding genes and their encoded proteins.

CRITICAL ISSUES

Although the canonical function of microRNAs (miRNAs) to inhibit the translation of protein-coding genes is well established, the number of functionally annotated long noncoding RNAs (lncRNAs) is still small, which is especially true in the heart.

FUTURE DIRECTIONS

Future studies must connect the epigenetic controls of various cellular phenomena by incorporating both miRNAs and lncRNAs. Antioxid. Redox Signal. 29, 832-845.

[Comparative proteomic profiling of nuclear and cytosolic fractions from cell lines of different origin]

Proteomic analysis of the nuclear fraction is of great importance, since many cellular processes are initiated in the nucleus. Refinement and choice of experimental procedures for cell lysate fractionation and parameters for mass spectrometric detection and data processing continue to be of current interest. The mass spectrometry analysis presented here was tested on human cell lines derived from different tissues: HL-60 (peripheral blood); HepG2 (liver); EA.hy926 (vascular endothelium). High reproducibility of results and their consistency with biological properties of the objects under study were demonstrated. The use of cells of different types made it possible to reveal a set of 16 proteins whose LFQ-values allow for the discrimination between proteome fractions regardless of cell origin. Also, a set of 16 proteins is suggested which are associated with individual characteristics of cell lines regardless of cell fraction. These protein panels can serve as parameters to verify the proteomic analysis done was of sufficient quality, in particular as indicators of successful fractionation of cell or tissue lysate.

Prohibitin 2 localizes in nucleolus to regulate ribosomal RNA transcription and facilitate cell proliferation in RD cells

Prohibitin 2 (PHB2), as a conserved multifunctional protein, is traditionally localized in the mitochondrial inner membrane and essential for maintenance of mitochondrial function. Here, we investigated the role of PHB2 in human rhabdomyosarcoma (RMS) RD cells and found substantial localization of PHB2 in the nucleolus. We demonstrated that PHB2 knockdown inhibited RD cell proliferation through inducing cell cycle arrest and suppressing DNA synthesis. Meanwhile, down-regulation of PHB2 also induced apoptosis and promoted differentiation in fractions of RD cells. In addition, PHB2 silencing led to altered nucleolar morphology, as observed by transmission electron microscopy, and impaired nucleolar function, as evidenced by down-regulation of 45S and 18S ribosomal RNA synthesis. Consistently, upon PHB2 knockdown, occupancy of c-Myc at the ribosomal DNA (rDNA) promoter was attenuated, while more myoblast determination protein 1 (MyoD) molecules bound to the rDNA promoter. In conclusion, our findings suggest that nucleolar PHB2 is involved in maintaining nucleolar morphology and function in RD cells by regulating a variety of transcription factors, which is likely to be one of the underlying mechanisms by which PHB2 promotes tumor proliferation and represses differentiation. Our study provides new insight into the pathogenesis of RMS and novel characterizations of the highly conserved PHB2 protein.

Prohibitin-2 is a novel regulator of p21WAF1/CIP1 induced by depletion of γ-glutamylcyclotransferase

Previous studies show that gamma-glutamylcyclotransferase (GGCT) is expressed at high levels in various cancer tissues and that its knockdown inhibits MCF7 cancer cell growth via upregulation of p21^WAF1/CIP1 (p21). However, the detailed underlying mechanism is unclear. Here, we used yeast two-hybrid screening and co-immunoprecipitation to identify Prohibitin-2 (PHB2) as a novel protein that interacts with GGCT. We also show that nuclear expression of PHB2 in MCF7 cells falls upon GGCT knockdown, and that overexpression of PHB2 inhibits p21 upregulation. A chromatin immunoprecipitation assay revealed that nuclear PHB2 proteins bind to the p21 promoter, and that this interaction is abrogated by GGCT knockdown. Moreover, knockdown of PHB2 alone led to significant upregulation of p21 and mimicked the cellular events induced by GGCT depletion, including G0/G1 arrest, cellular senescence, and growth inhibition, in a p21 induction-dependent manner. Taken together, the results indicate that PHB2 plays a central role in p21 upregulation following GGCT knockdown and as such may promote deregulated proliferation of cancer cells by suppressing p21.

A-kinase anchoring protein BIG3 coordinates oestrogen signalling in breast cancer cells

Approximately 70% of breast cancer cells express oestrogen receptor alpha (ERα). Previous studies have shown that the Brefeldin A-inhibited guanine nucleotide-exchange protein 3–prohibitin 2 (BIG3-PHB2) complex has a crucial role in these cells. However, it remains unclear how BIG3 regulates the suppressive activity of PHB2. Here we demonstrate that BIG3 functions as an A-kinase anchoring protein that binds protein kinase A (PKA) and the α isoform of the catalytic subunit of protein phosphatase 1 (PP1Cα), thereby dephosphorylating and inactivating PHB2. E2-induced PKA-mediated phosphorylation of BIG3-S305 and -S1208 serves to enhance PP1Cα activity, resulting in E2/ERα signalling activation via PHB2 inactivation due to PHB2-S39 dephosphorylation. Furthermore, an analysis of independent cohorts of ERα-positive breast cancers patients reveal that both BIG3 overexpression and PHB2-S39 dephosphorylation are strongly associated with poor prognosis. This is the first demonstration of the mechanism of E2/ERα signalling activation via the BIG3–PKA–PP1Cα tri-complex in breast cancer cells.

BIG3 is highly expressed in breast cancers and its interaction with PHB2 results in constitutive activation of E2/ERa signalling. Here the authors unveil the mechanistic details of this regulation showing that BIG3 binds PKA and regulates PP1Ca activity in an oestrogen-dependent manner.

Stapled BIG3 helical peptide ERAP potentiates anti-tumour activity for breast cancer therapeutics

Estradiol (E2) and the oestrogen receptor-alpha (ERα) signalling pathway play pivotal roles in the proliferative activity of breast cancer cells. Recent findings show that the brefeldin A-inhibited guanine nucleotide-exchange protein 3-prohibitin 2 (BIG3-PHB2) complex plays a crucial role in E2/ERα signalling modulation in breast cancer cells. Moreover, specific inhibition of the BIG3-PHB2 interaction using the ERα activity-regulator synthetic peptide (ERAP: 165–177 amino acids), derived from α-helical BIG3 sequence, resulted in a significant anti-tumour effect. However, the duration of this effect was very short for viable clinical application. We developed the chemically modified ERAP using stapling methods (stapledERAP) to improve the duration of its antitumour effects. The stapledERAP specifically inhibited the BIG3-PHB2 interaction and exhibited long-lasting suppressive activity. Its intracellular localization without the membrane-permeable polyarginine sequence was possible via the formation of a stable α-helix structure by stapling. Tumour bearing-mice treated daily or weekly with stapledERAP effectively prevented the BIG3-PHB2 interaction, leading to complete regression of E2-dependent tumours in vivo. Most importantly, combination of stapledERAP with tamoxifen, fulvestrant, and everolimus caused synergistic inhibitory effects on growth of breast cancer cells. Our findings suggested that the stapled ERAP may be a promising anti-tumour drug to suppress luminal-type breast cancer growth.

Prohibitin - At the crossroads of obesity-linked diabetes and cancer

The promoter of a gene that is selectively expressed in just a few cell types provides unique opportunities to study: (1) the pleiotropic function of a protein in two different cell types including the cell compartment specific function, and (2) the crosstalk between two cell/tissue types at the systemic level. This is not possible with a ubiquitous or a highly specific gene promoter. The adipocyte protein-2 ( aP2) is one such gene. It is primarily expressed in adipocytes, but also selectively in monocytic macrophages and dendritic cells, among various immune cell types. Thus, the adipocyte protein-2 gene promoter provides an opportunity to simultaneously manipulate adipose and immune functions in a transgenic animal. Prohibitin (PHB) is a pleiotropic protein that has roles in both adipocytes and immune cells. Adipocyte specific functions of prohibitin are mediated through its mitochondrial function, whereas its immune functions are mediated in a phosphorylation-dependent manner. We capitalized on this attribute of prohibitin to explore the crosstalk between adipose and immune functions, and to discern mitochondrial and plasma membrane-associated cell signaling functions of prohibitin, by expressing wild type prohibitin (Mito-Ob) and a phospho-mutant form of prohibitin (m-Mito-Ob) from the protein-2 gene promoter, individually. Both transgenic mice develop obesity in a sex-neutral manner, but develop obesity-related metabolic dysregulation in a male sex-specific manner. Subsequently, the male Mito-Ob mice spontaneously developed type 2 diabetes and liver cancer, whereas the male m-Mito-Ob mice developed lymph node tumors or autoimmune diabetes in a context-dependent manner. This review provides a point of view on the role of prohibitin in mediating sex differences in adipose and immune functions at the systemic level. We discuss the unique attributes of prohibitin and provide a new paradigm in adipose-immune crosstalk mediated through a pleiotropic protein. Impact statement Prohibitin (PHB) is ubiquitously expressed and plays a role in adipocyte-immune cell cross-talk. Both male and female transgenic mice expressing wild-type PHB in adipose tissue and in macrophages are obese, but only males develop diabetes and liver cancer. When the mice express PHB mutated on tyrosine-114 in adipocytes and macrophages, both males and females are still obese, but none develops liver cancer; instead, males develop lymph node tumors. Adipocyte specific functions of PHB are mediated through its mitochondrial function, whereas its immune functions are mediated in a phosphorylation-dependent manner. Thus, PHB appears to be an important molecule linking obesity, diabetes, and cancer. In addition, this link appears to be affected by sex steroids. Therefore, targeting PHB may lead to a better understanding of the pathogenesis of obesity, diabetes and cancer.

Minireview: The Link Between ERα Corepressors and Histone Deacetylases in Tamoxifen Resistance in Breast Cancer

Approximately 70% of breast cancers express the estrogen receptor (ER)α and are treated with the ERα antagonist, tamoxifen. However, resistance to tamoxifen frequently develops in advanced breast cancer, in part due to a down-regulation of ERα corepressors. Nuclear receptor corepressors function by attenuating hormone responses and have been shown to potentiate tamoxifen action in various biological systems. Recent genomic data on breast cancers has revealed that genetic and/or genomic events target ERα corepressors in the majority of breast tumors, suggesting that the loss of nuclear receptor corepressor activity may represent an important mechanism that contributes to intrinsic and acquired tamoxifen resistance. Here, the biological functions of ERα corepressors are critically reviewed to elucidate their role in modifying endocrine sensitivity in breast cancer. We highlight a mechanism of gene repression common to corepressors previously shown to enhance the antitumorigenic effects of tamoxifen, which involves the recruitment of histone deacetylases (HDACs) to DNA. As an indicator of epigenetic disequilibrium, the loss of ERα corepressors may predispose cancer cells to the cytotoxic effects of HDAC inhibitors, a class of drug that has been shown to effectively reverse tamoxifen resistance in numerous studies. HDAC inhibition thus appears as a promising therapeutic approach that deserves to be further explored as an avenue to restore drug sensitivity in corepressor-deficient and tamoxifen-resistant breast cancers.

Prohibitin( PHB) roles in granulosa cell physiology

Ovarian granulosa cells (GC) play an important role in the growth and development of the follicle in the process known as folliculogenesis. In the present review, we focus on recent developments in prohibitin (PHB) research in relation to GC physiological functions. PHB is a member of a highly conserved eukaryotic protein family containing the repressor of estrogen activity (REA)/stomatin/PHB/flotillin/HflK/C (SPFH) domain (also known as the PHB domain) found in diverse species from prokaryotes to eukaryotes. PHB is ubiquitously expressed in a circulating free form or is present in multiple cellular compartments including mitochondria, nucleus and plasma membrane. In mitochondria, PHB is anchored to the mitochondrial inner membrane and forms complexes with the ATPases associated with proteases having diverse cellular activities. PHB continuously shuttles between the mitochondria, cytosol and nucleus. In the nucleus, PHB interacts with various transcription factors and modulates transcriptional activity directly or through interactions with chromatin remodeling proteins. Many functions have been attributed to the mitochondrial and nuclear PHB complexes such as cellular differentiation, anti-proliferation, morphogenesis and maintenance of the functional integrity of the mitochondria. However, to date, the regulation of PHB expression patterns and GC physiological functions are not completely understood.

A Novel Class of Small Molecule Compounds that Inhibit Hepatitis C Virus Infection by Targeting the Prohibitin-CRaf Pathway

Identification of novel drug targets and affordable therapeutic agents remains a high priority in the fight against chronic hepatitis C virus (HCV) infection. Here, we report that the cellular proteins prohibitin 1 (PHB1) and 2 (PHB2) are pan-genotypic HCV entry factors functioning at a post-binding step. While predominantly found in mitochondria, PHBs localize to the plasma membrane of hepatocytes through their transmembrane domains and interact with both EGFR and CRaf. Targeting PHB by rocaglamide (Roc-A), a natural product that binds PHB1 and 2, reduced cell surface PHB1 and 2, disrupted PHB-CRaf interaction, and inhibited HCV entry at low nanomolar concentrations. A structure-activity analysis of 32 synthetic Roc-A analogs indicated that the chiral, racemic version of aglaroxin C, a natural product biosynthetically related to Roc-A, displayed improved potency and therapeutic index against HCV infection. This study reveals a new class of HCV entry inhibitors that target the PHB1/2-CRaf pathway.

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Cellular proteins prohibitins 1 and 2 are essential HCV entry factors that function at a post-binding step.

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The natural compound Roc-A potently blocks HCV infection by disrupting prohibitins-CRaf interaction

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The Roc-A derivative, aglaroxin C, displays improved potency and therapeutic index towards HCV infection

Current FDA-approved HCV drugs all target viral proteins. We now demonstrate that a group of small molecules, the rocaglates, potently block HCV entry at low nanomolar concentrations. Roc-A inhibits HCV entry by disrupting the important interaction between two pan-genomic HCV entry factors, PHB1 and 2, and the signaling molecule CRaf. Overall, Roc-A and related rocaglates represent a new class of compounds that hold significant therapeutic promise in treating HCV infection.

Proteomics approach to examine the cardiotoxic effects of Nemopilema nomurai Jellyfish venom

Nemopilema nomurai is one of the largest species of jellyfish in the world. It blooms mainly offshore of Korea, China, and Japan. Increasing population numbers of N. nomurai is increasing the risk of sea bathers to the jellyfish stings and accompanying envenomations. Cardiovascular effects, and cytotoxicity and hemolytic activities have been previously reported in rodent models. To understand the mechanism of cardiac toxicity, we examined the effect of N. nomurai jellyfish venom (NnV) at the proteome level on rat cardiomyocytes cell line H9c2 using two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/MS). Cells treated with NnV displayed dose-dependent inhibition of viability. Cellular changes at proteome level were investigated after 6h and 12h of venom treatment. Electrophoretic examination revealed 72 protein spots displaying significant quantitative changes. These proteins were analyzed by MALDI-TOF/MS. Thirty four differentially expressed proteins were successfully identified; 24 proteins increased in quantity and 10 proteins decreased, compared to the respective controls. Proteins altered in content in Western blot analyses included myosin VII, annexin A2, aldose reductase, suppressor of cytokine signaling 1 (SOCS1), and calumenin, which are well-known marker proteins of cardiac dysfunctions.

BIOLOGICAL SIGNIFICANCE

This is the first report revealing the cardiac toxicity of NnV at the proteome level. NnV directly targeted proteins involved in cardiac dysfunction or maintenance. Suppressor of cytokine signaling 1 (SOCS1), which inhibits the Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway, was upregulated by NnV. Other proteins related to cardiac arrest that were over-expressed included aldose reductase and calumenin. These results clarify the underlying mechanism of cardiomyocyte damage caused by NnV. By inhibiting these particular targets and more precisely identifying the components of NnV-mediated cardiac toxicity, jellyfish venom-associated poisoning could be reduced or prevented.

BIG3 Inhibits the Estrogen-Dependent Nuclear Translocation of PHB2 via Multiple Karyopherin-Alpha Proteins in Breast Cancer Cells

We recently reported that brefeldin A-inhibited guanine nucleotide-exchange protein 3 (BIG3) binds Prohibitin 2 (PHB2) in cytoplasm, thereby causing a loss of function of the PHB2 tumor suppressor in the nuclei of breast cancer cells. However, little is known regarding the mechanism by which BIG3 inhibits the nuclear translocation of PHB2 into breast cancer cells. Here, we report that BIG3 blocks the estrogen (E2)-dependent nuclear import of PHB2 via the karyopherin alpha (KPNA) family in breast cancer cells. We found that overexpressed PHB2 interacted with KPNA1, KPNA5, and KPNA6, thereby leading to the E2-dependent translocation of PHB2 into the nuclei of breast cancer cells. More importantly, knockdown of each endogenous KPNA by siRNA caused a significant inhibition of E2-dependent translocation of PHB2 in BIG3-depleted breast cancer cells, thereby enhancing activation of estrogen receptor alpha (ERα). These data indicated that BIG3 may block the KPNAs (KPNA1, KPNA5, and KPNA6) binding region(s) of PHB2, thereby leading to inhibition of KPNAs-mediated PHB2 nuclear translocation in the presence of E2 in breast cancer cells. Understanding this regulation of PHB2 nuclear import may provide therapeutic strategies for controlling E2/ERα signals in breast cancer cells.

Differential binding of prohibitin-2 to estrogen receptor α and to drug-resistant ERα mutants

Endocrine resistance is one of the most challenging problems in estrogen receptor alpha (ERα)-positive breast cancer. The transcriptional activity of ERα is controlled by several coregulators, including prohibitin-2 (PHB2). Because of its ability to repress the transcriptional activity of activated ERα, PHB2 is a promising antiproliferative agent. In this study, were analyzed the interaction of PHB2 with ERα and three mutants (Y537S, D538G, and E380Q) that are frequently associated with a lack of sensitivity to hormonal treatments, to help advance novel drug discovery. PHB2 bound to ERα wild-type (WT), Y537S, and D538G, but did not bind to E380Q. The binding thermodynamics of Y537S and D538G to PHB2 were favorably altered entropically compared with those of WT to PHB2. Our results show that PHB2 binds to the ligand binding domain of ERα with a conformational change in the helix 12 of ERα.

Molecular aspects of bovine cystic ovarian disease pathogenesis

Cystic ovarian disease (COD) is one of the main causes of reproductive failure in cattle and causes severe economic loss to the dairy farm industry because it increases both days open in the post partum period and replacement rates due to infertility. This disease is the consequence of the failure of a mature follicle to ovulate at the time of ovulation in the estrous cycle. This review examines the evidence for the role of altered steroid and gonadotropin signaling systems and the proliferation/apoptosis balance in the ovary with cystic structures. This evidence suggests that changes in the expression of ovarian molecular components associated with these cellular mechanisms could play a fundamental role in the pathogenesis of COD. The evidence also shows that gonadotropin receptor expression in bovine cystic follicles is altered, which suggests that changes in the signaling system of gonadotropins could play a fundamental role in the pathogenesis of conditions characterized by altered ovulation, such as COD. Ovaries from animals with COD exhibit a disrupted steroid receptor pattern with modifications in the expression of coregulatory proteins. These changes in the pathways of endocrine action would trigger the changes in proliferation and apoptosis underlying the aberrant persistence of follicular cysts.

Free Spanish abstract: A Spanish translation of this abstract is freely available at http://www.reproduction-online.org/content/149/6/R251/suppl/DC1.

Estradiol inhibits Th17 cell differentiation through inhibition of RORγT transcription by recruiting the ERα/REA complex to estrogen response elements of the RORγT promoter

The symptoms of vaginal candidiasis exacerbate in the second half of the menstrual cycle in premenopausal women when the serum estradiol level is elevated. Estradiol has been shown to inhibit Th17 differentiation and production of antifungal IL-17 cytokines. However, little is known about the mechanisms. In the present study, we used mouse splenocytes and found that estradiol inhibited Th17 differentiation through downregulation of Rorγt mRNA and protein expression. Estradiol activated estrogen receptor (ER)α to recruit repressor of estrogen receptor activity (REA) and form the ERα/REA complex. This complex bound to three estrogen response element (ERE) half-sites on the Rorγt promoter region to suppress Rorγt expression. Estradiol induced Rea mRNA and protein expression in mouse splenocytes. Using Rea small interfering RNA to knock down Rea expression enhanced Rorγt expression and Th17 differentiation. Alternatively, histone deacetylase 1 and 2 bound to the three ERE half-sites, independent of estradiol. Histone deacetylase inhibitor MS-275 dose- and time-dependently increased Rorγt expression and subsequently enhanced Th17 differentiation. In 15 healthy premenopausal women, high serum estradiol levels are correlated with low RORγT mRNA levels and high REA mRNA levels in the vaginal lavage. These results demonstrate that estradiol upregulates REA expression and recruits REA via ERα to the EREs on the RORγT promoter region, thus inhibiting RORγT expression and Th17 differentiation. This study suggests that the estradiol/ERα/REA axis may be a feasible target in the management of recurrent vaginal candidiasis.

Identification and characterisation of the anti-oxidative stress properties of the lamprey prohibitin 2 gene

The highly conserved protein prohibitin 2 (PHB2) has been implicated as a cell-surface receptor in the regulation of proliferation, apoptosis, transcription, and mitochondrial protein folding. In the present study, we identified a Lampetra morii homologue of PHB2, Lm-PHB2, showing greater than 61.8% sequence identity with its homologues. Phylogenetic analysis indicated that the position of Lm-PHB2 is consistent with lamprey phylogeny. Expression of the Lm-PHB2 protein was nearly equivalent in the heart, liver, kidneys, intestines, and muscles of normal lampreys. However, the Lm-PHB2 protein was down-regulated in the myocardia of lampreys challenged for 5 days with adriamycin (Adr), followed by a significant up-regulation 10 days after treatment. In vitro, recombinant Lm-PHB2 (rLm-PHB2) protein could significantly enhance the H2O2-induced oxidative stress tolerance in Chang liver (CHL) cells. Further mechanism studies indicated that the nucleus-to-mitochondria translocation of Lm-PHB2 was closely involved in the oxidative stress protection. Our results suggests that the strategies to modulate Lm-PHB2 levels may constitute a novel therapeutic approach for myocardial injury and liver inflammatory diseases, conditions in which oxidative stress plays a critical role in tissue injury and inflammation.

Prohibitin is required for transcriptional repression by the WT1-BASP1 complex

The Wilms' tumor-1 protein (WT1) is a transcriptional regulator that can either activate or repress genes controlling cell growth, apoptosis and differentiation. The transcriptional corepressor BASP1 interacts with WT1 and mediates WT1's transcriptional repression activity. BASP1 is contained within large complexes, suggesting that it works in concert with other factors. Here we report that the transcriptional repressor prohibitin is part of the WT1-BASP1 transcriptional repression complex. Prohibitin interacts with BASP1, colocalizes with BASP1 in the nucleus, and is recruited to the promoter region of WT1 target genes to elicit BASP1-dependent transcriptional repression. We demonstrate that prohibitin and BASP1 cooperate to recruit the chromatin remodeling factor BRG1 to WT1-responsive promoters and that this results in the dissociation of CBP from the promoter region of WT1 target genes. As seen with BASP1, prohibitin can associate with phospholipids. We demonstrate that the recruitment of PIP2 and HDAC1 to WT1 target genes is also dependent on the concerted activity of BASP1 and prohibitin. Our findings provide new insights into the function of prohibitin in transcriptional regulation and uncover a BASP1-prohibitin complex that plays an essential role in the PIP2-dependent recruitment of chromatin remodeling activities to the promoter.

HEXIM1 plays a critical role in the inhibition of the androgen receptor by anti-androgens

We show that HEXIM1 (hexamethylene bis-acetamide inducible 1) functions as an AR (androgen receptor) co-repressor as it physically interacts with the AR and is required for the ability of anti-androgens to inhibit androgen-induced target gene expression and cell proliferation. Oncomine™ database and IHC (immunohistochemistry) analyses of human prostate tissues revealed that expression of HEXIM1 mRNA and protein are down-regulated during the development and progression of prostate cancer. Enforced down-regulation of HEXIM1 in parental hormone-dependent LNCaP cells results in resistance to the inhibitory action of anti-androgens. Conversely, ectopic expression of HEXIM1 in the CRPC (castration-resistant prostate cancer) cell line, C4-2, enhances their sensitivity to the repressive effects of the anti-androgen bicalutamide. Novel insight into the mechanistic basis for HEXIM1 inhibition of AR activity is provided by the present studies showing that HEXIM1 induces expression of the histone demethylase KDM5B (lysine-specific demethylase 5B) and inhibits histone methylation, resulting in the inhibition of FOXA1 (forkhead box A1) licensing activity. This is a new mechanism of action attributed to HEXIM1, and distinct from what has been reported so far to be involved in HEXIM1 regulation of other nuclear hormone receptors, including the oestrogen receptor.

Selective estrogen receptor modulators: tissue specificity and clinical utility

Selective estrogen receptor modulators (SERMs) are a diverse group of nonsteroidal compounds that function as agonists or antagonists for estrogen receptors (ERs) in a target gene-specific and tissue-specific fashion. SERM specificity involves tissue-specific expression of ER subtypes, differential expression of co-regulatory proteins in various tissues, and varying ER conformational changes induced by ligand binding. To date, the major clinical applications of SERMs are their use in the prevention and treatment of breast cancer, the prevention of osteoporosis, and the maintenance of beneficial serum lipid profiles in postmenopausal women. However, SERMs have also been found to promote adverse effects, including thromboembolic events and, in some cases, carcinogenesis, that have proven to be obstacles in their clinical utility. In this review, we discuss the mechanisms of SERM tissue specificity and highlight the therapeutic application of well-known and emergent SERMs.

Estrogen receptor coregulators and pioneer factors: the orchestrators of mammary gland cell fate and development

The steroid hormone, 17β-estradiol (E2), plays critical role in various cellular processes such as cell proliferation, differentiation, migration and apoptosis, and is essential for reproduction and mammary gland development. E2 actions are mediated by two classical nuclear hormone receptors, estrogen receptor α and β (ERs). The activity of ERs depends on the coordinated activity of ligand binding, post-translational modifications (PTMs), and importantly the interaction with their partner proteins called “coregulators.” Because coregulators are proved to be crucial for ER transcriptional activity, and majority of breast cancers are ERα positive, an increased interest in the field has led to the identification of a large number of coregulators. In the last decade, gene knockout studies using mouse models provided impetus to our further understanding of the role of these coregulators in mammary gland development. Several coregulators appear to be critical for terminal end bud (TEB) formation, ductal branching and alveologenesis during mammary gland development. The emerging studies support that, coregulators along with the other ER partner proteins called “pioneer factors” together contribute significantly to E2 signaling and mammary cell fate. This review discusses emerging themes in coregulator and pioneer factor mediated action on ER functions, in particular their role in mammary gland cell fate and development.

Prohibitins role in cellular survival through Ras-Raf-MEK-ERK pathway

Prohibitins are members of a highly conserved protein family containing the stomatin/prohibitin/flotillin/HflK/C (SPFH) domain (also known as the prohibitin [PHB] domain) found in unicellular eukaryotes, fungi, plants, animals, and humans. Two highly homologous members of prohibitins expressed in eukaryotes are prohibitin (PHB; B-cell receptor associated protein-32, BAP-32) and prohibitin 2/repressor of estrogen receptor activity (PHB2, REA, BAP-37). Both PHB and REA/PHB2 are ubiquitously expressed and are present in multiple cellular compartments including the mitochondria, nucleus, and the plasma membrane. Multiple functions have been attributed to the mitochondrial and nuclear PHB and PHB2/REA including cellular differentiation, anti-proliferation, and morphogenesis. One of the major functions of the prohibitins are in maintaining the functional integrity of the mitochondria and protecting cells from various stresses. In the present review, we focus on the recent research developments indicating that PHB and PHB2/REA are involved in maintaining cellular survival through the Ras-Raf-MEK-Erk pathway. Understanding the molecular mechanisms by which the intracellular signaling pathways utilize prohibitins in governing cellular survival is likely to result in development of therapeutic strategies to overcome various human pathological disorders such as diabetes, obesity, neurological diseases, inflammatory bowel disease, and cancer.

Targeting BIG3-PHB2 interaction to overcome tamoxifen resistance in breast cancer cells

The acquisition of endocrine resistance is a common obstacle in endocrine therapy of patients with oestrogen receptor-α (ERα)-positive breast tumours. We previously demonstrated that the BIG3–PHB2 complex has a crucial role in the modulation of oestrogen/ERα signalling in breast cancer cells. Here we report a cell-permeable peptide inhibitor, called ERAP, that regulates multiple ERα-signalling pathways associated with tamoxifen resistance in breast cancer cells by inhibiting the interaction between BIG3 and PHB2. Intrinsic PHB2 released from BIG3 by ERAP directly binds to both nuclear- and membrane-associated ERα, which leads to the inhibition of multiple ERα-signalling pathways, including genomic and non-genomic ERα activation and ERα phosphorylation, and the growth of ERα-positive breast cancer cells both in vitro and in vivo. More importantly, ERAP treatment suppresses tamoxifen resistance and enhances tamoxifen responsiveness in ERα-positive breast cancer cells. These findings suggest inhibiting the interaction between BIG3 and PHB2 may be a new therapeutic strategy for the treatment of luminal-type breast cancer.

Oestrogen receptor-α (ERα) signalling has a role in breast cancer drug resistance. Here, the authors report a synthetic peptide that disrupts the interaction between the signalling molecules BIG3 and PHB2, and thereby suppresses tamoxifen resistance.

Prohibitin 2 regulates the proliferation and lineage-specific differentiation of mouse embryonic stem cells in mitochondria

Background

The pluripotent state of embryonic stem (ES) cells is controlled by a network of specific transcription factors. Recent studies also suggested the significant contribution of mitochondria on the regulation of pluripotent stem cells. However, the molecules involved in these regulations are still unknown.

Methodology/Principal Findings

In this study, we found that prohibitin 2 (PHB2), a pleiotrophic factor mainly localized in mitochondria, is a crucial regulatory factor for the homeostasis and differentiation of ES cells. PHB2 was highly expressed in undifferentiated mouse ES cells, and the expression was decreased during the differentiation of ES cells. Knockdown of PHB2 induced significant apoptosis in pluripotent ES cells, whereas enhanced expression of PHB2 contributed to the proliferation of ES cells. However, enhanced expression of PHB2 strongly inhibited ES cell differentiation into neuronal and endodermal cells. Interestingly, only PHB2 with intact mitochondrial targeting signal showed these specific effects on ES cells. Moreover, overexpression of PHB2 enhanced the processing of a dynamin-like GTPase (OPA1) that regulates mitochondrial fusion and cristae remodeling, which could induce partial dysfunction of mitochondria.

Conclusions/Significance

Our results suggest that PHB2 is a crucial mitochondrial regulator for homeostasis and lineage-specific differentiation of ES cells.

CARL lncRNA inhibits anoxia-induced mitochondrial fission and apoptosis in cardiomyocytes by impairing miR-539-dependent PHB2 downregulation

Abnormal mitochondrial fission participates in the pathogenesis of many diseases. Long non-coding RNAs (lncRNAs) are emerging as new players in gene regulation, but how lncRNAs operate in the regulation of mitochondrial network is unclear. Here we report that a lncRNA, named cardiac apoptosis-related lncRNA (CARL), can suppress mitochondrial fission and apoptosis by targeting miR-539 and PHB2. The results show that PHB2 is able to inhibit mitochondrial fission and apoptosis. miR-539 is responsible for the dysfunction of PHB2 and regulates mitochondrial fission and apoptosis by targeting PHB2. Further, we show that CARL can act as an endogenous miR-539 sponge that regulates PHB2 expression, mitochondrial fission and apoptosis. Our present study reveals a model of mitochondrial fission regulation that is composed of CARL, miR-539 and PHB2. Modulation of their levels may provide a new approach for tackling apoptosis and myocardial infarction.

TBX3 regulates splicing in vivo: a novel molecular mechanism for Ulnar-mammary syndrome

TBX3 is a member of the T-box family of transcription factors with critical roles in development, oncogenesis, cell fate, and tissue homeostasis. TBX3 mutations in humans cause complex congenital malformations and Ulnar-mammary syndrome. Previous investigations into TBX3 function focused on its activity as a transcriptional repressor. We used an unbiased proteomic approach to identify TBX3 interacting proteins in vivo and discovered that TBX3 interacts with multiple mRNA splicing factors and RNA metabolic proteins. We discovered that TBX3 regulates alternative splicing in vivo and can promote or inhibit splicing depending on context and transcript. TBX3 associates with alternatively spliced mRNAs and binds RNA directly. TBX3 binds RNAs containing TBX binding motifs, and these motifs are required for regulation of splicing. Our study reveals that TBX3 mutations seen in humans with UMS disrupt its splicing regulatory function. The pleiotropic effects of TBX3 mutations in humans and mice likely result from disrupting at least two molecular functions of this protein: transcriptional regulation and pre-mRNA splicing.

TBX3 is a protein with essential roles in development and tissue homeostasis, and is implicated in cancer pathogenesis. TBX3 mutations in humans cause a complex of birth defects called Ulnar-mammary syndrome (UMS). Despite the importance of TBX3 and decades of investigation, few TBX3 partner proteins have been identified and little is known about how it functions in cells. Unlike previous investigations focused on TBX3 as DNA binding factor that represses transcription, we took an unbiased approach to identify TBX3 partner proteins in mouse embryos and human cells. We discovered that TBX3 interacts with RNA binding proteins and binds mRNAs to regulate how they are spliced. The different mutations seen in human UMS patients produce mutant proteins that interact with different partners and have different splicing activities. TBX3 promotes or inhibits splicing depending on cellular context, its partner proteins, and the target mRNA. Eukaryotic cells have many more proteins than genes: alternative splicing is critical to generate the different mRNAs needed for production of the specific and vast repertoire of proteins a cell produces. Our finding that TBX3 regulates this process provides fundamental new insights into how altered quantity and molecular function of TBX3 contribute to human developmental disorders and cancer.

HEXIM1 down-regulates hypoxia-inducible factor-1α protein stability

We have previously reported on the inhibition of HIF-1α (hypoxia-inducible factor α)-regulated pathways by HEXIM1 [HMBA (hexamethylene-bis-acetamide)-inducible protein 1]. Disruption of HEXIM1 activity in a knock-in mouse model expressing a mutant HEXIM1 protein resulted in increased susceptibility to the development of mammary tumours, partly by up-regulation of VEGF (vascular endothelial growth factor) expression, HIF-1α expression and aberrant vascularization. We now report on the mechanistic basis for HEXIM1 regulation of HIF-1α. We observed direct interaction between HIF-1α and HEXIM1, and HEXIM1 up-regulated hydroxylation of HIF-1α, resulting in the induction of the interaction of HIF-1α with pVHL (von Hippel-Lindau protein) and ubiquitination of HIF-1α. The up-regulation of hydroxylation involves HEXIM1-mediated induction of PHD3 (prolyl hydroxylase 3) expression and interaction of PHD3 with HIF-1α. Acetylation of HIF-1α has been proposed to result in increased interaction of HIF-1α with pVHL and induced pVHL-mediated ubiquitination, which leads to the proteasomal degradation of HIF-1α. HEXIM1 also attenuated the interaction of HIF-1α with HDAC1 (histone deacetylase 1), resulting in acetylation of HIF-1α. The consequence of HEXIM1 down-regulation of HIF-1α protein expression is attenuated expression of HIF-1α target genes in addition to VEGF and inhibition of HIF-1α-regulated cell invasion.

Oestrogen receptors in breast cancer: basic mechanisms and clinical implications

Since the discovery of the connection between ovarian hormones and breast cancer, endocrine therapy has been an integral adjuvant treatment for patients with hormone-dependent breast cancers. Oestrogen receptor (ER) plays a central role in mediating the effects of endogenous hormones and therapeutic agents. ER serves as a prognostic marker for responsiveness to endocrine therapy and is targeted either directly by selective oestrogen receptor modulators (SERMs) and pure antagonists or indirectly by aromatase inhibitors (AIs) that block oestrogen production. A significant number of ER-positive patients, however, fail to respond to therapy or develop resistance over time. This review focuses on the current understanding of ER functions and recent advances in genomic technologies and research that have provided a global perspective on hormone and ER activity and led to a number of significant discoveries, including the roles of co-regulatory factors and non-coding RNAs. Mechanistic insights into normal ER functions and therapeutic actions of SERMs and AIs will enable the development of better predictive markers and more effective target mechanisms and ultimately facilitate improvements in disease outcomes and patient survival.