Farnesoid X receptor inhibits LNcaP cell proliferation via the upregulation of PTEN

Activation of farnesoid X receptor retards expansion of renal collecting duct cell-derived cysts via inhibition of CFTR-mediated Cl- secretion

The transcription factor farnesoid X receptor (FXR) regulates energy metabolism. Specifically, FXR functions to regulate cystic fibrosis transmembrane conductance regulator (CFTR)-mediated Cl- secretion in intestinal epithelial cells. Therefore, this study aimed to investigate the role of FXR in CFTR-mediated Cl- secretion in renal tubular cells and to further elucidate its effects on renal cyst formation and growth. CFTR-mediated Cl- transport was evaluated via short-circuit current (ISC) measurements in Madin-Darby canine kidney (MDCK) cell monolayers and primary rat inner medullary collecting duct cells. The role of FXR in renal cyst formation and growth was determined by the MDCK cell-derived cyst model. Incubation with synthesized (GW4064) and endogenous (CDCA) FXR ligands reduced CFTR-mediated Cl- secretion in a concentration- and time-dependent manner. The inhibitory effect of FXR ligands was not due to the result of reduced cell viability and was attenuated by cotreatment with an FXR antagonist. FXR activation significantly decreased CFTR protein but not its mRNA. In addition, FXR activation inhibited CFTR-mediated Cl- secretion in primary renal collecting duct cells. FXR activation decreased ouabain-sensitive ISC without altering Na+-K+-ATPase mRNA and protein levels. Furthermore, FXR activation significantly reduced the number of cysts and renal cyst expansion. These inhibitory effects were correlated with a decrease in the expression of protein synthesis regulators mammalian target of rapamycin/S6 kinase. This study shows that FXR activation inhibits Cl- secretion in renal cells via inhibition of CFTR expression and retards renal cyst formation and growth. The discoveries point to a physiological role of FXR in the regulation of CFTR and a potential therapeutic application in polycystic kidney disease treatment.NEW & NOTEWORTHY The present study reveals that farnesoid X receptor (FXR) activation reduces microcyst formation and enlargement. This inhibitory effect of FXR activation is involved with decreased cell proliferation and cystic fibrosis transmembrane conductance regulator-mediated Cl- secretion in renal collecting duct cells. FXR might represent a novel target for the treatment of autosomal dominant polycystic kidney disease.

The anticancer activity of bile acids in drug discovery and development

Bile acids (BAs) constitute essential components of cholesterol metabolites that are synthesized in the liver, stored in the gallbladder, and excreted into the intestine through the biliary system. They play a crucial role in nutrient absorption, lipid and glucose regulation, and the maintenance of metabolic homeostasis. In additional, BAs have demonstrated the ability to attenuate disease progression such as diabetes, metabolic disorders, heart disease, and respiratory ailments. Intriguingly, recent research has offered exciting evidence to unveil their potential antitumor properties against various cancer cell types including tamoxifen-resistant breast cancer, oral squamous cell carcinoma, cholangiocarcinoma, gastric cancer, colon cancer, hepatocellular carcinoma, prostate cancer, gallbladder cancer, neuroblastoma, and others. Up to date, multiple laboratories have synthesized novel BA derivatives to develop potential drug candidates. These derivatives have exhibited the capacity to induce cell death in individual cancer cell types and display promising anti-tumor activities. This review extensively elucidates the anticancer activity of natural BAs and synthetic derivatives in cancer cells, their associated signaling pathways, and therapeutic strategies. Understanding of BAs and their derivatives activities and action mechanisms will evidently assist anticancer drug discovery and devise novel treatment.

Targeting Farnesoid X Receptor in Tumor and the Tumor Microenvironment: Implication for Therapy

The farnesoid-X receptor (FXR), a member of the nuclear hormone receptor superfamily, can be activated by bile acids (BAs). BAs binding to FXR activates BA signaling which is important for maintaining BA homeostasis. FXR is differentially expressed in human organs and exists in immune cells. The dysregulation of FXR is associated with a wide range of diseases including metabolic disorders, inflammatory diseases, immune disorders, and malignant neoplasm. Recent studies have demonstrated that FXR influences tumor cell progression and development through regulating oncogenic and tumor-suppressive pathways, and, moreover, it affects the tumor microenvironment (TME) by modulating TME components. These characteristics provide a new perspective on the FXR-targeted therapeutic strategy in cancer. In this review, we have summarized the recent research data on the functions of FXR in solid tumors and its influence on the TME, and discussed the mechanisms underlying the distinct function of FXR in various types of tumors. Additionally, the impacts on the TME by other BA receptors such as takeda G protein-coupled receptor 5 (TGR5), sphingosine-1-phosphate receptor 2 (S1PR2), and muscarinic receptors (CHRM2 and CHRM3), have been depicted. Finally, the effects of FXR agonists/antagonists in a combination therapy with PD1/PD-L1 immune checkpoint inhibitors and other anti-cancer drugs have been addressed.

Transcription Factor FXR Activates DHRS9 to Inhibit the Cell Oxidative Phosphorylation and Suppress Colon Cancer Progression

Background. Colon cancer is a common gastrointestinal malignancy. It has been discovered that Farnesoid X receptor (FXR) plays an imperative regulatory role in multitype cancers in recent years. However, its regulatory mechanism in colon cancer has not been clearly explored. This study intended to explore the molecular regulatory mechanism of FXR and its downstream genes on the malignant progression of colon cancer. Methods. The mRNA and protein expression of FXR in colon cancer cells were measured by quantitative real-time polymerase chain reaction and Western blot. The effects of FXR on the biological function of colon cancer cells were measured by Cell Counting Kit-8, colony formation, and transwell assays. The downstream target gene of FXR was predicted by bioinformatics analysis and found to be associated with cellular oxidative phosphorylation. The binding relationship between FXR and its downstream gene dehydrogenase/reductase member 9 (DHRS9) was verified through luciferase reporter assay and chromatin immunoprecipitation assay. The changes of oxidative phosphorylation were detected by Western blot and oxygen consumption rate determination. The effect of FXR/DHRS9 axis on the malignant progression of colon cancer cells was further confirmed by rescue experiments. Results. FXR was underexpressed in colon cancer tissues and cells, and overexpressing FXR could repress the malignant behaviors of colon cancer cells. Besides, DHRS9 was a downstream gene of FXR, and FXR/DHRS9 inhibited the deterioration of colon cancer through inhibiting oxidative phosphorylation. Moreover, promoting FXR expression in colon cancer cells could partially reverse the biological function changes caused by silencing DHRS9 expression. Conclusion. FXR inhibited the oxidative phosphorylation and inhibited the malignant progression of colon cancer cells via targeting DHRS9.

Synergistic effect of obeticholic acid and fasting-mimicking on proliferative, migration, and survival signaling in prostate cancer

The systemic and resistant nature of the androgen-independent stage of prostate cancers makes it largely incurable even after intensive multimodal therapy. Apoptosis and epithelial-mesenchymal transition (EMT) are two fundamental events that are deeply linked to carcinogenesis. Hence, it is necessary to find a new combination of several therapies targeting apoptosis and EMT without causing side effects. Several recent studies have indicated that the Farnesoid X receptor is extensively associated with human tumorigenesis. The FXR agonist obeticholic acid (INT 747) has preliminarily exhibited a tumor suppressor potential. In this present study, we assess the potential synergism of FXR activation under nutrient deprivation in prostate cancer cell lines to investigate whether FXR activation enhances starvation-induced apoptosis in PC3 cells. In this study, PC-3 treatment with INT 747 significantly repressed cell proliferation and clonogenic potential. In addition, it significantly induced apoptosis of PC-3 cells and decreased their cancerogenic potential, as evaluated by annexin v apoptosis and transwell migration assay, respectively. The decreased expression of pro-caspase 3 by western blot analysis further confirmed INT 747-induced apoptosis. Furthermore, the fasting-mimicking diet (FMD) potentiated the antiproliferative, pro-apoptotic, and antimetastatic effects of INT 747. Mechanistically, these effects were mediated through the downregulation of cyclin D1 and upregulation of PTEN. In conclusion, INT 747 alone markedly decreases, and when combined with FMD abrogates the growth and migration of PC-3 cells.

The role of bile acids in carcinogenesis

Bile acids are soluble derivatives of cholesterol produced in the liver that subsequently undergo bacterial transformation yielding a diverse array of metabolites. The bulk of bile acid synthesis takes place in the liver yielding primary bile acids; however, other tissues have also the capacity to generate bile acids (e.g. ovaries). Hepatic bile acids are then transported to bile and are subsequently released into the intestines. In the large intestine, a fraction of primary bile acids is converted to secondary bile acids by gut bacteria. The majority of the intestinal bile acids undergo reuptake and return to the liver. A small fraction of secondary and primary bile acids remains in the circulation and exert receptor-mediated and pure chemical effects (e.g. acidic bile in oesophageal cancer) on cancer cells. In this review, we assess how changes to bile acid biosynthesis, bile acid flux and local bile acid concentration modulate the behavior of different cancers. Here, we present in-depth the involvement of bile acids in oesophageal, gastric, hepatocellular, pancreatic, colorectal, breast, prostate, ovarian cancer. Previous studies often used bile acids in supraphysiological concentration, sometimes in concentrations 1000 times higher than the highest reported tissue or serum concentrations likely eliciting unspecific effects, a practice that we advocate against in this review. Furthermore, we show that, although bile acids were classically considered as pro-carcinogenic agents (e.g. oesophageal cancer), the dogma that switch, as lower concentrations of bile acids that correspond to their serum or tissue reference concentration possess anticancer activity in a subset of cancers. Differences in the response of cancers to bile acids lie in the differential expression of bile acid receptors between cancers (e.g. FXR vs. TGR5). UDCA, a bile acid that is sold as a generic medication against cholestasis or biliary surge, and its conjugates were identified with almost purely anticancer features suggesting a possibility for drug repurposing. Taken together, bile acids were considered as tumor inducers or tumor promoter molecules; nevertheless, in certain cancers, like breast cancer, bile acids in their reference concentrations may act as tumor suppressors suggesting a Janus-faced nature of bile acids in carcinogenesis.

Farnesoid X Receptor Is Required for the Redifferentiation of Bipotential Progenitor Cells During Biliary-Mediated Zebrafish Liver Regeneration

BACKGROUND AND AIMS

Liver regeneration after extreme hepatocyte loss occurs through transdifferentiation of biliary epithelial cells (BECs), which includes dedifferentiation of BECs into bipotential progenitor cells (BPPCs) and subsequent redifferentiation into nascent hepatocytes and BECs. Although multiple molecules and signaling pathways have been implicated to play roles in the BEC-mediated liver regeneration, mechanisms underlying the dedifferentiation-redifferentiation transition and the early phase of BPPC redifferentiation that is pivotal for both hepatocyte and BEC directions remain largely unknown.

APPROACH AND RESULTS

The zebrafish extreme liver damage model, genetic mutation, pharmacological inhibition, transgenic lines, whole-mount and fluorescent in situ hybridizations and antibody staining, single-cell RNA sequencing, quantitative real-time PCR, and heat shock-inducible overexpression were used to investigate roles and mechanisms of farnesoid X receptor (FXR; encoded by nuclear receptor subfamily 1, group H, member 4 [nr1h4]) in regulating BPPC redifferentiation. The nr1h4 expression was significantly up-regulated in response to extreme liver injury. Genetic mutation or pharmacological inhibition of FXR was ineffective to BEC-to-BPPC dedifferentiation but blocked the redifferentiation of BPPCs to both hepatocytes and BECs, leading to accumulation of undifferentiated or less-differentiated BPPCs. Mechanistically, induced overexpression of extracellular signal-related kinase (ERK) 1 (encoded by mitogen-activated protein kinase 3) rescued the defective BPPC-to-hepatocyte redifferentiation in the nr1h4 mutant, and ERK1 itself was necessary for the BPPC-to-hepatocyte redifferentiation. The Notch activities in the regenerating liver of nr1h4 mutant attenuated, and induced Notch activation rescued the defective BPPC-to-BEC redifferentiation in the nr1h4 mutant.

CONCLUSIONS

FXR regulates BPPC-to-hepatocyte and BPPC-to-BEC redifferentiations through ERK1 and Notch, respectively. Given recent applications of FXR agonists in the clinical trials for liver diseases, this study proposes potential underpinning mechanisms by characterizing roles of FXR in the stimulation of dedifferentiation-redifferentiation transition and BPPC redifferentiation.

Targeting Farnesoid X receptor (FXR) for developing novel therapeutics against cancer

Cancer is one of the lethal diseases that arise due to the molecular alterations in the cell. One of those alterations associated with cancer corresponds to differential expression of Farnesoid X receptor (FXR), a nuclear receptor regulating bile, cholesterol homeostasis, lipid, and glucose metabolism. FXR is known to regulate several diseases, including cancer and cardiovascular diseases, the two highly reported causes of mortality globally. Recent studies have shown the association of FXR overexpression with cancer development and progression in different types of cancers of breast, lung, pancreas, and oesophagus. It has also been associated with tissue-specific and cell-specific roles in various cancers. It has been shown to modulate several cell-signalling pathways such as EGFR/ERK, NF-κB, p38/MAPK, PI3K/AKT, Wnt/β-catenin, and JAK/STAT along with their targets such as caspases, MMPs, cyclins; tumour suppressor proteins like p53, C/EBPβ, and p-Rb; various cytokines; EMT markers; and many more. Therefore, FXR has high potential as novel biomarkers for the diagnosis, prognosis, and therapy of cancer. Thus, the present review focuses on the diverse role of FXR in different cancers and its agonists and antagonists.

Farnesoid X Receptor Activation Impairs Liver Progenitor Cell-Mediated Liver Regeneration via the PTEN-PI3K-AKT-mTOR Axis in Zebrafish

BACKGROUND AND AIMS

Following mild liver injury, pre-existing hepatocytes replicate. However, if hepatocyte proliferation is compromised, such as in chronic liver diseases, biliary epithelial cells (BECs) contribute to hepatocytes through liver progenitor cells (LPCs), thereby restoring hepatic mass and function. Recently, augmenting innate BEC-driven liver regeneration has garnered attention as an alternative to liver transplantation, the only reliable treatment for patients with end-stage liver diseases. Despite this attention, the molecular basis of BEC-driven liver regeneration remains poorly understood.

APPROACH AND RESULTS

By performing a chemical screen with the zebrafish hepatocyte ablation model, in which BECs robustly contribute to hepatocytes, we identified farnesoid X receptor (FXR) agonists as inhibitors of BEC-driven liver regeneration. Here we show that FXR activation blocks the process through the FXR-PTEN (phosphatase and tensin homolog)-PI3K (phosphoinositide 3-kinase)-AKT-mTOR (mammalian target of rapamycin) axis. We found that FXR activation blocked LPC-to-hepatocyte differentiation, but not BEC-to-LPC dedifferentiation. FXR activation also suppressed LPC proliferation and increased its death. These defects were rescued by suppressing PTEN activity with its chemical inhibitor and ptena/b mutants, indicating PTEN as a critical downstream mediator of FXR signaling in BEC-driven liver regeneration. Consistent with the role of PTEN in inhibiting the PI3K-AKT-mTOR pathway, FXR activation reduced the expression of pS6, a marker of mTORC1 activation, in LPCs of regenerating livers. Importantly, suppressing PI3K and mTORC1 activities with their chemical inhibitors blocked BEC-driven liver regeneration, as did FXR activation.

CONCLUSIONS

FXR activation impairs BEC-driven liver regeneration by enhancing PTEN activity; the PI3K-AKT-mTOR pathway controls the regeneration process. Given the clinical trials and use of FXR agonists for multiple liver diseases due to their beneficial effects on steatosis and fibrosis, the detrimental effects of FXR activation on LPCs suggest a rather personalized use of the agonists in the clinic.

Differential roles of farnesoid X receptor (FXR) in modulating apoptosis in cancer cells

Cancer is one of the leading causes of mortality in the world. The conventional treatment strategies of cancer are surgery, radiation, and chemotherapy. However, in the advanced stage of the disease chemotherapy is the prime treatment and it is effective in only less than 10% of the patients. Therefore, there is an urgent need to find out novel therapeutic targets and delineate the mechanism of action of these targets for better management of this disease. Recent studies have shown that some of the proteins have differential role in different cancers. Therefore, it is pertinent that the targeting of these proteins should be based on the type of cancer. The nuclear receptor, FXR, is one of the vital proteins that regulate cell apoptosis. Besides, it also regulates other processes such as cell proliferation, angiogenesis, invasion, and migration. Studies suggest that the low or high expression of FXR is associated with the progression of carcinogenesis depending on the cancer types. Due to the diverse expression, it functions as both tumor suppressor and promoter. Previous studies suggest the overexpression of FXR in breast, lung, esophageal, and prostate cancer, which is related to poor survival and poor prognosis in patients. Therefore, targeting FXR with agonists and antagonists play different outcome in different cancers. Hence, this review describes the role of FXR in different cancers and the role of its inhibitors and activators for the prevention and treatment of various cancers.

Farnesoid X receptor as marker of osteotropism of breast cancers through its role in the osteomimetism of tumor cells

Background

The skeleton is the first and most common distant metastatic site for breast cancer. Such metastases complicate cancer management, inducing considerable morbidities and decreasing patient survival. Osteomimetism is part of the complex process of osteotropism of breast cancer cells. Recent data indicate that Farnesoid X Receptor (FXR) is involved in the transformation and progression of breast cancer.

Methods

The expression of FXR, Runt-related transcription factor 2 (RUNX2) and bone proteins were evaluated on two tumor cell lines (MCF-7 and MDA-MB-231) by immunohistochemistry, immunofluorescence and western blotting and quantified.

Results

In a series of 81 breast cancer patients who developed distant metastases, we found a strong correlation between FXR expression in primary breast tumors and the development of bone metastases, especially in patients with histological grade 3 tumors. In in vitro studies, FXR activation by Chenodeoxycholic acid (CDCA) increased the expression of numerous bone proteins. FXR inhibition by lithocholic acid and z-guggulsterone decreased bone protein expression. Short Hairpin RNA (ShRNA) against FXR validated the involvement of FXR in the osteomimetism of breast cancer cells.

Conclusion

Our experimental results point to a relationship between the expression of FXR in breast cancer cells and the propensity of these tumor cells to develop bone metastases. FXR induces the expression of RUNX2 which itself causes the synthesis of bone proteins by tumor cells.

Farnesoid X receptor alpha (FXRα) is a critical actor of the development and pathologies of the male reproductive system

The farnesoid-X-receptorα (FXRα; NR1H4) is one of the main bile acid (BA) receptors. During the last decades, through the use of pharmalogical approaches and transgenic mouse models, it has been demonstrated that the nuclear receptor FXRα controls numerous physiological functions such as glucose or energy metabolisms. It is also involved in the etiology or the development of several pathologies. Here, we will review the unexpected roles of FXRα on the male reproductive tract. FXRα has been demonstrated to play functions in the regulation of testicular and prostate homeostasis. Even though additional studies are needed to confirm these findings in humans, the reviewed reports open new field of research to better define the effects of bile acid-FXRα signaling pathways on fertility disorders and cancers.

The Role of Nuclear Receptors in Prostate Cancer

The nuclear receptor (NR) superfamily consists of 48 members that are divided into seven subfamilies. NRs are transcription factors that play an important role in a number of biological processes. The NR superfamily includes androgen receptor, which is a key player in prostate cancer pathogenesis, suggesting the functional roles of other NRs in prostate cancer. The findings on the roles of NRs in prostate cancer thus far have shown that several NRs such as vitamin D receptor, estrogen receptor β, and mineralocorticoid receptor play antioncogenic roles, while other NRs such as peroxisome proliferator-activated receptor γ and estrogen receptor α as well as androgen receptor play oncogenic roles. However, the roles of other NRs in prostate cancer remain controversial or uninvestigated. Further research on the role of NRs in prostate cancer is required and may lead to the development of novel preventions and therapeutics for prostate cancer.

Expression of FXR and HRG and their clinicopathological significance in benign and malignant pancreatic lesions

AIMS

The following study examines the FXR and HRG expression in benign and malignant lesions of the pancreas and evaluates the association between FXR and HRG expression with clinicopathological features and prognosis of pancreatic cancer.

MATERIALS AND METHODS

Immunohistochemistry of FXR and HRG was performed with EnVision™ in 106 pancreatic ductal adenocarcinoma (PDAC) specimens, 35 paracancer samples (2 cm away from the tumor, when possible or available), 55 benign lesions and 13 normal tissue samples.

RESULTS

The percentage of cases with positive FXR and negative HRG expression was significantly higher in PDAC compared to pericancerous tissues, benign lesions and normal tissues (P<0.05 or P<0.01). In pancreatic tissues with benign lesions, tissues with positive FXR and/or negative HRG protein expression exhibited dysplasia or intraepithelial neoplasia. The percentage of cases with positive FXR and negative HRG expressions was significantly higher in PDAC with lymph node metastasis, invasion, and TNM stage III+IV disease (P<0.05 or P<0.01). The expression of FXR was negatively correlated with HRG (P<0.05). In addition, the univariate Kaplan-Meier analysis showed that positive FXR and negative HRG expression, poor differentiation, large tumor size, high TNM stage, lymph node metastasis, and invasion were closely associated with decreased overall survival in PDAC patients (P<0.05 or P<0.01). Moreover, multivariate Cox regression analysis identified that positive FXR and negative HRG expression were independent factors for poor prognosis in PDAC. The AUC for FXR was (AUC=0.709, 95% CI: 0.632-0.787), and for HRG was (AUC=0.719, 95% CI: 0.643-0.796) in PDAC compared to benign lesions.

CONCLUSIONS

Positive FXR and negative HRG expression are closely associated with the carcinogenesis, clinical, pathological and biological behaviors, and poor prognosis in PDAC.

Bile acids promote gastric intestinal metaplasia by upregulating CDX2 and MUC2 expression via the FXR/NF-κB signalling pathway

Bile acids serve a critical role in the induction of gastric intestinal metaplasia (IM) and gastric carcinogenesis. The present study investigated the effects of bile acids on the induction of gastric IM formation. The results demonstrated that the expression levels of caudal-related homeobox transcription factor 2 (CDX2), mucin 2 (MUC2) and farnesoid X receptor (FXR) were increased in vitro and in vivo following treatment with bile acids, and CDX2 transcriptionally activated MUC2 expression. Furthermore, knockdown of FXR attenuated bile acid-enhanced CDX2 promoter activity and protein expression. Conversely, the FXR agonist GW4064 synergistically enhanced bile acid-induced CDX2 promoter activity. Bile acid treatment led to an increase in nuclear factor (NF)-κB activity and protein expression. Treatment with GW4064 or the FXR antagonist Z-guggulsterone enhanced or attenuated bile acid-induced NF-κB activity, respectively. In addition, quantitative chromatin immunoprecipitation confirmed that bile acids led to enhanced binding of p50 to the CDX2 promoter, whereas this effect was not observed for p65. Treatment with GW4064 or Z-guggulsterone enhanced and attenuated the binding activity of p50 to the CDX2 promoter, respectively. These results indicated that bile acids may activate the FXR/NF-κB signalling pathway, thereby upregulating CDX2 and MUC2 expression in normal gastric epithelial cells.

LXRs, SHP, and FXR in Prostate Cancer: Enemies or Ménage à Quatre With AR?

Androgens and androgen receptor (AR, NR3C4) clearly play a crucial role in prostate cancer progression. Besides, the link between metabolic disorders and the risk of developing a prostate cancer has been emerging these last years. Interestingly, “lipid” nuclear receptors such as LXRα/NR1H3 and LXRβ/NR1H2 (as well as FXRα/NR1H4 and SHP/NR0B2) have been described to decrease the lipid metabolism, while AR increases it. Moreover, these former orphan nuclear receptors can regulate androgen levels and modulate AR activity. Thus, it is not surprising to find such receptors involved in the physiology of prostate. This review is focused on the roles of liver X receptors (LXRs), farnesoid X receptor (FXR), and small heterodimeric partner (SHP) in prostate physiology and their capabilities to interfere with the androgen-regulated pathways by modulating the levels of active androgen within the prostate. By the use of prostate cancer cell lines, mice deficient for these nuclear receptors and human tissue libraries, several authors have pointed out the putative possibility to pharmacologically target these receptors. These data open a new field of research for the development of new drugs that could overcome the castration resistance in prostate cancer, a usual phenomenon in patients.

Lipid pathway deregulation in advanced prostate cancer

The link between prostate cancer (PC) development and lipid metabolism is well established, with AR intimately involved in a number of lipogenic processes involving SREBP1, PPARG, FASN, ACC, ACLY and SCD1. Recently, there is growing evidence implicating the role of obesity and peri-prostatic adipose tissue (PPAT) in PC aggressiveness and related mortality, suggesting the importance of lipid pathways in both localised and disseminated disease. A number of promising agents are in development to target the lipogenic axis in PC, and the likelihood is that these agents will form part of combination drug strategies, with targeting of multiple metabolic pathways (e.g. FASN and CPT1), or in combination with AR pathway inhibitors (SCD1 and AR).

Bile Acids and Cancer: Direct and Environmental-Dependent Effects

Bile acids (BAs) regulate the absorption of fat-soluble vitamins, cholesterol and lipids but have also a key role as singalling molecules and in the modulation of epithelial cell proliferation, gene expression and metabolism. These homeostatic pathways, when disrupted, are able to promote local inflammation, systemic metabolic disorders and, ultimately, cancer. The effect of hydrophobic BAs, in particular, can be linked with cancer in several digestive (mainly oesophagus, stomach, liver, pancreas, biliary tract, colon) and extra-digestive organs (i.e. prostate, breast) through a complex series of mechanisms including direct oxidative stress with DNA damage, apoptosis, epigenetic factors regulating gene expression, reduced/increased expression of nuclear receptors (mainly farnesoid X receptor, FXR) and altered composition of gut microbiota, also acting as a common interface between environmental factors (including diet, lifestyle, exposure to toxics) and the molecular events promoting cancerogenesis. Primary prevention strategies (i.e. changes in dietary habits and lifestyle, reduced exposure to environmental toxics) mainly able to modulate gut microbiota and the epigenome, and the therapeutic use of hydrophilic BAs to counterbalance the negative effects of the more hydrophobic BAs might be, in the near future, part of useful tools for cancer prevention and management.

Farnesoid X receptor ligand CDCA suppresses human prostate cancer cells growth by inhibiting lipid metabolism via targeting sterol response element binding protein 1

AIM

A wealth of studies have demonstrated that abnormal cellular lipid metabolism plays an important role in prostate cancer (PCa) development. Therefore, manipulating lipid metabolism is a potential PCa therapy strategy. In this study, our goal is to investigate the role of farnesoid X receptor (FXR) in regulating the proliferation and lipid metabolism of human PCa cells following its ligand chenodexycholic acid (CDCA) treatment.

METHODS

Oil Red O was used to stain lipid contents in PCa cells, and siRNA knockdown was performed to deplete FXR expression. To study the cell proliferation when treated by CDCA or FXR knockdown, cell counting kit 8 (CCK8) was adopted to evaluate tumor cell growth. Western blot was used for protein analysis.

RESULTS

Our data suggest that activation of FXR by CDCA reduces lipid accumulation and significantly inhibits cells proliferation in prostate tumor cells. Instead, CDCA treatment doesn't affect normal prostate epithelial RWPE-1 cells growth in vitro. FXR activation decreases mRNA and protein levels of sterol regulatory element binding protein 1 (SREBP1) and some other key regulators involved in lipid metabolism. Depletion of FXR by siRNA attenuates the inhibitory effects.

CONCLUSION

Our study indicates that activation of FXR inhibits lipid metabolism via SREBP1 pathway and further suppresses prostate tumor growth in vitro.

WOMEN IN CANCER THEMATIC REVIEW: New roles for nuclear receptors in prostate cancer

Prostate cancer has, for decades, been treated by inhibiting androgen signalling. This is effective in the majority of patients, but inevitably resistance develops and patients progress to life-threatening metastatic disease - hence the quest for new effective therapies for 'castrate-resistant' prostate cancer (CRPC). Studies into what pathways can drive tumour recurrence under these conditions has identified several other nuclear receptor signalling pathways as potential drivers or modulators of CRPC.The nuclear receptors constitute a large (48 members) superfamily of transcription factors sharing a common modular functional structure. Many of them are activated by the binding of small lipophilic molecules, making them potentially druggable. Even those for which no ligand exists or has yet been identified may be tractable to activity modulation by small molecules. Moreover, genomic studies have shown that in models of CRPC, other nuclear receptors can potentially drive similar transcriptional responses to the androgen receptor, while analysis of expression and sequencing databases shows disproportionately high mutation and copy number variation rates among the superfamily. Hence, the nuclear receptor superfamily is of intense interest in the drive to understand how prostate cancer recurs and how we may best treat such recurrent disease. This review aims to provide a snapshot of the current knowledge of the roles of different nuclear receptors in prostate cancer - a rapidly evolving field of research.

New insights into the androgen biotransformation in prostate cancer: A regulatory network among androgen, androgen receptors and UGTs

Androgen, as one kind of steroid hormones, is pivotal in the hormone-sensitive cancer, such as prostate cancer (PCa). The synthesis, elimination, and bioavailability of androgen in prostate cells have been proved to be a main cause of the carcinogenesis, maintenance and deterioration of PCa. This review illustrates the outlines of androgen biotransformation, and further discusses the different enzymes, especially UDP-glucuronyltransferases (UGTs) embedded in both benign and malignant prostate cells, which catalyze the reactions. Although many inhibitors of the enzymes responsible for the synthesis of androgens have been developed into drugs to fight against PCa, the elimination procedures metabolized by the UGTs are less emphasized. Thus the regulatory network among androgen, androgen receptors (AR) and UGTs is carefully reviewed in this article, indicating the determinant effects of UGTs on prostatic androgens and the regulation of AR. Finally, the hypothesis is also put forward that the regulators of UGTs may be developed to accelerate the androgen elimination and benefit PCa therapy.

Bile acids regulate intestinal cell proliferation by modulating EGFR and FXR signaling

Bile acids (BAs) are synthesized in the liver and secreted into the intestine. In the lumen, enteric bacteria metabolize BAs from conjugated, primary forms into more toxic unconjugated, secondary metabolites. Secondary BAs can be injurious to the intestine and may contribute to disease. The epidermal growth factor receptor (EGFR) and the nuclear farnesoid X receptor (FXR) are known to interact with BAs. In this study we examined the effects of BAs on intestinal epithelial cell proliferation and investigated the possible roles for EGFR and FXR in these effects. We report that taurine-conjugated cholic acid (TCA) induced proliferation, while its unconjugated secondary counterpart deoxycholic acid (DCA) inhibited proliferation. TCA stimulated phosphorylation of Src, EGFR, and ERK 1/2. Pharmacological blockade of any of these pathways or genetic ablation of EGFR abrogated TCA-stimulated proliferation. Interestingly, Src or EGFR inhibitors eliminated TCA-induced phosphorylation of both molecules, suggesting that their activation is interdependent. In contrast to TCA, DCA exposure diminished EGFR phosphorylation, and pharmacological or siRNA blockade of FXR abolished DCA-induced inhibition of proliferation. Taken together, these results suggest that TCA induces intestinal cell proliferation via Src, EGFR, and ERK activation. In contrast, DCA inhibits proliferation via an FXR-dependent mechanism that may include downstream inactivation of the EGFR/Src/ERK pathway. Since elevated secondary BA levels are the result of specific bacterial modification, this may provide a mechanism through which an altered microbiota contributes to normal or abnormal intestinal epithelial cell proliferation.