Salt Responsive Gut Microbiota Induces Sex Specific Blood Pressure Changes.

BACKGROUND: Tryptophan metabolism is important in blood pressure regulation. The tryptophan-indole pathway is exclusively mediated by the gut microbiota. ACE2 (angiotensin-converting enzyme 2) participates in tryptophan absorption, and a lack of ACE2 leads to changes in the gut microbiota. The gut microbiota has been recognized as a regulator of blood pressure. Furthermore, there is ample evidence for sex differences in the gut microbiota. However, it is unclear whether such sex differences impact blood pressure differentially through the tryptophan-indole pathway. METHODS: To study the sex-specific mechanisms of gut microbiota-mediated tryptophan-indole pathway in hypertension, we generated a novel rat model with Clustered Regularly Interspaced Short Palindromic Repeats/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats-associated protein 9)-targeted deletion of Ace2 in the Dahl salt-sensitive rat. Cecal microbiota transfers from donors of both sexes to female S recipients were performed. Also, Dahl salt-sensitive rats of both sexes were orally gavaged with indole to investigate blood pressure response. RESULTS: The female gut microbiota and its tryptophan-indole pathway exhibited greater buffering capacity when exposed to tryptophan, due to Ace2 deficiency, and salt. In contrast, the male gut microbiota and its tryptophan-indole pathway were more vulnerable. Female rats with male cecal microbiota responded to salt with a higher blood pressure increase. Indole, a tryptophan-derived metabolite produced by gut bacteria, increased blood pressure in male but not in female rats. Moreover, salt altered host-mediated tryptophan metabolism, characterized by reduced serum serotonin of both sexes and higher levels of kynurenine derivatives in the females. CONCLUSIONS: We uncovered a novel sex-specific mechanism in the gut microbiota-mediated tryptophan-indole pathway in blood pressure regulation. Salt tipped the tryptophan metabolism between the host and gut microbiota in a sex-dependent manner. Our study provides evidence for a novel concept that gut microbiota and its metabolism play sex-specific roles in the development of salt-sensitive hypertension.

Sex hormones, sex chromosomes, and microbiota: Identification of Akkermansia muciniphila as an estrogen-responsive microbiota.

Microbiota composition is known to be linked to sex. However, separating sex hormones and sex chromosome roles in gut microbial diversity is yet to be determined. To investigate the sex chromosome role independent of sex hormones, we used the four-core genotype mouse model. In this mouse model, males with testes and females with ovaries have XX or XY sex chromosome complement. In gonadectomized four-core genotype mice, we observed a significant decrease in the levels of estradiol (P<0.001) and progesterone (P<0.03) in female and testosterone (P<0.0001) in male mice plasma samples. Independent of sex chromosome complement, microbial α diversity was increased in gonadectomized female but not male mice compared to sex-matched gonad-intact controls. ß diversity analysis showed separation between male (P<0.05) but not female XX and XY mice. Importantly, Akkermansia muciniphila was less abundant in gonadectomized compared to gonadal intact female mice (P<0.0001). In the presence of ß-estradiol, Akkermansia muciniphila growth exponentially increased, providing evidence for the identification of a female sex hormone-responsive bacterium (P<0.001).

Genetically engineered Lactobacillus paracasei rescues colonic angiotensin converting enzyme 2 (ACE2) and attenuates hypertension in female Ace2 knock out rats.

Engineered gut microbiota represents a new frontier in medicine, in part serving as a vehicle for the delivery of therapeutic biologics to treat a range of host conditions. The gut microbiota plays a significant role in blood pressure regulation; thus, manipulation of gut microbiota is a promising avenue for hypertension treatment. In this study, we tested the potential of Lactobacillus paracasei, genetically engineered to produce and deliver human angiotensin converting enzyme 2 (Lacto-hACE2), to regulate blood pressure in a rat model of hypertension with genetic ablation of endogenous Ace2 (Ace2-/- and Ace2-/y). Our findings reveal a sex-specific reduction in blood pressure in female (Ace2-/-) but not male (Ace2-/y) rats following colonization with the Lacto-hACE2. This beneficial effect of lowering blood pressure was aligned with a specific reduction in colonic angiotensin II, but not renal angiotensin II, suggesting the importance of colonic Ace2 in the regulation of blood pressure. We conclude that this approach of targeting the colon with engineered bacteria for delivery of ACE2 represents a promising new paradigm in the development of antihypertensive therapeutics.

Epigenetic histone modification by butyrate downregulates KIT and attenuates mast cell function.

Short-chain fatty acid butyrate is produced from the bacterial fermentation of indigestible fiber in the intestinal lumen, and it has been shown to attenuate lung inflammation in murine asthma models. Mast cells (MCs) are initiators of inflammatory response to allergens, and they play an important role in asthma. MC survival and proliferation is regulated by its growth factor stem cell factor (SCF), which acts through the receptor, KIT. It has previously been shown that butyrate attenuates the activation of MCs by allergen stimulation. However, how butyrate mechanistically influences SCF signalling to impact MC function remains unknown. Here, we report that butyrate treatment triggered the modification of MC histones via butyrylation and acetylation, and inhibition of histone deacetylase (HDAC) activity. Further, butyrate treatment caused downregulation of SCF receptor KIT and associated phosphorylation, leading to significant attenuation of SCF-mediated MC proliferation, and pro-inflammatory cytokine secretion. Mechanistically, butyrate inhibited MC function by suppressing KIT and downstream p38 and Erk phosphorylation, and it mediated these effects via modification of histones, acting as an HDAC inhibitor and not via its traditional GPR41 (FFAR3) or GPR43 (FFAR2) butyrate receptors. In agreement, the pharmacological inhibition of Class I HDAC (HDAC1/3) mirrored butyrate's effects, suggesting that butyrate impacts MC function by HDAC1/3 inhibition. Taken together, butyrate epigenetically modifies histones and downregulates the SCF/KIT/p38/Erk signalling axis, leading to the attenuation of MC function, validating its ability to suppress MC-mediated inflammation. Therefore, butyrate supplementations could offer a potential treatment strategy for allergy and asthma via epigenetic alterations in MCs.

Loss of toll-like receptor 5 potentiates spontaneous hepatocarcinogenesis in farnesoid X receptor-deficient mice.

BACKGROUND: HCC is the most common primary liver cancer and a leading cause of cancer-related mortality. Gut microbiota is a large collection of microbes, predominately bacteria, that harbor the gastrointestinal tract. Changes in gut microbiota that deviate from the native composition, that is, "dysbiosis," is proposed as a probable diagnostic biomarker and a risk factor for HCC. However, whether gut microbiota dysbiosis is a cause or a consequence of HCC is unknown. METHODS: To better understand the role of gut microbiota in HCC, mice deficient of toll-like receptor 5 (TLR5, a receptor for bacterial flagellin) as a model of spontaneous gut microbiota dysbiosis were crossed with farnesoid X receptor knockout mice (FxrKO), a genetic model for spontaneous HCC. Male FxrKO/Tlr5KO double knockout (DKO), FxrKO, Tlr5KO, and wild-type (WT) mice were aged to the 16-month HCC time point. RESULTS: Compared with FxrKO mice, DKO mice had more severe hepatooncogenesis at the gross, histological, and transcript levels and this was associated with pronounced cholestatic liver injury. The bile acid dysmetabolism in FxrKO mice became more aberrant in the absence of TLR5 due in part to suppression of bile acid secretion and enhanced cholestasis. Out of the 14 enriched taxon signatures seen in the DKO gut microbiota, 50% were dominated by the Proteobacteria phylum with expansion of the gut pathobiont γ-Proteobacteria that is implicated in HCC. CONCLUSIONS: Collectively, introducing gut microbiota dysbiosis by TLR5 deletion exacerbated hepatocarcinogenesis in the FxrKO mouse model.

Survey and Evaluation of Hypertension Machine Learning Research.

Background Machine learning (ML) is pervasive in all fields of research, from automating tasks to complex decision-making. However, applications in different specialities are variable and generally limited. Like other conditions, the number of studies employing ML in hypertension research is growing rapidly. In this study, we aimed to survey hypertension research using ML, evaluate the reporting quality, and identify barriers to ML's potential to transform hypertension care. Methods and Results The Harmonious Understanding of Machine Learning Analytics Network survey questionnaire was applied to 63 hypertension-related ML research articles published between January 2019 and September 2021. The most common research topics were blood pressure prediction (38%), hypertension (22%), cardiovascular outcomes (6%), blood pressure variability (5%), treatment response (5%), and real-time blood pressure estimation (5%). The reporting quality of the articles was variable. Only 46% of articles described the study population or derivation cohort. Most articles (81%) reported at least 1 performance measure, but only 40% presented any measures of calibration. Compliance with ethics, patient privacy, and data security regulations were mentioned in 30 (48%) of the articles. Only 14% used geographically or temporally distinct validation data sets. Algorithmic bias was not addressed in any of the articles, with only 6 of them acknowledging risk of bias. Conclusions Recent ML research on hypertension is limited to exploratory research and has significant shortcomings in reporting quality, model validation, and algorithmic bias. Our analysis identifies areas for improvement that will help pave the way for the realization of the potential of ML in hypertension and facilitate its adoption.

Host-Microbiota Communication in Spontaneously Hypertensive Rats Generates Unique IgA-Coated Gut Microbes.

Background Hypertension is associated with gut dysbiosis, altered intestinal immunity, and gut pathology in animal models and humans. Although these findings have implicated impaired interactions between gut and gut microbiota in hypertension, little is known about the specific functional gut microbes that interact with intestinal mucosa. Methods and Results To identify these microbes, we sorted Immunoglobin A (IgA)-coated (IgA+) and IgA-noncoated (IgA-) bacteria using a combination of magnetic-activated cell sorting and fluorescence-activated cell sorting, and subsequently performed 16 S rRNA gene sequencing (IgA-SEQ) to determine the microbial composition of IgA+ and IgA- fractions in spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats. We observed a significant decrease in IgA+ bacteria in SHR compared with Wistar Kyoto and a distinct composition of IgA+ and IgA- bacteria between Wistar Kyoto and SHR, showing more IgA-bound Proteobacteria, Bacteroidetes and Actinobacteria but less of Firmicutes in SHR at the phylum level. We further identified enriched IgA-coated Romboutsia, Turicibacter, Ileibacterium, and Dubosiella in SHR that were negatively correlated with the various pathways including antigen presentation, immune response, cell junction organization, epithelium development, and defense response to virus. Conclusions We demonstrate new IgA-coated bacteria that participate in host-microbiota communication in hypertension, suggesting promising therapeutic interventions targeting these bacteria for hypertension management.

Combating hypertension beyond genome-wide association studies: Microbiome and artificial intelligence as opportunities for precision medicine.

The single largest contributor to human mortality is cardiovascular disease, the top risk factor for which is hypertension (HTN). The last two decades have placed much emphasis on the identification of genetic factors contributing to HTN. As a result, over 1,500 genetic alleles have been associated with human HTN. Mapping studies using genetic models of HTN have yielded hundreds of blood pressure (BP) loci but their individual effects on BP are minor, which limits opportunities to target them in the clinic. The value of collecting genome-wide association data is evident in ongoing research, which is beginning to utilize these data at individual-level genetic disparities combined with artificial intelligence (AI) strategies to develop a polygenic risk score (PRS) for the prediction of HTN. However, PRS alone may or may not be sufficient to account for the incidence and progression of HTN because genetics is responsible for <30% of the risk factors influencing the etiology of HTN pathogenesis. Therefore, integrating data from other nongenetic factors influencing BP regulation will be important to enhance the power of PRS. One such factor is the composition of gut microbiota, which constitute a more recently discovered important contributor to HTN. Studies to-date have clearly demonstrated that the transition from normal BP homeostasis to a state of elevated BP is linked to compositional changes in gut microbiota and its interaction with the host. Here, we first document evidence from studies on gut dysbiosis in animal models and patients with HTN followed by a discussion on the prospects of using microbiota data to develop a metagenomic risk score (MRS) for HTN to be combined with PRS and a clinical risk score (CRS). Finally, we propose that integrating AI to learn from the combined PRS, MRS and CRS may further enhance predictive power for the susceptibility and progression of HTN.

Repurposing a Drug Targeting Inflammatory Bowel Disease for Lowering Hypertension.

Background The gut and gut microbiota, which were previously neglected in blood pressure regulation, are becoming increasingly recognized as factors contributing to hypertension. Diseases affecting the gut such as inflammatory bowel disease (IBD) present with aberrant energy metabolism of colonic epithelium and gut dysbiosis, both of which are also mechanisms contributing to hypertension. We reasoned that current measures to remedy deficits in colonic energy metabolism and dysbiosis in IBD could also ameliorate hypertension. Among them, 5-aminosalicylic acid (5-ASA; mesalamine) is a PPARγ (peroxisome proliferator-activated receptor gamma) agonist. It attenuates IBD by a dual mechanism of selectively enhancing colonic epithelial cell energy metabolism and ameliorating gut dysbiosis. Methods and Results A total of 2 groups of 11- to 12-week-old male, hypertensive, Dahl salt-sensitive (S) rats were gavaged with (n=10) or without (n=10) 5-aminosalicylic acid (150 mg/kg) for 4 weeks. Rats receiving 5-aminosalicylic acid treatment had a lower mean blood pressure than controls (145±3 mm Hg versus 153±4 mm Hg; P<0.0001). This reduction in blood pressure was accompanied by increased activity of PPARγ, increased expression of energy metabolism-related genes, and lowering of the Firmicutes/Bacteroidetes ratio in the colon, the reduction of which is a marker for the correction of gut dysbiosis. Furthermore, these data were consistent with the American Gut Project wherein the Firmicutes/Bacteroidetes ratio of non-IBD (n=611) patients was significantly lower than patients with IBD (n=631). Conclusions 5-Aminosalicylic acid could be repurposed for hypertension by specifically enhancing the gut energy metabolism and correction of microbiota dysbiosis.

Quercetin Targets hnRNPA1 to Overcome Enzalutamide Resistance in Prostate Cancer Cells.

Prostate cancer remains dependent on androgen receptor signaling even after castration. Aberrant androgen receptor signaling in castration-resistant prostate cancer is mediated by mechanisms such as alterations in the androgen receptor and activation of interacting signaling pathways. Clinical evidence confirms that resistance to the next-generation antiandrogen, enzalutamide, may be mediated to a large extent by alternative splicing of the androgen receptor to generate constitutively active splice variants such as AR-V7. The splice variants AR-V7 and ARv567es have been implicated in the resistance to not only enzalutamide, but also to abiraterone and other conventional therapeutics such as taxanes. Numerous studies, including ours, suggest that splicing factors such as hnRNPA1 promote the generation of AR-V7, thus contributing to enzalutamide resistance in prostate cancer cells. In the present study, we discovered that quercetin, a naturally occurring polyphenolic compound, reduces the expression of hnRNPA1, and consequently, that of AR-V7. The suppression of AR-V7 by quercetin resensitizes enzalutamide-resistant prostate cancer cells to treatment with enzalutamide. Our results indicate that quercetin downregulates hnRNPA1 expression, downregulates the expression of AR-V7, antagonizes androgen receptor signaling, and resensitizes enzalutamide-resistant prostate cancer cells to enzalutamide treatment in vivo in mouse xenografts. These findings demonstrate that suppressing the alternative splicing of the androgen receptor may have important implications in overcoming the resistance to next-generation antiandrogen therapy. Mol Cancer Ther; 16(12); 2770-9. ©2017 AACR.

Lin28 induces resistance to anti-androgens via promotion of AR splice variant generation.

BACKGROUND: Prostate cancer (PCa) is androgen-dependent initially and progresses to a castration-resistant state after androgen deprivation therapy. Treatment options for castration-resistant PCa include the potent second-generation anti-androgen enzalutamide or CYP17A1 inhibitor abiraterone. Recent clinical observations point to the development of resistance to these therapies which may be mediated by constitutively active alternative splice variants of the androgen receptor (AR). METHODS: Sensitivity of LNCaP cells overexpressing Lin28 (LN-Lin28) to enzalutamide, abiraterone, or bicalutamide was compared to that of control LN-neo cells using cell growth assays, proliferation assays using MTT, anchorage-dependent clonogenic ability assays and soft agar assays. Ability of LN-Lin28 cells to maintain AR activation after treatment with enzalutamide, abiraterone, or bicalutamide was tested using immunofluorescence, Western blotting, ChIP assays, and qRT-PCR. Importance of Lin28 in enzalutamide resistance was assessed by the downregulation of Lin28 expression in C4-2B and 22Rv1 cells chronically treated with enzalutamide. Requirement for sustained AR signaling in LN-Lin28 cells was examined by the downregulation of either full length AR or AR-V7 using siRNA. RESULTS: We show that Lin28 promotes the development of resistance to currently used targeted therapeutics by enhancing the expression of AR splice variants such as AR-V7. PCa cells overexpressing Lin28 exhibit resistance to treatment with enzalutamide, abiraterone, or bicalutamide. Downregulation of Lin28 resensitizes enzalutamide-resistant PCa cells to enzalutamide treatment. We also show that the upregulation of splicing factors such as hnRNPA1 by Lin28 may mediate the enhanced generation of AR splice variants in Lin28-expressing cells. CONCLUSIONS: Our findings suggest that Lin28 plays a key role in the acquisition of resistance to AR-targeted therapies by PCa cells and establish the importance of Lin28 in PCa progression.

NF-κB2/p52:c-Myc:hnRNPA1 Pathway Regulates Expression of Androgen Receptor Splice Variants and Enzalutamide Sensitivity in Prostate Cancer.

Castration-resistant prostate cancer (CRPC) remains dependent on androgen receptor (AR) signaling. Alternative splicing of the AR to generate constitutively active, ligand-independent variants is one of the principal mechanisms that promote the development of resistance to next-generation antiandrogens such as enzalutamide. Here, we demonstrate that the splicing factor heterogeneous nuclear RNA-binding protein A1 (hnRNPA1) plays a pivotal role in the generation of AR splice variants such as AR-V7. hnRNPA1 is overexpressed in prostate tumors compared with benign prostates, and its expression is regulated by NF-κB2/p52 and c-Myc. CRPC cells resistant to enzalutamide exhibit higher levels of NF-κB2/p52, c-Myc, hnRNPA1, and AR-V7. Levels of hnRNPA1 and AR-V7 are positively correlated with each other in prostate cancer. The regulatory circuit involving NF-κB2/p52, c-Myc, and hnRNPA1 plays a central role in the generation of AR splice variants. Downregulation of hnRNPA1 and consequently of AR-V7 resensitizes enzalutamide-resistant cells to enzalutamide, indicating that enhanced expression of hnRNPA1 may confer resistance to AR-targeted therapies by promoting the generation of splice variants. These findings may provide a rationale for cotargeting these pathways to achieve better efficacy through AR blockade.

RhoGDIα downregulates androgen receptor signaling in prostate cancer cells.

INTRODUCTION: Treatment of primary prostate cancer (CaP) is the withdrawal of androgens. However, CaP eventually progresses to grow in a castration-resistant state due to aberrant activation of androgen receptor (AR). Understanding the mechanisms leading to the aberrant activation of AR is critical to develop effective therapy. We have previously identified Rho GDP Dissociation Inhibitor alpha (GDIα) as a novel suppressor in prostate cancer. In this study, we examine the effect of GDIα on AR signaling in prostate cancer cells. METHODS: GDIα was transiently or stably transfected into several prostate cancer cell lines including LNCaP, C4-2, CWR22Rv1, and DU145. The regulation of AR expression by GDIα was analyzed by qRT-PCR and Western blot. AR activity was measured by luciferase reporter assays and electrophoretic mobility shift analysis (EMSA). Immunofluorescence assay was performed to study AR nuclear translocation. The interaction between GDIα and AR was examined by co-immunoprecipitation assays. RESULTS: In this study, we have identified GDIα as a negative regulator of AR signaling pathway. Overexpression of GDIα downregulates AR expression at both mRNA and protein levels. Overexpression of GDIα is able to prevent AR nuclear translocation and inhibit transactivation of AR target genes. Co-immunoprecipitation assays showed that GDIα physically interacts with the N-terminal domain of AR. CONCLUSIONS: GDIα suppresses AR signaling through inhibition of AR expression, nuclear translocation, and recruitment to androgen-responsive genes. GDIα regulatory pathway may play a critical role in regulating AR signaling and prostate cancer growth and progression.

Inhibition of ABCB1 expression overcomes acquired docetaxel resistance in prostate cancer.

Docetaxel is the first-line standard treatment for castration-resistant prostate cancer. However, relapse eventually occurs due to the development of resistance to docetaxel. To unravel the mechanism of acquired docetaxel resistance, we established docetaxel-resistant prostate cancer cells, TaxR, from castration-resistant C4-2B prostate cancer cells. The IC50 for docetaxel in TaxR cells was about 70-fold higher than parental C4-2B cells. Global gene expression analysis revealed alteration of expression of a total of 1,604 genes, with 52% being upregulated and 48% downregulated. ABCB1, which belongs to the ATP-binding cassette (ABC) transporter family, was identified among the top upregulated genes in TaxR cells. The role of ABCB1 in the development of docetaxel resistance was examined. Knockdown of ABCB1 expression by its specific shRNA or inhibitor resensitized docetaxel-resistant TaxR cells to docetaxel treatment by enhancing apoptotic cell death. Furthermore, we identified that apigenin, a natural product of the flavone family, inhibits ABCB1 expression and resensitizes docetaxel-resistant prostate cancer cells to docetaxel treatment. Collectively, these results suggest that overexpression of ABCB1 mediates acquired docetaxel resistance and targeting ABCB1 expression could be a potential approach to resensitize docetaxel-resistant prostate cancer cells to docetaxel treatment.

Lin28 promotes growth of prostate cancer cells and activates the androgen receptor.

Prostate cancer (CaP) progresses to a castration-resistant state assisted by multifold molecular changes, most of which involve activation of the androgen receptor (AR). Having previously demonstrated the importance of the Lin28/let-7/Myc axis in CaP, we tested the hypothesis that Lin28 is overexpressed in CaP and that it activates AR and promotes growth of CaP cells. We analyzed human clinical CaP samples for the expression of Lin28 by quantitative real-time RT-PCR, Western blot analysis, and IHC. Growth characteristics of CaP cell lines transiently and stably expressing Lin28 were examined. The clonogenic ability of CaP cells expressing Lin28 was determined by colony formation and soft agar assays. Increase in expression of AR and subsequent increase in transcription of AR-target genes were analyzed by quantitative real-time RT-PCR, luciferase assays, and ELISA. LNCaP cells stably expressing Lin28 were injected into nude mice, and tumorigenesis was monitored. We found that Lin28 is overexpressed in clinical CaP compared to benign prostates. Overexpression of Lin28 enhanced, while down-regulation reduced, growth of CaP cells. Lin28 enhanced the ability of CaP cells to form colonies in anchorage-dependent and anchorage-independent conditions. LNCaP cells stably expressing Lin28 exhibited significantly higher tumorigenic ability in vivo. Lin28 induced expression of the AR and its target genes such as PSA and NKX3.1. Collectively, our findings demonstrate a novel role for Lin28 in CaP development and activation of the AR axis.

NF-κB2/p52 induces resistance to enzalutamide in prostate cancer: role of androgen receptor and its variants.

Resistance of prostate cancer cells to the next-generation antiandrogen enzalutamide may be mediated by a multitude of survival signaling pathways. In this study, we tested whether increased expression of NF-κB2/p52 induces prostate cancer cell resistance to enzalutamide and whether this response is mediated by aberrant androgen receptor (AR) activation and AR splice variant production. LNCaP cells stably expressing NF-κB2/p52 exhibited higher survival rates than controls when treated with enzalutamide. C4-2B and CWR22Rv1 cells chronically treated with enzalutamide were found to express higher levels of NF-κB2/p52. Downregulation of NF-κB2/p52 in CWR22Rv1 cells chronically treated with enzalutamide rendered them more sensitive to cell growth inhibition by enzalutamide. Analysis of the expression levels of AR splice variants by quantitative reverse transcription PCR and Western blotting revealed that LNCaP cells expressing p52 exhibit higher expression of AR splice variants. Downregulation of expression of NF-κB2/p52 in VCaP and CWR22Rv1 cells by short hairpin RNA abolished expression of splice variants. Downregulation of expression of either full-length AR or the splice variant AR-V7 led to an increase in sensitivity of prostate cancer cells to enzalutamide. These results collectively demonstrate that resistance to enzalutamide may be mediated by NF-κB2/p52 via activation of AR and its splice variants.

MicroRNA let-7c is downregulated in prostate cancer and suppresses prostate cancer growth.

PURPOSE: Prostate cancer (PCa) is characterized by deregulated expression of several tumor suppressor or oncogenic miRNAs. The objective of this study was the identification and characterization of miR-let-7c as a potential tumor suppressor in PCa. EXPERIMENTAL DESIGN: Levels of expression of miR-let-7c were examined in human PCa cell lines and tissues using qRT-PCR and in situ hybridization. Let-7c was overexpressed or suppressed to assess the effects on the growth of human PCa cell lines. Lentiviral-mediated re-expression of let-7c was utilized to assess the effects on human PCa xenografts. RESULTS: We identified miR-let-7c as a potential tumor suppressor in PCa. Expression of let-7c is downregulated in castration-resistant prostate cancer (CRPC) cells. Overexpression of let-7c decreased while downregulation of let-7c increased cell proliferation, clonogenicity and anchorage-independent growth of PCa cells in vitro. Suppression of let-7c expression enhanced the ability of androgen-sensitive PCa cells to grow in androgen-deprived conditions in vitro. Reconstitution of Let-7c by lentiviral-mediated intratumoral delivery significantly reduced tumor burden in xenografts of human PCa cells. Furthermore, let-7c expression is downregulated in clinical PCa specimens compared to their matched benign tissues, while the expression of Lin28, a master regulator of let-7 miRNA processing, is upregulated in clinical PCa specimens. CONCLUSIONS: These results demonstrate that microRNA let-7c is downregulated in PCa and functions as a tumor suppressor, and is a potential therapeutic target for PCa.

RhoGDIα suppresses growth and survival of prostate cancer cells.

BACKGROUND: Treatment for primary prostate cancer (CaP) is the withdrawal of androgens. However, CaP eventually progresses to grow in a castration-resistant state. The mechanisms involved in the development and progression of castration-resistant prostate cancer (CRPC) remain unknown. We have previously generated LNCaP-IL6+ cells by treating LNCaP cells chronically with interleukin-6 (IL-6), which have acquired the ability to grow in androgen-deprived conditions. METHODS: We compared the protein expression profile of LNCaP and LNCaP-IL6+ cells using two-dimensional gel electrophoresis. The gels were then silver stained in order to visualize proteins and the differentially expressed spots were identified and characterized by micro sequencing using MALDI-PMF mass spectrometry. RESULTS: In this study, we have identified RhoGDIα (GDIα) as a suppressor of CaP growth. Expression of GDIα was reduced in LNCaP-IL6+ cells and was down-regulated in more aggressive CaP cells compared to LNCaP cells. Over expression of GDIα inhibited the growth of CaP cells and caused LNCaP-IL6+ cells reversal to androgen-sensitive state, while down-regulation of GDIα enhanced growth of androgen-sensitive LNCaP CaP cells in androgen-deprived conditions. In addition, GDIα suppressed the tumorigenic ability of prostate tumor xenografts in vivo. CONCLUSIONS: These results demonstrate that loss of GDIα expression promotes the development and progression of prostate cancer.

MicroRNA let-7c suppresses androgen receptor expression and activity via regulation of Myc expression in prostate cancer cells.

Castration-resistant prostate cancer continues to rely on androgen receptor (AR) expression. AR plays a central role in the development of prostate cancer and progression to castration resistance during and after androgen deprivation therapy. Here, we identified miR-let-7c as a key regulator of expression of AR. miR-let-7c suppresses AR expression and activity in human prostate cancer cells by targeting its transcription via c-Myc. Suppression of AR by let-7c leads to decreased cell proliferation of human prostate cancer cells. Down-regulation of Let-7c in prostate cancer specimens is inversely correlated with AR expression, whereas the expression of Lin28 (a repressor of let-7) is correlated positively with AR expression. Our study demonstrates that the miRNA let-7c plays an important role in the regulation of androgen signaling in prostate cancer by down-regulating AR expression. These results suggest that reconstitution of miR-let-7c may aid in targeting enhanced and hypersensitive AR in advanced prostate cancer.

Andrographolide targets androgen receptor pathway in castration-resistant prostate cancer.

Androgen receptor (AR) signaling not only plays a pivotal role in the development of androgen-dependent prostate cancer but is also important in the growth and survival of castration-resistant prostate cancer (CRPC). The first line of treatment of androgen-dependent prostate cancer is the use of androgen deprivation therapy. However, most patients will eventually relapse due to development of CRPC. Thus, development of a strategy to target AR for treatment of CRPC is urgently needed. The authors have previously identified andrographolide as an inhibitor of interleukin-6, which can suppress tumor growth of prostate cancer cells by screening compounds from the Prestwick Natural compound library. In this study, they identified that andrographolide can inhibit AR expression and prostate cancer cell growth and induce apoptosis. Andrographolide is able to down-regulate AR expression at both mRNA and protein levels, prevents its nuclear translocation, and inhibits transactivation of its target genes. Andrographolide prevents the binding of Hsp90 to AR, resulting in proteasome-mediated AR degradation. Furthermore, andrographolide inhibits castration-resistant C4-2 cell growth by reducing AR expression and activity. Thus, andrographolide can be developed as a potential therapeutic agent for prostate cancer by inhibition of androgen receptor signaling.