Epigenetic regulation of inhibin alpha-subunit gene in prostate cancer cell lines

INHA acts as a novel and potential biomarker in lung adenocarcinoma and shapes the immune-suppressive tumor microenvironment

BACKGROUND

INHA expression has been correlated with the development, growth, and progression of multiple cancer types. However, the biological role of INHA has not been investigated in patients with lung adenocarcinoma (LUAD). Here, we performed a comprehensive bioinformatics analysis of the LUAD dataset to determine the mechanisms underlying the regulation of tumorigenesis by INHA.

MATERIALS AND METHODS

INHA expression and clinical information of patients with LUAD were obtained from The Cancer Genome Atlas (TCGA) database. Protein levels in LUAD cell lines and human lung epithelial cells were examined by western blotting. Next, the prognostic value of INHA in LUAD was assessed using Cox regression analysis, while the potential biological functions and the impact on the immune microenvironment of INHA were investigated using gene set enrichment analysis (GSEA) and single sample GSEA (ssGSEA). Finally, the effect of INHA on LUAD cell proliferation and invasion was determined in vitro and in vivo.

RESULTS

We found significantly high mRNA and protein expression levels of INHA in LUAD tissues and cell lines. Additionally, a higher expression of INHA was linked to a shorter overall survival (OS) and a worse pathological stage, while INHA expression was associated with immune cell infiltration and immune-related markers in the LUAD tumor microenvironment. LUAD with high INHA expression tends to be a cold tumor. Furthermore, GO and KEGG enrichment analysis indicated that INHA-related genes were enriched in the cell adhesion and immune signaling pathways of LUAD. INHA promoted LUAD cell proliferation and invasion, in vitro and in vivo, by inducing the EGFR pathway.

CONCLUSION

Our findings revealed that INHA is overexpressed in LUAD and is linked to a poor prognosis. Our study demonstrates the potential of INHA as an immunotherapeutic and predictive biomarker in LUAD.

Hypoxia-induced inhibin promotes tumor growth and vascular permeability in ovarian cancers

Hypoxia, a driver of tumor growth and metastasis, regulates angiogenic pathways that are targets for vessel normalization and ovarian cancer management. However, toxicities and resistance to anti-angiogenics can limit their use making identification of new targets vital. Inhibin, a heteromeric TGFβ ligand, is a contextual regulator of tumor progression acting as an early tumor suppressor, yet also an established biomarker for ovarian cancers. Here, we find that hypoxia increases inhibin levels in ovarian cancer cell lines, xenograft tumors, and patients. Inhibin is regulated primarily through HIF-1, shifting the balance under hypoxia from activins to inhibins. Hypoxia regulated inhibin promotes tumor growth, endothelial cell invasion and permeability. Targeting inhibin in vivo through knockdown and anti-inhibin strategies robustly reduces permeability in vivo and alters the balance of pro and anti-angiogenic mechanisms resulting in vascular normalization. Mechanistically, inhibin regulates permeability by increasing VE-cadherin internalization via ACVRL1 and CD105, a receptor complex that we find to be stabilized directly by inhibin. Our findings demonstrate direct roles for inhibins in vascular normalization via TGF-β receptors providing new insights into the therapeutic significance of inhibins as a strategy to normalize the tumor vasculature in ovarian cancer.

Hypoxia increases levels of the heteromeric TGFβ ligand inhibin in ovarian cancer and inhibin promotes tumor growth, endothelial cell invasion and permeability.

Methylation and mutation of the inhibin‑α gene in human melanoma cells and regulation of PTEN expression and AKT/PI3K signaling by a demethylating agent

Inhibin suppresses the pituitary secretion of follicle‑stimulating hormone and has been reported to act as a tumor suppressor gene in the gonad in mice. Epigenetic modifications, mutations, changes in the loss of heterozygosity (LOH) of the inhibin‑α gene and regulation of gene expression in response to a demethylating agent [5‑aza‑2'‑deoxycytidine (5‑Aza‑dC)] in human melanoma cells were assessed. In addition, the association between a mutation in the 5'‑untranslated region (5'‑UTR) of the inhibin‑α subunit and the expression of phosphatidylinositol 3,4,5‑trisphosphate‑dependent Rac exchanger 2 (PREX2) and phosphatase and tensin homolog (PTEN) as well as AKT/PI3K signaling was determined. The methylation status of the CpG sites of the inhibin‑α promoter was analyzed by methylation‑specific PCR in bisulfite‑treated DNA. Cell viability was counted using the trypan blue assay, mRNA expression was examined via reverse transcription‑quantitative PCR, and protein expression was examined via western blot analysis. The inhibin‑α promoter was hypermethylated in G361, SK‑MEL‑3, SK‑MEL‑24 and SK‑MEL‑28 cells and moderately methylated in SK‑MEL‑5 cells. Inhibin‑α gene mutations were observed in the 5'‑UTR exon 1 of G361, SK‑MEL‑5, SK‑MEL‑24 and SK‑MEL‑28 cells as well as in exon 2 of SK‑MEL‑3 cells. Allelic imbalance, including LOH, in the inhibin‑α gene was detected in human melanoma cells. Treatment with 5‑Aza‑dC increased inhibin‑α mRNA and protein levels, inhibited cell proliferation, and delayed the doubling times of surviving melanoma cells. In 5‑Aza‑dC‑treated cells, PREX2 protein expression was slightly increased in G361 and SK‑MEL‑24 cells and decreased in SK‑MEL3, SK‑MEL‑5 and SK‑MEL‑28 cells. However, the protein expression of PTEN was decreased in melanoma cells. In addition, AKT and PI3K protein phosphorylation levels increased in all melanoma cells, except of G361 cells, demonstrating decreased PI3K protein phosphorylation. These data provided evidence that methylation, mutation and LOH are observed in the inhibin α‑subunit gene and gene locus in human melanoma cells. Furthermore, the demethylating agent reactivated inhibin‑α gene expression and regulated PREX2 expression. AKT/PI3K signaling increased as PTEN expression decreased. In addition, mutations in the tumor suppressor inhibin‑α, PTEN and p53 genes were not associated with transcriptional silencing, gene expression and cell growth as analyzed through experiments and literature reviews. These data demonstrated that methylation and mutations were associated with the inhibin‑α gene in human melanoma cells and indicated the regulation of PTEN expression and AKT/PI3K signaling by a demethylating agent.

LINE1 CpG-DNA Hypomethylation in Granulosa Cells and Blood Leukocytes Is Associated With PCOS and Related Traits

CONTEXT

Altered global DNA methylation is indicative of epigenomic instability concerning chronic diseases. Investigating its incidence and association with polycystic ovary syndrome (PCOS) is essential to understand the etiopathogenesis of this disorder.

OBJECTIVES

We assessed global DNA methylation differences in peripheral blood leukocytes (PBLs) and cumulus granulosa cells (CGCs) of controls and women with PCOS; and their association with PCOS and its traits.

DESIGN, SETTING, PARTICIPANTS, MAIN OUTCOME MEASURE

This study included a total of 102 controls and women with PCOS. Forty-one women undergoing controlled ovarian hyperstimulation (COH) and 61 women not undergoing COH were recruited from in vitro fertilization (IVF) and infertility clinics. DNA methylation was measured by ELISA for 5'-methyl-cytosine content and bisulfite sequencing of 5'-untranslated region (5'-UTR) of long interspersed nucleotide element-1 (LINE1/L1).

RESULTS

Total 5'-methyl-cytosine and L1 methylation levels in PBLs and CGCs were similar between controls and women with PCOS. Methylation assessed at CpG sites of L1 5'-UTR revealed a single CpG-site (CpG-4) to be consistently hypomethylated in PBLs of both PCOS groups and CGCs of stimulated PCOS group. In unstimulated women, hypomethylation at CpG-4 was strongly associated with PCOS susceptibility, whereas in stimulated group it showed strong associations with PCOS and its hormonal traits. Furthermore, CGCs demonstrated consistent global and CpG-DNA hypomethylation relative to PBLs, irrespective of normal or disease states.

CONCLUSION

Our study revealed strong association of single hypomethylated CpG-site with PCOS. Identification and characterization of more such methyl-CpG signatures in repetitive elements in larger study populations would provide valuable epigenetic insights into PCOS.

Inhibin-α gene mutations and mRNA levels in human lymphoid and myeloid leukemia cells

The inhibin-α gene was identified as a tumor suppressor gene in the gonads and adrenal glands by functional studies using knockout mice. Methylation of CpG sites within the regulatory regions of tumor suppressor gene is frequently associated with their transcriptional silencing. We investigated epigenetic modifications, changes in loss of heterozygosity (LOH), and mutation of the inhibin-α gene, and regulation of transcriptional expression in response to inhibitors of DNA methylation (5-aza-2'-deoxycytidine, 5-AzaC) in human lymphoid (Jurkat, Molt-4, Raji, and IM-9) and myeloid (HL-60, Kasumi-1, and K562) leukemia cells. The inhibin-α promoter was hypermethylated in lymphoid (Molt-4 and Raji) and myeloid (HL-60 and Kasumi-1) leukemia cells. Inhibin-α gene mutations differed significantly between lymphoid (heterozygote) and myeloid (homozygote) leukemia cells. LOH in the inhibin-α gene was detected in lymphoid and myeloid leukemia cells, with the exception of Jurkat cells. Treatment with 5-AzaC, a demethylating agent, resulted in increased inhibin-α mRNA and protein levels in most of the cell lines. Also, 5-AzaC treatment inhibited cell proliferation and induced apoptosis. Taken together, our results reveal that the inhibin-α gene is transcriptionally silenced in human leukemia cells and that reactivation is suppressed by a demethylating agent. In addition, mutations in, and expression levels of, the inhibin-α gene differed between human lymphoid and myeloid leukemia cells.

DNA promoter methylation-dependent transcription of the double C2-like domain β (DOC2B) gene regulates tumor growth in human cervical cancer

Double C2-like domain β (DOC2B) gene encodes for a calcium-binding protein, which is involved in neurotransmitter release, sorting, and exocytosis. We have identified the promoter region of the DOC2B gene as hypermethylated in pre-malignant, malignant cervical tissues, and cervical cancer cell lines by methylation-sensitive dimethyl sulfoxide-polymerase chain reaction and bisulfite genome sequencing; whereas, it was unmethylated in normal cervical tissues (p < 0.05). The promoter hypermethylation was inversely associated with mRNA expression in SiHa, CaSki, and HeLa cells and treatment with demethylating agent 5-aza-2-deoxycytidine restored DOC2B expression. The region -630 to +25 bp of the DOC2B gene showed robust promoter activity by a luciferase reporter assay and was inhibited by in vitro artificial methylation with Sss1 methylase prior to transient transfections. Overexpression of the DOC2B gene in SiHa cells when compared with controls showed significantly reduced colony formation, cell proliferation, induced cell cycle arrest, and repressed cell migration and invasion (p < 0.05). Ectopic expression of DOC2B resulted in anoikis-mediated cell death and repressed tumor growth in a nude mice xenograft model (p < 0.05). DOC2B expressing cells showed a significant increase in intracellular calcium level (p < 0.05), impaired AKT1 and ERK1/2 signaling, and induced actin cytoskeleton remodeling. Our results show that promoter hypermethylation and silencing of the DOC2B gene is an early and frequent event during cervical carcinogenesis and whose reduced expression due to DNA promoter methylation may lead to selective cervical tumor growth.

DNA methylation and histone modifications are associated with repression of the inhibin α promoter in the rat corpus luteum

The transition from follicle to corpus luteum after ovulation is associated with profound morphological and functional changes and is accompanied by corresponding changes in gene expression. The gene encoding the α subunit of the dimeric reproductive hormone inhibin is maximally expressed in the granulosa cells of the preovulatory follicle, is rapidly repressed by the ovulatory LH surge, and is expressed at only very low levels in the corpus luteum. Although previous studies have identified transient repressors of inhibin α gene transcription, little is known about how this repression is maintained in the corpus luteum. This study examines the role of epigenetic changes, including DNA methylation and histone modification, in silencing of inhibin α gene expression. Bisulfite sequencing reveals that methylation of the inhibin α proximal promoter is low in preovulatory and ovulatory follicles but is elevated in the corpus luteum. Increased methylation during luteinization is observed within the cAMP response element in the promoter, and EMSA demonstrate that methylation of this site inhibits cAMP response element binding protein binding in vitro. Chromatin immunoprecipitation reveals that repressive histone marks H3K9 and H3K27 trimethylation are increased on the inhibin α promoter in primary luteal cells, whereas the activation mark H3K4 trimethylation is decreased. The changes in histone modification precede the alterations in DNA methylation, suggesting that they facilitate the recruitment of DNA methyltransferases. We show that the DNA methyltransferase DNMT3a is present in the ovary and in luteal cells when the inhibin α promoter becomes methylated and observe recruitment of DNMT3a to the inhibin promoter during luteinization.

Activins and activin antagonists in the prostate and prostate cancer

Activins are members of the TGF-β super-family. There are 4 mammalian activin subunits (β(A), β(B), β(C) and β(E)) that combine to form functional proteins. The role of activin A (β(A)β(A)) is well characterized and known to be a potent growth and differentiation factor. Two of the activin subunits (β(C) and β(E)) were discovered more recently and little is known about their biological functions. In this review the evidence that activin-β(C) is a significant regulator of activin A bioactivity is presented and discussed. It is concluded that activin-β(C), like other antagonists of activin A, is an important growth regulator in prostate health and disease.

Mutations in inhibin and activin genes associated with human disease

Inhibins and activins are members of the transforming growth factor (TGFβ) superfamily, that includes the TGFβs, inhibins and activins, bone morphogenetic proteins (BMPs) and growth and differentiation factors (GDFs). The family members are expressed throughout the human body, and are involved in the regulation of a range of important functions. The precise regulation of the TGFβ pathways is critical, and mutations of individual molecules or even minor alterations of signalling will have a significant affect on function, that may lead to development of disease or predisposition to the development of disease. The inhibins and activins regulate aspects of the male and female reproductive system, therefore, it is not surprising that most of the diseases associated with abnormalities of the inhibin and activin genes are focused on reproductive disorders and reproductive cancers. In this review, I highlight the role of genetic variants in the development of conditions such as premature ovarian failure, pre-eclampsia, and various reproductive cancers. Given the recent advances in human genetic research, such as genome wide association studies and next generation sequencing, it is likely that inhibins and activins will be shown to play more important roles in a range of human genetic diseases in the future.

Transcriptional silencing of the inhibin-α gene in human gastric carcinoma cells

Although inhibin was first identified as a hormone regulating pituitary FSH secretion, it was later recognized to act as a tumor suppressor in the gonad and adrenal glands. Recently, the alpha subunit of this dimeric hormone (inhibin‑α) was reported to be involved in prostate tumorigenesis. To identify additional roles outside the reproductive axis, we investigated inhibin‑α gene activity and subsequent cell fate in human gastric cancer cells. The results were as follows: all the gastric cancer cells had at least one of a set of abnormalities including hypermethylation of the promoter, mutation of the 5'‑UTR or allelic imbalance including LOH in the inhibin‑α gene. Hypermethylation of the promoter and mutation of the 5'‑UTR in inhibin‑α were observed in SNU‑1, SNU‑5 and SNU‑484 cells. LOH was observed in AGS, KATO III, SNU‑5, SNU‑484 and SNU‑668 cells. Treatment with 5‑AzaC, a demethylating agent, induced demethylation of the inhibin‑α promoter in the SNU‑1, SNU‑5 and SNU‑484 cell lines, with the CpG5 site being strongly influenced by 5‑AzaC. In addition, inhibin‑α mRNA and protein were maintained at low levels in most of the gastric cancer cell lines. These low levels of mRNA and protein expression could be increased in most lines by treatment with 5‑AzaC. These increased inhibin‑α expression levels seemed to be closely associated with apoptosis and suppression of cell growth. Taken together, our results reveal that the inhibin‑α gene is transcriptionally silenced in human gastric cancer cells, and that reactivation of the gene suppresses their growth characteristics. This suggests that inhibin‑α may have a more general tumor suppressor activity outside the reproductive axis.

The synthesis and secretion of inhibins

Inhibin A and B, dimeric glycoproteins comprising an α- and β((A/B))-subunit, negatively regulate follicle stimulating hormone (FSH) synthesis by the pituitary. The expression of α- and β-subunits within Sertoli cells of the testis and granulosa cells of the ovary is controlled by a range of transcription factors, including CREB, SP-1, Smads, and GATA factors. The inhibin α- and β-subunits are synthesized as precursor molecules consisting of an N-terminal propeptide and a C-terminal mature domain. Recently, we showed that hydrophobic residues within the propeptides of the α- and β-subunits interact noncovalently with their mature domains, maintaining the molecules in a conformation competent for dimerization. Dimeric precursors are cleaved by proprotein convertases and mature inhibins are secreted from the cell noncovalently associated with their propeptides. Propeptides may increase the half-life of inhibin A and B in circulation, but they are readily displaced in the presence of the high-affinity receptors, betaglycan, and ActRII.

New targets for old hormones: inhibins clinical role revisited

Inhibins are gonadal peptide hormones belonging to the transforming growth factor-β (TGF-β) superfamily that regulate the pituitary follicle stimulating hormone (FSH) secretion by negative feedback mechanisms. It is evident that the understanding of inhibins function in the hypothalamic-pituitary-gonadal axis will provide insights into physiology and pathology of the gonadal function. In recent years, a great deal of attention has been focussed on clinical relevance of measuring circulating inhibins in normal and disease state. The past few years also have witnessed the emergence and discovery of extra pituitary action of inhibins that might provide further insights into the underlying diseases like cancer especially in the reproductive axis and various other new endocrine target organs. In this review after systematic analysis of literature, we discuss briefly the known and recent advances in function of these hormones highlighting also its structure, production and mechanisms of signal transduction. Also this review discusses about the physiological relevance of inhibin association in the normal function to the development of reproductive cancers. Finally, we describe evidence from various emerging studies that inhibins make an important contribution to other physiological functions apart from reproduction which reveals new endocrine target organs of inhibins. The emerging view is inhibin participates in multiple ways to regulate the function in different cell types and still complete repertoire of its actions is under investigation.

Inhibins: from reproductive hormones to tumor suppressors

Inhibins are peptide hormones shown originally to be produced by the gonads to regulate the secretion of follicle stimulating hormone by pituitary gonadotropes. Although gonadotropes have been regarded as the canonical inhibin target cells, in recent years extrapituitary actions of inhibins have come into the spotlight. In particular, disruptions to the local actions of inhibins in peripheral tissues might underlie certain diseases, especially cancers of the reproductive tract. This review focuses on recent advances in the inhibin field, with a particular emphasis on the determinants of inhibin availability, mechanisms of inhibin action, and the physiological relevancy of local inhibin actions in the development and progression of reproductive cancers.

Vinclozolin exposure in utero induces postpubertal prostatitis and reduces sperm production via a reversible hormone-regulated mechanism

Vinclozolin is an endocrine-disrupting chemical (EDC) that binds with high affinity to the androgen receptor (AR) and blocks the action of gonadal hormones on male reproductive organs. An alternative mechanism of action of Vinclozolin involves transgenerational effects on the male reproductive tract. We previously reported in utero Vinclozolin exposure-induced prostatitis (prostate inflammation) in postpubertal rats concurrent with down-regulation of AR and increased nuclear factor-kappaB activation. We postulated the male reproductive abnormalities induced by in utero Vinclozolin exposure could be reversed by testosterone supplementation, in contrast to the permanent modifications involving DNA methyltransferases (Dnmts) described by others. To test this hypothesis, we administered high-dose testosterone at puberty to Vinclozolin-treated rats and determined the effect on anogenital distance (AGD); testicular germ cell apoptosis, concentration of elongated spermatids, and the onset of prostatitis. Concurrently we examined Dnmt1, -3A, -3B, and -3L mRNA expression. Consistent with previous reports, in utero exposure to Vinclozolin significantly reduced AGD, increased testicular germ cell apoptosis 3-fold, reduced elongated spermatid number by 40%, and induced postpubertal prostatitis in 100% of exposed males. Administration of high-dose testosterone (25 mg/kg) at puberty normalized AGD, reduced germ cell apoptosis, and restored elongated spermatid number. Testosterone restored AR and nuclear factor-kappaB expression in the prostate and abolished Vinclozolin-induced prostatitis. Altered Dnmt expression was evident with in utero Vinclozolin exposure and was not normalized after testosterone treatment. These data demonstrate in utero Vinclozolin-induced male reproductive tract abnormalities are AR mediated and reversible and involve a mechanism independent of Dnmt expression.

Estrogen receptor-beta activated apoptosis in benign hyperplasia and cancer of the prostate is androgen independent and TNFalpha mediated

Prostate cancer (PCa) and benign prostatic hyperplasia (BPH) are androgen-dependent diseases commonly treated by inhibiting androgen action. However, androgen ablation or castration fail to target androgen-independent cells implicated in disease etiology and recurrence. Mechanistically different to castration, this study shows beneficial proapoptotic actions of estrogen receptor-beta (ERbeta) in BPH and PCa. ERbeta agonist induces apoptosis in prostatic stromal, luminal and castrate-resistant basal epithelial cells of estrogen-deficient aromatase knock-out mice. This occurs via extrinsic (caspase-8) pathways, without reducing serum hormones, and perturbs the regenerative capacity of the epithelium. TNFalpha knock-out mice fail to respond to ERbeta agonist, demonstrating the requirement for TNFalpha signaling. In human tissues, ERbeta agonist induces apoptosis in stroma and epithelium of xenografted BPH specimens, including in the CD133(+) enriched putative stem/progenitor cells isolated from BPH-1 cells in vitro. In PCa, ERbeta causes apoptosis in Gleason Grade 7 xenografted tissues and androgen-independent cells lines (PC3 and DU145) via caspase-8. These data provide evidence of the beneficial effects of ERbeta agonist on epithelium and stroma of BPH, as well as androgen-independent tumor cells implicated in recurrent disease. Our data are indicative of the therapeutic potential of ERbeta agonist for treatment of PCa and/or BPH with or without androgen withdrawal.

Elevated level of inhibin-alpha subunit is pro-tumourigenic and pro-metastatic and associated with extracapsular spread in advanced prostate cancer

The biological function of inhibin-α subunit (INHα) in prostate cancer (PCa) is currently unclear. A recent study associated elevated levels of INHα in PCa patients with a higher risk of recurrence. This prompted us to use clinical specimens and functional studies to investigate the pro-tumourigenic and pro-metastatic function of INHα. We conducted a cross-sectional study to determine a link between INHα expression and a number of clinicopathological parameters including Gleason score, surgical margin, extracapsular spread, lymph node status and vascular endothelial growth factor receptor-3 expression, which are well-established prognostic factors of PCa. In addition, using two human PCa cell lines (LNCaP and PC3) representing androgen-dependent and -independent PCa respectively, we investigated the biological function of elevated levels of INHα in advanced cancer. Elevated expression of INHα in primary PCa tissues showed a higher risk of PCa patients being positive for clinicopathological parameters outlined above. Over-expressing INHα in LNCaP and PC3 cells demonstrated two different and cell-type-specific responses. INHα-positive LNCaP demonstrated reduced tumour growth whereas INHα-positive PC3 cells demonstrated increased tumour growth and metastasis through the process of lymphangiogenesis. This study is the first to demonstrate a pro-tumourigenic and pro-metastatic function for INHα associated with androgen-independent stage of metastatic prostate disease. Our results also suggest that INHα expression in the primary prostate tumour can be used as a predictive factor for prognosis of PCa.

Early-onset endocrine disruptor-induced prostatitis in the rat

BACKGROUND

Androgens are critical for specifying prostate development, with the fetal prostate sensitive to altered hormone levels and endocrine-disrupting chemicals (EDCs) that exhibit estrogenic or antiandrogenic properties. Prostatic inflammation (prostatitis) affects 9% of men of all ages, and > 90% of cases are of unknown etiology.

OBJECTIVES

In this study we aimed to evaluate effects of in utero exposure to the antiandrogenic EDC vinclozolin, during the period of male reproductive tract development, on neonatal, prepubertal, and postpubertal prostate gland function of male offspring.

METHODS

Fetal rats were exposed to vinclozolin (100 mg/kg body weight) or vehicle control (2.5 mL/kg body weight) in utero from gestational day 14 (GD14) to GD19 via oral administration to pregnant dams. Tissue analysis was carried out when male offspring were 0, 4, or 8 weeks of age.

RESULTS

In utero exposure to vinclozolin was insufficient to perturb prostatic development and branching, although expression of androgen receptor and mesenchymal fibroblast growth factor-10 was down-regulated. Prostate histology remained normal until puberty, but 100% of animals displayed prostatitis postpubertally (56 days of age). Prostatic inflammation was associated with phosphorylation and nuclear translocation of nuclear factor-kappa B (NFkappaB) and postpubertal activation of proinflammatory NFkappaB-dependent genes, including the chemokine interleukin-8 and the cytokine transforming growth factor-beta1. Significantly, inflammation arising from vinclozolin exposure was not associated with the emergence of premalignant lesions, such as prostatic intra-epithelial neoplasia or proliferative inflammatory atrophy, and hence mimics nonbacterial early-onset prostatitis that commonly occurs in young men.

CONCLUSIONS

These data are the first to unequivocally implicate EDCs as a causative factor and fill an important knowledge gap on the etiology of prostatitis.

Cancer progression: is inhibin alpha from Venus or Mars?

The inhibin field has been perplexed by the information that inhibin alpha is a tumour suppressor in mice yet is elevated in women with ovarian cancer. Furthermore, we have consistently observed a down-regulation or loss of inhibin alpha in prostate cancer patient samples and cell lines. However, our latest data have prompted us to re-evaluate the role of inhibin alpha in prostate and other cancers. Using the analogy of TGF-beta as a springboard for our hypothesis, we offer a unifying model whereby the previously conflicting observations in mice, men and women can be explained. We propose that initially inhibin alpha is tumour-suppressive and is expressed in benign and early-stage primary cancers. Tumour-suppressive inhibin alpha is then silenced as the tumour progresses but is reactivated as a pro-metastatic factor in advanced, aggressive cancers.

Re-evaluation of inhibin alpha subunit as a tumour suppressor in prostate cancer

Inhibin is a member of the TGF-beta superfamily of growth and differentiation factors and a tumor suppressor. Consistent with the tumor suppressive function of the inhibin alpha subunit in prostate cancer, we reported a loss of gene expression due to DNA hypermethylation and loss of heterozygosity (LOH) as well as down regulation of inhibin alpha subunit immunoreactivity. Paradoxically, an expanded study to evaluate the prognostic significance of inhibin alpha subunit expression in men with prostate cancer resulted in a contradictory outcome, whereby an up-regulation of subunit expression was recorded. In seeking a more comprehensive explanation for all data sets, we offer a unifying hypothesis. We propose that the tumor suppressor activities of the inhibin alpha subunit dominate in non-malignant tissue, but its oncogenic activities emerge during tumorigenesis. An explanation such as this, involving a switch in gene function from being tumor suppressive to pro-oncogenic, may account for the discrepant findings in other types of cancer.