Biomedical subjects

G P Risbridger

Publications and source records attributed to G P Risbridger.

At least 19 recordsLinked to original sources

PubMed2006

Aromatase and prostate cancer.

The normal growth and development of the prostate requires the presence and action of androgens, which are also known risk factors in the origins of benign and malignant prostate disease. Paradoxically, the incidence of prostate disease increases with age when serum androgen levels are in decline and emerging evidence suggests that estrogens may also be important in the normal prostate, as well as in the etiology of prostate disease. Both estrogen receptor subtypes are present in the prostate, demonstrating that the gland responds directly to estrogens. Recent data suggests that estrogens play a role in prostate disease and has demonstrated that high doses of estrogens induce premalignant dysplasia and in combination with high doses of androgens, malignancy. The production of estrogens from androgens is mediated by the aromatase enzyme, the aberrant expression of which plays a critical role in the disease process in other tissues, most notably the breast. The prostate expresses aromatase within the stroma of benign tissue, while in malignancy there is an induction of epithelial expression with altered promoter utilisation. Although the presence of aromatase in the prostate and its aberrant expression in prostate cancer is significant, its role and contribution to prostate carcinogenesis remains unclear. Transgenic mouse models lacking aromatase (ArKO) and over-expressing aromatase (AROM+) have provided an ideal means to examine aromatase expression in the prostate. Studies using these animals may lead to a better understanding of the role that aromatase--and therefore estrogen--plays in the development and progression of prostate disease.

Adenocarcinoma↗

PubMed2005

Early prostate development and its association with late-life prostate disease.

The development of the prostate is an emerging priority area for prostate biologists. Early changes in prostate development permanently alter prostate morphology and function and an understanding of the permanent nature of early events that may influence the onset of late-life disease is vital. Two of the inherent problems involve associating exposure in early life with outcome in late life or maturity and accounting for the influence of genetic, environmental, dietary or metabolic factors during the intervening period. Any one of these factors, alone or in combination, might lead to an explanation of the discrepancies found in the literature regarding the influence of early changes to the prostate in later life. Therefore, it is important to establish a causal link between the hormonal changes that occur during the fetal/neonatal period and that imprint the gland and the onset of late-life pathology. In order to achieve this goal, several technical challenges need to be overcome to permit the objective assessment of prostate branching morphogenesis. Stereological techniques now allow the quantification of several parameters of branching morphogenesis and the identification of specific early changes that are permanent and irreversible with a late-life outcome. This methodology provides the means to determine the action of a range of genes or hormone/growth factors that have been implicated in prostate development and disease.

Fetus↗

PubMed2005

17beta-estradiol induces apoptosis in the developing rodent prostate independently of ERalpha or ERbeta.

Estrogens induce both proliferative and antiproliferative responses in the prostate gland. To date, antiproliferative effects of estrogens are generally considered to be due to systemic antiandrogenic actions. However, estrogen action mediated through estrogen receptor (ER) beta was recently suggested as another mechanism of induction of apoptosis in the prostate. This study aimed to explore the hypothesis that the antiproliferative effects of estrogen are directly mediated through ERbeta using a prostate organ culture system. We previously reported effects of 17beta-estradiol (E2) using rat ventral prostate (VP) tissues, and adapted the system for culturing mouse tissues. In both rat and mouse models, estrogen-induced apoptosis was detected that was spatially and regionally localized to the epithelium of the distal tips. Using organ cultures of alphaER knockout (alphaERKO) and betaERKO prostates, we failed to demonstrate that apoptosis induced by E2 was mediated through either receptor subtype. Activation of ER-selective ligands (ERalpha, propyl pyrazole triol, ERbeta, diaryl-proprionitrile, and 5alpha-androstane-3beta,17beta-diol) in organ culture experiments failed to induce apoptosis, as did the membrane impermeable conjugate E2:BSA, discounting the possibility of nongenomic effects. Consequently, E2 regulation of androgen receptor (AR) expression was examined and, in the presence of nanomolar testosterone levels, E2 caused a specific reduction in AR protein expression in wild-type, alphaERKO, and betaERKO mice, particularly in the distal region where apoptosis was detected. This down-regulation of AR protein provides a possible mechanism for the proapoptotic action of E2 that is independent of ERs or nongenomic effects.

Animals↗

PubMed2005

betaA- and betaC-activin, follistatin, activin receptor mRNA and betaC-activin peptide expression during rat liver regeneration.

The mRNA expression of two activin growth factor subunits (betaA- and betaC-activin), activin receptor subunits (ActRIIA, ActRIIB) and the activin-binding protein follistatin, and peptide expression of betaA-activin and betaC-activin subunits, were examined in regenerating rat liver after partial hepatectomy (PHx). Liver samples were collected from adult, male Sprague-Dawley rats, 12-240 h (n=3-5 rats per time point) after PHx or from sham-operated controls at the same time points. Hepatocyte mitosis and apoptosis were assessed histologically and by in situ cell death detection. RT and PCR were used to assess relative gene expression. betaA- and betaC-activin peptide immunoreactivity was assessed in liver and serum samples by western blotting, whereas cellular expression was investigated by immunohistochemistry, using specific monoclonal antibodies. betaA- and betaC-activin mRNA dropped to < 50% of sham control values 12 h after PHx and remained at this level until 168 h post-PHx, when betaA-activin expression increased to three times sham control values and betaC-activin mRNA returned to pre-PHx levels. A peak in follistatin expression was observed 24-48 h post-PHx, coincident with an increase in hepatocyte mitosis. No changes were observed in ActRIIA mRNA, whereas ActRIIB expression paralleled that of betaA-activin mRNA. betaC-activin immunoreactive homo- and heterodimers were observed in regenerating liver and serum. Mitotic hepatocytes frequently contained betaC-activin immunoreactivity, whereas apoptotic hepatocytes were often immunoreactive for betaA-activin. We conclude that betaA- and betaC-activin subunit proteins are autocrine growth regulators in regenerating liver and when expressed independently lead to hepatocyte apoptosis or mitosis in a subset of hepatocytes.

Activin Receptors↗

PubMed2004

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.

Female↗

PubMed2004

Elevated expression of inhibin alpha in prostate cancer.

PURPOSE: Less than 50% of men who undergo radical prostatectomy for prostate cancer are cured of disease. We evaluate tumor expression of inhibin alpha, a putative tumor suppressor, and the related protein, follistatin, to determine whether expression correlated with failure to be cured by surgery. MATERIALS AND METHODS: Tissues were selected from an archival collection of 379 prostatectomy specimens from men with followup of at least 5 years after surgery. Since previous studies showed that such men with only Gleason grade 3 cancer had a greater than 95% chance of no biochemical recurrence (increase in serum prostate specific antigen), our investigation was confined to 174 men with 2% or greater grade 4/5 cancer. These men had an intermediate rate of failure, providing an opportunity to analyze the potential contribution of inhibin alpha or follistatin to progression. Intensity of immunohistochemical labeling for inhibin alpha and follistatin in each cancer was compared with that in normal glands within the same tissue section. RESULTS: The majority of cases showed more intense expression of inhibin alpha in cancer than in normal glands. Those individuals whose cancers had the most elevated expression of inhibin alpha had a higher risk of recurrence, although this association was not statistically significant. Follistatin was expressed equivalently in normal and cancer cells in the majority of cases and did not correlate with recurrence. CONCLUSIONS: Our finding that inhibin alpha is frequently overexpressed in high grade prostate cancer suggests that the role of inhibin alpha as a tumor suppressor needs to be reevaluated. Furthermore, assessment of inhibin alpha as a serum marker of prostate cancer, as used to diagnose ovarian cancer, may be warranted.

Aged↗

PubMed2004

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

Inhibin was first identified as a gonad-derived regulator of pituitary FSH; however, it has subsequently been shown to be a tumour suppressor in the gonad and adrenal glands. Whereas non-malignant regions of human primary prostate carcinomas express inhibin alpha-subunit (INHA), malignant tissues lack INHA transcript and protein, which is consistent with epigenetic regulation of the inhibin alpha-subunit gene (INHA) promoter. This study investigated whether methylation of the INHA promoter was responsible for inactivation of INHA transcription and translation in the prostate cancer cell lines, LNCaP, DU145 and PC3. Methylation of the promoter was revealed by bisulphite genomic sequencing and use of inhibitors of methylation and histone deacetylation resulted in reactivation of the INHA transcription and translation. Significant (P<0.05) downregulation of a luciferase reporter gene downstream from a methylated INHA promoter compared with unmethylated INHA promoter occurred in vitro. The data demonstrate that promoter methylation is associated with downregulation of the INHA gene in prostate cancer cell lines, which is consistent with its tumour suppressive role. Therefore INHA has a significant role in prostate tumorigenesis.

Base Sequence↗

PubMed2003

Oestrogens and prostate cancer.

Androgens are essential for stimulating normal development, growth and secretory activities of the prostate whereas oestrogens are generally regarded as inhibitors of growth. Evidence for the local synthesis of oestrogens includes the detection of aromatase mRNA and protein in the stroma of human non-malignant tissues and in malignant tissue, where it is detected in epithelial tumour cells. As well, aromatase activity was measured by biochemical assay and protein was detected in prostatic non-malignant and tumour cell lines. Taken together with the identification of direct oestrogenic actions on the prostate, these results suggest that alterations in local oestrogen synthesis may have significant consequences in malignancy of these organs. Genetically modified mouse models were studied in order to evaluate the action of oestrogens alone or in combination with androgens on the prostate gland. Hypogonadal (hpg) mice are deficient in gonadotrophins and androgens but showed direct proliferative responses to oestradiol. The responses were characterised by discrete lobe-specific changes including smooth-muscle regression, fibroblast proliferation, inflammation, and basal epithelial cell proliferation and metaplasia. The aromatase knockout (ArKO) mouse, deficient in oestrogens due to a non-functional aromatase enzyme, developed prostatic hyperplasia during the lifelong exposure to elevated androgens, however, no malignant changes were detected in the prostate at any time. In contrast, combined androgen and oestrogen treatment has been shown to induce prostatic dysplasia and adenocarcinoma. These results demonstrate that malignant changes to the prostate gland are dependent upon both androgenic and oestrogenic responses and that neither hormone alone is sufficient to evoke aberrant patterns of growth, resulting in malignancy.

Androgens↗

PubMed2001

Activins as regulators of branching morphogenesis.

Development of glandular organs such as the kidney, lung, and prostate involves the process of branching morphogenesis. The developing organ begins as an epithelial bud that invades the surrounding mesenchyme, projecting dividing epithelial cords or tubes away from the site of initiation. This is a tightly regulated process that requires complex epithelial-mesenchymal interactions, resulting in a three-dimensional treelike structure. We propose that activins are key growth and differentiation factors during this process. The purpose of this review is to examine the direct, indirect, and correlative lines of evidence to support this hypothesis. The expression of activins is reviewed together with the effect of activins and follistatins in the development of branched organs. We demonstrate that activin has both negative and positive effects on cell growth during branching morphogenesis, highlighting the complex nature of activin in the regulation of proliferation and differentiation. We propose potential mechanisms for the way in which activins modify branching and address the issue of whether activin is a regulator of branching morphogenesis.

Activins↗

PubMed2001

Regulation of prostate branching morphogenesis by activin A and follistatin.

Ventral prostate development occurs by branching morphogenesis and is an androgen-dependent process modulated by growth factors. Many growth factors have been implicated in branching morphogenesis including activins (dimers of beta(A) and beta(B) subunits); activin A inhibited branching of lung and kidney in vitro. Our aim was to examine the role of activins on prostatic development in vitro and their localization in vivo. Organ culture of day 0 rat ventral prostates for 6 days with activin A (+/- testosterone) inhibited prostatic branching and growth without increasing apoptosis. The activin-binding protein follistatin increased branching in vitro in the absence (but not presence) of testosterone, suggesting endogenous activins may reduce prostatic branching morphogenesis. In vivo, inhibin alpha subunit was not expressed until puberty, therefore inhibins (dimers of alpha and beta subunits) are not involved in prostatic development. Activin beta(A) was immunolocalized to developing prostatic epithelium and mesenchymal aggregates at ductal tips. Activin beta(B) immunoreactivity was weak during development, but was upregulated in prostatic epithelium during puberty. Activin receptors were expressed throughout the prostatic epithelium. Follistatin mRNA and protein were expressed throughout the prostatic epithelium. The in vitro evidence that activin and follistatin have opposing effects on ductal branching suggests a role for activin as a negative regulator of prostatic ductal branching morphogenesis.

Activin Receptors↗

PubMed2001

The contribution of inhibins and activins to malignant prostate disease.

The normal human prostate expresses inhibin and activin subunits. In prostate cancer, the inhibin alpha subunit gene is down regulated and this is associated with loss of heterozygosity (LOH) at the gene locus and methylation of the promoter. These data support the hypothesis that the inhibin alpha subunit is tumor suppressive in the prostate. The pluripotent effects of activins and the similarities to transforming growth factor beta (TFGbeta) suggest a role for activins in progression to malignancy, whereby, the normal growth inhibitory action of activin A observed on benign cells is lost with the acquisition of activin resistance in prostate cancer cells. The mechanisms of rendering tumor cells resistant to activin A may include: alteration in activin binding protein (follistatin) synthesis and/or dimerisation with activin beta(C) to form novel activin dimers. The contribution of the activin signalling cascade to malignancy requires further evaluation to identify the synergies and differences to other members of the TGFbeta superfamily.

Activins↗

PubMed2001

Fibroblast growth factor receptors and their ligands in the adult rat kidney.

BACKGROUND: Fibroblast growth factors (FGFs) are a family of at least 21 heparin-binding proteins involved in many biological processes, both during development and in the adult, including cell proliferation, differentiation, and angiogenesis. FGFs mediate their effects through high-affinity tyrosine kinase receptors (FGFRs), which are encoded by four genes. The aims of the present study were to localize FGFR-1 through FGFR-3 in the normal adult rat kidney and to determine which functional FGFR variants and FGFs were expressed. METHODS: Avidin-biotin-enhanced horseradish peroxidase immunohistochemistry was used on paraffin sections of rat kidney to localize FGFR-1 through FGFR-3, whereas reverse transcriptase-polymerase chain reaction was used to examine expression of the receptor variants and also of FGF-1 through FGF-10 in cortex, outer medulla, and inner medulla. RESULTS: By immunohistochemistry, each receptor was localized to distinct and overlapping nephron segments, such that one or more FGFRs were localized to all nephron and collecting duct epithelia. FGFR-1 and FGFR-3 were localized to glomeruli, FGFR-3 to proximal tubules and FGFR-1 to thin limbs. FGFR-1 through FGFR-3 were localized to distal straight tubules, with FGFR-1 and FGFR-3 localized to distal convoluted tubules. FGFR-1 and FGFR-3 were localized to medullary collecting ducts. In addition, FGFR-1 was localized to the smooth muscle of renal arteries. All seven FGFR variants were expressed in the cortex and outer medulla, with fewer FGFRs in the inner medulla. FGF-1, FGF-2, FGF-7, FGF-8, and FGF-9 were expressed in the kidney, with FGF-10 expression found only in the cortex. CONCLUSIONS: Mapping of these receptors is critical to the determination of the effects of FGF ligands in discrete regions of the kidney. The distributions of the FGFRs in the normal adult kidney and the restricted expression of FGF ligands suggest that specific FGFs have distinct and important roles in the maintenance of normal kidney structure and function.

Animals↗

PubMed2001

The in vivo effect of red clover diet on ventral prostate growth in adult male mice.

The incidence of clinically significant prostate disease in Asian men is lower than in Western men and appears to be influenced by dietary and environmental factors. The aim of this study was to examine the effect of dietary isoflavones on prostate growth in intact male mice using an extract of red clover. The results demonstrated that prostate, but not testis, size was significantly reduced over 28 days of a red clover isoflavone supplemented diet. Histological examination revealed an increase in apoptotic cells, rather than a reduction in proliferative activity in the epithelium. These findings support the hypothesis that dietary red clover isoflavones can induce apoptosis and lead to a reduction in prostate size.

Animal Feed↗

PubMed2001

Estrogenic effects on prostatic differentiation and carcinogenesis.

Estrogens, alone or in combination with androgens, can induce aberrant growth and/or malignancy of the prostate gland. Squamous metaplasia is an abnormal form of prostatic epithelial differentiation elicited by exogenous estrogen alone. Estrogens elicit their effects via estrogen receptors (ER) in the prostate. Experiments using ERalpha and ERbeta null mice demonstrated that ERalpha, but not ERbeta is essential in the induction of prostatic squamous metaplasia. To determine the respective roles of epithelial versus stromal ERalpha in this response, the following tissue recombinants were constructed with prostatic epithelium (PRE) and stroma (S) from wild-type (wt) and ERalpha knockout (alphaERKO) mice: wt-S + wt-PRE, alphaERKO-S + alphaERKO-PRE, wt-S + alphaERKO-PRE and alphaERKO-S + wt-PRE. A metaplastic response to diethylstilbestrol (DES) was only observed in wt-S + wt-PRE tissue recombinants. Tissue recombinants containing alphaERKO-PRE and/or alphaERKO-S (alphaERKO-S + alphaERKO-PRE, wt-S + alphaERKO-PRE and alphaERKO-S + wt-PRE) failed to respond to DES. Therefore, full and uniform epithelial squamous metaplasia requires ERalpha in both the epithelium and stroma. Estradiol (E2) in combination with testosterone (T) was shown to be effective in inducing prostatic carcinogenesis in a tissue recombinant model composed of rat urogenital sinus mesenchyme plus mouse prostatic epithelium. A particularly efficient model of prostatic carcinogenesis in mice involves T + E2 treatment of mice bearing grafts of wild-type rat urogenital mesenchyme (rUGM) plus retinoblastoma gene (Rb) knockout (Rb-KO) prostatic epithelium (rUGM + Rb-KO-PRE). Such rUGM + Rb-KO-PRE tissue recombinants developed hyperplasia, atypical hyperplasia and invasive prostatic carcinoma with high efficiency. During carcinogenesis in rUGM + Rb-KO-PRE tissue recombinants, epithelial E-cadherin almost totally disappeared and epithelial PCNA labeling was elevated. These epithelial changes were associated with almost total loss of smooth muscle cells in the stroma. The results of this study demonstrate that the absence of the Rb tumor suppressor gene predisposes prostatic epithelial cells to hormonal carcinogenesis.

Animals↗

PubMed2001

Activins and inhibins in endocrine and other tumors.

Inhibin and activin are members of the TGF beta superfamily of growth and differentiation factors. They were first identified as gonadal-derived regulators of pituitary FSH and were subsequently assigned multiple actions in a wide range of tissues. More recently, the inhibin alpha subunit was considered as a tumor suppressor based on functional studies employing transgenic mouse models. This review evaluates the functional and molecular evidence that the inhibin alpha subunit is a tumor suppressor in endocrine cancers. The evaluation highlights the discrepant results from the human and mouse studies, as well as the differences between endocrine tumor types. In addition, we examine the evidence that the activin-signaling pathway is tumor suppressive and identify organ-specific differences in the actions and putative roles of this pathway in endocrine tumors. In summary, there is a considerable body of evidence to support the role of inhibins and activins in endocrine-related tumors. Future studies will define the mechanisms by which inhibins and activins contribute to the process of initiation, promotion, or progression of endocrine-related cancers.

Activins↗

PubMed2001

Elevated androgens and prolactin in aromatase-deficient mice cause enlargement, but not malignancy, of the prostate gland.

Although androgens are the main steroids controlling the growth of the mammalian prostate, increasing evidence demonstrates that estrogens also regulate prostate development and growth. This study describes the effects of estrogen deficiency using aromatase knockout mice (ArKO) with targeted disruption of the cyp19 gene. Serum and tissue testosterone and 5alpha-dihydrotestosterone as well as serum PRL levels are significantly (P < 0.05) elevated in mature male ArKO mice. Histological, stereological, and immunohistochemical studies demonstrated enlargement of the ventral, anterior, and dorsolateral lobes of the prostate in young and older ArKO mice. Hyperplasia of the epithelial, interstitial, and luminal compartments was identified and associated with up-regulation of androgen receptors. There was no evidence of malignancy as the animals aged (up to 56 weeks). The changes observed in the prostates of ArKO mice were unaffected by maintaining mice on regular or soy-free diets. It is concluded in ArKO mice that, despite the long-term elevation of androgens and PRL, the absence of estrogen in these animals does not result in induction of malignancy in the prostate gland.

Androgens↗

PubMed2001

The metaplastic effects of estrogen on mouse prostate epithelium: proliferation of cells with basal cell phenotype.

The exogenous administration of estrogens to male mice alters the hypothalamic-pituitary-gonadal axis and reduces androgen levels, leading to a regression of the prostatic epithelium. As well, a specific direct response to estrogens is the induction of epithelial squamous metaplasia. The aims of this study were to identify the process by which the prostatic epithelium is transformed in intact adult male mice using the synthetic estrogen, diethylstilbestrol. A comparison of the effects of diethylstilbestrol in the three lobes revealed a hierarchy of response, with the anterior lobe being the most responsive, the dorsolateral lobe less responsive, and the ventral lobe the least responsive. The effect of castration was used to distinguish between the epithelial responses to estrogen administration and androgen deprivation. The results demonstrate that transformation of the epithelium involved proliferation of cells with a basal cell phenotype, the onset of cytokeratin 10 expression, up-regulation of progesterone receptor expression, and loss of the cell cycle inhibitor, p27(Kip1) expression; none of these changes was observed after castration. Mice lacking functional estrogen receptor alpha failed to respond, demonstrating a requirement for estrogen receptor alpha in the epithelium and/or stroma to mediate the proliferative response to estrogen in the prostate gland.

Animals↗

PubMed2000

Evidence that estrogens directly alter androgen-regulated prostate development.

Neonatal exposure to high doses of estrogen results in permanent suppression of prostate growth and reduced sensitivity to androgens in adulthood. It is unclear whether alterations in prostate growth are due to a direct effect of estrogens on the gland or are the result of hypothalamic-pituitary-gonadal axis suppression and a subsequent reduction in androgen levels. Therefore, the aim of this study was to determine whether estrogens have a direct effect on the prostate using a defined method of culturing neonatal prostates. Newborn rat ventral prostates were microdissected and cultured in the presence of testosterone, which resulted in branching morphogenesis and ductal canalization. Solid cords of epithelium differentiated into acini lined by tall columnar epithelial cells; these acini were surrounded by stromal cells, expressing smooth muscle alpha-actin. When cultured in the presence of 17beta-estradiol or diethylstilbestrol in addition to testosterone, androgen-induced prostatic growth was reduced, and differentiation was altered. Although estrogen-treated explants were smaller than controls, quantification of epithelial, stromal, and luminal volumes using unbiased stereology revealed significant changes; the proportion of epithelial cells and lumen decreased, and the proportion of stroma increased compared with control values. Concurrent with this reduced growth rate, we observed a disturbance in the branching pattern and a reduction in ductal canalization. Specifically, stromal differentiation and organization were disrupted, so that a discontinuous smooth muscle layer was observed around the epithelial ducts, and epithelial differentiation was altered. The effects of estrogens were not accompanied by a decrease in androgen response via the androgen receptor, because immunolocalization of this receptor remained constant. These data demonstrate that high doses of estrogens are growth inhibitory and have direct effects on prostate development in vitro, which may occur in vivo in addition to indirect effects via suppression of the hypothalamic-pituitary-gonadal axis.

Actins↗