New perspectives on growth factor-sex steroid interaction in the prostate

The effect of oxytocin on cell proliferation in the human prostate is modulated by gonadal steroids: implications for benign prostatic hyperplasia and carcinoma of the prostate

BACKGROUND

Oxytocin (OT) is implicated in regulating prostate growth. OT concentrations are increased in benign, and decreased in malignant prostate disease. This study investigated whether the altered concentrations of OT present in prostate disease affect the proliferation of malignant and non-malignant human prostate cells.

METHODS

The effects of varying concentrations of OT and gonadal steroids on cell proliferation of non-malignant prostatic epithelial (PrEC) and stromal (PrSC) cells and androgen dependent (LNCaP) and independent (PC-3) malignant cell lines were assessed.

RESULTS

OT (>0.5 nmol . L(-1)) had no effect on PrEC proliferation when cells were cultured alone. When co-cultured with PrSC and gonadal steroids, OT inhibited epithelial cell proliferation. OT inhibited PrSC proliferation, when cells were cultured alone. When PrSC were co-cultured in the presence of estrogen physiological concentrations of OT were inhibitory. No effect on cell proliferation was observed with higher concentrations of OT. OT did not affect the proliferation of malignant cell lines in the absence of androgens but, in the presence of testosterone, low concentrations of OT (<1 nmol . L(-1)) stimulated proliferation of PC-3 cells. Disruption of caveolae in the plasma membrane removed the inhibitory effect of OT on PrSC proliferation but did not affect the stimulatory effect of OT on PC-3 cells cultured in the presence of androgens.

CONCLUSIONS

Changes in prostatic concentrations of OT that occur with aging and malignant disease may act to facilitate cell proliferation. The localization of the OT receptor within the plasma membrane modulates OT's proliferative response in the prostate.

Interaction of testosterone with inhibin alpha and betaA subunits to regulate prostate gland growth

Testosterone regulation of prostate gland growth has been shown to involve reciprocal interaction with inhibin and activin. This study was therefore conducted to correlate the effect of testosterone on prostate gland proliferation and differentiation with the level of expression of inhibin alpha and betaA subunits. Immature dogs were treated with testosterone for 0, 3, 7, and 14 days and prostate gland growth was assessed by morphological and immunohistological localization of differentiation and proliferation markers. The results showed that testosterone treatment resulted in an initial significant increase in PCNA proliferation index by days 3 and 7, followed by a significant decrease by day 14 post-treatment. Interestingly, the decrease of cell proliferation was associated with structural and biochemical changes characteristic of glandular and stromal differentiation of the prostate gland. These changes include progressive glandular ductal canalization and inter-ductal stroma differentiation which were apparent from a gradual shift from vimentin expression to vimentin and alpha-actin expression. Testosterone also had a differential effect on inhibin alpha and beta subunits. Although testosterone treatment resulted in significant and constant inhibition of alpha subunit mRNA expression, it resulted in a significant increase of betaA mRNA expression by day 3, followed by a decrease by days 7 and 14. These results indicated that testosterone acts first to drive proliferation of undifferentiated prostatic cells and then to maintain a low proliferation turnover of differentiated cells. Because it has been shown that activin is an antagonistic regulator of androgens, the attenuated stimulatory effect of testosterone on cell proliferation by day 14 might be mediated, at least in part, by interplay between testosterone and activin.

Testosterone effect on immature prostate gland development associated with suppression of transforming growth factor-β

The aim of this study was to evaluate the effect of testosterone treatment on the pattern of prostate cell proliferation and differentiation and their correlation with the expression of transforming growth factor-beta (TGF-beta). Prostate gland development was compared in intact immature dogs with one-month testosterone-treated immature dogs. Testosterone treatment resulted in a tenfold increase in prostate gland weight compared to untreated dogs, with a typical organization of the gland into a structure similar to that observed in mature dogs. The narrow acini which contain flat basal cells in immature glands were transformed into tubuloacinar structures containing columnar secretory cells and basal cells. The stromal compartments showed an increase in the muscular component as evidenced by the high reactivity to alpha-actin with no remarkable changes in the vimentin expression. In addition, testosterone treatment induced a significant reduction in the proliferation capacity of stromal cells but with no noticeable changes in the proliferation pattern of epithelial cells. These changes in the prostate are associated with a twofold decrease in TGF-beta mRNA expression as assessed by Real-Time PCR. However, the immunolocalization of TGF-beta was shifted slightly from the epithelial cells in untreated animals to the stromal cells of treated animals. Based on these results it appears that testosterone acts to coordinate prostatic cell proliferation and differentiation and direct their organization into a structure resembling that of the mature gland. The testosterone regulation of the prostate gland appears to involve the regulation of TGF-beta gene expression.

Rat activin-betaE mRNA expression during development and in acute and chronic liver injury

Activin-βE mRNA expression was investigated in male and female rats using gel-based and quantitative RT-PCR, in fetal and post-natal liver during development and in a variety of tissues from 200 gm adult animals. Activin-βE expression was also assessed in rat liver after partial hepatectomy, and after repeated toxic insult. Male Sprague Dawley rats were subjected to partial hepatectomy or sham operations. Samples were collected from the caudate liver lobe during regeneration, from 12 to 240 hr after surgery. Three groups of 5 male rats were treated with CCl₄ for 0 (control), 5 or 10 weeks, to induce liver fibrosis and cirrhosis. Activin-βE mRNA was predominantly expressed in liver, with much lower amounts of mRNA observed in pituitary, adrenal gland and spleen, in both males and females. Low activin-βE expression was observed in liver at fetal day 16, with higher levels seen between post-natal days 3 and 35 and a further increase noted by day 47, in both males and females. Liver activin-βE mRNA concentrations did not change from control values 12-72 hr after PHx, but significantly increased over six fold, 168 hr post-hepatectomy, when liver mass was restored. Activin-βE mRNA was up-regulated after 5 weeks of CCl₄ treatment, but not after 10 weeks. The changes in activin-βE mRNA concentrations after liver insult did not always parallel those reported for the activin-βC subunit, suggesting activin-βE may have an independent role in liver under certain conditions.

Castration induced changes in dog prostate gland associated with diminished activin and activin receptor expression

This study was conducted to evaluate the effect of androgen ablation on dog prostate gland structure and the proliferation capacity of the prostatic cells and their association with the expression of Activin A and Activin RIIA receptor. The effect of androgen on the prostate gland was compared in intact and castrated dogs after one and two weeks. Specific primary antibodies were used to immunolocalize activin-A, activin receptor type II A and the proliferation marker (PCNA). The results showed that the glandular acini of the prostate gland of intact dogs are lined by tall columnar secretory cells and less abundant flattened basal cells and surrounded by a thin fibromuscular tissue. The cytoplasm of the glandular cells exhibited an intense immunoreaction for activin A and activin RIIA receptor while basal cells expressed PCNA. Castration induced a remarkable atrophy of the prostatic acini associated with a progressive loss of secretory epithelial cells, which showed a dramatic decrease to complete disappearance of Activin A and Activin RIIA receptor immunoreactions. The remaining cells of the atrophied acini continue to express PCNA and the inter-acinar fibromuscular tissue showed a remarkable increase in its mass and are induced to express PCNA. These results indicated that androgen is required for the survival of epithelial cells and to maintain growth-quiescent fibromuscular cells, while basal cell proliferation is androgen independent. The changes in the Activin A and Activin RIIA receptor localization and their association with the dynamic pattern of prostate gland regression after castration suggested that Activin A and Activin RIIA receptor expression are androgen dependent.