Prolactin is a survival factor for androgen-deprived rat dorsal and lateral prostate epithelium in organ culture

Prostate hyperplasia in a transgenic mouse with prostate-specific expression of prolactin

Prolactin (PRL) is one of several polypeptide factors known to exert trophic effects on the prostate. We have previously reported a dramatic prostate enlargement with concurrent chronic hyperprolactinemia and elevated serum androgen levels in a PRL transgenic mouse (Mt-PRL) with ubiquitous expression of the transgene. To address the role of local PRL action in the prostate, a new transgenic mouse model (Pb-PRL) was generated using the prostate-specific rat probasin (Pb) minimal promoter to drive expression of the rat PRL gene. Pb-PRL transgenic males developed a significant enlargement of both the dorsolateral and ventral prostate lobes evident from 10 wk of age and increasing with age. Expression of the transgene was restricted to the prostate and detected from 4 wk of age. Low levels of transgenic rat PRL were detectable in the serum of adult Pb-PRL animals. Serum androgen levels were normal. The Pb-PRL prostate displayed significant stromal hyperplasia, ductal dilation, and focal areas of epithelial dysplasia. Quantitative analysis of prostatic tissue cellularity demonstrated a marked increase in the stromal to epithelial ratio in all lobes of Mt-PRL and Pb-PRL transgenic prostates compared with controls. Microdissections demonstrated an increased ductal morphogenesis in dorsolateral and ventral prostate lobes of Mt-PRL prostate vs. Pb-PRL and controls. In conclusion, this study indicates the ability of PRL to promote, directly or indirectly, ductal morphogenesis in the developing prostate and further to induce abnormal growth primarily of the stroma in the adult gland in a setting of normal androgen levels.

Prolactin overexpression by MDA-MB-435 human breast cancer cells accelerates tumor growth

Prolactin (PRL) is an important hormone in mammary tumorigenesis in rodents but its involvement in human breast cancer has been controversial. A role for locally produced PRL in breast carcinogenesis is suggested by its mitogenic action on breast cancer cells and the expression of both PRL and its receptor (PRL-R) in breast carcinomas. Our objective was to examine whether PRL, overexpressed by breast cancer cells, forms an autocrine/paracrine loop that confers a growth advantage for tumors. MDA-MB-435 breast cancer cells overexpressing 23K human PRL were generated, and PRL production and secretion by the clones were confirmed by RT-PCR, western blotting, and the Nb2 bioassay; control clones contain vector only. In vitro the 23K PRL clones proliferated faster and expressed higher levels of the PRL-R protein than controls only when incubated in charcoal-stripped serum (CSS) devoid of lactogenic hormones. When injected into the mammary fatpad of female nude mice or subcutaneously into males, the PRL-overexpressing clones formed tumors that grew 2-4-fold faster than tumors derived from control clones or wild type MDA-MB-435 cells. Western analysis demonstrated significantly higher PRL, PRL-R, and bcl-2 levels in the tumors overexpressing PRL compared to control tumors. These data support a role for breast PRL as a growth/anti-apoptotic factor and suggest that it may serve as a novel therapeutic target for the treatment of breast cancer.

Opposite effects of unmodified prolactin and a molecular mimic of phosphorylated prolactin on morphology and the expression of prostate specific genes in the normal rat prostate

BACKGROUND

In the current study, we have investigated the individual roles of unmodified, wild-type prolactin (WT PRL) and a molecular mimic of phosphorylated prolactin (S179D PRL) in the normal rat prostate.

METHODS

In the first animal experiment, recombinant WT PRL and S179D PRL were delivered to adult male rats at a rate of 14 microg/kg per day for 3 weeks. In the second animal experiment, two subcutaneous (200 microg/kg) injections of long-acting forms of the two PRLs were given to adult male rats on day 1 and day 22 for a total of 5.5 weeks of treatment.

RESULTS

The different forms of PRL had opposite effects on the normal rat prostate, independently of androgens. WT PRL promoted morphologic changes in prostate epithelium consistent with preparation for cell proliferation, whereas S179D PRL produced morphologic evidence of a more differentiated epithelium. Northern blot analysis of expression of the two major prostate specific proteins, prostatein and probasin, showed that WT PRL decreased, whereas S179D PRL increased, the expression of the mRNAs for these two proteins. At the same time, S179D PRL reduced both testosterone and dihydrotestosterone levels.

CONCLUSION

We conclude that PRL is an important modulator of normal rat prostate biology and that different forms of PRL have specific functions. The molecular mimic of phosphorylated PRL, S179D PRL, is the most important in terms of epithelial cell differentiation.

Progressive prostate hyperplasia in adult prolactin transgenic mice is not dependent on elevated serum androgen levels

BACKGROUND

Transgenic mice overexpressing the rat prolactin (PRL) gene under control of the metallothionein-1 promoter (Mt-1) develop a dramatic prostatic enlargement. These animals also display significantly elevated testosterone serum levels. In this study, we aim to clarify the role of circulating androgen levels in the promotion of abnormal prostate growth in the adult PRL transgenic mouse prostate.

METHODS

Prostate morphology and androgen-receptor distribution patterns were analyzed in castrated and testosterone substituted adult PRL transgenic and in wild-type males.

RESULTS

Progressive prostatic hyperplasia in adult PRL transgenic males was not affected by substitution to serum testosterone levels corresponding to wild-type. Furthermore, prolonged testosterone treatment in adult wild-type males did not produce any significant changes in prostate growth or morphology compared with wild-type controls. Immunohistochemical studies revealed a significantly increased proportion of androgen receptor positive epithelial cells in all lobes of the PRL transgenic prostate versus wild-type.

CONCLUSION

The present study demonstrates that progressive prostate hyperplasia in adult PRL transgenic mice is not dependent on elevated serum androgen levels. Furthermore, prolonged androgen treatment in adult wild-type male mice appears to have no significant effect on prostate growth. In addition, our results suggest that prolonged hyperprolactinemia results in changes in prostate epithelial and stromal cell androgen receptor distribution.

Molecular characterization of prostate hyperplasia in prolactin-transgenic mice by using cDNA representational difference analysis

BACKGROUND

Transgenic mice overexpressing the rat prolactin (PRL) gene develop a dramatic enlargement of the prostate gland. The objective of this study was to characterize the molecular mechanisms in the prostate of importance for the prostate hyperplasia seen in these transgenic mice.

METHODS

cDNA representational difference analysis (cDNA RDA) was used to isolate differentially expressed transcripts in the prostate hyperplasia of the transgenic mice compared with wildtype littermates. Furthermore, cDNA microarray analysis was used to verify the RDA output.

RESULTS

Here we report 10 transcripts, some of them described to be involved in proliferation and apoptosis, which are differentially expressed in the enlarged transgenic prostates compared with controls.

CONCLUSION

The identified differentially expressed transcripts presented herein supports molecular similarities between the prostate hyperplasia of PRL-transgenic mice and human BPH that may contribute to explain the molecular basis of prostate hyperplasia.

PRL signal transduction in the epithelial compartment of rat prostate maintained as long-term organ cultures in vitro

Using long-term organ cultures of rat prostate tissue explants, we previously demonstrated that PRL both stimulates proliferation and acts as an androgen-independent suppressor of apoptosis in prostate epithelial cells, leading to epithelial hyperplasia. In this work we delineate intracellular signaling molecules activated by PRL in prostate tissue to identify candidate signaling proteins that are responsible for maintaining survival and proliferation of prostate epithelium in androgen-deprived growth environment. We now show that signal transducer and activator of transcription-5a (Stat5a) and Stat5b become tyrosine phosphorylated in response to PRL stimulation in rat prostate using prostate organ culture as an experimental model. Stat5 was translocated to the nuclei of epithelial cells of prostate tissue as demonstrated by immunohistochemistry. Furthermore, EMSA showed PRL-inducible binding of Stat5a homodimers and Stat5a/5b heterodimers to the PRL response element of the beta-casein gene promoter. Signaling molecules Stat3, Stat1, MAPK, or protein kinase B, which can be activated by PRL in other target cells, were not activated by PRL in prostate tissue. Furthermore, we show that Stat5a and Stat5b are continuously phosphorylated in rat prostate in vivo, although they are expressed to varying degree in separate lobes of rat prostate. Collectively, our results suggest that PRL signaling in rat prostate tissue is primarily transduced via Stat5a and Stat5b. The Stat5 pathway represents one candidate signaling mechanism, used by PRL and possibly other growth factors and cytokines, that supports the viability of prostate epithelial cells during long-term androgen deprivation.

PRL antiapoptotic effect in the rat decidua involves the PI3K/protein kinase B-mediated inhibition of caspase-3 activity

During gestation, the uterus undergoes severe changes to accommodate and protect the developing conceptus. In particular, stromal endometrial cells proliferate and differentiate to form the decidual tissue, which produces PRL. Once the conceptus begins to grow, extensive regression by apoptosis take place in the decidua coincident with the loss of the PRL receptor in this tissue. In this report we have established for the first time that PRL, acting through the long form of the PRL receptor and the PI3K pathway, exerts an antiapoptotic effect in rat decidua. We have also shown that protein kinase B phosphorylation on serine 473 as well as its nuclear translocation are stimulated by PRL in decidual cells. Moreover, we have found that caspase-3, a well known effector of apoptosis, becomes expressed and active in the rat decidua just at a time when this tissue undergoes extensive apoptosis. PRL was able to down-regulate both caspase-3 mRNA levels as well as activity. Furthermore, using a protein kinase B dominant-negative expression vector, we provide evidence that PRL inhibition of caspase-3 requires an intact protein kinase B pathway. Finally, we have also found that rat placental lactogen I and II dose-dependently inhibit caspase-3 mRNA, suggesting multiple sources of PRL in the hormonal control of rat decidual regression. In summary, the results of this study have defined an important role for decidual PRL in the normal progress of pregnancy, specifically in the regression and reorganization of the decidua.

Effects of hyperprolactinemia on rat prostate growth: evidence of androgeno-dependence

The effects of the polypeptide hormone prolactin (PRL) in the development and regulation of benign prostate hyperplasia (BPH) and also in prostate cancer are not very well characterized. This study examines the action of PRL, either alone or in association with androgens [testosterone (T) or dihydrotestosterone (DHT)], in the rat prostate gland. The effects of PRL and androgens were investigated after 30 and 60 days in control, castrated, castrated with a substitutive implant of T or DHT, and sham-operated Wistar rats. To enhance PRL release, we induced hyperprolactinemia by administering chronic injections of sulpiride (40 mg. kg(-1). day(-1)). Chronic hyperprolactinemia induces enlargement and inflammation of the lateral rat prostate without any histological changes on ventral and dorsal lobes. We also demonstrate that hyperprolactinemia induces Bcl-2 overexpression in the lateral rat prostate and that this could inhibit the level of apoptosis. The in vivo model established here is a useful in vivo approach for studying the hormonal regulation of normal and pathological prostate development.

Epithelial defect in prostates of Stat5a-null mice

The transcription factor Stat5a critically mediates prolactin (PRL)-induced mammary gland development and lactogenesis. PRL also stimulates growth and differentiation of prostate tissue. Specifically, hyperprolactinemia gives rise to prostate hyperplasia, and prostate size is reduced in PRL-deficient mice. We therefore investigated the importance of Stat5a for prostate development and function by examining Stat5a-null mice. The absence of Stat5a in mice was associated with a distinct prostate morphology characterized by an increased prevalence of local disorganization within acinar epithelium of ventral prostates. Affected acini were typically filled with desquamated, granular epithelial cells that had become embedded in dense, coagulated secretory material. These features were reminiscent of acinar cyst formation and degeneration frequently observed in human benign prostate hyperplasia, however, cystic changes in prostate acini of Stat5a-deficient mice were not associated with increased prostate size or morphologic hallmarks of epithelial hyperplasia. Instead, immunohistochemistry of the prostate-specific secretory marker, probasin, suggested that hypersecretory function of the epithelium could underlie local congestion and cyst formation in prostates of Stat5a-null mice. Serum testosterone and PRL levels were normal in Stat5a knockout mice, but prostate PRL receptor expression was reduced as determined by immunohistochemistry. Expression levels or activation states of other PRL signal transduction proteins, including Stat5b, Stat3, Stat1, ERK1, and ERK2 were not altered. The present study offers the first evidence for a direct role of Stat5a in the maintenance of normal tissue architecture and function of the mouse prostate.