Identification and functional properties of the pituitary adenylate cyclase activating peptide (PAC1) receptor in human benign hyperplastic prostate

Suppressive action of pituitary adenylate cyclase activating polypeptide (PACAP) on proliferation of immature mouse Leydig cell line TM3 cells

We aimed in the current study to understand the participation of PACAP in stage-specific Leydig and Sertoli cell functions. For this purpose, clonal cell lines TM3 (Leydig) and TM4 (Sertoli) cells, derived from the testis of immature BALB/c mice, were used. PACAP-specific receptors were detected in TM3 cells, but not in TM4 cells, which were characterized as PAC1 (type I) receptors. Stimulation of cAMP accumulation and testosterone secretion were observed in TM3 cells during 1-2 h treatment with PACAP38 (10(-10)-10(-7) M) or PACAP27 (10(-11)-10(-7) M). After around 10 h treatment with 10(-11)-10(-7) M PACAP38 or PACAP27, proliferation of TM3 cells was suppressed in time- and dose-dependent manners, which was confirmed by real-time cell electronic sensing (RT-CES) system and phase-contrast microscopy. At 6 h after the addition of PACAP38, the percent cell population in G(2)/M phases increased significantly, while that in S phase showed significant decrease with little change in G(0)/G(1) phases. The results revealed that PACAP exerts, in addition to early stimulatory effect on cAMP formation-steroidogenesis, sustained suppressive effect on cell proliferation in TM3 cells by controlling progression of the cell cycle. The suppressive action of PACAP on proliferation in TM3 cells supports the stage-specific participation of the peptide in differentiation of immature mouse Leydig cells.

Human hepatic progenitor cells express vasoactive intestinal peptide receptor type 2 and receive nerve endings

BACKGROUND

We recently showed that human hepatic progenitor cells (HPCs) express muscarinic acetylcholine (Ach) receptor subtype 3 and that--following liver transplantation--HPC numbers are significantly reduced. To further elaborate on this, we examined whether HPC also express receptors for vasoactive intestinal peptide (VIP), which, besides Ach, also is an important parasympathetic neurotransmitter. VIP expressing nerves are known to be present in the liver.

METHODS

We performed immunohistochemistry for VIP receptor subtypes 1 and 2 (VIPR1 and 2), on sections of normal and diseased human liver (n=17), and double staining for VIPR2 and known HPC markers. We performed RT-PCR for VIPR1 and 2 on total RNA from purified rat HPC. To document the probability of direct interaction, we also performed double immunostaining for nerve markers and HPC markers on human liver sections.

RESULTS

VIPR2 immunostaining was clearly positive in HPC and reactive bile ductules on paraffin-embedded and frozen tissue sections. We could not demonstrate VIPR1 protein expression in the liver, with either of two VIPR1 antibodies tested. The presence of VIPR2 mRNA in HPC was confirmed by RT-PCR. Nerve endings were shown to abut on reactive bile ductules.

CONCLUSION

We show here for the first time that HPC express VIPR2 and receive nerve endings. These features, and the fact that HPC numbers are influenced by the presence or absence of the autonomic innervation of the liver, suggest a direct interaction.

[Importance of heterotrimeric G proteins in prostate cancer molecular biology]

OBJECTIVE

To deep in the knowledge of the involvement of G-protein alphas and alphai subunits in human prostate cancer.

METHODS

Prostate tissue from 9 patients undergoing radical prostatectomy for prostate cancer and 5 controls undergoing cystoprostatectomy for bladder carcinoma. G-protein alphas and alphai subunits were studied for expression (mRNA by RT-PCR and protein by Western-blot), functionality (adenylyl cyclase activity, AC) and possibility of mutations (analysis with restriction enzymes and cDNA sequentiation).

RESULTS

At mRNA level, the expression of alphas, alphai1, alphai2 y alphai3 was detected in healthy and cancerous tissues. At protein level, the expression of alphas y alphai1,2 diminished (25% and 40%, respectively) in prostate cancer. The expression of alphai3/0 also diminished, whereas that of beta subunit was not modified. Basal AC activity in adenocarcinoma membranes was 40% inferior to the control. Digestion with restriction enzymes Eag I or AlwN I did not allow to locate mutations in alphas. However, digestion at alphai2 level with BstU I enzyme served to observe a change of Gln205 (CAG triplet) to Pro (CCG).

CONCLUSIONS

The functionality and expression of heterotrimeric G proteins are selectively modified in human prostate adenocarcinoma, occurring in addition some punctual mutation. The observed substitution of Gln205 by Pro may result in a low GTPase activity for alphai2 that, therefore, is stabilized in its active form.

PAC1-R null isoform expression in human prostate cancer tissue

BACKGROUND

PACAP is a member of the VIP/GHRH family of neuropeptides and has important effects on prostate cell proliferation. Here we analyze the expression and localization of PACAP and its specific receptor variants (PAC(1)-R) in tissues collected from patients undergoing prostate biopsy and surgery for benign prostatic hyperplasia (BPH) and prostate cancer (PCa).

METHODS

Reverse transcriptase (RT)-polymerase chain reaction (PCR), DNA sequencing, and immunohistochemistry.

RESULTS

PACAP and PAC(1)-R were localized by immunohistochemistry in the prostate tissue. While in healthy and BPH tissues PAC(1)-R positive staining is present in all the epithelial cells lining the lumen of the acini and in some stromal cells (mostly in the apical portion of the cells), in PCa tissues, anti-PAC(1)-R antibody stained the apical portion of the cells. We provide evidence that PAC(1)-R null and SV(1)/SV(2) variants are all present in normal and hyperplastic tissues, while in PCa tissue PAC(1)-R null is the most relevant receptor variant expressed.

CONCLUSIONS

Our data demonstrates that the PAC(1)-R null variant is the most relevant isoform expressed in human PCa tissue being suggestively related with the events determining the outcome of prostate cancer.

Dual effect of pituitary adenylate cyclase activating polypeptide on prostate tumor LNCaP cells: short- and long-term exposure affect proliferation and neuroendocrine differentiation

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that elicits the increase of intracellular cAMP levels and protein kinase A activity in various cell systems. Here we show that the pattern of cAMP elevation triggered by PACAP is critical for the fate of LNCaP prostate cancer cells. We demonstrate that these cells express PACAP and its type 1 receptor. A short-term stimulation with PACAP, which generates a transient cAMP rise, induces proliferation of LNCaP cells through a protein kinase A-dependent activation of the MAPK cascade. On the contrary, we observed that chronic PACAP stimulation, giving rise to a sustained cAMP accumulation, leads to proliferation arrest and neuroendocrine differentiation. Moreover, PACAP stimulates phosphory-lation and activation of the cAMP response element binding transcription factor (CREB), and MAPK activation is necessary for its full transcriptional activity, indicating a direct involvement of cAMP response element in PACAP action. These findings demonstrate that a crucial event determining the outcome of prostatic cancer cells progression is the sustained vs. transient intracellular cAMP increase.

Expression and distribution of pituitary adenylate cyclase-activating peptide in human prostate and prostate cancer tissues

The presence, expression and distribution of pituitary adenylate cyclase-activating peptide (PACAP) in human prostate cancer and healthy tissue were investigated by means of biochemical and morphological procedures. Reverse transcription-polymerase chain reaction (RT-PCR) analysis demonstrated the presence of its precursor encoding mRNA in both normal and pathological conditions (amplification products with 577 or 226 bp were identified). Immunochemistry using an appropriate antibody served to detect in both classes of tissues a 19.9-kDa product corresponding to the PACAP preproprotein and another protein of 14.6 kDa that may represent a product partially processed by convertases. However, a 5-kDa band characteristic of PACAP-38 peptide was not observed. Immunohistochemistry on tissue sections indicated the location of PACAP in the epithelial layer of prostate glands (and in some scarce leucocytes) but not in the stroma, either in normal or carcinomatous tissues. No clear differences could be established when comparing samples from patients with different tumor Gleason grades. These results are the first demonstration of the localization of PACAP or its precursors and its mRNA in the human prostate gland and their presence during the progression of prostate carcinoma.

Cholinergic innervation and function in the prostate gland

The mammalian prostate is densely innervated by hypogastric and pelvic nerves that play an important role in regulating the growth and function of the gland. While there has been much interest in the role of the noradrenergic innervation and adrenoceptors in prostate function, the role of cholinergic neurones in prostate physiology and pathophysiology is not well understood. This review focuses on the role of acetylcholine and cholinoceptors in prostate function. Nitric oxide, vasoactive intestinal polypeptide, and/or neuropeptide Y are co-localised with cholinesterase and/or acetylcholine transporter in some of the nerve fibres supplying the prostate. Their roles are also briefly discussed in this review. A dense network of cholinesterase-staining fibres supplies both prostate epithelium and stroma, suggesting a role of acetylcholine and/or co-localised neuropeptides in the modulation of prostatic secretions, as well as smooth muscle tone. A predominantly epithelial location for prostate muscarinic receptors indicated a major secretomotor role for acetylcholine. The muscarinic receptor subtype mediating muscarinic agonist-induced smooth muscle contraction or enhancement of contractions evoked by nerve stimulation differs in different species. In the human, there is evidence for M(1) receptors on the epithelium, M(2) receptors on the stroma, and both M(1) and M(3) receptors in some prostate cancer cell lines. Several recent investigations indicate that muscarinic receptors may also mediate or modulate normal, benign, and malignant prostate growth. The role of muscarinic agonists and their receptors and the influences of age, testicular, and other steroids in regulating the effects are reviewed.

Neuroendocrine differentiation of the LNCaP prostate cancer cell line maintains the expression and function of VIP and PACAP receptors

The molecular mechanisms involved in differentiation of prostate cancer cells to a neuroendocrine (NE) cell phenotype are not well understood. Here we used the androgen-dependent human prostate cancer cell line LNCaP to perform a systematic and broad analysis of the expression, pharmacology, and functionality of vasoactive intestinal peptide (VIP)/pituitary adenylate cyclase-activating peptide (PACAP) receptors. Reverse transcription polymerase chain reaction experiments, together with pharmacological approaches with a set of specific agonists and antagonists, demonstrated the presence of the three VIP/PACAP receptor subtypes (PAC1, VPAC1, and VPAC2 with a major role for VPAC1, acting through adenylate cyclase (AC) stimulation. An essentially similar pattern was observed by NE differentiated cells (4 days after serum deprivation) in spite of the important morphological changes observed. However, the expression of the prostate-specific antigen (PSA) decreased in NE cells (and increased again by dihydrotestosterone, DHT, treatment). The present demonstration of the induction of NE transdifferentiation in LNCaP cells by increasing concentrations of VIP adds value to previous observations on the role of cAMP in this process, an interesting topic in the comprehension of the molecular changes that are involved in the progression of prostate cancer to androgen independence.

Vasoactive intestinal peptide (VIP) stimulates rat prostatic epithelial cell proliferation

BACKGROUND

Androgens play a major role in supporting normal growth and functional maintenance in the prostate. However, this gland contains an array of neuroendocrine peptides that can play a regulatory role in its physiopathology. Among these peptides, one of the best studied is vasoactive intestinal peptide (VIP), which is abundant in autonomic nerves surrounding both human and rat prostatic acini. This neuropeptide may act through interaction with two types of high-affinity receptors, named VPAC(1) and VPAC(2) receptors. Another regulatory peptide, the pituitary adenylate cyclase-activating peptide (PACAP), interacts with these receptors with the same affinity as VIP, but binds with higher affinity to PAC(1) receptors. Human prostate tumors and rat prostate show a major presence of VPAC(1) receptors, whereas various findings suggest a role for VIP in prostatic development. Here we studied the effects of VIP on the proliferation of rat prostatic epithelial cells in culture.

METHODS

We studied the [(3)H]-thymidine uptake by rat prostatic epithelial cells in culture, characterized previously by using biomarkers such as cytokeratin and vimentin. In these cells we tested the effect of VIP and PACAP-27 on two different signaling pathways, the cyclic AMP (cAMP) and the inositol phosphate (IPs).

RESULTS

The rat prostatic cells in culture were cytokeratin (5,6,8) and vimentin positive, indicating that the culture was predominantly epithelial. The proliferation curves showed that the cells followed different states of growth: a quiescent, an exponential proliferative, and a steady state. Cyclic AMP production, but not inositol phosphate production, was increased in the presence of VIP and PACAP-27, which suggests the expression of VPAC(1) and/or VPAC(2) receptors primarily. VIP significantly increased prostatic cell proliferation in a bimodal manner, as shown for dibutyryl cyclic AMP (dbcAMP), which suggests that the effect of VIP upon prostatic proliferation is cAMP-dependent.

CONCLUSIONS

Here, we demonstrate that VIP increased [(3)H]thymidine uptake by rat prostatic epithelial cells in culture, conceivably by the activation of the adenylate cyclase.

Effects of the luteinising hormone-releasing hormone (LH-RH) agonist leuprolide on adenylyl cyclase regulation through G-protein coupled receptors in rat ventral prostate

Luteinising hormone-releasing hormone (LH-RH) agonists are widely used for the therapy of advanced prostate cancer through the suppression of testosterone secretion. Furthermore, recent studies indicate the existence of prostate LH-RH receptors coupled to signalling pathways resulting in direct antiproliferative effects. In order to shed light on the mechanisms through which these compounds inhibit prostate cell growth, we investigated the effects of leuprolide (a LH-RH agonist) treatment of rats compared with the effects of surgical castration on the behaviour of G-protein coupled receptors acting through adenylyl cyclase in the ventral prostate. Important decreases of both plasma testosterone levels and ventral prostate weight were observed 5 weeks after subcutaneous (s.c.) injection of a leuprolide-depot preparation (1.5 mg/kg body weight (b.w.)) or 5 days after bilateral gonadectomy. However, leuprolide treatment increased the number of vasoactive intestinal peptide (VIP) receptors and the ability of this neuropeptide to stimulate adenylyl cyclase activity in prostate membranes, whereas surgical castration decreased both parameters. Moreover, leuprolide resulted in significant increases of prostate alpha(s) and alpha(i1-3) (but not alpha(i1) and beta) G-protein levels, while the four G-protein subunits were overexpressed after gonadectomy. The estimation of alpha(s) and alpha(i) activity by experiments with Gpp[NH]p and forskolin indicated a potentiation of the two arms of adenylyl cyclase regulation in leuprolide-treated rats. Present observations suggest that leuprolide treatment leads to an antimitogenic response by acting mainly through the activation of Gi proteins negatively coupled to adenylyl cyclase.