Functional vasopressin V1 type receptors are present in variant as well as classical forms of small-cell carcinoma

dDAVP Downregulates the AQP3-Mediated Glycerol Transport via V1aR in Human Colon HCT8 Cells

Vasopressin (AVP) plays a key function in controlling body water and salt balance through the activation of the vasopressin receptors V1aR and V2R. Abnormal secretion of AVP can cause the syndrome of inappropriate antidiuresis that leads to hyponatremia, which is an electrolyte disorder often observed in the elderly hospitalized and oncologic patients. Beyond kidneys, the colonic epithelium modulates water and salt homeostasis. The water channel AQP3, expressed in villus epithelial cells is implicated in water absorption across human colonic surface cells. Here, the action of dDAVP, a stable vasopressin analog, was evaluated on the AQP3 expression and function using human colon HCT8 cells as an experimental model. Confocal and Western Blotting analysis revealed that HCT8 cells express both V1aR and V2R. Long-term (72 h) treatment with dDAVP reduced glycerol uptake and cell viability. These effects were prevented by SR49059, a synthetic antagonist of V1aR, but not by tolvaptan, a specific V2R antagonist. Of note, the SR49059 action was impaired by DFP00173, a selective inhibitor of AQP3. Interestingly, compared to the normal colonic mucosa, in the colon of patients with adenocarcinoma, the expression of V1aR was significantly decreased. These findings were confirmed by gene expression analysis with RNA-Seq data. Overall, data suggest that dDAVP, through the V1aR dependent pathway, reduces AQP3 mediated glycerol uptake, a process that is reversed in adenocarcinoma, suggesting that the AVP-dependent AQP3 pathway may represent a novel target in colon diseases associated with abnormal cell growth.

Arginine vasopressin receptor 1a is a therapeutic target for castration-resistant prostate cancer

Castration-resistant prostate cancer (CRPC) recurs after androgen deprivation therapy (ADT) and is incurable. Reactivation of androgen receptor (AR) signaling in the low androgen environment of ADT drives CRPC. This AR activity occurs through a variety of mechanisms, including up-regulation of AR coactivators such as VAV3 and expression of constitutively active AR variants such as the clinically relevant AR-V7. AR-V7 lacks a ligand-binding domain and is linked to poor prognosis. We previously showed that VAV3 enhances AR-V7 activity to drive CRPC progression. Gene expression profiling after depletion of either VAV3 or AR-V7 in CRPC cells revealed arginine vasopressin receptor 1a (AVPR1A) as the most commonly down-regulated gene, indicating that this G protein-coupled receptor may be critical for CRPC. Analysis of publicly available human PC datasets showed that AVPR1A has a higher copy number and increased amounts of mRNA in advanced PC. Depletion of AVPR1A in CRPC cells resulted in decreased cell proliferation and reduced cyclin A. In contrast, androgen-dependent PC, AR-negative PC, or nontumorigenic prostate epithelial cells, which have undetectable AVPR1A mRNA, were minimally affected by AVPR1A depletion. Ectopic expression of AVPR1A in androgen-dependent PC cells conferred castration resistance in vitro and in vivo. Furthermore, treatment of CRPC cells with the AVPR1A ligand, arginine vasopressin (AVP), activated ERK and CREB, known promoters of PC progression. A clinically safe and selective AVPR1A antagonist, relcovaptan, prevented CRPC emergence and decreased CRPC orthotopic and bone metastatic growth in mouse models. Based on these preclinical findings, repurposing AVPR1A antagonists is a promising therapeutic approach for CRPC.

Expression of the oxytocin and V1a vasopressin receptors in human myometrium in differing physiologic states and following misoprostol administration

OBJECTIVE

To assess relative expression levels of mRNA for the oxytocin receptor (OTR) and the V1a vasopressin receptor (V1aR) in human myometrium in various physiologic states and to determine if misoprostol exposure affects the expression of mRNA for these receptors.

STUDY DESIGN

Using semiquantitative reverse transcription-polymerase chain reaction, we analyzed myometrial samples from 37 women (10 menopausal, 10 nongravid premenopausal, 10 gravidae, 7 premenopausal misoprostol-treated nongravid women) for the specific expression of mRNA messages for OTR and V1aR. The presence of the OTR and V1aR protein was confirmed by immunohistochemistry.

RESULTS

We found that the expression of OTR was significantly higher in gravid compared to premenopausal nongravid (p < 0.0001), misoprostol-treated (p < 0.001) and menopausal myometrium (p < 0.0001). Differences in V1aR expression were not statistically significant among the four study groups.

CONCLUSION

The expression of OTR mRNA in myometrium is markedly increased during late gestation. V1aR expression is present in all physiologic states, and does not appear to be altered by the presence or absence of labor. Misoprostol administration does not appear to have an effect on OTR and V1aR mRNA receptor expression.

Increased gastrin-releasing peptide (GRP) receptor expression in tumour cells confers sensitivity to [Arg6,D-Trp7,9,NmePhe8]-substance P (6-11)-induced growth inhibition

[Arg(6),D-Trp(7,9),N(me)Phe(8)]-substance P (6-11) (SP-G) is a novel anticancer agent that has recently completed phase I clinical trials. SP-G inhibits mitogenic neuropeptide signal transduction and small cell lung cancer (SCLC) cell growth in vitro and in vivo. Using the SCLC cell line series GLC14, 16 and 19, derived from a single patient during the clinical course of their disease and the development of chemoresistance, it is shown that there was an increase in responsiveness to neuropeptides. This was paralleled by an increased sensitivity to SP-G. In a selected panel of tumour cell lines (SCLC, non-SCLC, ovarian, colorectal and pancreatic), the expression of the mitogenic neuropeptide receptors for vasopressin, gastrin-releasing peptide (GRP), bradykinin and gastrin was examined, and their sensitivity to SP-G tested in vitro and in vivo. The tumour cell lines displayed a range of sensitivity to SP-G (IC(50) values from 10.5 to 119 microM). The expression of the GRP receptor measured by reverse transcriptase-polymerase chain reaction, correlated significantly with growth inhibition by SP-G. Moreover, introduction of the GRP receptor into rat-1A fibroblasts markedly increased their sensitivity to SP-G. The measurement of receptor expression from biopsy samples by polymerase chain reaction could provide a suitable diagnostic test to predict efficacy to SP-G clinically. This strategy would be of potential benefit in neuropeptide receptor-expressing tumours in addition to SCLC, and in tumours that are relatively resistant to conventional chemotherapy.

Characterization of a pituitary GnRH-receptor from a perciform fish, Morone saxatilis: functional expression in a fish cell line

Gonadotropin-releasing hormones (GnRHs) bind to the specific receptor present on the gonadotrophs to activate the synthesis and release of gonadotropins (follicle stimulating hormone or FSH and luteinizing hormone or LH), which in turn control gonadal maturation, gametogenesis and gamete release. Perciform species have three endogenous GnRHs. The main objective of this study was to characterize the gonadotropin-releasing hormone receptor (GnRH-R) present in the pituitary of a perciform species, striped bass (Morone saxatilis) and demonstrate how it interacts with its potential ligand. In this study, a cDNA for GnRH-R from the pituitaries of striped bass was cloned. The cloned cDNA has an open reading frame (ORF) that codes for a 419 amino acids peptide. Like other G-protein coupled receptors including the non-mammalian GnRH-Rs, the peptide has seven putative transmembrane domains and a C-terminal tail. Comparative analysis of the amino acid sequence of striped bass (stb) GnRH-R shows 38-87% similarity with the known GnRH-Rs. A Northern blot analysis revealed a single GnRH-R transcript in the pituitary; however, its expression in various extrapituitary tissues was demonstrated by a reverse-transcription-PCR (RT-PCR). Functionally, upon induction by endogenous forms of GnRHs (seabream, chicken II and salmon GnRHs) and a mammalian GnRH-agonist, the recombinant stbGnRH-R mediated a reporter gene (luciferase) activity in a fish cell line (CHSE-214). A real-time relative quantitation method established that significantly higher (P<0.05) levels of stbGnRH-R mRNA were present in the pituitaries of striped bass with advanced stages of ovarian development, compared to the pituitaries of fish with less developed ovaries.

Gene regulation of vasopressin and vasopressin receptors in cancer

It is proposed that neuropeptide production by tumours is an important part of a special process of oncogenic transformation rather than a pre-existing condition of progenitor cells; this concept is called Selective Tumour gene Expression of Peptides essential for Survival (STEPS). All small-cell lung cancers and breast cancers evidently express the vasopressin gene, and this gene seems to be structurally normal in all but exceptional cases. Vasopressin gene expression in cancer cells leads to the production of both normal and abnormal forms of tumour vasopressin mRNA and proteins. Although the necessary post-translational processing enzymes are expressed in these cells, most processing seems to be extragranular, and most of the protein products become components of the plasma membrane. Small-cell lung cancer and breast cancer cells also express normal genes for all vasopressin receptors and produce normal vasopressin receptor mRNAs and V1a and V1b receptor proteins, and the vasopressin-activated calcium mobilising (VACM) protein; plus both normal and abnormal forms of the V2 receptor. Through these receptors, vasopressin exercises multifaceted effects on tumour growth and metabolism. A normal protein vasopressin gene promoter seems to be present in small-cell lung cancer cells, and this promoter contains all of the transcriptional elements known to be involved in gene regulation within hypothalamic neurones. Since these elements largely account for regulation of tumour gene expression observed in vitro, it is likely that as yet unknown factors are selectively produced by tumours in vivo to account for the observed seemingly autonomous or unregulated production of hormone in tumour patients. Promoter elements thought to be responsible for selective vasopressin gene expression in small-cell lung cancer probably include an E-box and a neurone restrictive silencer element close to the transcription start site. It is possible that transcription factors acting at these same elements can explain selective vasopressin expression, not only in small-cell tumours, but also in all other tumours such as breast cancer. By extrapolation, similar mechanisms might also be responsible for the expression of additional features that characterize the 'neuroendocrine' profile of these cancers.

MCF-7 breast cancer cells express normal forms of all vasopressin receptors plus an abnormal V2R

We have previously provided evidence that an autocrine loop involving vasopressin is present in perhaps all breast cancers. This study now shows MCF-7 breast cancer cells express mRNAs for all currently recognized vasopressin receptor subtypes (V1a, V1b, and V2). Cloning and DNA sequencing over the entire open reading frame of each mRNA revealed that normal sequences representing each receptor were present. However, in addition, an abnormal mRNA for the V2 receptor, expected to give rise to a truncated 'diabetic' protein, was also expressed. Western analysis revealed that all three normal mRNAs gave rise to proteins of sizes compatible with them being functional receptors. The abnormal V2 receptor mRNA also gave rise to proteins.

Key peptide processing enzymes are expressed by a variant form of small-cell carcinoma of the lung

Small-cell carcinoma of the lung (SCCL) is a neuroendocrine tumor characterized by having the capacity to produce and secrete a number of small neuropeptides. These peptides serve the tumor as autocrine growth factors. SCCL is known to undergo a process of dedifferentiation to a variant (drug-resistant) form, and this process is associated with loss of marker enzymes such as neuron-specific enolase (NSE) and dopa decarboxylase (DDC). The current study was designed to discover if variant SCCL, represented by cell line NCI H82, retains some capacity to generate active neuropeptides (like vasopressin) from their precursors by continuing to express the three key classes of enzymes necessary for such conversions, namely prohormone convertases (PCs), carboxypeptidases (CPs), and peptidylglycine a-amidating monooxygenase (PAM). RT-PCR for mRNAs representing PC1, PC2, CPE, and PAM was performed on total RNA extracted from NCI H82. The primers selected for PCR and partial sequencing were synthetic 20, 21, 22, and 24 oligomers designed to yield products of 533, 880, 405, and 560 base pairs (bp) for PC1, PC2, CPE, and PAM, respectively. For the conditions used, we were able to demonstrate products for all four enzymes. Each of the four products generated were of the expected size. Cloning and sequencing of these products revealed that each had a structure identical to that published for the human form of the respective enzyme. Western analysis with antibodies against PC1, PC2, CPE, and PAM, provided evidence that mRNAs for the four enzymes are translated into proteins that could represent functional forms. Our findings therefore demonstrate that key enzymes involved in the generation of active neuropeptides, unlike the marker enzymes NSE and DDC, continue to be expressed by variant SCCL.