Vasopressin gene related products are markers of human breast cancer

Cancer and the Vasopressin Gene: Radioimmunoassay Values and Commentary on Copeptin as a Plasma Marker

Background

Vasopressin gene expression has been demonstrated to be a common feature of all small-cell lung cancer (SCLC) and breast cancer. Provasopressin (ProVP) is a component of the cancer cell membrane and a likely target for treatment. However, a measurable fraction of this cancer provasopressin is also normally processed and products are released into the circulation. Vasopressin (VP) and vasopressin-associated human neurophysin (VP-HNP), two of three products of processing, were earlier shown to be reliable plasma markers for determining the presence of SCLC and monitoring response to treatment.

Material and Methods

In this study, copeptin, the third product of provasopressin processing, was preliminarily evaluated as a plasma marker for SCLC or breast cancer using radioimmunoassay (RIA). Antibodies directed against the 18 residue C-terminal peptide fragment of copeptin were used to avoid interference from the large-carbohydrate component of this endogenous glycopeptide.

Results

The levels of copeptin in 8 male and 6 female patients with SCLC before treatment ranged from 16 to 319 pmol/L, and these levels were elevated (>2.5 times) in 10 of 14 cases (70%) when compared with healthy volunteers (normal mean, 18 ± 6 pmol/L). Volunteer values for males were smaller than for females (15± 4 pmol/L and 20± 9 pmol/L), but numbers were small. Patients with breast cancer had plasma levels ranging from 12 to 68 pmol/L, with only three of the six elevated.

Conclusion

While cancer patients displayed a wide range of plasma copeptin levels over 70% with SCLC and 50% with breast cancer had clearly elevated levels. This finding indicates that for such patients, plasma copeptin, like plasma VP and VP-HNP, could be used to detect disease. The control values found for healthy volunteers using our RIA were in a range predictable from established normal plasma levels of both VP and VP-HNP.

Insulin-Regulated Aminopeptidase in Women with Breast Cancer: A Role beyond the Regulation of Oxytocin and Vasopressin

Simple Summary

Insulin-regulated aminopeptidase (IRAP) is a well-known enzyme involved mainly in the regulation of the peptide hormones, oxytocin and vasopressin. However, this enzyme activity has hardly been analyzed in breast cancer patients. Additionally, the influence of both the hormonal status (pre or postmenopause) and the administration of neoadjuvant chemotherapy have rarely been studied. We show that there is a weak association between IRAP activity and the circulating levels of peptide hormones with variations depending on the hormonal status and the neoadjuvant treatment, and propose a role beyond oxytocin and vasopressin regulation that is related to the local mammary renin-angiotensin system and glucose transportation to the cells.

Abstract

Insulin-regulated aminopeptidase (IRAP) is the only enzyme known to cleave oxytocin and vasopressin; however, it is also the high-affinity binding site for angiotensin IV (AngIV) receptor type 4 (AT4) ligands and it is related to insulin-dependent glucose transporters through the translocation of the glucose transporter type 4 (GLUT4). Previous studies have demonstrated an association between IRAP activity and the number and size of mammary tumors in an animal model of breast cancer (BC). Also, a highly significant increase in IRAP activity has been found in BC tissue from women patients. Here, we found no changes in circulating IRAP in premenopausal (preMP) women, but it increased significantly in postmenopausal (postMP) women not treated with neoadjuvant chemotherapy (NACH). However, in women treated with NACH, IRAP activity increased in both preMP and postMP women. Two years of follow-up indicated lower levels of IRAP activity in untreated preMP women, but a return to control levels in untreated postMP women, while IRAP activity returned to control levels in women treated with NACH. Circulating oxytocin decreased in both preMP and postMP women during the follow-up period. Differences in Oxytocin appeared between preMP and postMP women treated with NACH, but not in women who were not treated with NACH. On the contrary, circulating vasopressin increased in untreated and treated preMP and postMP women, with most of the differences related to the hormonal status as well as the neoadjuvant treatment during the two year follow-up We propose that IRAP is involved in mechanisms related not only to oxytocin and/or vasopressin regulation, but also to the local mammary RAS through AngIV and its role in glucose transportation through the IRAP/GLUT4 system.

Yohimbine as a Starting Point to Access Diverse Natural Product-Like Agents with Re-programmed Activities against Cancer-Relevant GPCR Targets

G protein-coupled receptors (GPCRs) constitute the largest protein superfamily in the human genome. GPCRs play key roles in mediating a wide variety of physiological events including proliferation and cancer metastasis. Given the major roles that GPCRs play in mediating cancer growth, they present promising targets for small molecule therapeutics. One of the principal goals of our lab is to identify complex natural products (NPs) suitable for ring distortion, or the dramatic altering of the inherently complex architectures of NPs, to rapidly generate an array of compounds with diverse molecular skeletal systems. The overarching goal of our ring distortion approach is to re-program the biological activity of select natural products and identify new compounds of importance to the treatment of disease, such as cancer. Described herein are the results from biological screens of diverse small molecules derived from the indole alkaloid yohimbine against a panel of GPCRs involved in various diseases. Several analogues displayed highly differential antagonistic activities across the GPCRs tested. We highlight the re-programmed profile of one analogue, Y7g, which exhibited selective antagonistic activities against AVPR2 (IC₅₀ = 459 nM) and OXTR (IC₅₀ = 1.16 µM). The activity profile of Y7g could correlate its HIF-dependent anti-cancer activity to its GPCR antagonism since these receptors are known to be upregulated in hypoxic cellular environments. Our findings demonstrate that the ring distortion of yohimbine can lead to the identification of new compounds capable of interacting with distinct cancer-relevant targets.

Development and therapeutic potential of vasopressin synthetic analog [V4Q5]dDAVP as a novel anticancer agent

Since its discovery, arginine vasopressin (AVP) was subjected to several modifications with the aim of obtaining novel derivatives with increased potency and selectivity for biomedical use. Desmopressin (dDAVP) is a first generation synthetic analog of AVP with hemostatic and antimetastatic activity. dDAVP acts as a selective agonist of the arginine vasopressin type 2 receptor (AVPR2) present in microvascular endothelium and cancer cells. Considering its selective effects on AVPR2-expressing malignant and vascular tissue, and interesting antitumor profile, dDAVP was used as a lead compound for the development of novel peptide analogs with enhanced anticancer efficacy. After conducting different structure-activity relationship studies to determine key aminoacidic positions for its antitumor activity against AVPR2-expressing malignant cells, dDAVP was rationally modified and a wide panel of synthetic analogs with different sequence and structural modifications was assessed. As a result of this structure-based drug derivatization novel AVP analog [V⁴Q⁵]dDAVP (1-deamino-4-valine-5-glutamine-8-d-arginine vasopressin) was selected as the most active candidate and further developed. [V⁴Q⁵]dDAVP was evaluated in highly aggressive and metastatic cancer preclinical models deploying enhanced cytostatic, antimetastatic and angiostatic effects in comparison to parental peptide dDAVP. In addition, novel compound demonstrated good tolerability as evaluated in several toxicological studies, and cooperative therapeutic effects after combination with standard-of-care chemotherapy. In summary, due to its ability to inhibit growth and tumor-associated angiogenesis, as well as impairing progression of metastatic disease, AVP analogs such as novel [V⁴Q⁵]dDAVP are promising compounds for further development as coadjuvant agents for the management of advance or recurrent cancers.

Addition of vasopressin synthetic analogue [V(4)Q(5)]dDAVP to standard chemotherapy enhances tumour growth inhibition and impairs metastatic spread in aggressive breast tumour models

[V(4)Q(5)]dDAVP is a novel 2nd generation vasopressin analogue with robust antitumour activity against metastatic breast cancer. We recently reported that, by acting on vasopressin V2r membrane receptor present in tumour cells and microvascular endothelium, [V(4)Q(5)]dDAVP inhibits angiogenesis and metastatic progression of the disease without overt toxicity. Despite chemotherapy remaining as a primary therapeutic option for aggressive breast cancer, its use is limited by low selectivity and associated adverse effects. In this regard, we evaluated potential combinational benefits by adding [V(4)Q(5)]dDAVP to standard-of-care chemotherapy. In vitro, combination of [V(4)Q(5)]dDAVP with sub-IC50 concentrations of paclitaxel or carmustine resulted in a cooperative inhibition of breast cancer cell growth in comparison to single-agent therapy. In vivo antitumour efficacy of [V(4)Q(5)]dDAVP addition to chemotherapy was first evaluated using the triple-negative MDA-MB-231 breast cancer xenograft model. Tumour-bearing mice were treated with i.v. injections of [V(4)Q(5)]dDAVP (0.3 μg/kg, thrice weekly) in combination with weekly cycles of paclitaxel (10 mg/kg i.p.). After 6 weeks of treatment, combination regimen resulted in greater tumour growth inhibition compared to monotherapy. [V(4)Q(5)]dDAVP addition was also associated with reduction of local aggressiveness, and impairment of tumour invasion and infiltration of the skin. Benefits of combined therapy were confirmed in the hormone-independent and metastatic F3II breast cancer model by combining [V(4)Q(5)]dDAVP with carmustine (25 mg/kg i.p.). Interestingly, [V(4)Q(5)]dDAVP plus cytotoxic agents severely impaired colony forming ability of tumour cells and inhibited breast cancer metastasis to lung. The present study shows that [V(4)Q(5)]dDAVP may complement conventional chemotherapy by modulating metastatic progression and early stages of microtumour establishment, and thus supports further preclinical testing of the compound for the management of aggressive breast cancer.

A phase II dose-escalation trial of perioperative desmopressin (1-desamino-8-d-arginine vasopressin) in breast cancer patients

Desmopressin (dDAVP) is a well-known peptide analog of the antidiuretic hormone vasopressin, used to prevent excessive bleeding during surgical procedures. dDAVP increases hemostatic mediators, such as the von Willebrand factor (vWF), recently considered a key element in resistance to metastasis. Studies in mouse models and veterinary trials in dogs with locally-advanced mammary tumors demonstrated that high doses of perioperative dDAVP inhibited lymph node and early blood-borne metastasis and significantly prolonged survival. We conducted a phase II dose-escalation trial in patients with breast cancer, administering a lyophilized formulation of dDAVP by intravenous infusion in saline, 30–60 min before and 24 h after surgical resection. Primary endpoints were safety and tolerability, as well as selection of the best dose for cancer surgery. Secondary endpoints included surgical bleeding, plasma levels of vWF, and circulating tumor cells (CTCs) as measured by quantitative PCR of cytokeratin-19 transcripts. Only 2 of a total of 20 patients experienced reversible adverse events, including hyponatremia (grade 4) and hypersensitivity reaction (grade 2). Reactions were adequately managed by slowing the infusion rate. A reduced intraoperative bleeding was noted with increasing doses of dDAVP. Treatment was associated with higher vWF plasma levels and a postoperative drop in CTC counts. At the highest dose level evaluated (2 μg/kg) dDAVP appeared safe when administered in two slow infusions of 1 μg/kg, before and after surgery. Clinical trials to establish the effectiveness of adjunctive perioperative dDAVP therapy are warranted. This trial is registered on www.clinicaltrials.gov (NCT01606072).

The novel desmopressin analogue [V4Q5]dDAVP inhibits angiogenesis, tumour growth and metastases in vasopressin type 2 receptor-expressing breast cancer models

Desmopressin (dDAVP) is a safe haemostatic agent with previously reported antitumour activity. It acts as a selective agonist for the V2 vasopressin membrane receptor (V2r) present on tumour cells and microvasculature. The purpose of this study was to evaluate the novel peptide derivative [V⁴Q⁵]dDAVP in V2r-expressing preclinical mouse models of breast cancer. We assessed antitumour effects of [V⁴Q⁵]dDAVP using human MCF-7 and MDA-MB-231 breast carcinoma cells, as well as the highly metastatic mouse F3II cell line. Effect on in vitro cancer cell growth was evaluated by cell proliferation and clonogenic assays. Cell cycle distribution was analysed by flow cytometry. In order to study the effect of intravenously administered [V⁴Q⁵]dDAVP on tumour growth and angiogenesis, breast cancer xenografts were generated in athymic mice. F3II cells were injected into syngeneic mice to evaluate the effect of [V⁴Q⁵]dDAVP on spontaneous and experimental metastatic spread. In vitro cytostatic effects of [V⁴Q⁵]dDAVP against breast cancer cells were greater than those of dDAVP, and associated with V2r-activated signal transduction and partial cell cycle arrest. In MDA-MB-231 xenografts, [V⁴Q⁵]dDAVP (0.3 μg/kg, thrice a week) reduced tumour growth and angiogenesis. Treatment of F3II mammary tumour-bearing immunocompetent mice resulted in complete inhibition of metastatic progression. [V⁴Q⁵]dDAVP also displayed greater antimetastatic efficacy than dDAVP on experimental lung colonisation by F3II cells. The novel analogue was well tolerated in preliminary acute toxicology studies, at doses ≥300-fold above that required for anti-angiogenic/antimetastatic effects. Our data establish the preclinical activity of [V⁴Q⁵]dDAVP in aggressive breast cancer, providing the rationale for further clinical trials.

Reduction of tumor angiogenesis induced by desmopressin in a breast cancer model

Desmopressin (DDAVP), a synthetic peptide analog of vasopressin, is a safe antidiuretic and hemostatic compound that acts as a selective agonist for the vasopressin V2 membrane receptor. It is known that DDAVP can inhibit progression of residual metastatic cells and also improves chemotherapy effects in preclinical breast cancer models. Here, we explored the effects of DDAVP on tumor angiogenesis using the aggressive F3II mammary carcinoma in syngeneic Balb/c mice. Intravenous administration of the compound (2 μg/kg) markedly decreased vascularization of growing subcutaneous tumors, as well as inhibited the early angiogenic response around intradermal inoculation sites. In vitro studies confirmed the presence of vasopressin V2 receptors on F3II cells and a modest antiproliferative activity of DDAVP. Interestingly, conditioned media from F3II monolayers exposed to low doses of DDAVP (100 nM) significantly increased angiostatin formation in the presence of purified plasminogen. Such increase was associated with an enhancement of tumor-secreted urokinase-type plasminogen activator, suggesting the proteolytic conversion of plasminogen to angiostatin in vitro. Similar results were observed with the MCF-7 human breast carcinoma, a cell line known to express the vasopressin V2 receptor. No direct effects of DDAVP (100 nM–1 μM) were found on capillary-like tube formation by human microvascular cells HMVEC. Our studies showed that DDAVP induces anti-angiogenic effects that may be associated with the generation of angiostatin by tumor cells. Further preclinical studies with DDAVP and other vasopressin analogs are warranted to determine their potential in cancer management.

Structure-activity relationship of 1-desamino-8-D-arginine vasopressin as an antiproliferative agent on human vasopressin V2 receptor-expressing cancer cells

The synthetic nonapeptide 1‑desamino‑8‑D‑arginine vasopressin (dDAVP) can reduce tumor cell growth through agonist action on the vasopressin V2 receptor. A structure‑antiproliferative activity relationship analysis of dDAVP was performed using the alanine scanning technique on the aggressive MDA‑MB‑231 human breast carcinoma cell line. The results from this analysis demonstrated that the amino acids located at the loop of dDAVP are important for the antiproliferative activity of dDAVP, highlighting the key role of the N‑terminal region of the peptide in the interaction with the tumor cell surface receptor. The findings from this study present novel strategies for designing improved compounds with enhanced stability for cancer therapy.

Metastasis: recent discoveries and novel perioperative treatment strategies with particular interest in the hemostatic compound desmopressin

Metastatic disease is responsible for most of cancer lethality. A main obstacle for therapy of advanced cancers is that the outcome of metastasis depends on a complex interplay between malignant and host cells. The perioperative period represents an underutilized window of opportunity for cancer treatment where tumor-host interactions can be modulated, reducing the risk of local recurrences and distant metastases. Blood-saving agents are attractive compounds to be administered during tumor surgery. Desmopressin (DDAVP) is a safe and convenient hemostatic peptide with proved antimetastastic properties in experimental models and veterinary clinical trials. The compound seems to induce a dual angiostatic and antimetastatic effect, breaking the cooperative function of cancer cells and endothelial cells during residual tumor progression. DDAVP is therefore an interesting lead compound to develop novel synthetic peptide analogs with enhanced antitumor properties.

Antiproliferative effect of 1-deamino-8-D-arginine vasopressin analogs on human breast cancer cells

BACKGROUND

Desmopressin (dDAVP), a synthetic nonapeptide derivative of arginine vasopressin, is a safe antidiuretic and hemostatic compound that acts as a selective agonist for the vasopressin V2 membrane receptor (V2R). It is known that dDAVP can inhibit progression of residual metastatic cells in preclinical models. Among other mechanisms, the compound induces an agonist effect on V2R present in tumor cells.

RESULTS/DISCUSSION

Looking for novel analogs with improved anti-tumor activity, positions 4 and 5, at the conformational peptide loop, were substituted. The analog [V(4)Q(5)]dDAVP ([4-valine 5-glutamine] desmopressin) exhibited a significantly higher antiproliferative effect than dDAVP in cultures of MCF-7, a V2R-expressing human breast carcinoma cell line. The chiral isomer of this analog and tetrapeptide fragments corresponding to the loop region were also assessed.

CONCLUSION

Preclinical evaluation of the anti-tumor activity of [V(4)Q(5)]dDAVP in animal models is warranted.

Breast cancer expresses functional NMDA receptors

We demonstrate here that functional NMDAR1 and NMDAR2 receptors are expressed by Mcf-7 and SKBR3 breast cancer cell lines, and possibly by most or all high-grade breast tumors, and that these receptors are important for the growth of human breast cancer xenografts in mice. RT-PCR demonstrated mRNA for both NMDAR1 and NMDAR2 receptors are expressed in both Mcf-7 and SKBR3 cell lines, and these messages likely have sequences identical to those reported for human mRNAs. Proteins of the expected respective sizes 120 and 170 kD are generated from these mRNAs by the tumor cells. Cell growth was found to be significantly (P < 0.0001) impaired down to 10% of normal growth by the irreversible NMDAR1 antagonists MK-801 and memantine with IC 50s ranging from 600 to >800 microM and from 200 to 300 microM for the two lines. Paradoxically, memantine with a lower binding affinity had the greater influence of the two inhibitors on cell viability. Immunohistochemical examination of high-grade invasive ductal and lobular breast cancer with our polyclonal antibodies against a peptide (-Met-Ser-Ile-Tyr-Ser-Asp-Lys-Ser-Ile-His-) in the extracellular domain of the NMDAR1 receptor gave specific positive staining for the receptor in all 10 cases examined. Positive staining was chiefly concentrated at the membranes of these tumor tissues. No staining with these antibodies was found for normal breast and kidney tissues. When Mcf-7 cells were grown as tumor xenografts in nu/nu mice, the growth of these tumors was completely arrested by daily treatments with MK-801 over 5 days. All of these data point to active NMDAR receptors being expressed by most breast cancers, and having an important influence on their survival.

Detection of Provasopressin in Invasive and Non-invasive (DCIS) Human Breast Cancer Using a Monoclonal Antibody Directed against the C-terminus (MAG1)

The provasopressin protein (proAVP) is expressed by invasive breast cancer and non-invasive breast cancer, or ductal carcinoma in situ (DCIS). Here we demonstrate the ability of the monoclonal antibody MAG1 directed against the C-terminal end of proAVP to identify proAVP in all cases examined of human invasive cancer and DCIS (35 and 26, respectively). Tissues were chosen to represent a relevant variation in tumor type, grade, patient age, and menopausal status. By comparison, there was 65% positive staining for estrogen receptor, 61% for progesterone receptor, 67% for nuclear p53, and 39% for c-Erb-B2 with the invasive breast cancer sections. Reaction with the normal tissue types examined (67) was restricted to the vasopressinergic magnocellular neurons of the hypothalamus, where provasopressin is normally produced, and the posterior pituitary, where these neurons terminate. The breast epithelial tissue sections on the tissue microarray did not react with MAG1. Previously, we demonstrated that polyclonal antibodies to proAVP detected that protein in all breast cancer samples examined, but there was no reaction with breast tissue containing fibrocystic disease. The results presented here not only expand upon those earlier results, but they also demonstrate the specificity and effectiveness of what may be considered a more clinically-relevant agent. Thus, proAVP appears to be an attractive target for the detection of invasive breast cancer and DCIS, and these results suggest that MAG1 may be a beneficial tool for use in the development of such strategies.

Provasopressin expression by breast cancer cells: implications for growth and novel treatment strategies

The arginine vasopressin (AVP) gene is expressed in certain cancers such as breast cancer, where it is believed to act as an autocrine growth factor. However, little is known about the regulation of the AVP protein precursor (proAVP) or AVP-mediated signaling in breast cancer and this study was undertaken to address some of the basic issues. The cultured cell lines examined (Mcf7, Skbr3, BT474, ZR75, Mcf10a) and human breast cancer tissue extract were found to express proAVP mRNA. Western analysis revealed multiple forms of proAVP protein were present in cell lysates, corresponding to those detected in human hypothalamus extracts. Monoclonal antibodies directed against different regions of proAVP bound to intact live Mcf7 and Skbr3 cells. Dexamethasone increased the amount of proAVP-associated glycopeptide (VAG) secreted by Skbr3 cells and a combination of dexamethasone, IBMX and 8br-cAMP increased cellular levels of VAG. Exogenous AVP (1, 10, and 100 nM) elevated phospho-ERK1/2 levels, and increased cell proliferation was observed in the presence of 10 nM AVP. Concurrent treatment with the V1a receptor antagonist SR49059 reduced the effects of AVP on proliferation in Mcf7 cells, and abolished it in Skbr3 cells. Results here show that proAVP components are found at the surface of Skbr3 and Mcf7 cells and are also secreted from these cells. In addition, they show that AVP promotes cancer cell growth, apparently through a V1-type receptor-mediated pathway and subsequent ERK1/2 activation. Thus, strategies for targeting proAVP should be examined for their effectiveness in diagnosing and treating breast cancer.

Serum oxytocinase activity is related to tumor growth parameters in N-methyl nitrosourea induced rat breast cancer

Oxytocinase has been reported to hydrolyse the peptide hormone oxytocin (OT). We have previously described changes in oxytocinase activity in human breast cancer, where a highly significant increase occurred in tumoral tissue. In the present work, we analysed oxytocinase activity in serum of rats with breast cancer induced by N-methyl-nitrosourea (NMU). We also correlated these data with the number and size of tumors and the body weight of the animals to evaluate the putative value of this activity as a biological marker of the disease. Our results confirm the involvement of OT in carcinogenesis and suggest a mayor role for oxytocinase activity in the development of breast cancer.

Immunohistochemical evaluation of vasopressin expression in breast fibrocystic disease and ductal carcinoma in situ (DCIS)

We previously found that expression of the vasopressin gene is a common feature of human breast cancer. In the present study we first examined 21 different cases of benign fibrocystic breast disease for vasopressin expression using immunohistochemistry and antibodies directed against vasopressin (anti-VP) and against vasopressin-associated glycopeptide (anti-VAG). All cases examined were negative for vasopressin gene expression using these antibodies. Alternatively, we examined 16 cases of breast ductal carcinoma in situ (DCIS) using the second of these antibodies (anti-VAG), and all of these cases were positive for vasopressin gene expression. Our results suggest that products of vasopressin gene expression are not markers of cellular proliferation in the breast, and might rather represent an early part of the carcinogenic process in this tissue.

Key peptide processing enzymes are expressed by breast cancer cells

The expression of the three key peptide processing enzyme families, represented by CPE, PAM, and PC1/3 plus PC2, were examined in MCF-7 and ZR-75-1 breast cancer cell lines. Both of these cell lines express vasopressin receptors as well as the vasopressin gene, but the processing of vasopressin gene-related proteins appears to be limited. Products of the expected size for, CPE, PAM and PC1/PC3 could be amplified by reverse transcription-polymerase chain reaction (RT-PCR) from both cell lines. Cloning and sequencing of these RT-PCR products revealed that each enzyme mRNA had a structure identical to that published for the human form of the respective enzyme. Western analysis provided evidence that mRNAs for these enzymes are translated into proteins. Alternatively, PC2 mRNA was identified to be present in MCF-7 cells both by RT-PCR and Western blot analysis, but could not be demonstrated for ZR-75-1 cells. Our findings suggest that the key processing enzymes needed to generate active vasopressin and other neuropeptide growth factors are present in breast cancer cells.

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.

Aminopeptidase Activities in Breast Cancer Tissue

Background: Endopeptidases such as cathepsins help determine the prognosis of breast cancer (BC). However, little information is available about the role in BC of aminopeptidases (APs), which have been implicated in the metabolism of several local hormonal factors.

Methods: Using aminoacyl-β-naphthylamides as substrates, we measured fluorometrically alanyl-AP, arginyl-AP, cystinyl-AP, glutamyl-AP, aspartyl-AP, and pyroglutamyl-AP activities in their soluble and membrane-bound forms in surgically removed BC tissue from which we separated samples of neoplastic, adjacent tumoral, and unaffected surrounding tissue.

Results: Compared with unaffected tissue, neoplastic tissue had significantly higher activities of soluble alanyl-AP (553.9 ± 82.8 vs 1615.2 ± 183.0 pmol/mg protein; P &lt;0.001), arginyl-AP (372.4 ± 56.6 vs 1027.2 ± 143.5 pmol/mg protein; P &lt;0.001), and cystinyl-AP (74.8 ± 10.0 vs 282.9 ± 37.2 pmol/mg protein; P &lt;0.001), and of membrane-bound arginyl-AP (457.7 ± 97.9 vs 886.6 ± 140.0 pmol/mg protein; P &lt;0.01). However, membrane-bound aspartyl-AP activity was significantly lower in neoplastic tissue (17.3 ± 1.4 vs 9.2 ± 1.2 pmol/mg protein; P &lt;0.05) and pyroglutamyl-AP activity was significantly lower in neoplastic and adjacent tissues (12.8 ± 0.9 vs 7.0 ± 1.2 and 8.0 ± 1.3 pmol/mg protein; P &lt;0.001 for both comparisons).

Conclusions: The present results document changes in AP activities in BC tissue. These changes may reflect the functional status of the AP substrates, which can be selectively activated or inhibited locally in the affected tissue as a result of specific conditions brought about by the tumor.

Mutations in the vasopressin prohormone involved in diabetes insipidus impair endoplasmic reticulum export but not sorting

Familial neurohypophysial diabetes insipidus is characterized by vasopressin deficiency caused by heterozygous expression of a mutated vasopressin prohormone gene. To elucidate the mechanism of this disease, we stably expressed five vasopressin prohormones with a mutation in the neurophysin moiety (NP14G-->R, NP47E-->G, NP47DeltaE, NP57G-->S, and NP65G-->V) in the neuroendocrine cell lines Neuro-2A and PC12/PC2. Metabolic labeling demonstrated that processing and secretion of all five mutants was impaired, albeit to different extents (NP65G-->V >/= NP14G-->R > NP47DeltaE >/= NP47E-->G > NP57G-->S). Persisting endoglycosidase H sensitivity revealed these defects to be due to retention of mutant prohormone in the endoplasmic reticulum. Mutant prohormones that partially passed the endoplasmic reticulum were normally targeted to the regulated secretory pathway. Surprisingly, this also included mutants with mutations in residues involved in binding of vasopressin to neurophysin, a process implicated in targeting of the prohormone. To mimick the high expression in vasopressin-producing neurons, mutant vasopressin prohormones were transiently expressed in Neuro-2A cells. Immunofluorescence displayed formation of large accumulations of mutant prohormone in the endoplasmic reticulum, accompanied by redistribution of an endoplasmic reticulum marker. Our data suggest that prolonged perturbation of the endoplasmic reticulum eventually leads to degeneration of neurons expressing mutant vasopressin prohormones, explaining the dominant nature of the disease.

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.