Estradiol down regulates expression of vasoactive intestinal polypeptide receptor type-1 in breast cancer cell lines

Pituitary Adenylate Cyclase-Activating Polypeptide: 30 Years in Research Spotlight and 600 Million Years in Service

Emerging from the depths of evolution, pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors (i.e., PAC1, VPAC1, VPAC2) are present in multicellular organisms from Tunicates to humans and govern a remarkable number of physiological processes. Consequently, the clinical relevance of PACAP systems spans a multifaceted palette that includes more than 40 disorders. We aimed to present the versatility of PACAP1-38 actions with a focus on three aspects: (1) when PACAP1-38 could be a cause of a malfunction, (2) when PACAP1-38 could be the cure for a malfunction, and (3) when PACAP1-38 could either improve or impair biology. PACAP1-38 is implicated in the pathophysiology of migraine and post-traumatic stress disorder whereas an outstanding protective potential has been established in ischemia and in Alzheimer’s disease. Lastly, PACAP receptors could mediate opposing effects both in cancers and in inflammation. In the light of the above, the duration and concentrations of PACAP agents must be carefully set at any application to avoid unwanted consequences. An enormous amount of data accumulated since its discovery (1989) and the first clinical trials are dated in 2017. Thus in the field of PACAP research: “this is not the end, not even the beginning of the end, but maybe the end of the beginning.”

Nuclear localization of vasoactive intestinal peptide (VIP) receptors in human breast cancer

Vasoactive intestinal peptide (VIP) and its receptors (VPACs) are involved in proliferation, survival, and differentiation in human breast cancer cells. Its mechanism of action is traditionally thought to be through specific plasma membrane receptors. There is compelling evidence for a novel intracrine mode of genomic regulation by G-protein-coupled receptors (GPCRs) that implies both endocytosis and nuclear translocation of peripheral GPCR and/or the activation of nuclear-located GPCRs by endogenously-produced, non-secreted ligands. Regarding to VPAC receptors, which are GPCRs, there is only a report suggesting them as a dynamic system for signaling from plasma membrane and nuclear membrane complex. In this study, we show that VPAC(1) receptor is localized in cell nuclear fraction whereas VPAC(2) receptor presents an extranuclear localization and its protein expression is lower than that of VPAC(1) receptor in human breast tissue samples. Both receptors as well as VIP are overexpressed in breast cancer as compared to non-tumor tissue. Moreover, we report the markedly nuclear localization of VPAC(1) receptors in estrogen-dependent (T47D) and independent (MDA-MB-468) human breast cancer cell lines. VPAC(1) receptors are functional in plasma membrane and nucleus as shown by VIP stimulation of cAMP production in both cell lines. In addition, VIP increases its own intracellular and extracellular levels, and could be involved in the regulation of VPAC(1)-receptor traffic from the plasma membrane to the nucleus. These results support new concepts on function and regulation of nuclear GPCRs which could have an impact on development of new therapeutic drugs.

Vasoactive intestinal peptide (VIP) increases vascular endothelial growth factor (VEGF) expression and secretion in human breast cancer cells

Previous studies have shown that vasoactive intestinal peptide (VIP) and its receptors (VPAC(1) and VPAC(2) receptors) are involved in promotion and growth of many human tumours including breast cancer. Here we investigated whether VIP regulates the expression of the main angiogenic factor, vascular endothelial cell growth factor (VEGF) in human oestrogen-dependent (T47D) and oestrogen-independent (MDA-MB-4687) breast cancer cells. Semiquantitative and quantitative real-time RT-PCRs were used at mRNA level whereas enzyme immunoanalysis was performed at protein level. Both cancer cell lines expressed VIP and VPAC(1) (but not VPAC(2)) receptors that were functional as shown by VIP stimulation of adenylate cyclase activity. VIP induced VEGF expression at both mRNA and protein levels following a time-dependent pattern. The responses were faster in T47D than in MDA-MB-468 cells. The observed VIP regulation of VEGF expression appears to be modulated at least by the cAMP/protein kinase A (PKA) and the phosphoinositide 3-kinase (PI3-K) signalling systems as shown by studies of adenylate cyclase stimulation and using specific kinase inhibitors such as H89 and wortmannin. These actions suggest a proangiogenic potential of VIP in breast cancer.

VPAC1 expression is regulated by FXR agonists in the human gallbladder epithelium

Vasoactive intestinal peptide receptor-1 (VPAC1) is the high-affinity receptor of vasoactive intestinal peptide (VIP), a major regulator of bile secretion. To better define the level at which VPAC1 stimulates bile secretion, we examined its expression in the different cell types participating in bile formation (i.e., hepatocytes, bile duct, and gallbladder epithelial cells). Because VPAC1 expression was previously shown to be regulated by nuclear receptors, we tested the hypothesis that it may be regulated by the farnesoid X receptor (FXR). Quantitative RT-PCR and immunoblot analyses of cell isolates indicated that VPAC1 is expressed in all three cell types lining the human biliary tree, with predominant expression in the gallbladder. In primary cultures of human gallbladder epithelial cells, VIP induced cAMP production and chloride secretion. Analysis of the VPAC1 gene revealed the presence of potential FXR response element sequences, and both FXR and RXRalpha expressions were detected in gallbladder epithelial cells. In these cells, the FXR pharmacological agonist GW4064 upregulated VPAC1 expression in a dose-dependent manner, and this effect was antagonized by the RXRalpha ligand, 9-cis retinoic acid. Chenodeoxycholate activated endogenous FXR in gallbladder epithelial cells, as ascertained by electromobility shift assay and upregulation of the FXR target gene, small heterodimer partner. Chenodeoxycholate also provoked an increase in VPAC1 mRNA and protein content in these cells. In conclusion, FXR agonists may increase gallbladder fluid secretion through transcriptional activation of VPAC1, which may contribute to the regulation of bile secretion by bile salts and to a protective effect of FXR pharmacological agonists in gallstone disease.

Clinical endocrinology and metabolism. Potential clinical applications of vasoactive intestinal peptide: a selected update

Neuropeptides are expressed in neurons innervating endocrine cells or in endocrine cells and cancer cells, and are released on site to act as hormones and growth factors. Vasoactive intestinal peptide (VIP) was first discovered in the early 1970s and has since become the area of research for many laboratories. VIP has a neuroendocrine role as it is intimately involved with the synthesis, secretion and action of other neuroendocrine hormones as well as cytokines and chemokines. Major outcomes of VIP downregulation encompass developmental and behavioral dysfunctions, including impaired diurnal rhythms. Overexpression of VIP has been associated with diarrhea and cancer, and overexpression of VIP receptors is associated with cancerous growth. This short review outlines some of the recent progress made in VIP research.

Effects of ovariectomy and steroid hormones on vaginal smooth muscle contractility

The role of steroid hormones in regulating vaginal smooth muscle contractility was investigated. Rabbits were kept intact or ovariectomized. After 2 weeks, animals were continuously infused with vehicle or supraphysiological levels of testosterone (100 microg/day), or estradiol (200 microg/day), for an additional 2 weeks. The distal vaginal tissue was used to assess contractility in organ baths and changes in tissue structure were assessed by histology. Ovariectomized animals infused with vehicle exhibited significant atrophy of the muscularis and decreased epithelial height, resulting in thinning of the vaginal wall. Estradiol infusion increased epithelial height, comparable to that of intact animals, but only partially restored the muscularis layer. In contrast, testosterone infusion completely restored the muscularis layer, but only partially restored the epithelial height. In vaginal tissue strips contracted with norepinephrine and treated with bretylium, electrical field stimulation (EFS) caused frequency-dependent relaxation that was slightly attenuated with vehicle, significantly inhibited with estradiol and significantly enhanced with testosterone. VIP-induced relaxation was slightly attenuated in tissues from vehicle and estradiol-infused groups, but was enhanced in tissues from testosterone-infused animals. Contraction elicited by EFS or exogenous norepinephrine was not significantly altered with ovariectomy or steroid hormone infusion when data were normalized to potassium contraction. However, the tissue from testosterone-infused animals developed significantly greater contractile force to norepinephrine. These observations suggest that steroid hormones may be important regulators of vaginal tissue structure and contractility.

Vasoactive intestinal peptide receptor-1 (VPAC-1) is a novel gene target of the hemolymphopoietic transcription factor Ikaros

Vasoactive intestinal peptide and its G-protein-coupled receptors, VPAC-1 and VPAC-2, are highly expressed in the immune system and modulate diverse T cell functions. The human VPAC-1 5'-flanking region (1.4 kb) contains four high affinity Ikaros (IK) consensus sequences. Ikaros native protein from T cell nuclear extracts and IK-1 and IK-2 recombinant proteins recognized an IK high affinity binding motif in the VPAC-1 promoter in electrophoretic mobility shift assays by a sequence-specific mechanism, and anti-IK antibodies supershifted this complex. Stable NIH-3T3 clones overexpressing IK-1 or IK-2 isoforms were generated to investigate Ikaros regulation of endogenous VPAC-1 expression as assessed by quantifying VPAC-1 mRNA and protein. By traditional and fluorometric-based kinetic reverse transcription-PCR and (125)I-labeled vasoactive intestinal peptide binding, both IK-1 and IK-2 suppressed endogenous VPAC-1 expression in NIH-3T3 clones by a range of 50-93%. When a series of nested deletions of the VPAC-1 luciferase reporter construct were transiently transfected into IK-2 clones there was up to a 41% decrease in transcriptional activity compared with vector control. Two major IK-2 binding domains also were identified at -1076 to -623 bp and at -222 to -35 bp, respectively. As both Ikaros and its novel target VPAC-1 are highly expressed in T cells, this system may be a dominant determinant of the VPAC-1 expression in immune responses.