Limited signal transduction repertoire of human Y(5) neuropeptide Y receptors expressed in HEC-1B cells

Neuropeptide Y in cancer-biological functions and potential clinical implications

Neuropeptide Y (NPY) is a sympathetic neurotransmitter widely distributed in the peripheral and central nervous system, affecting many physiological functions. Consequently, dysregulation of the NPY system contributes to numerous pathological disorders, including stress, obesity, and cancer. The pleiotropic functions of NPY in humans are mediated by G protein-coupled receptors (Y1R, Y2R, Y5R), which activate several signaling pathways and thereby regulate cell growth, differentiation, apoptosis, proliferation, angiogenesis, and metabolism. These activities of NPY are highly relevant to tumor biology and known hallmarks of cancer, including sustained proliferative potential, resisting cell death, angiogenesis, invasion, and metastases. In this comprehensive review, we describe the cellular functions of NPY and discuss its role in cancer pathobiology, as well as provide the current state of knowledge pertaining to NPY and its receptors in various cancer types. Moreover, we focus on potential clinical applications targeting the NPY system, such as its role as a prognostic and predictive factor, as well as its utility in cancer diagnostics, imaging, and treatment. Altogether, growing evidence supports the significant role of the NPY system in tumor pathobiology and implicates its potential therapeutic and diagnostic value in modern oncology.

Effects of Nifedipine on Renal and Cardiovascular Responses to Neuropeptide Y in Anesthetized Rats

Neuropeptide Y (NPY) acts via multiple receptor subtypes termed Y₁, Y₂ and Y₅. While Y₁ receptor-mediated effects, e.g., in the vasculature, are often sensitive to inhibitors of L-type Ca²⁺ channels such as nifedipine, little is known about the role of such channels in Y₅-mediated effects such as diuresis and natriuresis. Therefore, we explored whether nifedipine affects NPY-induced diuresis and natriuresis. After pre-treatment with nifedipine or vehicle, anesthetized rats received infusions or bolus injections of NPY. Infusion NPY (1 µg/kg/min) increased diuresis and natriuresis, and this was attenuated by intraperitoneal injection of nifedipine (3 µg/kg). Concomitant decreases in heart rate and reductions of renal blood flow were not attenuated by nifedipine. Bolus injections of NPY (0.3, 1, 3, 10 and 30 μg/kg) dose-dependently increased mean arterial pressure and renovascular vascular resistance; only the higher dose of nifedipine (100 μg/kg/min i.v.) moderately inhibited these effects. We conclude that Y₅-mediated diuresis and natriuresis are more sensitive to inhibition by nifedipine than Y₁-mediated renovascular effects. Whether this reflects a general sensitivity of Y₅ receptor-mediated responses or is specific for diuresis and natriuresis remains to be investigated.

Neuropeptide Y receptor interactions regulate its mitogenic activity

Neuropeptide Y (NPY) is a multifunctional neurotransmitter acting via G protein-coupled receptors - Y1R, Y2R and Y5R. NPY activities, such as its proliferative effects, are mediated by multiple receptors, which have the ability to dimerize. However, the role of this receptor interplay in NPY functions remains unclear. The goal of the current study was to identify NPY receptor interactions, focusing on the ligand-binding fraction, and determine their impact on the mitogenic activity of the peptide. Y1R, Y2R and Y5R expressed in CHO-K1 cells formed homodimers detectable on the cell surface by cross-linking. Moreover, Y1R and Y5R heterodimerized, while no Y2R/Y5R heterodimers were detected. Nevertheless, Y5R failed to block internalization of its cognate receptor in both Y1R/Y5R and Y2R/Y5R transfectants, indicating Y5R transactivation upon stimulation of the co-expressed receptor. These receptor interactions correlated with an augmented mitogenic response to NPY. In Y1R/Y5R and Y2R/Y5R transfectants, the proliferative response started at picomolar NPY concentrations, while nanomolar concentrations were needed to trigger proliferation in cells transfected with single receptors. Thus, our data identify direct and indirect heterotypic NPY receptor interactions as the mechanism amplifying its activity. Understanding these processes is crucial for the design of treatments targeting the NPY system.

Neuropeptide Y Y5 receptor promotes cell growth through extracellular signal-regulated kinase signaling and cyclic AMP inhibition in a human breast cancer cell line

Overexpression of neuropeptide Y (NPY) and its receptor system has been reported in various types of cancers. NPY Y5 receptor (Y5R) has been implicated in cell growth and angiogenesis. However, the role of Y5R in breast cancer is unknown. To identify the role of Y5R in breast cancer, we screened several breast cancer cell lines to examine the expression of Y5R and its function in breast cancer. All screened cell lines express both Y1 receptor and Y5R except BT-549, which expresses mainly Y5R. Binding studies showed that NPY, Y5R-selective agonist peptide, and Y5R-selective antagonist (CGP71683A) displaced (125)I-PYY binding in BT-549 cell membranes in a dose-dependent manner. The displacement studies revealed the presence of two binding sites in Y5R with IC(50) values of 29 pmol/L and 531 nmol/L. NPY inhibited forskolin-stimulated cyclic AMP accumulation with an IC(50) value of 52 pmol/L. NPY treatment of BT-549 cells induced extracellular signal-regulated kinase phosphorylation but did not alter intracellular calcium. Y5R activation stimulates BT-549 cell growth, which is inhibited by CGP71683A, pertussis toxin, and extracellular signal-regulated kinase blockade. CGP71683A alone induced cell death in a time- and dose-dependent manner in Y5R-expressing cells. The stimulation of MDA MB-231 cell migration by NPY is inhibited by CGP71683A. Together, our results suggest that Y5R plays an important role in cancer cell growth and migration and could be a novel therapeutic target for breast cancer.

Interactions of multiple signaling pathways in neuropeptide Y-mediated bimodal vascular smooth muscle cell growth

Neuropeptide Y (NPY), a sympathetic cotransmitter, acts via G protein-coupled receptors to stimulate constriction and vascular smooth muscle cell (VSMC) proliferation through interactions with its Y1 receptors. However, VSMC proliferation appears bimodal, with high- and low-affinity peaks differentially blocked by antagonists of both Y1 and Y5 receptors. Here, we sought to determine the signaling mechanisms of NPY-mediated bimodal mitogenesis. In rat aortic VSMCs, NPY's mitogenic effect at all concentrations was blocked by pertussis toxin and was associated with decreased forskolin-stimulated cAMP levels. NPY also increased intracellular calcium levels; in contrast to mitogenesis, this effect was dose dependent. The rise in intracellular Ca2+ depended on extracellular Ca2+ and was mediated via activation of Y1 receptors, but not Y5 receptors. Despite differences in calcium, the signaling pathways activated at low and high NPY concentrations were similar. The mitogenic effect of the peptide at all doses was completely blocked by inhibitors of calcium/calmodulin-dependent kinase II (CaMKII), protein kinase C (PKC), and mitogen-activated protein kinase kinase, MEK1/2. Thus, in VSMCs, NPY-mediated mitogenesis signals primarily via Y1 receptors activating 2 Ca2+-dependent, growth-promoting pathways -- PKC and CaMKII. At the high-affinity peak, these 2 pathways are amplified by Y5 receptor-mediated, calcium-independent inhibition of the adenylyl cyclase - protein kinase A (PKA) pathway. All 3 mechanisms converge to the extracellular signal-regulated kinases (ERK1/2) signaling cascade and lead to VSMC proliferation.

Pertussis toxin induces parallel loss of neuropeptide Y Y1 receptor dimers and Gi alpha subunit function in CHO cells

Treatment with pertussis toxin in addition to a stable inhibition of G(i)alpha subunits of G-proteins also strongly reduced human neuropeptide Y Y(1) receptors expressed in Chinese hamster ovary (CHO) cells. This was reflected in abolition of the inhibition by Y(1) agonists of forskolin-stimulated adenylyl cyclase in intact cells, and of Y(1) agonist stimulation of GTPgammaS binding to particulates from disrupted cells. The loss of both receptor and G(i)alpha subunit function was attenuated by ammonium chloride, an inhibitor of acid proteinases, pointing to a chaperoning co-protection of active pertussis toxin-sensitive Galpha subunits and Y(1) receptors. The surface complement of the Y(1) receptor was changed a little in conditions of approximately 85% decrease of the Y(1) population, but the rate of the Y(1) receptor-linked internalization of agonist peptides was reduced about 70%. The preserved receptor fraction consisted of monomers significantly coupled to G(q)alpha subunits. The persistent pertussis toxin-insensitive internalization of agonists with the Y(1) receptor may reflect a rescue or alternative switching that could be important for cell functioning in neuropeptide Y-rich environments. The results are compatible with a loss, due to G(i)alpha subunit inactivation by the toxin, of a large Y(1) receptor reserve constituted of oligomers associating with heterotrimeric G-proteins.

Parallel inactivation of Y2 receptor and G-proteins in CHO cells by pertussis toxin

The Y(2) receptor for neuropeptide Y (NPY) interacts with pertussis toxin (PTX)-sensitive G-proteins, but little is known about interdependence of their levels and functions. We found that PTX reduces Y(2) receptors expressed in CHO cells in parallel to inactivation of Gi G-proteins, to loss of inhibition by Y(2) agonists of forskolin-stimulated adenylyl cyclase, and to decrease in the binding of GTP-gamma-S. These losses were attenuated by the endosome alkalinizer ammonium chloride. Affinity of the Y(2) receptor was not changed by PTX treatment. Prolonged treatment induced a large decrease of Y(2) receptor immunoreactivity (more than 70% in 48 h). The Gi(3) alpha-subunit immunoreactivity decreased slowly (about 46% in 48 h). There was a significant increase in Gq alpha immunoreactivity and in fraction of Y(2) binding sensitive to a Gq-selective antagonist. Possibly linked to that, the surface Y(2) sites and the internalization of the Y(2) receptor were less than 40% reduced. However, the abundant masked Y(2) sites were eliminated by the toxin, and could be mainly coupled to PTX-sensitive G-proteins.

Effects of peptides, with emphasis on feeding, pain, and behavior A 5-year (1999-2003) review of publications in Peptides

Novel effects of naturally occurring peptides are continuing to be discovered, and their mechanisms of actions as well as interactions with other substances, organs, and systems have been elucidated. Synthetic analogs may have actions similar or antagonistic to the endogenous peptides, and both the native peptides and analogs have potential as drugs or drug targets. The journal Peptides publishes many leading articles on the structure-activity relationship of peptides as well as outstanding reviews on some families of peptides. Complementary to the reviews, here we extract information from the original papers published during the past five years in Peptides (1999-2003) to summarize the effects of different classes of peptides, their modulation by other chemicals and various pathophysiological states, and the mechanisms by which the effects are exerted. Special attention is given to peptides related to feeding, pain, and other behaviors. By presenting in condensed form the effects of peptides which are essential for systems biology, we hope that this summary of existing knowledge will encourage additional novel research to be presented in Peptides.

From Transcription Profile to Expression: The Signaling Repertoire of the SK-N-MC Neuroepithelioma Cell-Line

SK-N-MC neuroepithelioma cells are routinely cultured and widely used as a model system in biochemical and pharmacological experiments. To clarify the gene expression patterns of SK-N-MC cells with respect to G protein-coupled receptors and signaling network components, we describe in this report the transcription profile of the cell line. Following the traditional pathway from genome to proteome, selected examples are further examined at the level of protein expression and by functional assays. cRNA targets derived from total RNA extracts were hybridized to Affymetrix Human Genome U133A GeneChip arrays, and the data were analyzed and grouped according to functional aspects. Results obtained for neuropeptide Y (NPY) Y1, Y5, and orexin Ox1 receptors were confirmed by RT-PCR. It is surprising that we found the presence of both NPY receptor subtypes and the absence of the orexin receptor at the mRNA level. Receptor-binding experiments confirmed NPY binding of the Y1 receptor in the nanomolar range but gave no evidence for high expression levels of Y5 receptor subtypes on the cell surface. Protein expression was assayed with immunoblots by using antibodies directed against selected Galpha protein subunits. The presence of at least Galphas, Galphai3, and Galphai2 subunits was indicated.

Bis(31/31')[[Cys(31), Nva(34)]NPY(27-36)-NH(2)]: a neuropeptide Y (NPY) Y(5) receptor selective agonist with a latent stimulatory effect on food intake in rats

The actions of neuropeptide Y (NPY) are mediated by at least six G-protein coupled receptors denoted as Y(1), Y(2), Y(3), Y(4), Y(5), and y(6). Investigations using receptor selective ligands and receptor knock-out mice suggest that NPY effects on feeding are mediated by both Y(1) and Y(5) receptors. We have previously shown that Cys-dimers of NPY C-terminal peptides exhibit Y(1) selectivity relative to Y(2) receptors. Re-investigation of their selectivity with respect to the newly cloned receptors, has identified bis(31/31') [[Cys(31), Nva(34)]NPY(27-36)-NH(2)] (BWX-46) as a Y(5) receptor selective agonist. BWX-46 selectively bound Y(5) receptors, and inhibited cAMP synthesis by Y(5) cells with potencies comparable to that of NPY. Moreover, BWX-46 (10 microM) exhibited no significant effect on the cAMP synthesis by Y(1), Y(2), and Y(4) cells. Thus, BWX-46 constitutes the lowest molecular weight Y(5) selective agonist reported to date. Intrahypothalamic (i.h.t)-injection of 30 and 40 microg of BWX-46 stimulated the food intake by rats in a gradual manner, reaching maximal level 8 h after injection. This response was similar to that exhibited by other Y(5) selective agonists, but differed from that of NPY, which exhibited a rapid orexigenic stimulus within 1 h. It is suggested that the differences in the orexigenic stimuli of NPY and Y(5) agonists may be due to their differences in the signal transduction mechanisms.

Activation of extracellular signal regulated protein kinase by neuropeptide Y and pancreatic polypeptide in CHO cells expressing the NPY Y(1), Y(2), Y(4) and Y(5) receptor subtypes

Neuropeptide Y (NPY), 36-amino acid amidated peptide expressed in central and peripheral neurons, regulates a variety of physiological activities, including food intake, energy expenditure, vasoconstriction, anxiolysis, nociception and ethanol consumption. NPY binds to a family of G-protein coupled receptors whose activation results in inhibition of adenylyl cyclase activity. To more fully characterize the signal transduction pathways utilized by the NPY receptor subtypes, the pathways leading to phosphorylation of the extracellular signal regulated protein kinases 1 and 2 (ERK) have been compared in CHO cells expressing each of the four cloned human NPY receptor subtypes, Y(1), Y(2), Y(4) and Y(5). NPY Y(1), Y(2), Y(4) and Y(5) receptor-mediated ERK phosphorylation was blocked by pertussis toxin (PTX) exposure, indicating that all four receptors are coupled to inhibitory G(i/o) proteins. Exposure to the protein kinase C (PKC) inhibitor GF109203X diminished Y(1), Y(2) and Y(4) receptor-mediated ERK phosphorylation but completely blocked Y(5) receptor-mediated ERK phosphorylation. Additionally, Y(5) receptor-mediated ERK phosphorylation was inhibited by the phosphatidylinositol 3-kinase inhibitors LY294002 and wortmannin to a greater extent than was Y(1)-mediated ERK phosphorylation. These results demonstrate that in CHO cells, the Y(5) receptor and the Y(1), Y(2) and Y(4) receptors utilize different pathways to activate ERK.