Molecular characterization and peptide specificity of two vasoactive intestinal peptide (VIP) binding sites in the chicken pineal

Receptors for VIP and PACAP in guinea pig cerebral cortex: effects on cyclic AMP synthesis and characterization by 125I-VIP binding

Receptors for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) in guinea pig cerebral cortex were characterized by (1) radioreceptor binding of 125I-labeled VIP (human/rat/porcine), and (2) cyclic AMP (cAMP) formation. Saturation analysis of 125I-VIP binding to membranes of guinea pig cerebral cortex resulted in a linear Scatchard plot, suggesting the presence of a single class of high-affinity receptor-binding sites, with a Kd of 0.63 nM and a B(max) of 77 fmol/mg protein. Various peptides from the PACAP/VIP/secretin family displaced the specific binding of 125I-VIP to guinea pig cerebrum with the relative rank order of potency: chicken VIP (cVIP) > or = PACAP38 approximately PACAP27 approximately guinea pig VIP (gpVIP) > or = mammalian (human/rat/porcine) VIP (mVIP) > peptide histidine-methionine (PHM) > peptide histidine-isoleucine (PHI) > secretin. Analysis of the competition curves revealed displacement of 125I-VIP from high- and lower-affinity binding sites, with IC50 values in the picomolar and the nanomolar range, respectively. About 70% of the specific 125I-VIP-binding sites in guinea pig cerebral cortex were sensitive to Gpp(NH)p, a nonhydrolyzable analog of GTP. Pituitary adenylate cyclase-activating polypeptide 38 (PACAP38), PACAP27, cVIP, gpVIP, mVIP, PHM, and PHI stimulated cAMP production in [3H]adenine-prelabeled slices of guinea pig cerebral cortex in a concentration-dependent manner. Of the tested peptides, the most effective were PACAP38 and PACAP27, which at a 1 microM concentration produced a 17- to 19-fold rise in cAMP synthesis, increasing the nucleotide production to approx 11% conversion above the control value. The three forms of VIP (cVIP, mVIP, and gpVIP) at the highest concentration used, i.e., 3 microM, produced net increases in cAMP production in the range of 8-9% conversion, whereas 5 microM PHM and PHI, by, respectively, 6.7% and 4.9% conversion. It is concluded that cerebral cortex of guinea pig contains VPAC- type receptors positively linked to cAMP formation. In addition, the observed stronger action of PACAP (both PACAP38 and PACAP27), when compared to any form of VIP, on cAMP production in this tissue, suggests its interaction with both PAC1 and VPAC receptors.

Receptors for vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide in turkey cerebral cortex: characterization by [125I]-VIP binding and effects on cyclic AMP synthesis

Receptors for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) in turkey cerebral cortex were characterized using two approaches: (1) in vitro radioreceptor binding of [125I]-VIP, and (2) effects of peptides from the PACAP/VIP/secretin family on cyclic AMP formation. The binding of [125I]-VIP to turkey cortical membranes was rapid, stable, and reversible. Saturation analysis resulted in a linear Scatchard plot, suggesting binding to a single class of high affinity receptor binding sites with a Kd of 0.70 nM and a Bmax of 52 fmol/mg protein. Various peptides displaced the specific binding of 0.12 nM [125I]-VIP to turkey cerebral cortical membranes in a concentration-dependent manner. The relative rank order of potency of the tested peptides to inhibit [125I]-VIP binding to turkey cerebrum was: PACAP38 approximately PACAP27 approximately chicken VIP approximately mammalian VIP >>> PHI >> secretin, chicken VIP16-28 (inactive). About 65% of specific [125I]-VIP binding sites in turkey cerebral cortex was sensitive to Gpp(NH)p, a nonhydrolysable analogue of GTP. PACAP38, PACAP27, chicken VIP and, to a lesser extent, mammalian VIP potently stimulated cyclic AMP formation in turkey cerebral cortical slices in a concentration-dependent manner, displaying EC50 values of 8.7 nM (PACAP38), 21.3 nM (PACAP27), 67.4 nM (chicken VIP), and 202 nM (mammalian VIP). On the other hand, PHI and secretin very weakly affected the nucleotide production. The obtained results indicate that cerebral cortex of turkey contains VPAC type receptors that are positively linked to cyclic AMP-generating system and are labeled with [125I]-VIP.

Characterization of vasoactive intestinal peptide/pituitary adenylate cyclase-activating polypeptide receptors in chick cerebral cortex

In this study receptors for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) were characterized in chick cerebral cortex by an in vitro binding technique, using 125I-labeled VIP ([125I]-VIP) as a ligand. The specific binding of [125I]-VIP to chick cerebral cortical membranes was found to be rapid, stable, saturable, reversible, and of high affinity. Saturation analysis resulted in a linear Scatchard plot, suggesting binding to a single class of receptor binding sites with high affinity (Kd = 0.21 nM) and low capacity (Bmax = 19.5 fmol/mg protein). The relative rank order of potency of the tested peptides to inhibit [125I]-VIP binding to chick cerebrum was VIP (chicken) > or = VIP (mammalian) > or = PACAP27 > or = PACAP38 >> VIP6-28 (mammalian) > PHI (porcine) >> neurotensin6-11-chicken VIP7-28 > neurotensin6-11-mammalian VIP7-28 >>> VIP16-28 (chicken; inactive) approximately secretin (inactive). About 60% of [125I]-VIP-binding sites in chick cerebral cortex were sensitive to Gpp(NH)p, a nonhydrolyzable analog of GTP. It has been concluded that the cerebral cortex of chick, in addition to PAC1 receptors, contains a population of VPAC-type receptors.

Quantitative evaluation of the lengths of homobifunctional protein cross-linking reagents used as molecular rulers

Homobifunctional chemical cross-linking reagents are important tools for functional and structural characterization of proteins. Accurate measures of the lengths of these molecules currently are not available, despite their widespread use. Stochastic dynamics calculations now provide quantitative measures of the lengths, and length dispersions, of 32 widely used molecular rulers. Significant differences from published data have been found.

SUPPLEMENTAL MATERIAL

See www.proteinscience.org

Cellular circadian clocks in the pineal

Daily rhythms are a fundamental feature of all living organisms; most are synchronized by the 24 hr light/dark (LD) cycle. In most species, these rhythms are generated by a circadian system, and free run under constant conditions with a period close to 24 hr. To function properly the system needs a pacemaker or clock, an entrainment pathway to the clock, and one or more output signals. In vertebrates, the pineal hormone melatonin is one of these signals which functions as an internal time-keeping molecule. Its production is high at night and low during day. Evidence indicates that each melatonin producing cell of the pineal constitutes a circadian system per se in non-mammalian vertebrates. In addition to the melatonin generating system, they contain the clock as well as the photoreceptive unit. This is despite the fact that these cells have been profoundly modified from fish to birds. Modifications include a regression of the photoreceptive capacities, and of the ability to transmit a nervous message to the brain. The ultimate stage of this evolutionary process leads to the definitive loss of both the direct photosensitivity and the clock, as observed in the pineal of mammals. This review focuses on the functional properties of the cellular circadian clocks of non-mammalian vertebrates. How functions the clock? How is the photoreceptive unit linked to it and how is the clock linked to its output signal? These questions are addressed in light of past and recent data obtained in vertebrates, as well as invertebrates and unicellulars.

The small G-proteins Rap 1 as potential targets of vasoactive intestinal peptide effects in the human clonic cancer cells HT29

We recently reported that the vasoactive intestinal peptide (VIP) potently inhibited proliferation and induced in parallel a strong cAMP rise, in the human colonic cancer cell line HT29. In this study, we investigated whether Rap 1 proteins could be potential targets of VIP effects in HT29 cells. These Ras-related proteins in which activity was demonstrated to be regulated by PKA phosphorylation, are considered as potential modulators of the Ras / Raf / MAP kinases cascade that governs cell growth control. Our data revealed that the Rap 1a isoform is highly expressed in HT29 cells and mainly localized in a late endosomal compartment. In these cells, VIP induces Rap 1 phosphorylation and a yet unidentified modification that leads to their acidification. This latter Rap 1 acidification seems to be, at least partially, cAMP-dependent. It is concluded that in HT29 cells, Rap 1 proteins may be part of a VIP-induced signaling cascade.

Histamine in the chick pineal gland: origin, metabolism, and effects on the pineal function

The chick pineal gland contains histamine and tele-methylhistamine. The levels of both substances are elevated after treatment of chicks with the amino acid precursor of histamine, L-histidine (1 g/kg, ip). In control and L-histidine-loaded animals the pineal levels of histamine and tele-methylhistamine are higher in light-exposed than in dark-adapted animals (measured at the end of the light phase and in the middle of the dark phase of 12 hr light, 12 hr dark illumination cycle, respectively). The chick pineal gland contains histamine-immunofluorescent cells displaying mast cell morphology; they are seen in the vicinity of the capsule and in the parenchyma. Enzymatic studies showed the presence of the activity of histamine synthesizing and inactivating enzyme, i.e., L-histidine decarboxylase (HDC) and histamine-methyltransferase (HMT). The detected enzyme activities were sensitive to specific inhibitors of HDC (alpha-fluoromethylhistidine and alpha-hydrazinohistidine) and HMT (quinacrine and metoprine); inhibitors of aromatic amino acid decarboxylase alpha-methyl-DOPA and NSD-1015 were inactive on HDC. Exogenous histamine added to organ-cultured chick pineals strongly stimulated endogenous cyclic AMP accumulation and moderately increased melatonin secretion. The data, considered collectively, suggest that in avians histamine, probably originating from the pineal mast cell compartment, may function as a regulator of pineal gland activity.

VIP as a cell-growth and differentiation neuromodulator role in neurodevelopment

In addition to its commonly recognized status as a neuromodulator of virtually all vital functions, including neurobiological, the neuropeptide VIP plays a role in the control of cell growth and differentiation and of neuronal survival. Through these actions, VIP, whose impact appears early in ontogeny, may possess developmental functions. VIP can be stimulatory or inhibitory on cell growth in function of the model considered. The growth regulatory actions of VIP, which are often independent of cAMP, are most likely significant when mitogenic or trophic factors, eventually released by nontarget cells, are simultaneously present in the extracellular medium. The intracellular mechanisms that mediate these actions of VIP may involve different transduction cascades triggered by subsets of VIP binding sites that may coexist in the same tissue.

Extrahypothalamic distribution of vasoactive intestinal polypeptide (VIP)-like immunoreactivity in the chicken brain, Gallus domesticus

The distribution of VIP-immunoreactive neurons and fibers was detected in the extrahypothalamic areas of chicken brain by immunohistochemistry and light microscopy VIP-ir perikarya were found in the hippocampus and in the area parahippocampalis; in the area ventralis of Tsai, in the n. interpeduncularis, in the substantia nigra, in the substantia grisea centralis, in the locus coeruleus, in the n. subcoeruleus ventralis and in the n. pontis lateralis. VIP-ir fibers were seen in the lobus parolfactorius and throughout the brainstem mainly arranged in lateral and midsagittal position. This finding was discussed in relation to other studies performed on chicken and/or other avian brain. The distributional pattern of VIP-ergic system in the chicken brain suggests a possible involvement of VIP or VIP-like peptide in several neuroregulatory mechanisms.

Prostaglandins stimulate serotonin acetylation in chick pineal cells: involvement of cyclic AMP-dependent and calcium/calmodulin-dependent mechanisms

The effects of prostaglandins (PGs) on the activity of the rate-limiting enzyme of melatonin biosynthesis, arylalkylamine-N-acetyltransferase (NAT) were investigated on primary cultures of dispersed chick pineal cells. In indomethacin-treated cells, PGs caused a four-fold increase in NAT activity. This response was associated with an eight-fold increase in cyclic AMP (cAMP) levels. The potency order of PGs was the same for NAT and for cAMP responses (PGE1 > PGE2 > PGF2 alpha >> cloprostenol). However, each PG tested was 30- to 200-fold more potent to increase NAT activity than to stimulate cAMP accumulation. As a result, half-maximal stimulation of NAT by PGs was not associated with an increase in cAMP levels. Half-maximal stimulation of NAT by PGE1 was highly sensitive to inhibition by a calcium/calmodulin antagonist (W-7). In contrast, maximal stimulation of NAT by PGE1 as well as stimulations evoked by either forskolin or 8-bromo-cAMP were poorly sensitive to inhibition by W-7. These results indicate that an increase in cAMP levels may be responsible for the maximal stimulation of NAT evoked by PGs, whereas half-maximal stimulation of NAT by PGs would rely principally on a calcium/calmodulin-dependent mechanism.

Prostaglandins of the E Series Stimulate Cyclic AMP Accumulation and N-Acetylation of Serotonin in Chick Pineal Cells

We investigated the effects of prostaglandins on cyclic AMP (cAMP) levels and on the activity of the rate-limiting enzyme of melatonin biosynthesis, arylalkylamine-N-acetyltransferase (NAT). The study was performed on primary cultures of dispersed chick pineal cells. Prostaglandin E, (PGE,) increased cAMP levels 2-fold and this stimulation went up to 4-fold in the presence of a phosphodiesterase inhibitor. The PGE,- evoked increase in cAMP levels did not desensitize over 6 h. The potency order of a series of prostaglandins to increase cAMP levels (PGE(1) PGE(1) >PGA2>PGD(2) ≃PGF(2) α) agreed with the pharmacological profile of the adenylate cyclase-coupled prostaglandin receptor. Inhibition of endogenous prostaglandin synthesis by two cyclooxygenase inhibitors (indomethacin and aspirin) caused a 30% decrease in cAMP levels. This effect was completely reversed by the addition of exogenous PGE(1) or PGE(2) . Indomethacin and aspirin also caused a 50% decrease in NAT activity. Prostaglandins of the E series increased NAT activity up to 2-fold above basal level and restored NAT activity after inhibition by indomethacin or aspirin. These results are the first illustration of a role for prostaglandins in chick pineal cells. The correlations observed between cAMP levels and NAT activity suggest that the regulation of NAT activity by prostaglandins of the E series might be mediated by changes in cAMP concentration.