Calcitonin receptor-stimulating peptide: Its evolutionary and functional relationship with calcitonin/calcitonin gene-related peptide based on gene structure

A Critical Review of Zebrafish Neurological Disease Models-1. The Premise: Neuroanatomical, Cellular and Genetic Homology and Experimental Tractability

The last decade has seen a dramatic rise in the number of genes linked to neurological disorders, necessitating new models to explore underlying mechanisms and to test potential therapies. Over a similar period, many laboratories adopted zebrafish as a tractable model for studying brain development, defining neural circuits and performing chemical screens. Here we discuss strengths and limitations of using the zebrafish system to model neurological disorders. The underlying premise for many disease models is the high degree of homology between human and zebrafish genes, coupled with the conserved vertebrate Bauplan and repertoire of neurochemical signaling molecules. Yet, we caution that important evolutionary divergences often limit the extent to which human symptoms can be modeled meaningfully in zebrafish. We outline advances in genetic technologies that allow human mutations to be reproduced faithfully in zebrafish. Together with methods that visualize the development and function of neuronal pathways at the single cell level, there is now an unprecedented opportunity to understand how disease-associated genetic changes disrupt neural circuits, a level of analysis that is ideally suited to uncovering pathogenic changes in human brain disorders.

Involvement of the calcitonin gene-related peptide system in the modulation of inflamed uterus contractile function in pigs

This study analyzed severe acute endometritis action on myometrial density and distribution of protein gene product (PGP)9.5- and calcitonin gene-related peptide (CGRP)-like immunoreactive nerve fibers and calcitonin receptor-like receptor (CLR) expression, and on CGRP receptor (CGRPR) participation in uterine contractility in pigs. E. coli suspension (E. coli group) or saline (SAL group) were injected into the uteri, or only laparotomy was performed (CON group). In the E. coli group myometrium, a lack of significant changes in PGP9.5 and CGRP innervation patterns and increased CLR protein level were revealed. In all groups, compared to the pretreatment period, human αCGRP increased amplitude in the myometrium, while reducing it in endometrium/myometrium. In the E. coli group endometrium/myometrium, human αCGRP lowered amplitude vs other groups. Human αCGRP reduced frequency in CON and SAL groups and enhanced it in the E. coli group endometrium/myometrium. The frequency in E. coli group increased vs other groups. CGRPR antagonist, human αCGRP8-37, reversed (CON, SAL groups) and eliminated (E. coli group) the rise in human αCGRP-induced myometrial amplitude. In endometrium/myometrium, human αCGRP8-37 abolished (CON group) and reversed (SAL group) a decrease in frequency, and reduced the rise in frequency (E. coli group) caused by human αCGRP. Collectively, in the myometrium, endometritis did not change PGP9.5 and CGRP innervation patterns and enhanced CLR protein level. CGRPR also mediated in CGRP action on inflamed uterus contractility.

Evolution of calcitonin/calcitonin gene-related peptide family in chordates: Identification of CT/CGRP family peptides in cartilaginous fish genome

The calcitonin (CT)/CT gene-related peptide (CGRP) family is a peptide gene family that is widely found in bilaterians. CT, CGRP, adrenomedullin (AM), amylin (AMY), and CT receptor-stimulating peptide (CRSP) are members of the CT/CGRP family. In mammals, CT is involved in calcium homeostasis, while CGRP and AM primarily function in vasodilation. AMY and CRSP are associated with anorectic effects. Diversification of the molecular features and physiological functions of the CT/CGRP family in vertebrate lineages have been extensively reported. However, the origin and diversification mechanisms of the vertebrate CT/CGRP family of peptides remain unclear. In this review, the molecular characteristics of CT/CGRP family peptides and their receptors, along with their major physiological functions in mammals and teleosts, are introduced. Furthermore, novel candidates of the CT/CGRP family in cartilaginous fish are presented based on genomic information. The CT/CGRP family peptides and receptors in urochordates and cephalochordates, which are closely related to vertebrates, are also described. Finally, a putative evolutionary scenario of the CT/CGRP family peptides and receptors in chordates is discussed.

Changes in Neuropeptide Prohormone Genes among Cetartiodactyla Livestock and Wild Species Associated with Evolution and Domestication

The impact of evolution and domestication processes on the sequences of neuropeptide prohormone genes that participate in cell–cell signaling influences multiple biological process that involve neuropeptide signaling. This information is important to understand the physiological differences between Cetartiodactyla domesticated species such as cow, pig, and llama and wild species such as hippopotamus, giraffes, and whales. Systematic analysis of changes associated with evolutionary and domestication forces in neuropeptide prohormone protein sequences that are processed into neuropeptides was undertaken. The genomes from 118 Cetartiodactyla genomes representing 22 families were mined for 98 neuropeptide prohormone genes. Compared to other Cetartiodactyla suborders, Ruminantia preserved PYY2 and lost RLN1. Changes in GNRH2, IAPP, INSL6, POMC, PRLH, and TAC4 protein sequences could result in the loss of some bioactive neuropeptides in some families. An evolutionary model suggested that most neuropeptide prohormone genes disfavor sequence changes that incorporate large and hydrophobic amino acids. A compelling finding was that differences between domestic and wild species are associated with the molecular system underlying ‘fight or flight’ responses. Overall, the results demonstrate the importance of simultaneously comparing the neuropeptide prohormone gene complement from close and distant-related species. These findings broaden the foundation for empirical studies about the function of the neuropeptidome associated with health, behavior, and food production.

Beyond CGRP: The calcitonin peptide family as targets for migraine and pain

The CGRP system has emerged as a key pharmacological target for the treatment of migraine. However, some individuals who suffer from migraine have low or no response to anti-CGRP or other treatments, suggesting the need for additional clinical targets. CGRP belongs to the calcitonin family of peptides, which includes calcitonin, amylin, adrenomedullin and adrenomedullin 2. These peptides display a range of pro-nociceptive and anti-nociceptive actions, in primary headache conditions such as migraine. Calcitonin family peptides also show expression at sites relevant to migraine and pain. This suggests that calcitonin family peptides and their receptors, beyond CGRP, may be therapeutically useful in the treatment of migraine and other pain disorders. This review considers the localisation of the calcitonin family in peripheral pain pathways and discusses how they may contribute to migraine and pain. LINKED ARTICLES: This article is part of a themed issue on Advances in Migraine and Headache Therapy (BJP 75th Anniversary). To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.3/issuetoc.

Adrenomedullin - Current perspective on a peptide hormone with significant therapeutic potential

The peptide hormone adrenomedullin (ADM) consists of 52 amino acids and plays a pivotal role in the regulation of many physiological processes, particularly those of the cardiovascular and lymphatic system. Like calcitonin (CT), calcitonin gene-related peptide (CGRP), intermedin (IMD) and amylin (AMY), it belongs to the CT/CGRP family of peptide hormones, which despite their low little sequence identity share certain characteristic structural features as well as a complex multicomponent receptor system. ADM, IMD and CGRP exert their biological effects by activation of the calcitonin receptor-like receptor (CLR) as a complex with one of three receptor activity-modifying proteins (RAMP), which alter the ligand affinity. Selectivity within the receptor system is largely mediated by the amidated C-terminus of the peptide hormones, which bind to the extracellular domains of the receptors. This enables their N-terminus consisting of a disulfide-bonded ring structure and a helical segment to bind within the transmembrane region and to induce an active receptor confirmation. ADM is expressed in a variety of tissues in the human body and is fundamentally involved in multitude biological processes. Thus, it is of interest as a diagnostic marker and a promising candidate for therapeutic interventions. In order to fully exploit the potential of ADM, it is necessary to improve its pharmacological profile by increasing the metabolic stability and, ideally, creating receptor subtype-selective analogs. While several successful attempts to prolong the half-life of ADM were recently reported, improving or even retaining receptor selectivity remains challenging.

The calcitonin-like system is an ancient regulatory system of biomineralization

Biomineralization is the process by which living organisms acquired the capacity to accumulate minerals in tissues. Shells are the biomineralized exoskeleton of marine molluscs produced by the mantle but factors that regulate mantle shell building are still enigmatic. This study sought to identify candidate regulatory factors of molluscan shell mineralization and targeted family B G-protein coupled receptors (GPCRs) and ligands that include calcium regulatory factors in vertebrates, such as calcitonin (CALC). In molluscs, CALC receptor (CALCR) number was variable and arose through lineage and species-specific duplications. The Mediterranean mussel (Mytilus galloprovincialis) mantle transcriptome expresses six CALCR-like and two CALC-precursors encoding four putative mature peptides. Mussel CALCR-like are activated in vitro by vertebrate CALC but only receptor CALCRIIc is activated by the mussel CALCIIa peptide (EC50 = 2.6 ×10-5 M). Ex-vivo incubations of mantle edge tissue and mantle cells with CALCIIa revealed they accumulated significantly more calcium than untreated tissue and cells. Mussel CALCIIa also significantly decreased mantle acid phosphatase activity, which is associated with shell remodelling. Our data indicate the CALC-like system as candidate regulatory factors of shell mineralization. The identification of the CALC system from molluscs to vertebrates suggests it is an ancient and conserved calcium regulatory system of mineralization.

Calcitonin and Bone Physiology: In Vitro, In Vivo, and Clinical Investigations

Calcitonin was discovered as a peptide hormone that was known to reduce the calcium levels in the systemic circulation. This hypocalcemic effect is produced due to multiple reasons such as inhibition of bone resorption or suppression of calcium release from the bone. Thus, calcitonin was said as a primary regulator of the bone resorption process. This is the reason why calcitonin has been used widely in clinics for the treatment of bone disorders such as osteoporosis, hypercalcemia, and Paget's disease. However, presently calcitonin usage is declined due to the development of efficacious formulations of new drugs. Calcitonin gene-related peptides and several other peptides such as intermedin, amylin, and adrenomedullin (ADM) are categorized in calcitonin family. These peptides are known for the structural similarity with calcitonin. Aside from having a similar structure, these peptides have few overlapping biological activities and signal transduction action through related receptors. However, several other activities are also present that are peptide specific. In vitro and in vivo studies documented the posttreatment effects of calcitonin peptides, i.e., positive effect on bone osteoblasts and their formation and negative effect on osteoclasts and their resorption. The recent research studies carried out on genetically modified mice showed the inhibition of osteoclast activity by amylin, while astonishingly calcitonin plays its role by suppressing osteoblast and bone turnover. This article describes the review of the bone, the activity of the calcitonin family of peptides, and the link between them.

Peptide receptors and immune-related proteins expressed in the digestive system of a urochordate, Ciona intestinalis

The digestive system is responsible for nutrient intake and defense against pathogenic microbes. Thus, identification of regulatory factors for digestive functions and immune systems is a key step to the verification of the life cycle, homeostasis, survival strategy and evolutionary aspects of an organism. Over the past decade, there have been increasing reports on neuropeptides, their receptors, variable region-containing chitin-binding proteins (VCBPs) and Toll-like receptors (TLRs) in the ascidian, Ciona intestinalis. Mass spectrometry-based peptidomes and genome database-searching detected not only Ciona orthologs or prototypes of vertebrate peptides and their receptors, including cholecystokinin, gonadotropin-releasing hormones, tachykinin, calcitonin and vasopressin but also Ciona-specific neuropeptides including Ci-LFs and Ci-YFVs. The species-specific regulation of GnRHergic signaling including unique signaling control via heterodimerization among multiple GnRH receptors has also been revealed. These findings shed light on the remarkable significance of ascidians in investigations of the evolution and diversification of the peptidergic systems in chordates. In the defensive systems of C. intestinalis, VCBPs and TLRs have been shown to play major roles in the recognition of exogenous microbes in the innate immune system. These findings indicate both common and species-specific functions of the innate immunity-related molecules between C. intestinalis and vertebrates. In this review article, we present recent advances in molecular and functional features and evolutionary aspects of major neuropeptides, their receptors, VCBPs and TLRs in C. intestinalis.

The Activity of Peptides of the Calcitonin Family in Bone

Calcitonin was discovered over 50 yr ago as a new hormone that rapidly lowers circulating calcium levels. This effect is caused by the inhibition of calcium efflux from bone, as calcitonin is a potent inhibitor of bone resorption. Calcitonin has been in clinical use for conditions of accelerated bone turnover, including Paget's disease and osteoporosis; although in recent years, with the development of drugs that are more potent inhibitors of bone resorption, its use has declined. A number of peptides that are structurally similar to calcitonin form the calcitonin family, which currently includes calcitonin gene-related peptides (αCGRP and βCGRP), amylin, adrenomedullin, and intermedin. Apart from being structurally similar, the peptides signal through related receptors and have some overlapping biological activities, although other activities are peptide specific. In bone, in vitro studies and administration of the peptides to animals generally found inhibitory effects on osteoclasts and bone resorption and positive effects on osteoblasts and bone formation. Surprisingly, studies in genetically modified mice have demonstrated that the physiological role of calcitonin appears to be the inhibition of osteoblast activity and bone turnover, whereas amylin inhibits osteoclast activity. The review article focuses on the activities of peptides of the calcitonin family in bone and the challenges in understanding the relationship between the pharmacological effects and the physiological roles of these peptides.

Characterization of an evolutionarily conserved calcitonin signaling system in a lophotrochozoan, the Pacific oyster (Crassostrea gigas)

In Protostoma, the diuretic hormone 31 (DH31) signaling system was long considered as the orthologue of the chordate calcitonin (CT) signaling system. Using the Pacific oyster (Crassostrea gigas) transcriptomic database GigaTON (http://ngspipelines-sigenae.toulouse.inra.fr/), we characterized seven G-protein-coupled receptors (GPCRs) named Cragi-CTR1/7 and phylogenetically related to chordate CT receptors (CTRs) and to protostome DH31 receptors. Two CT Precursors (Cragi-CTP1 and Cragi-CTP2) containing two CT-type peptides and encoded by two distinct genes with a similar organization were also characterized. These oyster neuropeptides (Cragi-CT1/2) exhibit the two N-terminal paired cysteine residues and except CTP2 derived peptide (Cragi-CTP2dp) the C-terminal proline-amide motif typical of deuterostome CT-type peptides. All mature Cragi-CTs but Cragi-CTP2dp were detected in visceral ganglion (VG) extracts using mass spectrometry. Cell-based assays revealed that the formerly characterized oyster receptors Cg-CTR and Cragi-CTR2 were specifically activated by Cragi-CT1b and Cragi-CT2, respectively. This activation does not require the co-expression of receptor activity-modifying proteins (RAMPs). Thus, the oyster CT signaling appears functionally more closely related to the vertebrate CT/CTR signaling than to the (Calcitonin Gene Related Peptide) CGRP/CLR signaling. Gene expression profiles in different adult tissues and in oysters acclimated to brackish water suggest the potential implication of both Cg-CT-R/Cragi-CT1b and Cragi-CTR2/Cragi-CT2 in water and ionic regulations, though with apparently opposite effects. The present study represents the first comprehensive characterization of a functional CT-type signaling system in a protostome and provides evidence for its evolutionarily ancient origin and its early role in osmotic homeostasis.

Neuropeptides, Peptide Hormones, and Their Receptors of a Tunicate, Ciona intestinalis

The critical phylogenetic position of the ascidian, Ciona intestinalis, as the closest relative of vertebrates, suggested its potential applicability as a model organism in a wide variety of biological events including the nervous, neuroendocrine, and endocrine regulation. To date, approximately 40 neuropeptides and/or peptide hormones and several cognate receptors have been identified. These peptides are categorized into two types: (1) orthologs of vertebrate peptides, such as cholecystokinin, GnRH, tachykinin, vasopressin, and calcitonin, and (2) novel family peptides such as LF peptides and YFL/V peptides. Ciona GnRH receptors (Ci-GnRHR) were found to be multiplicated in the Ciona-specific lineages and to form unique heterodimers between Ci-GnRHR1 and R4 and between Ci-GnRHR2 and R4, leading to fine-tuning of the generation of second messengers. Furthermore, Ciona tachykinin was shown to regulate a novel protease-associated follicle growth pathway. These findings will pave the way for the exploration of both conserved and diversified endocrine, neuroendocrine, and nervous systems in the evolutionary lineage of invertebrate deuterostomes and/or chordates. In this chapter, we provide an overview of primary sequences, functions, and evolutionary aspects of neuropeptides, peptide hormones, and their receptors in C. intestinalis.

The Calcitonin/Calcitonin Gene-Related Peptide Family in Invertebrate Deuterostomes

Calcitonin (CT)/CT gene-related peptide (CGRP) family peptides (CT/CGRP family peptides) including CT, CGRP, adrenomedullin, amylin, and CT receptor-stimulating peptide have been identified from various vertebrates and perform a variety of important physiological functions. These peptides bind to two types of receptors including CT receptor (CTR) and CTR-like receptor (CLR). Receptor recognition of CT/CGRP family peptides is determined by the heterodimer between CTR/CLR and receptor activity-modifying protein (RAMP). Comparative studies of the CT/CGRP family have been exclusively performed in vertebrates from teleost fishes to mammals and strongly manifest that the CGRP family system containing peptides, their receptors, and RAMPs was derived from a common ancestor. In addition, CT/CGRP family peptides and their receptors are also identified and inferred from various invertebrate species. However, the evolutionary process of the CT/CGRP family from invertebrates to vertebrates remains enigmatic. In this review, I principally summarize the CT/CGRP family peptides and their receptors in invertebrate deuterostomes, highlighting the study of invertebrate chordates including ascidians and amphioxi. The CT/CGRP family peptide that shows similar molecular structure and function with that of vertebrate CT has been identified from ascidian, Ciona intestinalis. Amphioxus, Branchiostoma floridae also possessed three CT/CGRP family peptides, one CTR/CLR receptor, and three RAMP-like proteins. The molecular function of the receptor complex formed by amphioxus CTR/CLR and a RAMP-like protein was clarified. Moreover, CT/CGRP family peptides have been identified in the superphylum Ambulacraria, which is close to Chordata. Finally, this review provides potential hypotheses of the evolution of CGRP family peptides and their receptors from invertebrates to vertebrates.

Update on the pharmacology of calcitonin/CGRP family of peptides: IUPHAR Review 25

The calcitonin/CGRP family of peptides includes calcitonin, α and β CGRP, amylin, adrenomedullin (AM) and adrenomedullin 2/intermedin (AM2/IMD). Their receptors consist of one of two GPCRs, the calcitonin receptor (CTR) or the calcitonin receptor-like receptor (CLR). Further diversity arises from heterodimerization of these GPCRs with one of three receptor activity-modifying proteins (RAMPs). This gives the CGRP receptor (CLR/RAMP1), the AM₁ and AM₂ receptors (CLR/RAMP2 or RAMP3) and the AMY_1, AMY₂ and AMY₃ receptors (CTR/RAMPs1-3 complexes, respectively). Apart from the CGRP receptor, there are only peptide antagonists widely available for these receptors, and these have limited selectivity, thus defining the function of each receptor in vivo remains challenging. Further challenges arise from the probable co-expression of CTR with the CTR/RAMP complexes and species-dependent splice variants of the CTR (CT_(a) and CT_(b) ). Furthermore, the AMY_1(a) receptor is activated equally well by both amylin and CGRP, and the preferred receptor for AM2/IMD has been unclear. However, there are clear therapeutic rationales for developing agents against the various receptors for these peptides. For example, many agents targeting the CGRP system are in clinical trials, and pramlintide, an amylin analogue, is an approved therapy for insulin-requiring diabetes. This review provides an update on the pharmacology of the calcitonin family of peptides by members of the corresponding subcommittee of the International Union of Basic and Clinical Pharmacology and colleagues.

Platypus and opossum calcitonins exhibit strong activities, even though they belong to mammals

In mammalian assay systems, calcitonin peptides of non-mammalian species exhibit stronger activity than those of mammals. Recently, comparative analyses of a wide-range of species revealed that platypus and opossum, which diverged early from other mammals, possess calcitonins that are more similar in amino acid sequence to those of non-mammals than mammals. We herein determined whether platypus and opossum calcitonins exhibit similar biological activities to those of non-mammalian calcitonins using an assay of actin ring formation in mouse osteoclasts. We also compared the dose-dependent effects of each calcitonin on cAMP production in osteoclasts. Consistent with the strong similarities in their primary amino acid sequences, platypus and opossum calcitonins disrupted actin rings with similar efficacies to that of salmon calcitonin. Human calcitonin exhibited the weakest inhibitory potency and required a 100-fold higher concentration (EC₅₀=3×10^-11M) than that of salmon calcitonin (EC₅₀=2×10^-13M). Platypus and opossum calcitonins also induced cAMP production in osteoclast cultures with the same efficacies as that of salmon calcitonin. Thus, platypus and opossum calcitonins exhibited strong biological activities, similar to those of the salmon. In addition, phylogenetic analysis revealed that platypus and opossum calcitonins clustered with the salmon-type group but not human- or porcine-type group. These results suggest that platypus and opossum calcitonins are classified into the salmon-type group, in terms of the biological activities and amino acid sequences.

Calcitonin receptor increases invasion of prostate cancer cells by recruiting zonula occludens-1 and promoting PKA-mediated TJ disassembly

Almost all primary prostate cancers (PCs) and PC cell lines express calcitonin (CT) and/or its receptor (CTR), and their co-expression positively correlates with their invasiveness. Activation of the CT-CTR axis in non-invasive LNCaP cells induces an invasive phenotype. In contrast, silencing of CT/CTR expression in highly metastatic PC-3M cells markedly reduces their tumorigenicity and abolishes their ability to form distant metastases in nude mice. Our recent studies suggest that CTR interacts with zonula occludens 1 (ZO-1) through PDZ interaction to destabilize tight junctions and increase invasion of PC cells. Our results show that CTR activates AKAP2-anchored cAMP-dependent protein kinase A, which then phosphorylates tight junction proteins ZO-1 and claudin 3. Moreover, PKA-mediated phosphorylation of tight unction proteins required CTR-ZO-1 interaction, suggesting that the interaction may bring CTR-activated PKA in close proximity of tight junction proteins. Furthermore, inhibition of PKA activity attenuated CT-induced loss of TJ functionality and invasion, suggesting that the phosphorylation of TJ proteins is responsible for TJ disassembly. Finally, we show that the prevention of CTR-ZO-1 interaction abolishes CT-induced invasion, and can serve as a novel therapeutic tool to treat aggressive prostate cancers. In brief, the present study identifies the significance of CTR-ZO-1 interaction in progression of prostate cancer to its metastatic form.

Effects of intrathecal amylin on formalin-induced nociception and on cAMP accumulation in the rat embryonic spinal cells

Amylin (AMY) is a member of calcitonin family of peptides. In this study, the effects of intrathecal (i.t) injection of AMY on the inflammatory pain and on the cAMP accumulation in the rat spinal cells were investigated. By using AMY receptor antagonists, we also studied the pharmacology of AMY receptors in the spinal cells. Formalin model of inflammatory pain was induced by intraplantar injection of formalin. AMY (0.06250-2500pmol/rat) was administrated i.t 15min before the injection of formalin. Antagonists were injected i.t 10min before the injection of AMY and/or morphine. AMY reduced formalin-induced pain in a dose dependent mode. This effect was inhibited by the potent AMY antagonist, AC187 but not CGRP8-37. rAMY8-37, most commonly reported as a weak AMY antagonist, showed to be equally or more potent than AC187 in antagonizing the above effects. The opioid antagonist, naloxone, had no significant effects on AMY antinociceptive effects. Primary dissociated cell culture was used to investigate the effect of AMY on cAMP production and to characterize AMY receptors in the spinal cells. AMY moderately increases cAMP accumulation in the spinal cells with an EC50 value of 74.62nM. This effect was not affected by CGRP8-37 but was inhibited by AC187 and rAMY8-37 with pA2 values of 7.94 and 7.87 respectively. In conclusion, effects of AMY in reducing formalin induced pain and on the cAMP accumulation by spinal cells are mediated through undefined receptors.

Calcitonin receptor family evolution and fishing for function using in silico promoter analysis

In the present study the calcitonin receptor (CTR) sub-family of family B G-protein coupled receptors (GPCRs) in teleosts is evaluated and put in the context of the families overall evolution from echinodermates to vertebrates. Echinodermates, hemichordates, cephalochordates and tunicates have a single gene that encodes a receptor that bears similarity to the vertebrate calcitonin receptor (CTR) and calcitonin-like receptor (CTR/CLR). In tetrapods one gene encodes the calcitonin receptor (CALCR) and another gene the calcitonin receptor-like receptor (CALCRL). The evolution of CALCR has been under strong conservative pressure and a single copy is also found in fishes and high conservation of gene organisation and synteny exits from teleosts to human. A teleost specific CTR innovation that occurred after their divergence from holostei is the presence of several HBDs in the N-terminus. CALCRL had a different evolutionary trajectory from CALCR and although a single gene copy is present in tetrapods the sarcopterygii fish, the coelacanth, has 1 copy of CALCRL but also a fish specific form CALCRL3. The ray-finned fish, the spotted gar, has 1 copy of CALCRL and 1 of CALCRL3 but the teleost specific whole genome duplication has resulted in a CALCRL1 and CALCRL2 in addition to the fish specific CALCRL3. Strong conservation of CALCRL gene structure exists from human to fish. Promoter analysis in silico reveals that the duplicated CALCRL genes in the teleosts, zebrafish, takifugu, tetraodon and medaka, have divergent promoters and different putative co-regulated gene partners suggesting their function is different.

Structure-activity relationships of the N-terminus of calcitonin gene-related peptide: key roles of alanine-5 and threonine-6 in receptor activation

BACKGROUND AND PURPOSE

The N-terminus of calcitonin gene-related peptide (CGRP) is important for receptor activation, especially the disulphide-bonded ring (residues 1-7). However, the roles of individual amino acids within this region have not been examined and so the molecular determinants of agonism are unknown. This study has examined the role of residues 1, 3-6 and 8-9, excluding Cys-2 and Cys-7.

EXPERIMENTAL APPROACH

CGRP derivatives were substituted with either cysteine or alanine; further residues were introduced at position 6. Their affinity was measured by radioligand binding and their efficacy by measuring cAMP production in SK-N-MC cells and β-arrestin 2 translocation in CHO-K1 cells at the CGRP receptor.

KEY RESULTS

Substitution of Ala-5 by cysteine reduced affinity 270-fold and reduced efficacy for production of cAMP in SK-N-MCs. Potency at β-arrestin translocation was reduced by ninefold. Substitution of Thr-6 by cysteine destroyed all measurable efficacy of both cAMP and β-arrestin responses; substitution with either alanine or serine impaired potency. Substitutions at positions 1, 4, 8 and 9 resulted in approximately 10-fold reductions in potency at both responses. Similar observations were made at a second CGRP-activated receptor, the AMY(1(a)) receptor.

CONCLUSIONS AND IMPLICATIONS

Ala-5 and Thr-6 are key determinants of agonist activity for CGRP. Ala-5 is also very important for receptor binding. Residues outside of the 1-7 ring also contribute to agonist activity.