PACAP38

Gene, mRNA, and precursor

The human preproPACAP gene, ADCYAP1, location 18p11, consists of five exons. PACAP mRNA of about 3.0 kb has been detected in the human and rat by northern blotting analysis. Bioactive PACAP27 and PACAP38 were generated by processing with PC1 and PC2 from the precursor. The gene structure and its mRNA size are well conserved among teleosts, amphibians, and mammals. 

Synthesis and release

PACAP synthesis and release are stimulated by nerve growth factor (NGF) and cAMP inducer in nervous tissues. PACAP stimulates biosynthesis by itself, indicating that PACAP regulates its expression level via the autocrine/paracrine system

Receptors

PACAP and VIP share three types of GPCRs with seven transmembrane domains: PAC1 receptor (PAC1R), and VPAC1 and VPAC2 receptors (VPAC1R, VPAC2R). PACAP binds to VPAC1R and VPAC2R with a similar affinity to that of VIP, while PACAP interacts with PAC1R with 1000 times higher affinity than VIP. PAC1R has various splicing forms that differ in the presence or absence of two cassettes, termed HIP and HOP, in the region of the third cytoplasmic loop (e.g., PAC1R-short, PAC1R-hop1, PAC1R-hop2, PAC1R-hip). These cassettes contribute to the regulation of the signal transduction pathway.

Agonist and antagonist

Maxadilan is a specific agonist of PAC1R isolated from the sand fly saliva, and the modification peptide M65 works as a PAC1R-specific antagonist. PACAP6–38, missing 1–5 aa residues from the N-terminal of PACAP38, is a potential antagonist of PAC1R and VPAC2-R. VIP-6-28, missing 1–5 aa residues from the N-terminal of VIP, is a potential antagonist of VPAC1- R and VPAC2-R.

Biological functions

PACAP has pleiotropic functions in the central nervous system and peripheral tissues. PACAP acts as a neurotransmitter (neuromodulator), neuroprotectant, neurite outgrowth factor, and inducer of neural stem cell differentiation into astrocytes in nervous tissues. In peripheral tissues, PACAP acts as a bronchodilator, vasodilator, smooth muscle relaxant, adrenergic secretagogue in the adrenal gland, insulin secretagogue in the pancreas, inducer of spermatogenesis in testis, and immunosuppressor. PACAP also regulates the synthesis and secretion of hormones from the pituitary gland.

Clinical implications

PACAP may play an important role in primary headaches. The intravenous injection of PACAP induces migraine-like attacks in migraineurs and cluster-like attacks in cluster headache patients, and plasma concentrations of PACAP are elevated in spontaneous attacks of cluster headache and migraines.

Description

PACAP consists of 27 or 38 aa residues and belongs to the secretin/glucagon superfamily. PACAP has pleiotropic functions, acting as a neurotransmitter and neurotrophic factor in the central nervous system as well as a vasodilator, insulin secretagogue, smooth muscle relaxant, and immunosuppressor in peripheral tissues. PACAP was first isolated in 1989 from the extract of ovine hypothalamus on the basis of its ability to elevate cAMP levels in rat anterior pituitary cells.

Uses

Pituitary adenylate cyclase activating polypeptide-38 has been used to test its effect in stimulating the formation of cyclic AMP hypothalamus and cerebral cortex slices of chicken and to treat glioblastoma cells (U87MG) in cell migration assay to test its anti-invasive effects.

General Description

Pituitary adenylate cyclase activating polypeptide-38 (PACAP38) is mapped to human chromosome 18. 27-residue-amidated fragment (PACAP27) comprises another isoform. The PACAP38 is major isoform associated with mammals.

Biological Activity

Endogenous neuropeptide showing considerable homology with vasoactive intestinal peptide (VIP). Potently stimulates adenylyl cyclase.

Biochem/physiol Actions

Pituitary adenylate cyclase activating polypeptide-38 (PACAP38) is a cardioprotectant and may help in treating radiation-induced heart disease (RIHD). It plays a protective role during oxidative stress in cardiomyocytes. PACAP38 has antioxidant, anti-apoptotic and anti-inflammatory property. It is implicated in the pathophysiology of migraine and cluster headache.

storage

Store at -20°C

Structure and conformation

PACAP38, consisting of 38 aa residues, was the first isolated, followed by PACAP27, lacking 11 aa residues from the C-terminal of PACAP38. The C-terminal of both PACAPs was amidated. PACAP belongs to the secretin/ glucagon superfamily, and its closest member is the vasoactive intestinal polypeptide (VIP), which shows 68% aa sequence identity. Human PACAPs are derived from a 176-aa residue precursor, located in the C-terminus, next to the PACAP-related peptide (PRP) . The PACAP precursor is cleaved by various prohormone convertases (PCs) to generate PACAP27 or PACAP38. From the evolutionary aspect of the superfamily, the ancestral peptide emerged about 700 million years ago, and PACAP was established by gene duplication, exon duplication, and exon deletion. The PACAP sequence is well conserved in vertebrates, and is perfectly conserved in mammals. Stingray PACAP has 44 aa residues with two predicted processing sites, suggesting that the processing site of preproPACAP shows diversity in species. Human PACAP27, theoretical Mr 3147.6, pI 9.70; human PACAP38, theoretical Mr 4534.3, pI 10.41. PACAP is freely soluble in water and ethanol. PACAP solution in water is unstable at 4°C, but is stable for a year at -80°C at 0.1mM.