Characterization of GPRA, a Novel G Protein–Coupled Receptor Related to Asthma

Abstract

We recently identified a novel positional asthma susceptibility gene, GPRA, which belongs to the G protein-coupled receptor family. In the present studies, we show that isoform specific activation of GPRA-A with its agonist, Neuropeptide S (NPS) resulted in significant inhibition of cell growth. GPRA has several variants due to extensive alternative splicing. We observed that only the full-length variants, GPRA-A and GPRA-B, with 7 transmembrane topology are transported into the plasma membrane, while the truncated proteins retain intracellular compartments. To clarify disease mechanism, we studied co-expression of the variants without finding any indication that truncated variants would inhibit the receptor transport into the plasma membrane. By using in situ hybridization and immunohistochemistry, we detected ubiquitous expression of GPRA-B, and frequent expression of GPRA-A in the epithelia of several organs including bronchi and gastrointestinal tract. Furthermore, we observed aberrant mRNA and protein expression levels of GPRA in the asthmatic bronchi. Finally, we demonstrate that GPRA and NPS are co-expressed in bronchial epithelium. In summary, this study provides evidence that GPRA might have functional relevance in modulating asthma by increased expression levels in the relevant tissues under diseased state and by potential inhibitory effect of GPRA-A activation on cell growth.

Structure-Function Relationships in the Neuropeptide S Receptor

“…Activation of NPSR by NPS results in increased intracellular cAMP levels and Ca 2ϩ mobilization, leading to the conclusion that it is coupled to G s and G q proteins (7,9). Reinforcing the genetic evidence that NPSR is involved in asthma, it has been reported that expression of the NPSR-B isoform, but not the NPSR-A isoform, is increased in bronchiolar smooth muscle and epithelial cells of asthmatics compared with healthy controls (4,12). It has also been shown that lung NPSR is up-regulated in a murine model of allergic asthma (4).…”

“…One of these, GPR154, encoding neuropeptide S receptor (NPSR) 4 (4,7), also known as G protein receptor for asthma susceptibility (GPRA) (4), GPR154 (8), and vasopressin receptor-related receptor 1 (VRR1) (9), has been confirmed as an asthma-linked gene in five distinct Caucasian populations (4,10,11). The gene for NPSR encodes at least two splice variants that differ only in their C termini (4,12) and are referred to herein as NPSR-A and NPSR-B, corresponding to GPRA-A and GPRA-B (4), respectively. A number of single nucleotide polymorphisms in the NPSR sequence are associated with asthma, elevated serum IgE levels, and bronchial hyperresponsiveness (4,10,11).…”

Alternative splicing of G protein-coupled receptors: physiology and pathophysiology

“…Interestingly, another isoform, the short one that is expressed in intracellular compartments does not affect the cell surface expression of the full-length receptors when co-expressed [67].…”

“…A genome-wide scan suggested that one of the contributory factors to asthma and other IgE-mediated diseases could be GPRA (also known as GPR154 and the neuropeptide S receptor) [134]. Several splice variants of the receptor have been described [67]. Two splice variants that encode GPRA isoforms with distinct C-termini (termed A and B isoforms) are full-length isoforms that traffic to the plasma membrane.…”

“…[59][60][61][62][63][64] Neurokinin receptor 2 Exon exclusion Impaired ligand binding and signalling [65,66] Neuropeptide S receptor (GPRA) Alternative C-terminal exons, trancation Intracellular localization of truncated isoform [67] Opioid receptors Several Various Reviewed in [68] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 Overview of GPCRs encoded by more than one exon. In the "pre-human genome era" it was assumed that more than 90% of human GPCRs were intronless [15].…”