Molecular cloning, tissue-specific expression, and chromosomal localization of a novel nerve growth factor-regulated G-protein-coupled receptor, nrg-1

A novel and differentially expressed gene, named nrg-1, was identified by EST expression profiling and subsequently isolated as a 2.2-kb full-length clone from a rat PC12 cell cDNA library. Sequence analysis reveals that nrg-1 encodes a putative seven transmembrane spanning domain protein with structural features characteristic of receptors belonging to the G-protein-coupled receptor gene superfamily. The 400-amino-acid protein encoded by nrg-1 exhibits a high degree of sequence identity (40-44%) to the Edg receptor family; members include Edg-1, Edg-2, Edg-3, Edg-4, and H218. Both Northern analysis and EST expression profiling revealed that whole-tissue distribution of nrg-1 mRNA is restricted, found almost exclusively in brain. Transcripts of nrg-1 could be ubiquitously detected in different brain regions, with very prominent expression in lower brain regions such as the midbrain, pens, medulla, and spinal cord. In PC12 cells, nerve growth factor induces neuronal differentiation and repressed expression of nrg-1. Two other agents that differentiate PC12 cells, fibroblast growth factor and dibutyryl cAMP, down-regulated nrg-1 mRNA levels. Epidermal growth factor, an agent that does not induce differentiation, did not repress nrg-1 mRNA levels. In a PC12 cell mutant that is deficient in protein kinase A activity (AB.11), all three differentiating agents were unable to downregulate nrg-1 mRNA. Hence, protein kinase A appears to be an obligatory cellular component in nrg-1 mRNA regulation. Chromosomal mapping employing a rat somatic cell radiation hybrid panel demonstrated that nrg-1 is linked to marker D8Rat54 and tightly associated with H218 on chromosome 8.