The bovine chromogranin A gene: Structural basis for hormone regulation and generation of biologically active peptides

Abstract

The structure of the gene encoding bovine chromo granin-A has been determined by characterization of two isolated genomic clones. Chromogranin-A is encoded by eight exons, which organize the coding region into several distinct structural and functional domains. Exons 1-5 represent the highly conserved signal peptide and N-terminal domain, which are separated into regions corresponding to the signal peptide, N-terminal sequence, disulfide-bonded loop, and remainder of the conserved N-terminal domain. Exon 6 represents the variable domain and encodes a region that is identical to the novel chro-mogranin-A-derived peptide chromostatin. Exon 7 encodes the biologically active peptide pancreas-tatin as well as most of the conserved C-terminal domain, with the remainder found on exon 8. The mRNA sequence obtained from the gene contains five nucleotide differences from the consensus sequence of four reported bovine chromogranin-A cDNA clones. Two of the differences in the gene result in two amino acid changes in the region encoded by exon 6. The structural organization of the chromogranin-A gene resembles that of the chro-mogranin-B gene in the exons corresponding to the signal peptide, N-terminal sequence, disulfide loop, and C-terminal sequence. Sequence analysis of the promoter region reveals the presence of a cAMP-responsive element located 24 bases up-stream of the TATA box, a site positioned 125 bases from the cAMP-responsive element that is similar to the consensus sequence established for glucocorticoid-re-sponsive elements, and two elements located further up-stream which each match six of seven bases of the AP-l-binding consensus sequence TGAG/ CTCA, a heptanucleotide sequence in which the fourth base is G or C. Changes in chromogranin-A mRNA abundance after treatment with dexametha-sone, forskolin, and phorbol ester indicate a potential role for all of these elements in the regulation of the chromogranin-A gene in endocrine cells.