Molecular cloning and characterization of NESP55, a novel chromogranin- like precursor of a peptide with 5-HT(1B) receptor antagonist activity

The chromogranins comprise a class of acidic proteins that are secreted from large dense core vesicles and expressed in neuronal and endocrine tissues. We describe here the molecular characterization of NESP55 (neuroendocrine secretory protein of M(r) 55,000), a novel member of the chromogranins. Several NESP55 cDNA clones were isolated from bovine chromaffin cell libraries. The cDNA sequence of NESP55 totals 1499 nucleotides. All of the clones that were isolated contained in their 3'- untranslated mRNA a sequence that was homologous to exon 2 of the G-protein G(s)α. The open reading frame encodes for an acidic and hydrophilic protein of 241 amino acids with a predicted molecular mass of 27,494 Da. An antiserum directed against the C terminus of NESP55 labeled a band of M(r) 55,000 with an acidic pI ranging from 4.4 to 5.2 in one- and two-dimensional immunoblots of secretory proteins from chromaffin granules. NESP55 is localized within the cell to the large dense secretory vesicles and is expressed, apart from the adrenal medulla, in the anterior and posterior pituitary and various regions of the brain. For the physiological function, one interesting factor has emerged. NESP55 is proteolytically processed within the chromaffin granule to smaller peptides that might be physiologically active. One tetrapeptide, Leu-Ser-Ala-Leu (LSAL), present in the NESP55 sequence and flanked by arginine residues suitable for cleavage by prohormone convertases, has been identified recently as an endogenous antagonist of the serotonergic 5-HT₁(B) receptor subtype. Alterations in the serotonergic system are thought to play an important role in mental disorders, especially depression, and might be related to abnormal ethanol consumption. It is tempting to speculate that increased expression of NESP55 or its proteolytically derived peptide LSAL might contribute to the pathophysiology of the serotonergic transmission.