SPECIFIC BINDING OF A I-125 SECRETONEURIN ANALOG TO A HUMAN MONOCYTICCELL-LINE

Secretoneurin (SN) is a novel neuropeptide expressed in the central an d peripheral nervous system as well as in various endocrine tissues. S N inhibits growth of aortic pulmonary and endothelial cells and is a p otent chemoattractant for endothelial cells, skin fibroblasts and mono cytes. We investigated here the presence of specific high affinity bin ding sites for SN on a target tissue. SN was iodinated with the Bolton -Hunter (BH) reagent and purified by isocratic reversed phase chromato graphy. Specific binding sites for I-125-BHSN were identified on human Mono Mac 6 cells, a monocytic cell Line. Scatchard analysis revealed a single class of binding sites with a Kd value of 7.3 nM and a B-max of 322 (fmol/mg protein). Competition studies demonstrated that the 15 C-terminal amino acids of SN could displace authentic SN, whereas sho rter fragments were inactive. Other sensory neuropeptides like substan ce P, calcitonin gene-related peptide or galanin as well as the chemok ine receptor ligand Rantes or the typical chemoattractant FMLP could n ot displace SN. Our studies demonstrate specific high affinity binding sites for SN on a monocytic cell line. Since SN exerts a potent chemo tactic activity towards monocytes and increases cytosolic calcium in t hese cells, these binding sites might well represent a putative functi onal plasma membrane receptor for SN. (C) 1998 Elsevier Science B.V. A ll rights reserved.