PROHORMONE AND PRONEUROPEPTIDE SYNTHESIS AND SECRETION

Hormones and neuropeptides in eukaryotic cells, are synthesised as lar ge precursor molecules in the rough endoplasmic reticulum (RER), from where they are translocated to the Golgi apparatus. The sorting of pro teins destined for the regulated secretory pathway from those which wi ll be released constitutively takes place in the trans-Golgi network ( TGN). In both these pathways, vesicles need to be transported to the p lasma membrane before their contents can be released by exocytosis. Ho rmones and neuropeptides need to be secreted from the cells in which a re synthesised to exert their biological actions, although they can al so play paracrine and autocrine actions. Prohormones and proneuropepti des must undergo post-translational modifications which occur in deter mined subcellular compartments within eukaryotic cells and are carried out in a strict succession of intracellular events, which give rise t o biologically active products. The biosynthesis of prohormones/proneu ropeptides is mediated by the action of endoproteolytic enzymes and ot her post-translational modifying enzymes within the secretory pathway. The major focus of this review will be the biosynthetic pathway, sort ing and intracellular trafficking of prohormone and proneuropeptide pr ecursors within the secretory pathway of eukaryotic cells.