Biogenesis and Transport of Secretory Granules to Release Site in Neuroendocrine Cells

Biogenesis and post-Golgi transport of peptidergic secretory granules to the release site are crucial for secretion of neuropeptides from neuroendocrine cells. Recent studies have uncovered multilevel molecular mechanisms for the regulation of secretory granule biogenesis. Insulinoma-associated protein 2 (ICA512/IA-2), polypyrimidine-tract binding protein, and chromogranin A have been identified to regulate secretory granule biogenesis at the transcriptional, posttranscriptional, and posttranslational levels, respectively, by increasing granule protein levels, which in turn drives granule formation after stimulation. Post-Golgi transport of secretory granules is microtubule-based and mediated by transmembrane carboxypeptidase E (CPE). The cytoplasmic tail of CPE anchors secretory granules to the microtubule motors, kinesin-2 and -3, or dynein, via interaction with the adaptor, dynactin, to mediate anterograde and retrograde transport, respectively.