Regulated secretion

Conference website: http://www.faseb.org/ascb/meetings/am99/main99mtg.htm webciteDespite the apparent differences in cellular architecture and behavior of different cell types and of cells from organisms separated by long evolutionary times, it is increasingly apparent that the core mechanisms and many of the components are common and can be usefully studied in a wide variety of cell types. Intracellular protein transport is one area in which studying a variety of cell types has provided many more insights than could have come from studies of a single cell type or organism. Proteins traveling through the secretory pathways of cells are processed and targeted to a variety of cellular destinations. This delivery system can be constitutive, or cargo can be stored within a regulated secretory vesicle or granule until an external stimulus causes it to fuse with the cell surface. The minisymposium on regulated secretion at the American Society of Cell Biology meeting concentrated on the two distinguishing features of the secretory pathway: namely the process by which specialized secretory vesicles are formed and cargo specifically sorted into them; and the molecular mechanism by which such vesicles rapidly fuse with the plasma membrane upon receipt of a signal. Although neuronal cells have traditionally been the predominant model for studying regulated secretion, Chris Kaiser (Massachusetts Institute of Technology) presented evidence that the yeast Saccharomyces cerevisiae can serve as a model organism for investigating regulated sorting of cargo. By altering the nutrients in the growth media of yeast cells, some proteins can be redirected from the vacuolar membrane to the plasma membrane. For example, in low nitrogen conditions, an amino acid permease, GAP1, is thus redirected, and using genetics several candidate proteins were identified that can modulate the differential localization of GAP1. As a result, complex assemblies of proteins are emerging as mechanisms by whi