Maturation of Secretory Granules
Secretory granules are found in most endocrine, exocrine, and neuronal cells. Their function is to store secretory proteins, such as horomes, in a highly concentrated form within the cell. A hallmark of secretory granules (SGs) is the presence of an electron dense-cored interior which contains the stored secretory proteins. The release of these stored molecules can only be induced by an extracellular signal, which causes the SGs to fuse with the plasma membrane and thereby release the contents. This situation is in contrast to the secretion of proteins by the constitutive pathway: fusion of the constitutive vesicle with the plasma membrane and release of the content occurs very rapidly and is independent of extracellular signals (Burgess and Kelly, 1987). As has been well documented morphologically (for example see Tooze and Tooze, 1986), SGs form in the trans-Golgi network (TGN) when a condensed core of secretory proteins becomes enveloped by membrane, and buds into the cytoplasm. The formation of SGs from the TGN is also being dissected using biochemical approaches. The first event in the formation of SGs, the condensation, or aggregation, of the secretory proteins in the TGN, has been demonstrated in vitro to require conditions similiar to those thought to exist in the TGN, specifically 110mM Calcium and pH6.4 (Chanat and Huttner, 1991). The second event, the budding of the newly formed granules from the TGN has been reconstituted in a cell-free assay (Tooze and Huttner, 1990), and appears to be regulated by a heterotrimeric G-protein (Barr, Leyte et al., 1991; and see abstract from F. Barr).
KeywordsPC12 Cell Secretory Protein Secretory Granule Dense Core AtT20 Cell
Unable to display preview. Download preview PDF.
- Aherne, W. A. and M. S. Dunnill. (1982). Methods of estimating size distributions. Morphometry, Edward Arnold Ltd., LondonGoogle Scholar
- Barr, F. A., A. Leyte, S. Mollner, T. Pfeuffer, S. A. Tooze and W. B. Huttner (1991). Trimeric G-proteins of the trans-Golgi network are involved in the formation of constitutive secretory vesicles and immature secretory granules. FEBS 294:: 239 - 243Google Scholar
- Burgess, T. L. and R. B. Kelly (1987). Constitutive and regulated secretion of proteins. Ann. Rev. Cell Biol. 3: 243-293Google Scholar
- Chanat, E. and W. B. Huttner (1991). Milieu-induced, selective aggregation of regulated secretory proteins in the trans-Golgi network. J. Cell Biol. 115: 1505 1519Google Scholar
- Farquhar, M. G., J. J. Reid and L. W. Daniell (1978). Intracellular transport and packaging of prolactin: a quantitative electron microscope autoradiographic study of mammotrophs dissociated from rat pituitaries. Endocrinology 102: 296311Google Scholar
- Slinde, E. and T. Flatmark (1973). Determination of sedimentation coefficients of subcellular particles of rat liver homogenates. Anal. Biochem. 56: 324-340Google Scholar
- Tatham, P. E. R. and B. D. Gomperts (1991). Late events in regulated exocytosis.Bioessays 13:397-401Google Scholar
- Tooze, S. A. (1991). Biogenesis of secretory granules. Implications arising from the immature secretory granule in the regulated pathway of secretion. FEBS 285: 220-224Google Scholar