N- and C-terminal Domains Direct Cell Type-specific Sorting of Chromogranin A to Secretory Granules

Section: Discussionmentioning

confidence: 95%

Biosynthesis of Surfactant Protein C (SP-C)

Wang

Russo

Mulugeta

et al. 2002

“…Disruption of the disulfide loop of CgB resulted in its missorting to a constitutive pathway in PC12 cells (13). However, removal of the N-terminal loop from CgA did not affect its targeting to SGs in GH 4 C 1 cells (14), AtT-20 cells (8), and PC12 cells (15). For recognizing the N-terminal loop of POMC, carboxypeptidase E (CPE) has been proposed for its sorting receptor (10) but the sorting of CgA was not disturbed in Neuro-2a cells depleting CPE (16), Thus, the Nterminal loop-carrying CgA, CgB, and POMC appear to depend on distinct mechanisms for their sorting to SGs.…”

mentioning

confidence: 99%

Secretogranin III Binds to Cholesterol in the Secretory Granule Membrane as an Adapter for Chromogranin A

Hosaka

Suda

Sakai

et al. 2004

102

Granin-family proteins, including chromogranin A (CgA) and secretogranin III (SgIII), are transported to secretory granules (SGs) in neuroendocrine cells. We previously showed that SgIII binds strongly to CgA in an intragranular milieu and targets CgA to SGs in pituitary and pancreatic endocrine cells. In this study, we demonstrated that with a sucrose density gradient of rat insulinoma-derived INS-1 cell homogenates, SgIII was localized to the SG fraction and was fractionated to the SG membrane (SGM) despite lacking the transmembrane region. With depletion of cholesterol from the SGM using methyl-␤-cyclodextrin, SgIII was impaired to bind to the SGM. Both SgIII and CgA were solubilized from the SGM by Triton X-100 in contrast to the Triton X-100 insolubility of carboxypeptidase E. SgIII and carboxypeptidase E strongly bound to the SGM-type liposome in intragranular conditions, but CgA did not. Instead, CgA bound to the SGM-type liposome only in the presence of SgIII. Immunocytochemical and pulse-chase experiments revealed that SgIII deleting the N-terminal lipid-binding region missorted to the constitutive pathway in mouse corticotroph-derived AtT-20 cells. Thus, we suggest that SgIII directly binds to cholesterol components of the SGM and targets CgA to SGs in pituitary and pancreatic endocrine cells.

“…For example, the C terminus of the prohormone convertase PC2 is capable of directing sorting to secretory granules in Neuro2A cells (6) but is not required for PC2 sorting to granules in corticotrophic AtT-20 cells (22). Likewise, chromogranin A has been reported to require an N-terminal sorting signal for granule entry in PC12 cells, whereas a C-terminal domain is required for granule sorting in GH4C1 cells (23). Second, several distinct secretory granulesorting signals have been reported suggesting that there is more than one mechanism for sorting proteins to secretory granules.…”

Section: Discussionmentioning

confidence: 99%

Modulation of Secretory Granule-targeting Efficiency by Cis and Trans Compounding of Sorting Signals

Lacombe¹,

Mercure²,

Dikeakos

et al. 2005

Several protein domains acting through seemingly different mechanisms have been reported to have the capacity to target proteins to dense core secretory granules. Because proteins enter secretory granules with different efficiencies and because some of these proteins contain more than one granule-targeting motif, we have investigated whether compounding sorting signals could alter the efficiency of protein entry into secretory granules. In the current study we demonstrate that a paired basic cleavage site from human prorenin and an ␣-helix-containing secretory granulesorting signal from the prohormone convertase PC1/3 can synergize to increase granule-sorting efficiency not only when located on the same protein, but also when located on distinct proteins that associate in the secretory pathway.