| Budget Amount *help |
¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2004: ¥1,800,000 (Direct Cost: ¥1,800,000)
Fiscal Year 2003: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
Granin-family proteins, including chromogranin A(CgA), chromogranin B, secretogranin II, secretogranin III(SgIII), and 7B2, are thought to condense peptide hormones to SGs of neuroendocrine cells. I previously showed that SgIII targets CgA to SGs in neuroendocrine cells. In this study, we investigated the sorting mechanism of SgIII to the SGs and the interaction between SgIII and carboxypeptidase E(CPE;a different candidate molecule of a sorting receptor for prohormones).
The sorting mechanism of SgIII to the SGs ; Analyses with subcellular fractionation showed that significant amounts of SgIII are bound to the secretory granule membrane(SGM). The membrane-bound SgIII could be dissociated with Triton X-100 or depleting cholesterol of the SGM. Subsequent analyses with liposome-binding assays demonstrated that SgIII binds to the cholesterol-rich liposome that mimics the composition of the SGM. Although CgA does not bind directly to the SGM-type liposome, CgA binds to the SGM-type liposome
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only in the presence of SgIII. Thus, these findings suggest that SgIII directly binds to cholesterol components of the SGM and targets CgA to the SGs in neuroendocrine cells.
The interaction between SgIII and CPE ; We investigated the binding of SgIII and CPE, because they frequently localized closely. They bound each other in neuroendocrine cells. In Cpefat mouse corticotropes having defective CPE, SgIII independently localized on the secretory granule membrane. Moreover, proopiomelanocortin(POMC) distributed over the entire secretory granules, and displayed a regulated secretion by secretagogues in Cpefat mouse. The Cpefat pltuitary exhibited elevated levels of SgIII and CgA, suggesting their compensation for a sorting function of CPE for POMC. Indeed, both SgIII and CgA were able to bind POMC. These data suggest that SgIII and CPE core the separate functional sorting complex by anchoring to cholesterol-rich secretory granule membranes, and POMC-derived peptides are transferred from CPE to SgIII, and further to CgA. Less
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