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  • Title: Trafficking of mutant carboxypeptidase E to secretory granules in a beta-cell line derived from Cpe(fat)/Cpe(fat) mice.
    Author: Cawley NX, Rodriguez YM, Maldonado A, Loh YP.
    Journal: Endocrinology; 2003 Jan; 144(1):292-8. PubMed ID: 12488357.
    Abstract:
    We have reinvestigated the stability and intracellular routing of mutant carboxypeptidase E in NIT3 cells, a pancreatic beta-cell line derived from the Cpe(fat)/Cpe(fat) mouse. Pulse-chase experiments demonstrated that this protein has a half-life of approximately 3 h in these cells and that up to 45% of the proCPE(202) can escape degradation by the proteosome. In double-label immunofluorescence microscopy, a portion of the mutant CPE did not colocalize with calnexin, an endoplasmic reticulum marker, but was found in prohormone convertase 2-containing secretory granules, demonstrating that it had escaped degradation and arrived at a post-Golgi compartment. The mutant CPE as well as prohormone convertase 2 were secreted into the medium in a stimulated manner by treatment with the physiological secretagogue, glucagon-like peptide-1, consistent with its presence in granules of the regulated secretory pathway. The presence of mutant carboxypeptidase E in granules supports a potential role for its involvement as a sorting/retention receptor in the trafficking of proinsulin to the regulated secretory pathway.
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