NDLI: Proinsulin Endoproteolysis Confers Enhanced Targeting of Processed Insulin to the Regulated Secretory Pathway

Content Provider	PubMed Central
Author	Regina, Kuliawat Daniel, Prabakaran Arvan, Peter
Editor	Juan, Bonifacino
Copyright Year	2000
Abstract	Recently, two different prohormone-processing enzymes, prohormone convertase 1 (PC1) and carboxypeptidase E, have been implicated in enhancing the storage of peptide hormones in endocrine secretory granules. It is important to know the extent to which such molecules may act as “sorting receptors” to allow the selective trafficking of cargo proteins from the trans-Golgi network into forming granules, versus acting as enzymes that may indirectly facilitate intraluminal storage of processed hormones within maturing granules. GH4C1 cells primarily store prolactin in granules; they lack PC1 and are defective for intragranular storage of transfected proinsulin. However, proinsulin readily enters the immature granules of these cells. Interestingly, GH4C1 clones that stably express modest levels of PC1 store more proinsulin-derived protein in granules. Even in the presence of PC1, a sizable portion of the proinsulin that enters granules goes unprocessed, and this portion largely escapes granule storage. Indeed, all of the increased granule storage can be accounted for by the modest portion converted to insulin. These results are not unique to GH4C1 cells; similar results are obtained upon PC1 expression in PC12 cells as well as in AtT20 cells (in which PC1 is expressed endogenously at higher levels). An in vitro assay of protein solubility indicates a difference in the biophysical behavior of proinsulin and insulin in the PC1 transfectants. We conclude that processing to insulin, facilitated by the catalytic activities of granule proteolytic enzymes, assists in the targeting (storage) of the hormone.
Starting Page	1959
File Format	PDF
ISSN	10591524
Journal	Molecular Biology of the Cell
Issue Number	6
Volume Number	11
Language	English
Publisher	The American Society for Cell Biology
Publisher Date	2000-06-01
Access Restriction	Open
Rights Holder	The American Society for Cell Biology
Subject Keyword	Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Cell Biology Molecular Biology

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