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Updated: Sep 30, 2026

Modified Yeast-Two-Hybrid System to Identify Proteins Interacting with the Growth Factor Progranulin
Published on: January 17, 2012
Calpain inhibitor inhibits secretory granule maturation and secretion of GH
K Ohkawa1, K Takada, T Asakura
1Department of Biochemistry, Jikei University School of Medicine, Tokyo, Japan.
Abstract:
Clathrin- and AP-1-coated buds are present on immature secretory granules of endocrine cells that mature into clathrin-uncoated granules. The mechanism of clathrin and adaptor protein uncoating has remained obscure. Benzyloxycarbonyl-L-leucyl-L-leucinal (ZLLal), a calpain inhibitor, reduced growth hormone (GH) secretion with intracellular accumulation, in a GH-secreting rat pituitary tumor cell. Pulse and chase demonstrated that ZLLal retarded the turnover of clathrin (Clt.H) and adaptins. ZLLal-treatment co-immunoprecipitated the increased amounts of GH with Clt.H and adaptins compared to control cells, suggesting the intracellular accumulation of immature secretory granules. Clt.H and adaptins were limited-proteolyzed by m-calpain in vitro, indicating that calpain may be involved partly in the maturation of secretory granules in endocrine cells via the process of clathrin uncoating.
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