Regulation of insulin granule turnover in pancreatic beta-cells by cleaved ICA512

Trajkovski M, Mziaut H, Schubert S, Kalaidzidis Y, Altkrueger A, Solimena M
Source: J Biol Chem
Publication Date: (2008)
Issue: epub: online
Research Area:
Cancer Research/Cell Biology
Cells used in publication:
Species: rat
Tissue Origin: pancreas
Species: rat
Tissue Origin: pancreas
Nucleofectorâ„¢ I/II/2b
Insulin maintains homeostasis of glucose by promoting its uptake into cells from the blood. Hyperglycemia triggers secretion of insulin from pancreatic beta-cells. This process is mediated by secretory granule exocytosis. However, how beta-cells keep granule stores relatively constant is still unknown. ICA512 is an intrinsic granule membrane protein whose cytosolic domain binds beta2-syntrophin, an F-actin associated protein, and is cleaved upon granule exocytosis. The resulting cleaved cytosolic fragment, ICA512-CCF, reaches the nucleus and up-regulates the transcription of granule genes, including insulin and ICA512. Here, we show that ICA512-CCF also dimerizes with intact ICA512 on granules, thereby displacing it from beta2-syntrophin. This lead to increased granule mobility and insulin release. Based on these findings, we propose a model whereby the generation of ICA512-CCF first amplifies insulin secretion. The ensuing reduction of granule stores would then increase the probability of newly generated ICA512-CCF to reach the nucleus and enhance granule biogenesis, thus allowing beta-cells to constantly adjust production of granules to their storage size and consumption. Pharmacological modulation of these feedback loops may alleviate deficient insulin release in diabetes.