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J Biol Chem. 2003 Aug 22;278(34):31924-9. Epub 2003 Jun 17.

Ferritins can regulate the secretion of apolipoprotein B.

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  • 1Molecular Medicine Unit Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA.


Apolipoprotein B is secreted with atherogenic lipids as lipoprotein particles from hepatocytes. Regulation of the secretion of apolipoprotein B is largely post-translational and reflects the balance between processes that leads to particle assembly or to intracellular degradation. Previously, we conducted a proteomic screen to find proteins that bind apolipoprotein B in rat liver microsomes. We identified ferritin heavy and light chains in this screen among other proteins and showed that the two ferritins bind apolipoprotein B directly in vitro. In hepatocytes and other cells, ferritin heavy and light chains form cytosolic cages that store iron. We now show that ferritin heavy or light chains post-translationally inhibit the secretion of apolipoprotein B without altering the export of other hepatic proteins including albumin, factor XIII, and apolipoprotein A-I. This inhibition of apolipoprotein B secretion is not due to diminished lipid synthesis and can be partially overcome by stimulating triglyceride synthesis. The block in apolipoprotein B secretion by ferritins leads to an increase in endoplasmic reticulum-associated degradation of the apolipoprotein. Thus, despite being cytosolic proteins without known chaperone activity, ferritins can specifically regulate the secretion of apolipoprotein B post-translationally. The metabolic pathways for iron storage and intercellular cholesterol and triglyceride transport could intersect.

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