Ferritins can regulate the secretion of apolipoprotein B.
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.
Hevi
Sarah
S
Molecular Medicine Unit Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA.
Chuck
Steven L
SL
D001055:Apolipoproteins B / Q000378:metabolism*; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D005293:Ferritins / Q000502:physiology*; D006801:Humans; D011499:Protein Processing, Post-Translational
D001055:Apolipoproteins B; D017931:DNA Primers; D005293:Ferritins