title: Insulin suppression of apolipoprotein B in McArdle RH7777 cells involves increased sortilin 1 interaction and lysosomal targeting.
abstract: Insulin suppresses secretion of very low density lipoprotein (VLDL) apolipoprotein (apo) B in primary rodent hepatocytes (RH) by favoring the degradation of B100, the larger form of apo B, through post-endoplasmic reticulum proteolysis. Sortilin 1 (sort1), a multi-ligand sorting receptor, has been proposed as a mediator of lysosomal B100 degradation by directing B100 in pre-VLDL to lysosomes rather than allowing maturation to VLDL and secretion. The purpose of our studies was to investigate the role of sort1 in insulin-dependent degradation of apo B. Using liver derived McArdle RH7777 (McA) cells, we demonstrate that insulin suppresses VLDL B100 secretion via a phosphatidylinositide 3-kinase (PI3K) dependent process that is inhibitable by wortmannin in a fashion similar to RH. Using McA cells and in situ cross-linking, we demonstrate that insulin acutely (30min) stimulates the interaction of B100 with sort1. The insulin-induced interaction of sort1-B100 is markedly enhanced when lysosomal degradation is inhibited by Bafilomycin A1 (BafA1), an inhibitor of lysosomal acidification. As BafA1 also prevents insulin suppressive effects on apo B secretion, our results suggest that sort1-B100 interaction stimulated by insulin transiently accumulates with BafA1 and favors B100 secretion by default.
authors.affiliation: Department of Pathology & Laboratory Medicine, University of Rochester School of Medicine & Dentistry, Box 626, 601 Elmwood Avenue, Rochester, NY 14642, USA.
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Chamberlain
authors.forename: Colleen
authors.initials: C
authors.lastname: O'Dell
authors.forename: Charles E
authors.initials: CE
authors.lastname: Sparks
authors.forename: Janet D
authors.initials: JD
authors.lastname: Sparks
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism*; D000818:Animals; D001055:Apolipoproteins B / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002460:Cell Line; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D008079:Lipoproteins, VLDL / Q000037:antagonists & inhibitors / Q000378:metabolism; D008247:Lysosomes / Q000187:drug effects* / Q000378:metabolism; D018942:Macrolides / Q000494:pharmacology; D051381:Rats; D000099183:Sortilin
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D001055:Apolipoproteins B; D007328:Insulin; D008079:Lipoproteins, VLDL; D018942:Macrolides; D000099183:Sortilin; C040929:bafilomycin A1