Inhibition of apolipoprotein B secretion by taurocholate is controlled by the N-terminal end of the protein in rat hepatoma McArdle-RH7777 cells.
Bile salts (BS) inhibit the secretion of apolipoprotein B (apoB) and triacylglycerol (TG) in primary rat, mouse and human hepatocytes and in mice in vivo. We investigated whether lipidation of apoB into a lipoprotein particle is required for this inhibitory action of BS. The sodium/taurocholate co-transporting polypeptide (Ntcp) was co-expressed in McArdle-RH7777 (McA-RH7777) cells stably expressing the full-length human apoB100 (h-apoB100, secreted as TG-rich lipoprotein particles) or carboxyl-truncated human apoB18 (h-apoB18, secreted in lipid-free form). The doubly transfected cell lines (h-apoB/r-Ntcp) effectively accumulated taurocholic acid (TC). TC incubation decreased the secretion of endogenous rat apoB100 (-50%) and h-apoB18 (-35%), but did not affect secretion of rat apoA-I. Pulse-chase experiments (35S-methionine) indicated that the impaired secretion of radiolabeled h-apoB18 and h-apoB100 was associated with accelerated intracellular degradation. The calpain protease inhibitor N-acetyl-leucyl-leucyl-norleucinal (ALLN) partially inhibited intracellular apoB degradation but did not affect the amount of either h-apoB18 or h-apoB100 secreted into the medium, indicating that inhibition of apoB secretion by TC is not due to calpain-dependent proteasomal degradation. We conclude that TC does not inhibit apoB secretion by interference with its lipidation, but rather involves a mechanism dependent on the N-terminal end of apoB.
Elzinga
Baukje M
BM
Department of Pediatrics, Groningen University Institute for Drug Exploration, Pediatric Gastroenterology, Academic Hospital, The Netherlands.
Baller
Julius F W
JF
Mensenkamp
Arjen R
AR
Yao
Zemin
Z
Agellon
Luis B
LB
Kuipers
Folkert
F
Verkade
Henkjan J
HJ
D000818:Animals; D016632:Apolipoprotein A-I / Q000378:metabolism; D053299:Apolipoprotein B-100; D001055:Apolipoproteins B / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D022781:Hepatocytes / Q000737:chemistry / Q000378:metabolism; D007976:Leupeptins / Q000494:pharmacology; D008079:Lipoproteins, VLDL / Q000378:metabolism; D008114:Liver Neoplasms, Experimental; D026901:Membrane Transport Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D051381:Rats; D027981:Symporters; D013656:Taurocholic Acid / Q000378:metabolism* / Q000494:pharmacology; D013997:Time Factors; D014162:Transfection; D014280:Triglycerides / Q000378:metabolism
D016632:Apolipoprotein A-I; D053299:Apolipoprotein B-100; D001055:Apolipoproteins B; D002352:Carrier Proteins; D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; D008079:Lipoproteins, VLDL; D026901:Membrane Transport Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D027981:Symporters; D014280:Triglycerides; C030106:very low density lipoprotein triglyceride; C063261:acetylleucyl-leucyl-norleucinal; C071908:sodium-bile acid cotransporter; D013656:Taurocholic Acid