Introduction. Familial Hypobetalipoproteinemia (FHBL) is acodominant disorder characterized by reduced levels of LDL andapolipoprotein B (apoB) in plasma. In approximately 50% of FHBLcases is due to mutations in APOB gene resulting in truncatedapoBs of various size. Only a few missense mutations have beenreported so far as the cause of FHBL. In vitro studies have shownthat these mutations induce retention of the mutant apoB in the endoplasmicreticulum and impair the secretion of apoB-containinglipoproteins.We identi ed two novel amino acid variants (Thr26-27del andTyr102Cys) located in the N-terminal 1000 amino acids of matureapoB in two hypocholesterolemic blood donors.Methods. To investigate the functional effect of these variants weconstructed plasmids containing human apoB-48 cDNAs harbouringthe novel mutations. Rat hepatoma cells (McA-RH7777) weretransiently and stably transfected with wild-type or the mutantforms of human apoB-48. The secretion ef ciency of human apoB-48 was determined by immunoblotting with human anti-apoB andthe incorporation of apoB into medium lipoproteins. Immunocytochemistrywas used to monitor the intracellular localization of themutant proteins. The post-translational stability and the intracellulardegradation pathways of mutant apoB-48 was evaluated.Results and Conclusions. The mutation Tyr102Cys had no effecton apoB-48 secretion. The mutant apoB-48-Thr26-27del almostentirely abolished the secretion of apoB-48 and apoB-containinglipoproteins in the medium, suggesting that the deletion of twoamino acids alters the structure of the beta-barrel (the rst 267amino acids) of N-terminal domain of apoB. This mutant apoB-48appears to be retained in endoplasmic reticulum. The addictionof a proteasome inhibitor partially blocked the decay of cellularapoB-48-Thr26-27del suggesting that a signi cant proportion ofthe mutant protein was degraded by the proteasomal pathway.The role of autophagy in the degradation of the mutant apoB wasexcluded.
|Numero di pagine||2|
|Stato di pubblicazione||Published - 2013|