Abstract
Two different molecular weight forms of apoB are produced from a common initial transcript via editing of a Gln codon (CAA) to a stop codon (UAA), leading to a truncated translation product (apo BS) that consists of the amino terminal half of the larger form (apoBL). Previous studies have shown that fasting coordinately decreases lipogenesis and the secretion of very low density lipoprotein (VLDL) lipids and apoBS. Secretion of the apoBL is unaffected by fasting. We studied whether editing of apoB RNA is repressed by fasting, thus accounting for the selective decreased secretion of apoBS. Column chromatography of [35S]methionine-labeled lipoproteins secreted by hepatocytes from fed rats showed that essentially all of apoBL is secreted in the VLDL fraction, whereas a significant amount (15%) of apoBS is secreted associated as lipoproteins eluting in the HDL fractions. Fasting decreased the relative amount of apoBS that eluted in the VLDL fractions and increased the amount secreted in the HDL fractions. Consistent with previous results, hepatocytes from fasted rats show a selective twofold decrease in apoBS secretion. Fasting did not affect the relative abundance of apoB RNA, determined by slot blot hybridization assays using two different 32P-labeled cDNA probes coding either for both molecular weight forms or for only the large molecular weight form. However, quantitative of the editing of apoB RNA showed that fasting caused a 60% decrease in the amount of apoB RNA possessing the stop codon. These data show that the editing of apoB RNA is sensitive to metabolic state (i.e., fasting) resulting in a selective decrease in the secretion of apoBS. However, since the total secretion of apoB was decreased by fasting, while apoB mRNA levels remained constant, additional (post-transcriptional) mechanisms play a role in regulating apoB secretion.
Highlights
Two different molecular weight forms of small apolipoprotein B apoBL (apoBs) are produced from a common initial transcript via editing of a Gln codon (CAA) to a stop codon (UAA), leading to a truncated translation product that consists of the amino terminal half of the larger form
We examined whether decreased apoB mRNA could account for the decreased secretion of apoBs
Previous studies show that fasting affects the secretion of individualapolipoproteinsdifferently;apoBs is reduced, apoBLis unchanged, and apoE is increased [16]
Summary
Two different molecular weight forms of apoB are produced from a common initial transcript via editing of a Gln codon (CAA) to a stop codon (UAA), leading to a truncated translation product (apo Bs) that consists of the amino terminal half of the larger form (apoBL). Fasting decreases apolipoprotein B mRNA editing and the secretion of small molecular weight apoB by rat hepatocytes: evidence that the total amount of apoB secreted LS regulated post-transcriptionally. RNA editing has been shown to account for the selective synthesis of the small molecular weight form of apoB by both the intestine and rat liver [14].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
