Disease relevance of APOB

• Single marker and haplotype analysis of the chicken apolipoprotein B gene T123G and D9500D9- polymorphism reveals association with body growth and obesity [1].
• Estrogen dependence of synthesis and secretion of apolipoprotein B-containing lipoproteins in the chicken hepatoma cell line, LMH-2A [2].

High impact information on APOB

• We have used the newly isolated clones, as well as the yolk protein cDNAs previously available [VTGII, apolipoprotein II (apoVLDLII), and apolipoprotein B], as probes to examine several aspects of the regulation of these genes by estradiol [3].
• Comparison of the rates of movement of triacyl[3H]glycerol, apolipoprotein B, apolipoprotein II, and apolipoprotein A-I through the ER and Golgi and of their secretion in nascent VLDL suggests that assembly of triacyglycerol with apolipoproteins occurs in the Golgi [4].
• Specific postendocytic proteolysis of apolipoprotein B in oocytes does not abolish receptor recognition [5].
• The C to U editing of apolipoprotein B (apoB) mRNA converts a glutamine codon in apoB100 mRNA into a stop translation codon thereby generating apoB48 [6].
• Mammalian small intestine secretes a truncated apolipoprotein B (apoB48) species as a result of tissue-specific post-transcriptional RNA editing [7].

Biological context of APOB

• Regulation of chicken apolipoprotein B: cloning, tissue distribution, and estrogen induction of mRNA [8].
• While all five of these genes, vitellogenins I, II, and III, very low density apolipoprotein II (apo VLDLII), and apolipoprotein B, respond to estrogen, individual controls are superimposed on their coordinate regulation with respect to the kinetics of induction, magnitude of response, and developmental expression [9].

Anatomical context of APOB

• Octanoate reduces very low-density lipoprotein secretion by decreasing the synthesis of apolipoprotein B in primary cultures of chicken hepatocytes [10].
• Evolution of intestinal apolipoprotein B mRNA editing. Chicken apolipoprotein B mRNA is not edited, but chicken enterocytes contain in vitro editing enhancement factor(s) [11].
• In addition to their different Mr values, another distinctive feature of the two proteins was revealed by ligand blotting experiments: the oocyte receptor bound rabbit beta-VLDL (a class of apolipoprotein-B and -E containing lipoprotein particles), whereas the fibroblast receptor did not [12].
• Binary and ternary complexes of apolipoprotein B (apo B) with egg yolk lecithin and with lecithin plus cholesterol have been formed from detergent-lipid-protein mixed micelles [13].
• Once taken up by the growing zygote, apolipoprotein B, the major protein constituent of VLDL, is proteolytically cleaved by a chicken-specific cathepsin-D [14].

Associations of APOB with chemical compounds

• As compared to the cycloheximide-treated cells in which apolipoprotein B nascent chains were arrested intracellularly, the puromycin-treated cells secreted discharged apolipoprotein B nascent chains as VLDL constituents assembled with triacylglycerol [15].
• In mammals it is a discrete process confined to the editing of apolipoprotein B (apoB) mRNA in eutherians and the editing of the mitochondrial tRNA for glycine in marsupials [16].
• The ability of apoII/PC, as well as of physiological particles containing apoII but devoid of apolipoprotein B (apoB), namely high density lipoproteins (HDL) from laying hens, to interact with the oocyte receptor was tested [17].
• Microsomal triglyceride transfer protein (MTP) catalyzes the assembly of triglyceride (TG)-rich apolipoprotein B-containing liver (e.g., VLDL) and intestinal (e.g., chylomicron) lipoproteins [18].
• Apolipoprotein B nascent chains discharged by puromycin assemble with glycerolipid (mainly triacylglycerol) and are secreted as immunoprecipitable VLDL [19].

Other interactions of APOB

• Serum-free culture conditions have been established that allow expression of apolipoprotein B, very low density apolipoprotein II (apoVLDLII), serum albumin, and transferrin at levels detectable by Northern blot analysis [20].

Analytical, diagnostic and therapeutic context of APOB

• In microalbuminuric patients, apolipoprotein B levels were lower after the chicken (113.5 +/- 36.0 mg/dl) and low-protein diets (103.5 +/- 40.1 mg/dl) than after the usual diet (134.3 +/- 30.7 mg/dl; P < 0.05) [21].
• Plasma and egg yolk VLDL were isolated by ultracentrifugation and free epsilon-amino groups of lysines of apolipoprotein B (apo B), the protein constituent of VLDL that mediates binding to the 95-kDa oocyte membrane receptor, were biotinylated using D-biotin-N-hydroxysuccinimide ester [22].
• Here, we demonstrate directly that the catalyst for the intraoocytic processing of both apolipoprotein B and vitellogenin is cathepsin D. The enzyme was purified from oocytic yolk, preovulatory follicle homogenates, and liver by affinity chromatography [23].

References