The ACAT2 gene encodes a gatekeeper of intestinal cholesterol absorption that regulates cholesterolemia and gallstone disease.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
S Zanlungo
Publications and source records attributed to S Zanlungo.
Transfer of the mitochondrial rps10 gene to the nucleus in rice: acquisition of the 5' untranslated region followed by gene duplication.
Mitochondrial ribosomal protein S10 (rps10) is encoded by the mitochondrial genome in potato and pea. Here we show that the rps10 gene is absent from the mitochondrial genome of rice and has been transferred to the nucleus. Cloning and transcriptional analysis show that there are two rps10 genes in the rice nuclear genome and that their transcripts differ in abundance. Western analysis detected the RPS10 protein in the soluble fraction of rice mitochondria, although neither RPS10 has any obvious N-terminal presequence for targeting to mitochondria. This result suggests that targeting information is present in the internal region of rice RPS10. Genomic sequence analysis indicated that each rps10 gene has an intron in the 5' untranslated region (5' UTR) and that these intron sequences are homologous to each other. This result strongly suggests that a duplication event occurred after transfer of the rps10 gene to the nucleus. The duplicated rps10 genes have since been translocated to different chromosomes, because the two rps10 genes were mapped on chromosomes 6 and 12 by RFLP analysis. Interestingly, the 5' UTR and the intron of the rice rps10 genes are homologous to sequences found in several rice genes with various functions, such as osk4, EF-1beta2 and RAG1, suggesting a common origin and a functional role for the 5' UTR. Acquisition of the 5' flanking region might have accelerated the activation of the mitochondrial rps10 gene which was transferred to the nuclear genome.
5' Untranslated Regions↗
Impaired biliary cholesterol secretion and decreased gallstone formation in apolipoprotein E-deficient mice fed a high-cholesterol diet.
BACKGROUND & AIMS: Because apolipoprotein E (apoE) is a key cholesterol transport molecule involved in the hepatic uptake of chylomicron cholesterol, it may play a critical role in controlling bile cholesterol elimination and cholesterol gallstone formation induced by dietary cholesterol. To test this hypothesis, we studied biliary lipid secretion and gallstone formation in apoE-deficient mice fed cholesterol-rich diets. METHODS: Bile lipid outputs and gallstone sequence events were analyzed in apoE-deficient mice fed a high-cholesterol diet or a lithogenic diet compared with control animals. RESULTS: A high-cholesterol diet increased biliary cholesterol secretion and gallbladder bile cholesterol concentration in wild-type mice; the increase in bile cholesterol secretion was significantly attenuated in apoE-deficient mice. ApoE knockout mice fed a high-cholesterol lithogenic diet had a markedly lower frequency of gallbladder bile cholesterol crystal and gallstone formation than wild-type mice, which was most likely a result of the decreased cholesterol saturation index found in gallbladder bile of apoE-deficient mice. CONCLUSIONS: These results show that apoE expression is an important factor for regulating both biliary secretion of diet-derived cholesterol as well as diet-induced cholesterol gallstone formation in mice.
Animals↗
Sterol carrier protein 2 gene transfer changes lipid metabolism and enterohepatic sterol circulation in mice.
BACKGROUND & AIMS: Sterol carrier protein 2 (SCP-2) enhances sterol cycling and facilitates cholesterol translocation between intracellular organelles and plasma membrane in cultured cells, including hepatocytes. We examined the role of SCP-2 in hepatic cholesterol and lipid trafficking through the sinusoidal and canalicular secretory pathways of the liver in vivo. METHODS: Recombinant adenovirus-mediated SCP-2 gene transfer was used to obtain hepatic overexpression of SCP-2 in C57BL/6 mice. RESULTS: SCP-2 overexpression in the mouse liver resulted in an 8-fold increase of SCP-2 protein levels and determined various effects on lipid metabolism. It decreased high-density lipoprotein cholesterol and increased low-density lipoprotein (LDL) cholesterol concentrations. The expressions of hepatic LDL receptor, apolipoprotein (apo) A-I, apoB, and apoE were decreased. SCP-2 overexpression also increased hepatic cholesterol concentration, associated with decreased cholesterol neosynthesis. Increased biliary cholesterol and bile acid secretion, bile acid pool size, and intestinal cholesterol absorption were also observed. CONCLUSIONS: These results indicate that modulation of SCP-2 expression in the liver determines important modifications on lipoprotein metabolism, hepatic cholesterol synthesis and storage, biliary lipid secretion, bile acid metabolism, and intestinal cholesterol absorption.
Animals↗
Enrichment of canalicular membrane with cholesterol and sphingomyelin prevents bile salt-induced hepatic damage.
These studies were undertaken to characterize the role of plasma membrane cholesterol in canalicular secretory functions and hepatocyte integrity against intravenous taurocholate administration. Cholesterol and sphingomyelin concentrations and cholesterol/phospholipid ratios were significantly increased in canalicular membranes of diosgenin-fed rats, suggesting a more resistant structure against solubilization by taurocholate. During taurocholate infusion, control rats had significantly decreased bile flow, whereas diosgenin-fed animals maintained bile flow. Maximal cholesterol output increased by 176% in diosgenin-fed rats, suggesting an increased precursor pool of biliary cholesterol in these animals. Maximal phospholipid output only increased by 43% in diosgenin-fed rats, whereas bile salt output remained at control levels. The kinetics of glutamic oxalacetic transaminase, lactic dehydrogenase, and alkaline phosphatase activities in bile showed a significantly faster release in control than in diosgenin-fed rats. After 30 min of intravenous taurocholate infusion, necrotic hepatocytes were significantly increased in control animals. Preservation of bile secretory functions and hepatocellular cytoprotection by diosgenin against the intravenous infusion of toxic doses of taurocholate was associated with an increased concentration of cholesterol and sphingomyelin in the canalicular membrane. The increase of biliary cholesterol output induced by diosgenin was correlated to the enhanced concentration of cholesterol in the canalicular membrane.
Alkaline Phosphatase↗
[Molecular biology and medicine: basic concepts].
Through the advancements of molecular genetics, physicians and researchers are in an extraordinary period of study concerning the molecular basis of medicine. Molecular biology is making a tremendous impact on both diagnosis and treatment of diseases through the clinical introduction of molecular methods. These techniques, restricted for many years to basic biological research, include the polymerase chain reaction, DNA and protein electrophoresis, cloning of genes into viral or bacterial vectors and methods to rapidly sequence DNA and identify mutations. In this article the authors attempt to provide basic concepts on these themes for the non-trained physicians in order to help them to understand recent developments and foresee their future implications.
DNA↗
[Molecular medicine: present and future].
The genetic background of individuals is recognized as an important clue in the analysis of classical hereditary and multifactorial acquired diseases. This new concept derives from the development and increasing use of molecular genetics in clinical medicine. The application of molecular biology techniques in biomedical investigation has encompassed the identification of the pathogenesis and etiology of diseases, prenatal diagnosis the production of new therapeutic agents, gene therapy and the development of pharmacogenetics. The impact on the fundamentals and practice of clinical medicine that will have the use of molecular biology is analyzed in this review.
Animals↗
The rpl5-rps14-cob gene arrangement in Solanum tuberosum: rps14 is a transcribed and unedited pseudogene.
The L5 ribosomal protein gene (rpl5) and a S14 ribosomal protein pseudogene were identified by sequence analysis in the potato mitochondrial genome. The two genes are separated by one nucleotide and are found upstream of the apocytochrome b gene (cob), an arrangement conserved also in Arabidopsis and Brassica. The rpl5 gene has an intact open reading frame while the rps14 locus is disrupted by a five nucleotide duplication that introduces a frameshift in the reading frame. Editing of rpl5 and pseudorps14 cotranscripts has been studied by cDNA sequence analysis. Eight C residues are edited into U in the rpl5 coding region, resulting in eight amino acid changes that increase the homology between potato and other RPL5 polypeptides. Interestingly, the rps14 pseudogene sequence is not edited at any nucleotide position.
Amino Acid Sequence↗
Splicing and editing of rps10 transcripts in potato mitochondria.
The structure and expression of the potato mitochondrial gene rps10, encoding ribosomal protein S10, has been characterized. The RPS10 polypeptide of 129 amino acids is encoded by two exons of 307 bp and 80 bp respectively, which are separated by a 774-bp class-II intron. Editing of the complete rps10 coding region was studied by sequence analysis of spliced cDNAs. Four C residues are edited into U, resulting in the creation of a putative translational initiation codon, a new stop codon which eliminated ten carboxy-terminal residues, and two additional amino-acid alterations. All these changes increase the similarity between the potato and liverwort polypeptides. One additional C-to-U RNA editing event, observed in the intron sequence of unspliced cDNAs, improves the stability of the secondary structure in stem I (i) of domain I and may thus be required for the splicing reaction. All spliced cDNAs, and most unspliced cDNAs, were completely edited, suggesting that editing is an early step of rps10 mRNA processing and precedes splicing. Earlier work on potato rps10 (Zanlungo et al. 1994) is now known to comprise only a partial analysis of the gene, since the short downstream exon was not identified.
Amino Acid Sequence↗
The cox1 initiation codon is created by RNA editing in potato mitochondria.
Explore the source record for details and available documents.
Codon, Initiator↗
A ribosomal protein S10 gene is found in the mitochondrial genome in Solanum tuberosum.
The S10 ribosomal protein gene (rps10), which has not been previously reported in any angiosperm mitochondrial genome, was identified by sequence analysis in the potato mitochondrial DNA. This gene is found downstream of a truncated non-functional apocytochrome b (cob) pseudogene, and is expressed as multiple transcripts ranging in size from 0.8 to 5.0 kb. Southern hybridization analysis indicates that rps10-homologous sequences are not present in the wheat mitochondrial genome. Sequence analysis of a single-copy region of the pea mitochondrial genome located upstream of cox1 [11] shows that a non-functional rps10 pseudogene is present in this species. These results suggest that the functional genes coding for wheat and pea mitochondrial RPS10 polypeptides have been translocated to the nucleus.
Amino Acid Sequence↗
RNA editing of apocytochrome b (cob) transcripts in mitochondria from two genera of plants.
Editing of the complete coding region of cob transcripts from two genera of plants has been studied by cDNA sequence analysis. Eighteen and nine C residues are edited into U in the mitochondrial transcripts from wheat and potato respectively. Both systems share eight common editing sites; ten codons edited in wheat are "pre-edited" at the genomic level in potato, and one codon edited in potato is "pre-edited" in wheat. Most amino-acid modifications lead to hydrophobic residues and increase the homology between the COB polypeptides and the corresponding protein of other species. In two out of the nine potato cDNA clones, an additional C-to-T modification, which also leads to a change in the encoded amino acid, was identified. Heterogeneity observed at the carboxy-terminus of the COB open reading frame in Triticum aestivum and Triticum timopheevi is not corrected by editing.
Apoproteins↗
Isolation and nucleotide sequence of the potato mitochondrial gene for apocytochrome b.
Explore the source record for details and available documents.
Amino Acid Sequence↗
Risk factors and pathogenesis of cholesterol gallstones: state of the art.
The aim of this article is to present an update of selected aspects of the pathogenesis and risk factors of cholesterol gallstones, a highly prevalent Western disease. The etiology of cholesterol cholelithiasis is considered to be multifactorial, with interaction of genetic and environmental factors. Mechanisms of cholesterol lithogenesis include biliary cholesterol hypersecretion, supersaturation and crystallization, stone formation and growth, and bile stasis within the gallbladder. Each of these various steps could be under genetic control and/or be influenced through intermediate pathogenic steps linked to a variety of environmental factors.
Cholelithiasis↗
Discovery of the hepatic canalicular and intestinal cholesterol transporters. New targets for treatment of hypercholesterolemia.
Arteriosclerosis and cholesterol cholelithiasis are characterized by abnormal regulation of cholesterol trafficking and solubilization, and subsequent development of the arteriosclerotic plaque in the artery walls and gallstone formation in the gallbladder, respectively. Cholesterol metabolism is controlled by many complex polygenetic - environmental interactions that contribute to the regulation of serum lipoprotein cholesterol levels and biliary cholesterol and bile acids secretion, which constitute the only pathway for sterol elimination from the organism. Much of our understanding of cholesterol metabolism has arisen from studies of the pathways controlling cholesterol synthesis and the uptake and degradation of LDL and HDL lipoproteins. Recently, two new members of the ABC transporter family (ABCG5 and ABCG8 heterodimers) have been discovered in the apical pole of the enterocyte and in the canalicular membrane of hepatocytes. Experiments in genetically engineered mice have demonstrated that ABCG5/G8 represent the physiological canalicular transporter of biliary cholesterol and the intestinal secretory mechanism of absorbed dietary plant sterols. Interestingly, mutation of ABCG5 and or ABCG8 genes in man causes sitosterolemia, a rare genetic disease characterized by massive absorption of plant sterols and premature arteriosclerosis. The potential pharmacological manipulation of biliary cholesterol secretion represents another important therapeutic target to treat hypercholesterolemia, if this manipulation is simultaneously accompanied by measures aimed to avoid gallbladder cholesterol crystallization. The best theoretical drug should decrease serum lipoprotein cholesterol levels, increase biliary cholesterol secretion and fecal elimination and favoring at the same time gallbladder emptying to prevent gallstone formation.
ATP-Binding Cassette Transporters↗