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L Chan

Publications and source records attributed to L Chan.

At least 163 records · Page 9Linked to original sources
PubMed1998

Phenotype interaction of apobec-1 and CETP, LDLR, and apoE gene expression in mice: role of apoB mRNA editing in lipoprotein phenotype expression.

Apolipoprotein (apo) B mRNA editing determines the amount of apoB-100 and apoB-48 produced. Surprisingly, apobec-1 knockout mice, which do not edit apoB, have an essentially normal lipoprotein phenotype. By selected cross-breeding of mice of different genotypes, we show in this report that inactivation of editing produces profound phenotypic effects in cholesteryl ester transfer protein (CETP) transgenic mice and in apoE and low density lipoprotein receptor (LDLR) knockout mice. Compared with mice with an apobec-1+/+ background, CETP expression in apobec-1-/- mice caused a doubling of the plasma apoB-100 concentration (from 3.5+/-0.6 to 8.8+/-1.9 mg/dL, P<.01) and a much greater shift of plasma cholesterol from HDL to IDL/LDL as assayed by fast protein liquid chromatography analysis; the ratio of non-HDL to HDL cholesterol was 0.47, 0.46, 0.76, and 1.43 in apobec-1(+/+)/CETP-/-, apobec-1(-/-)/CETP-/-, apobec-1(+/+)/CETP+/-, and apobec-1(-/-)/CETP+/- animals, respectively. Feeding of a Western-type diet further exaggerated the shift in this ratio. In LDLR-/- mice, inactivation of apobec-1 caused an approximately 200% rise in plasma apoB-100 concentration, an approximately 60% increase in apoE concentration, and a 70% increase in total plasma cholesterol, which resulted exclusively from an increase in non-HDL cholesterol. The exaggerated hypercholesterolemia involving the VLDL+LDL fractions was further enhanced by a Western-type diet. In contrast, in apoE-/- mice, inactivation of apobec-1 caused a massive increase (from <0.5 to 55.5+/-16.4 mg/dL) in plasma apoB-100 concentration but an approximately 55% reduction in hypercholesterolemia due to partial amelioration of the marked VLDL+IDL elevation. However, the difference in lipid profiles between apobec-1(+/+)/apoE-/- and apobec-1(-/-)/apoE-/- mice was abolished in a time-dependent manner as further increases in total plasma cholesterol were induced by a Western-type diet. Whereas apobec-1 inactivation in wild-type mice produced little or no change in lipoprotein phenotype, giving rise to speculation that apoB mRNA editing does not have significant effect on lipoprotein dynamics, we show herein that there is important gene-gene interaction between apobec-1 and the CETP, LDLR, and apoE loci, which is subject to further substantial modulation by environmental factors such as a Western-type diet in mice.

APOBEC-1 Deaminase↗
PubMed1998

Hemodynamic factors affecting uterine artery Doppler waveform pulsatility in sheep.

Quantitative analysis of vascular resistance from the Doppler time-velocity waveform relies on measuring arterial pulsatility. However, input pressure waveform pulsatility, impedance, and resistance have all been found to effect artery flow waveform pulsatility in circulatory mathematic models and in umbilical sheep preparations in vivo. The present study used an in vivo sheep preparation to determine that embolization of the uteroplacental circulation and maternal angiotensin II administration caused changes in the uterine Doppler time-velocity waveform pulsatility that were dependent on input pressure waveform pulsatility, fundamental impedance, and resistance changes. Uteroplacental vascular embolization increased vascular resistance and the uterine artery Doppler waveform resistive index; the mean component of flow (mean pressure/resistance) decreased. Decreased uterine artery Doppler resistive index occurred despite angiotensin II-induced vasoconstriction and increased vascular resistance because the pulse component of flow (pulse pressure/impedance) decreased.

Angiotensin II↗
PubMed1998

Bacterial infection of central venous catheters in short-term total parenteral nutrition.

Fourteen severely ill ventilated patients in an intensive care unit, requiring short-term total parenteral nutrition, were examined for catheter-related infection. Microbiological analysis using Maki's SQ technique was carried out on catheter exit site, catheter hub, proximal subcutaneous segment of catheter and catheter up. Qualitative cultures were carried out on total parenteral nutrition and peripheral blood samples. Twenty six of 29 catheters removed (90%) were culture positive but only 7 catheters were related to positive blood cultures, giving a catheter-related bacteremia (CRB) rate of 24%. Haematogenous seeding was strongly implicated in 7/29 (24%) of catheters. Patients' skin flora appeared to be the main source of catheter-related infection. The organisms isolated for patients with CRB included coagulase-negative staphylococci, Acinetobacter and Klebsiella. It is suggested that to control infective complications of central venous catheters, emphasis should be focused on specialised intravenous therapy teams and the use of strict protocols for insertion and care of central lines.

Adolescent↗
PubMed1998

Intrauterine adenoviral infection associated with fetal non-immune hydrops.

A 27-week fetus with hydrops fetalis associated with fetal tachyarrhythmia and adenovirus infection was documented by viral polymerase chain reaction (PCR). The fetal tachyarrhythmia was converted to normal sinus rhythm by maternal pharmacological therapy with digoxin. Subsequently, resolution of the hydropic changes occurred and a viable normal-appearing preterm fetus at 29 weeks' gestation was delivered after preterm labour. This case demonstrates the first documented report of intrauterine adenovirus-associated fetal tachyarrhythmia and hydrops fetalis.

Adenoviridae↗
PubMed1998

Human apolipoprotein A-II is a pro-atherogenic molecule when it is expressed in transgenic mice at a level similar to that in humans: evidence of a potentially relevant species-specific interaction with diet.

We report on the effect of human apolipoprotein (apo) A-II transgene expression on atherosclerosis susceptibility in two transgenic lines (25.3 and 11.1) whose plasma human apoA-II concentrations (approximately 23 and 96 mg/dl, respectively) span the normal range in humans. After 9 months of an atherogenic diet, 25.3 and 11.1 transgenic mice developed aortic atherosclerotic lesions that were approximately 1.7- and 7-fold, respectively, more extensive than those of non-transgenic control mice. However, there was no difference in the area of atherosclerosis of transgenic and control mice when fed a regular chow diet This contrasts with the findings in murine apoA-II transgenic mice and provides evidence of a species-specific characteristic that could be of relevance with respect to the high fat intake diets common in most industrialized countries. A possible mechanism of the pro-atherogenic action of human apoA-II could be the inhibition of reverse cholesterol transport and, in support of this, we observed an impairment of apoA-I-HDL particle interconversion in the plasma of 11.1 transgenic mice caused, at least in part, by a marked decrease in the endogenous lecithin:cholesterol acyltransferase activity.

Animals↗
PubMed1998

Bridging the discharge process.

Current mental health initiatives are decreasing the number of psychiatric beds and thus increasing the number of clients with serious mental illness who are being served in the community. Such changes have implications for clients' quality of life and health care economics. To implement the changes while addressing the unique needs of psychiatric clients, appropriate models of discharge planning and community integration are critical.

Adult↗
PubMed1998

Cross cultural adaptation and validation of the Chinese Health Assessment Questionnaire for use in rheumatoid arthritis.

OBJECTIVE: The Health Assessment Questionnaire - Disability Index (HAQ), used as a disability and outcome measurement in rheumatoid arthritis (RA), has been validated in several languages, but not in Chinese. Our aim was to validate the Chinese version of HAQ (Chinese-HAQ) to suit the needs of Chinese speaking patients with RA in an Asian setting. METHODS: The original HAQ was modified in the context of Chinese culture and translated into Chinese by 2 translators aware of the objective of the questionnaire. The Chinese HAQ was self-administered by 42 patients with RA during their routine followup visit and one week later. RESULTS: The test-retest reliability assessed using Spearman's correlation coefficient was 0.84. Between dimensions measured in the HAQ, the highest test-retest reliability was observed for walking (Spearman correlation coefficient rs=0.80) and the lowest was for eating (rs=0.54). The internal consistency of the scale using Cronbach's alpha was high at 0.86. In terms of criterion validity, the Chinese-HAQ score was found to correlate well with American College of Rheumatology functional status (rs=0.501, p=0.01). The Chinese-HAQ scores also correlated well with markers of disease activity such as patient's perception of pain measured on a visual analog scale (rs=0.55, p < 0.001), grip strength in mm Hg (rs=-0.55. p < 0.001 ), and physician's assessment of disease activity (rs=0.59, p < 0.001). CONCLUSION: The Chinese HAQ is a reliable and valid instrument for studies measuring disability of patients with RA in Singapore.

Adult↗
PubMed1998

Resistance of chylomicron and VLDL remnants to post-heparin lipolysis in ApoE-deficient mice: the role of apoE in lipoprotein lipase-mediated lipolysis in vivo and in vitro.

The interaction of lipoprotein lipase (LPL) with triglyceride-rich lipoproteins is governed by a number of factors, such as apolipoprotein (apo) C-II. The role of apoE in lipolysis is controversial. We made the unexpected observation that apoE-deficient mice were resistant to heparin-induced lipolysis; this study aims at examining the underlying mechanism for this observation. Compared to wild-type mice, apoE-deficient mice had significantly higher very low density lipoprotein (VLDL) and chylomicron remnant (VLDL/CMR) concentrations and moderately lower lipase activity (15.5 +/- 1.3 mU/ml vs. 22.9 +/- 2.5 mU/ml). Unlike in wild-type mice where the injection of heparin reduced total plasma triglycerides by 50% and VLDL/CMR triglycerides by over 95%, the injection of heparin into apoE-deficient mice did not significantly affect plasma lipids. Similarly, in vitro, purified human LPL (hLPL) almost completely hydrolyzed VLDL/CMR isolated from wild-type mice, but had no effect on VLDL/CMR from apoE-deficient mice. However, when the amount of apoE-deficient VLDL/CMR was reduced to an equivalent level as in wild-type mice, LPL hydrolyzed 94% of VLDL/CMR triglycerides. In order to increase the ratio of LPL to VLDL/CMR in vivo, we injected an adenovirus containing the human LPL cDNA into apoE-deficient mice, which produced marked liver-specific overexpression of LPL and significant reduction of VLDL/CMR (93%) and total plasma triglyceride concentrations (87%). Thus, apoE is not required for LPL activity in vivo or in vitro. Under certain pathological conditions, such as severe hyperlipidemia, the LPL pathway may be saturated and efficient lipolysis can proceed only if the ratio of substrate particles to LPL is adjusted to a more normal range.

Animals↗
PubMed1998

Limitations of pediatric donor kidneys for transplantation.

BACKGROUND: The shortage of grafts for kidney transplantation (Tx) has resulted in an expansion of criteria for pediatric donors. However, the limitations of pediatric donors for kidney Tx are not yet clearly established. We investigated the outcomes of recipients with pediatric kidney grafts from Colorado to elucidate the state of pediatric kidney grafts distributed in the nation and to clarify the limitations of pediatric donor kidneys for Tx. METHODS: Between January 1989 and July 1997, 675 organ donors in Colorado were utilized for Tx. Fifty-seven of these (8.4%) were 10 yr old or younger. Thirty-two of the 57 pediatric donors provided kidneys for 50 recipients both inside and outside Colorado. Forty-four of the 50 recipients were followed and are available for this study. RESULTS: Graft survival rates were 85.6, 77.3, 71.3 and 65.4% for 1, 2, 3 to 5, and 6 yr of follow-up, respectively. Thirteen recipients lost the grafts, including three graft losses within 2 wk, due to primary nonfunction, venous and arterial thrombosis. The mean serum creatinine value in 31 recipients with functioning grafts was 1.3 +/- 0.4 mg/dL at the time with follow-up of 45.9 +/- 28.3 months (5-96 months). Six grafts from 13-month to 3-yr-old donors were transplanted en-bloc and 5 of these have survived. Four of the 5 single grafts from 3 to 5-yr-old donors have functioned. Of the 33 grafts from donors aged 6-10 yr, including 30 single and 3 en-bloc grafts, 22 were still functioning. With respect to donor weight, 4 of the 5 en-bloc grafts from donors weighting 9-15 kg, and 6 of the 7 single and the 1 en-bloc grafts from donors weighing 15-20 kg were still functioning. Cold ischemic time (CIT) within 37.5 h was not associated with early graft outcome. CONCLUSIONS: The kidneys from donors 1-3 yr old and/or weighing 9-15 kg could be successfully transplanted en-bloc and those from donors more than 3 yr old and/or weighing 15 kg were best transplanted by single grafts.

Adolescent↗
PubMed1997

Mycophenolate mofetil decreases rejection in simultaneous pancreas-kidney transplantation when combined with tacrolimus or cyclosporine.

BACKGROUND: Historically, the acute rejection rates in simultaneous pancreas-kidney (SPK) recipients have been extremely high (50-80%), with many second and third rejection episodes despite the use of quadruple immunosuppression (antibody induction and cyclosporine [CsA]-azathioprine [AZA]-based maintenance immunosuppression). Although this acute rejection has rarely led to graft loss, it has been a great cause of morbidity and of significantly increased cost. In an attempt to decrease the acute rejection rate and related morbidity in SPK transplant recipients, we compared two "state-of-the-art" immunosuppression regimens in a prospective, randomized, single-center study. METHODS: Patients who received SPK transplants were randomized to receive either tacrolimus (TAC) and mycophenolate mofetil (MMF, n=18) or CsA (Neoral formulation) and MMF (n=18). All patients received OKT3 induction and prednisone, which was tapered to 5 mg/day by 6 months after transplantation. All rejection episodes were biopsy proven. In addition, metabolic control (HgbA1C, hypertension, serum cholesterol), drug toxicity, and infection also were measured. Data were compared with that of a historical group (n=18) who received conventional CsA (Sandimmune formulation) and AZA-based immunosuppression. RESULTS: The incidence of biopsy-proven acute rejection was 11% in both the TAC-MMF and CsA-MMF groups with only two patients in each group experiencing a rejection episode. This rejection rate was significantly decreased from that of the CsA-AZA historical group (77%, P<0.01). There were no significant differences in infection rates, including cytomegalovirus, or in metabolic control (HgbA1C, hypertension, and cholesterol levels). All patients remained on their initial immunosuppression regimen for the first 3 months after transplantation. Between 3 and 6 months after transplantation, three patients were switched from TAC to CsA for recurrent migraine headaches, posttransplant diabetes, and chronic cytomegalovirus infection. Two patients in the CsA-MMF group died of nonimmunologic causes (aspiration pneumonia and arrhythmia) between 3 and 6 months after transplantation. CONCLUSIONS: The data from this study show that MMF treatment significantly decreases the incidence of biopsy-proven acute rejection in SPK transplant recipients compared with AZA-treated historical controls. In addition, we conclude that TAC and CsA (Neoral), when combined with MMF, yield similar, low acute rejection rates with similar graft function and metabolic control.

Adult↗
PubMed1997

Adenovirus-mediated gene transfer of human lipoprotein lipase ameliorates the hyperlipidemias associated with apolipoprotein E and LDL receptor deficiencies in mice.

Lipoprotein lipase (LPL) is the rate-limiting enzyme for the hydrolysis of triglyceride-rich lipoproteins. We tested the efficacy of adenovirus-mediated gene transfer of LPL as treatment of experimental hyperlipidemias associated with apolipoprotein (apoE) deficiency (apoE-/-) and low-density lipoprotein receptor (LDLr) deficiency (LDLr-/-) in mice. Replication-defective adenovirus containing the human LPL cDNA driven by a cytomegalovirus promoter (Ad.hLPL) efficiently transduced CHO-ldlA7 cells in vitro, inducing in these cells the production of bioactive LPL (73 mU/ml). Intravenous injection of Ad.hLPL (2 x 10(9) pfu) led to high-level expression of hLPL mRNA and LPL activity in the liver (88.3 mU/ml) and in post-heparin plasma (116.1 mU/ml). Overexpression of LPL resulted in marked reductions in total plasma cholesterol (TC; 48%, 43%, 25%) and triglycerides (TTg; 63%, 40%, 70%, p < 0.01) in apoE-/-, LDLr-/-, and wild-type (WT) mice, respectively. Fast protein liquid chromatography (FPLC) fractionation of plasma lipoproteins showed a marked decrease in very-low-density lipoprotein (VLDL)/chylomicron remnant cholesterol (V/CR-C) in apoE-/- (83%), LDLr-/- (84%), and WT mice (58%, p < 0.01). VLDL/chylomicron remnant triglycerides (V/CR-Tg) were virtually eliminated in apoE-/- (92%), LDLr-/- (86%), and WT mice (84%, p < 0.05). No significant changes were detected in LPL activities, plasma lipids, or lipoproteins of mice injected with a control virus, Ad.Luc, containing the luciferase instead of the LPL cDNA. In summary, infusion of Ad.hLPL leads to increased liver and post-heparin plasma LPL activities, significantly reduced TC, TTg, V/CR-C, and V/CR-Tg in WT mice, as well as in mice with apoE and LDLr deficiencies. Adenovirus-mediated LPL gene transfer to the liver is an effective means of reversing many of the lipoprotein abnormalities in apoE- and LDLr-deficient mice.

Adenoviridae↗
PubMed1997

The effect of Medicare's payment system for rehabilitation hospitals on length of stay, charges, and total payments.

BACKGROUND: Medicare's system for the payment of rehabilitation hospitals is based on limits derived from a hospital's average allowable charges per patient discharged during a base year. Thereafter, payments are capped but hospitals receive incentive payments if charges per patient are reduced in succeeding years. We hypothesized that per-patient charges would increase during the base year and then decrease in subsequent years. Hospitals would thus have higher reimbursement limits and receive incentive payments for reducing their charges. METHODS: We analyzed Medicare claims data for 190,921 discharges from 69 rehabilitation hospitals from 1987 through 1994. We compared total charges, length of stay, and interim payments before, during, and after each hospital's base year. RESULTS: After we controlled for inflation and temporal and seasonal trends, mean charges per patient discharged increased from $25,131 for patients discharged before the base year to $32,167 for patients discharged in the base year (a 28 percent increase, P<0.001) and the mean length of stay increased from 22.1 to 26.7 days (a 21 percent increase, P<0.001). After the base year, mean charges decreased to $29,307 (a 9 percent decrease) and the mean length of stay decreased to 24.0 days (a 10 percent decrease) (P<0.001 for both comparisons). Analysis of data on patients according to diagnosis -- for example, spinal cord injury, brain injury, stroke, amputations and deformities, hip fracture, and arthritis and joint disorders -- showed similar findings for each, with increases in charges and length of stay in the base year, followed by smaller reductions thereafter. For-profit hospitals had greater increases than nonprofit hospitals in their per-patient charges (mean increase, $7,434 vs. $2,929; P<0.001) and length of stay (mean increase, 4.6 vs. 2.3 days, P<0.001) during the base year. CONCLUSIONS: Although Medicare's reimbursement system for rehabilitation hospitals put an upper limit on total payments, its design was associated with substantial extra costs, including significantly increased payments to hospitals and doctors and increased numbers of hospital days for the average patient.

Aged↗
PubMed1997

Specificity of serine proteinase/serpin complex binding to very-low-density lipoprotein receptor and alpha2-macroglobulin receptor/low-density-lipoprotein-receptor-related protein.

Very-low-density lipoprotein receptor (VLDLR) and alpha2-macroglobulin receptor/low-density-lipoprotein-receptor-related protein (alpha2MR/LRP) are multifunctional endocytosis receptors of the low-density lipoprotein receptor family. Both have been shown to mediate endocytosis and degradation of complex between plasminogen activators and type-1 plasminogen-activator inhibitor (PAI-1) by cultured cells. We have now studied the specificity of binding and endocytosis by VLDLR and alpha2MR/LRP among a variety of serine proteinase/serpin complexes, including various combinations of the serine proteinases urokinase-type and tissue-type plasminogen activators, plasmin, thrombin, human leukocyte elastase, cathepsin G, and plasma kallikrein with the serpins PAI-1, horse leukocyte elastase inhibitor, protein C inhibitor, C1-inhibitor, alpha2-antiplasmin, alpha1-proteinase inhibitor, alpha1-antichymotrypsin, protease nexin-1, heparin cofactor II, and antithrombin III. Binding was estimated with radiolabelled ligands in ligand blotting analysis and microtiter well assays. Endocytosis was estimated by measuring receptor-associated protein (RAP)-sensitive degradation of radiolabelled complexes by Chinese hamster ovary cells transfected with VLDLR cDNA and by COS-1 cells, which have a high endogenous expression of alpha2MR/LRP. We found that the receptors bind with high affinity to some, but not all, combinations of plasminogen activators and thrombin with PAI-1, protease nexin-1, protein C inhibitor, and antithrombin III, while complexes of many serine proteinases with their primary inhibitor, i.e. plasmin/alpha2-antiplasmin complex, do not bind, or bind with a very low affinity. Both the serine proteinase and the serpin moieties contribute to the binding specificity. The binding specificities of VLDLR and alpha2MR/LRP are overlapping, but not identical. The results suggest that VLDLR and alpha2MR/LRP have different biological functions by having different binding specificities as well as by being expressed by different cell types.

Amyloid beta-Protein Precursor↗
PubMed1997

Breast carcinoma epithelial cells express a very low-density lipoprotein receptor variant lacking the O-linked glycosylation domain encoded by exon 16, but with full binding activity for serine proteinase/serpin complexes and Mr-40,000 receptor-associated protein.

Very-low density lipoprotein receptor (VLDLR) belongs to the low-density lipoprotein receptor family of endocytosis receptors. It binds a variety of different ligands, including apolipoprotein E, Mr-40,000 receptor-associated-protein (RAP), and some serine proteinase/serpin complexes. We previously demonstrated the occurrence of two forms of VLDLR in SDS/PAGE, migrating with Mr 105,000 and Mr 130,000, respectively [Heegaard, C. W., Simonsen, A. C. W., Oka, K., Kjøller, L., Christensen, A., Madsen, B., Ellgaard, L., Chan, L. & Andreasen, P. A. (1995) J. Biol. Chem. 270, 20,855-20,869]. We now demonstrate that these two forms correspond to forms with the absence (type-II) and presence (type-I) of the O-linked glycosylation domain encoded by exon 16, respectively. We show that the two forms have the same binding affinity to RAP and serine proteinase/serpin complexes. Using reverse transcription and PCR, we demonstrate that the splice variation giving rise to the two forms is highly cell specific. In particular, we demonstrate that human breast carcinomas express predominantly or exclusively the variant lacking exon 16. By immunohistochemistry, we demonstrate that VLDLR is mainly expressed by the epithelial cancer cells in these carcinomas. The VLDLR variant expressed by epithelial cancer cells could function in the clearance of cell-surface-associated serine proteinase/serpin complexes in breast carcinomas.

Amino Acid Sequence↗
PubMed1997

Apobec-1 and apolipoprotein B mRNA editing.

Apolipoprotein (apo)B mRNA editing is a novel mechanism for the post-transcriptional regulation of gene expression in mammals. It consists of a C-->U conversion of the first base of the codon CAA, encoding glutamine-2153, to UAA, an in-frame stop codon, in apoB mRNA. Since its initial description in 1987, substantial progress has been made in the last few years on the mechanism of editing. Apobec-1, the catalytic component of the apoB mRNA editing enzyme complex, has been cloned. This article begins with an overview of the general biology of apoB mRNA editing. It then provides an in-depth analysis of the structure, evolution and possible mechanism of action of apobec-1. ApoB mRNA editing is the prototype of RNA editing in mammals. What we learn from apoB mRNA editing will be useful in our understanding of other examples of RNA editing in vertebrates which are being described with increasing frequency.

APOBEC-1 Deaminase↗
PubMed1997

Cloning of an Apobec-1-binding protein that also interacts with apolipoprotein B mRNA and evidence for its involvement in RNA editing.

Apolipoprotein (apo)B mRNA editing is mediated by a multiprotein editosome complex. Apobec-1 is the catalytic component of this complex, but other proteins involved in editing have not been identified. We used the yeast two-hybrid system to identify an apobec-1-interacting protein, ABBP-1. ABBP-1 contains 331 amino acid residues and is identical to a previously reported human type A/B hnRNP except for a 47-residue insertion at its C-terminal region. It contains typical RNP motifs at its N-terminal half and glycine-rich motifs in the C-terminal region. Northern blot analysis indicates that ABBP-1 mRNA is distributed in multiple human tissues. By deletion analysis, we mapped the apobec-1-binding region to the glycine-rich domain. ABBP-1 also binds to apoB mRNA transcripts around the editing site and can be UV-cross-linked to them in vitro. Immnodepletion of ABBP-1 from an active apoB mRNA editing tissue extract inhibits its editing activity. Down-regulation of ABBP-1 in an apobec-1-expressing HepG2 cell line by transfection with an antisense ABBP-1 cDNA construct leads to inhibition of endogenous apoB mRNA editing. We conclude that ABBP-1 is an apobec-1-interacting protein that may play an important role in apoB mRNA editing.

APOBEC-1 Deaminase↗
PubMed1997

Tissue-specific inhibition of apolipoprotein B mRNA editing in the liver by adenovirus-mediated transfer of a dominant negative mutant APOBEC-1 leads to increased low density lipoprotein in mice.

APOBEC-1 is a catalytic subunit of an apolipoprotein B (apoB) mRNA editing enzyme complex. In humans it is expressed only in the intestine, whereas in mice it is expressed in both the liver and intestine. APOBEC-1 exists as a spontaneous homodimer (Lau, P. P., Zhu, H.-J., Baldini, A., Charnsangavej, C., and Chan, L. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 8522-8526). We tested the editing activity and dimerization potential of three different mouse APOBEC-1 mutants using in vitro editing activity assay and immunoprecipitation in the presence of epitope-tagged APOBEC-1. One catalytically inactive mutant, mu1 (H61K/C93S/C96S), that retains its capacity to dimerize with wild-type APOBEC-1 was found to inhibit the editing activity of the latter and was thus a dominant negative mutant. Two other inactive mutants that dimerized poorly with APOBEC-1 failed to inhibit its activity. Intravenous injection of a mu1 adenovirus, Admu1, in C57BL/6J mice in vivo resulted in liver-specific expression of mu1 mRNA. On days 4 and 9 after virus injection, endogenous hepatic apoB mRNA editing was 23.3 +/- 5.0 and 36.8 +/- 5.7%, respectively, compared with 65.3 +/- 11 and 71.3 +/- 5.2%, respectively, for luciferase adenovirus-treated animals. Plasma apoB-100 accounted for 95 and 93% of total plasma apoB in Admu1 animals on days 4 and 9, respectively, compared with 78 and 72% in luciferase adenovirus animals. Plasma cholesterol on day 9 was 98 +/- 17 mg/dl in the mu1-treated animals, substantially higher than phosphate-buffered saline-treated (57 +/- 9 mg/dl) or luciferase-treated (71 +/- 12 mg/dl) controls. Fast protein liquid chromatography analysis of mouse plasma showed that the intermediate density/low density lipoprotein fractions in the animals treated with the dominant negative mutant adenovirus were much higher than those in controls. We conclude that active APOBEC-1 functions as a dimer and its activity is inhibited by a dominant negative mutant. Furthermore, apoB mRNA editing determines the availability of apoB-100, which in turn limits the amount of intermediate density/low density lipoprotein that can be formed in mice. Liver-specific inhibition of apoB mRNA editing is an important component of any strategy to enhance the value of mice as a model for human lipoprotein metabolism.

APOBEC-1 Deaminase↗