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M C Cheung

Publications and source records attributed to M C Cheung.

At least 55 records · Page 3Linked to original sources
PubMed1995

Structure, expression, and chromosomal localization of the type I human vasoactive intestinal peptide receptor gene.

Vasoactive intestinal peptide (VIP) and other members of the pituitary adenylyl cyclase-activating peptide (PACAP) and secretin neuroendocrine peptide family are recognized with specificity by related G protein-coupled receptors. We report here the cloning, characterization, and chromosomal location of the gene encoding the human type I VIP receptor (HVR1), also termed the type II PACAP receptor. The gene spans approximately 22 kb and is composed of 13 exons ranging from 42 to 1400 bp and 12 introns ranging from 0.3 to 6.1 kb. Primer extension analysis with poly(A)+ RNA from human HT29 colonic adenocarcinoma cells indicated that the transcription initiation site is located at position -110 upstream of the first nucleotide (+1) of the translation start codon, and 75 nt downstream of a consensus CCAAT-box motif. The G+C-rich 5' flanking region contains potential binding sites for several nuclear factors, including Sp1, AP2, ATF, interferon regulatory factor 1, NF-IL6, acute-phase response factor, and NF-kappa B. The HVR1 gene is expressed selectively in human tissues with a relative prevalence of lung > prostate > peripheral blood leukocytes, liver, brain, small intestine > colon, heart, spleen > placenta, kidney, thymus, testis. Fluorescence in situ hybridization localized the HVR1 gene to the short arm of human chromosome 3 (3p22), in a region associated with small-cell lung cancer.

Adenocarcinoma↗
PubMed1995

Chromosomal localization of the human NF-E2 family of bZIP transcription factors by fluorescence in situ hybridization.

A family of human genes encoding basic-leucine zipper (bZIP) transcription factors, p45-NF-E2, Nrf1 and Nrf2, have been isolated independently. Whereas the encoded proteins of the three genes share highly conserved regions distinct from other bZIP families such as Jun or Fos, remaining regions diverged considerably from each other. Chromosomal localization by fluorescence in situ hybridization demonstrates that these genes are non-syntenic. p45-NF-E2 mapped to chromosome 12q13.1-13.3, whereas Nrf1 and 2 mapped to 17q21.3 and 2q31, respectively. However, these three genes were probably derived from a single ancestor by chromosomal duplication as other genes that also map in these regions are related to one another.

Amino Acid Sequence↗
PubMed1994

The human sorbitol dehydrogenase gene: cDNA cloning, sequence determination, and mapping by fluorescence in situ hybridization.

The cDNA for human sorbitol dehydrogenase (SORD) has been cloned and sequenced. It translates into a peptide of 356 amino acid residues, one more than the sequence previously reported from peptide analysis. An extra alanine was found at the acetyl-blocked N-terminal, between positions 1 and 4. This matches the rat cDNA, which also has 356 amino acids, with an extra proline at position 3. Four other mis-matches were also observed, but these are all amino acid substitutions that occur outside proposed functionally important regions. Further work must be performed to determine whether these discrepancies represent polymorphic forms of the enzyme. The SORD gene was mapped by fluorescence in situ hybridization and found to occupy a single site on chromosome 15q15, indicating that it is a single-copy gene. This was confirmed by Southern blot hybridization. SORD is thought to be involved in the etiology of diabetic complications, and its deficiency has been linked to congenital cataracts. The cloned gene could be used as a probe to study the role of this enzyme in the pathogenesis of these diseases.

Amino Acid Sequence↗
PubMed1994

Effects of a diet restricted in saturated fatty acids and cholesterol on the composition of apolipoprotein A-I--containing lipoprotein particles in the fasting and fed states.

To test the hypothesis that diet may exert differential effects on apolipoprotein (apo) A-I--containing high-density-lipoprotein (HDL) particles with (w) and without (w/o) apo A-II [Lp(A-I w A-II) and Lp(A-I w/o A-II)], the effects of a diet low in saturated fatty acids and cholesterol [National Cholesterol Education Panel (NCEP) Step 2 diet] on these lipoproteins were determined in eight normolipidemic subjects, aged 53-74 y, in both the fasting and nonfasting states. Compared with a diet high in saturated fatty acid and cholesterol, consumption of an NCEP diet (6 mo) lowered fasting plasma, low-density-lipoprotein, and HDL cholesterol, and nonfasting plasma cholesterol, triglyceride, and HDL cholesterol (P < 0.05- < 0.005). Phospholipid in fasting and nonfasting Lp(A-I w A-II) and Lp(A-I w/o A-II) was lower during the NCEP diet (P < 0.05-0.001), but reductions in apo A-I or A-II were observed only in Lp(A-I w A-II). In contrast, differences in particle-size profiles were detected in Lp(A-I w/o A-II) but not in Lp(A-I w A-II). These observations provide further evidence that Lp(A-I w A-II) and Lp(A-I w/o A-II) are distinct metabolic entities.

Adult↗
PubMed1994

Gender effects on the distribution of the cholesteryl ester transfer protein in apolipoprotein A-I-defined lipoprotein subpopulations.

Two subpopulations of apolipoprotein A-I-containing lipoproteins, those containing only apoA-I (LpA-I) and those containing both apoA-I and apoA-II (LpA-I/A-II), were isolated by immunoaffinity chromatography of plasma from 44 subjects, comprising four groups (male or female, with or without hyperlipidemia). ApoA-I-defined particles (LpAs) were assessed for their content of cholesteryl ester transfer protein (CETP) and for their ability to act as substrates for CETP. Although plasma CETP concentration was similar in all groups, the plasma concentration of LpA-I-associated CETP was significantly higher in females than in males (1.56 +/- 0.11 versus 0.93 +/- 0.13 mg/l, P < 0.05). In females, the major fraction of CETP was found in LpA-I, whereas in normolipidemic males CETP was evenly distributed between LpA-I and LpA-I/A-II, and in hyperlipidemic males the majority of CETP was found in LpA-I/A-II. In all groups, the percentage of CETP in LpA-I was correlated with the concentration of apoA-I in LpA-I (r = 0.64, P < 0.001). Native gradient gel electrophoresis of isolated LpAs showed that CETP was broadly distributed within different sized particles. LpA-I and LpA-I/A-II showed similar efficiency of CETP-mediated cholesteryl ester exchange with LDL. In conclusion, even though LpA-I has a much higher apparent affinity for CETP than LpA-I/A-II, both LpAs can bind CETP and act as equivalent CETP substrates in vitro. Thus, in subjects with low levels of LpA-I (notably hyperlipidemic males), most of the plasma neutral lipid exchange will involve LpA-I/A-II.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1993

Effects of high-density lipoprotein particles containing apo A-I, with or without apo A-II, on intracellular cholesterol efflux.

Previous reports have shown a differential effect of high-density lipoprotein (HDL) particles which contain apolipoprotein (apo) A-I without apo A-II (Lp A-I) and particles containing both apo A-I and apo A-II (Lp A-I/A-II) on cholesterol efflux from the mouse adipocyte cell line Ob1771, with Lp A-I and Lp A-I/A-II being active and inactive cholesterol efflux promotors, respectively. The present study was conducted to examine the roles of these two populations of apo-specific HDL particles on reverse cholesterol transport from cholesterol-loaded human skin fibroblasts and bovine aortic endothelial cells. The ability of HDL particles to remove intracellular cholesterol was tested by measuring depletion of the substrate pool for acylCoA:cholesterol acyltransferase (ACAT) and efflux of newly synthesized cholesterol, while removal of plasma membrane cholesterol was assessed by measuring efflux of [3H]cholesterol from prelabeled cells. Lp A-I and Lp A-I/A-II isolated from HDL2, HDL3 or plasma by immunoaffinity techniques each decreased esterification of cholesterol by both fibroblasts and endothelial cells. A mixture of Lp A-I and Lp A-I/A-II isolated from HDL3 decreased cholesterol esterification by fibroblasts in an additive manner, thus demonstrating that Lp A-I/A-II did not inhibit Lp A-I-mediated cholesterol efflux. Both Lp A-I and Lp A-I/A-II promoted efflux of sterol newly synthesized by fibroblasts, and no significant differences were observed between the apo-specific particles. Apo-specific particles were also similarly effective at preventing the accumulation of LDL-derived cholesterol in cholesterol-depleted fibroblasts. Efflux of [3H]cholesterol from plasma membranes was stimulated to similar extents by Lp A-I and Lp A-I/A-II isolated from either HDL2, HDL3 or plasma. Thus, the apo-specific HDL particles Lp A-I and Lp A-I/A-II are both effective promoters of cholesterol efflux from fibroblasts and aortic endothelial cells.

Animals↗
PubMed1993

Distribution of lecithin-cholesterol acyltransferase in normolipidemic and dyslipidemic plasma.

Plasma lecithin-cholesterol acyltransferase levels and cholesterol esterification rates have been reported to be different between normolipidemic and dyslipidemic subjects. Since apolipoprotein A-I is the presumed primary physiological activator of lecithin-cholesterol acyltransferase, the distribution of the enzyme among A-I-containing lipoprotein particles and A-I-free plasma in normolipidemic and dyslipidemic subjects was examined. A-I-containing lipoprotein particles with and without apolipoprotein A-II were isolated from plasma by immunoaffinity chromatography, and the lecithin-cholesterol acyltransferase mass in these particles and in the A-I-free plasma was quantified by radioimmunoassay. The plasma lecithin-cholesterol acyltransferase concentration was comparable between normolipidemic men (5.9 +/- 1.1 micrograms/ml, n = 15) and women (5.8 +/- 1.1 micrograms/ml, n = 19), with 71 +/- 8% located in particles without apolipoprotein A-II, 17.6 +/- 6% in particles containing A-II, and 12 +/- 6% in the A-I-free plasma. In patients with elevated cholesterol (n = 12), triglyceride (n = 10), and with renal failure (n = 15) plasma levels of the enzyme were significantly higher (6.7 +/- 1.2, 6.9 +/- 1.3, and 6.6 +/- 1.3 micrograms/ml, respectively) (P < 0.05). In all three patient groups, a higher proportion of the enzyme (27 +/- 12%, 33 +/- 12%, and 19 +/- 9%) was not apo A-I associated. This phenomenon was also observed in plasma samples after incubation at 37 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Apolipoproteins A↗
PubMed1993

Effects of pravastatin on apolipoprotein-specific high density lipoprotein subpopulations and low density lipoprotein subclass phenotypes in patients with primary hypercholesterolemia.

UNLABELLED: The HMG-CoA reductase inhibitor class of cholesterol-lowering agents reduces very low density lipoproteins (VLDL) and low density lipoproteins (LDL) and slightly increases high density lipoproteins (HDL). However, the effects of these agents on subclasses within the LDL and HDL fractions are not well understood. We have employed an HMG-CoA reductase inhibitor, pravastatin, to determine if LDL subclass phenotypes, as determined by gradient gel electrophoresis, and HDL particles containing both apolipoprotein (apo) A-I and A-II, Lp(AI w AII), and those containing apo A-I but not A-II, Lp(AI w/o AII) are affected by pravastatin (10 mg daily). Twenty-four subjects with LDL-cholesterol (LDL-C) > 160 mg/dl, triglyceride (TG) < 350 mg/dl and no recent myocardial infarction or secondary causes of hypercholesterolemia were enrolled. Compared with an age- and sex-matched normolipidemic reference group (controls), the hypercholesterolemic subjects had reduced levels of Lp(AI w/o AII) and increased levels of Lp(AI w AII) at baseline. In addition, both of their HDL subpopulations had significantly more small (7.0-8.2 nm) particles (P < 0.02 and 0.0001) but significantly fewer large (9.2-11.2 nm) particles (P < 0.002 and 0.0001). Pravastatin induced statistically significant (P < 0.001) reductions in plasma total C (15%), LDL-C (18%), and apo B (16%). While apo A-I and A-II levels increased 5% (P < 0.001) and 6% (P < 0.05), respectively, concentration, composition, and size abnormalities in Lp(AI w AII) and Lp(AI w/o AII) persisted. Lp(a), apo E and cholesteryl ester transfer protein (CETP) levels also did not change. Although changes in LDL subclass phenotypes were observed, all changes involved the intermediate phenotype, and no significant changes in LDL peak particle diameter were seen in either group. Interrelationships between CETP, LDL subclass phenotypes and HDL subpopulations were also seen. CONCLUSIONS: Although pravastatin decreased plasma apo B and LDL lipid concentrations, no major changes were seen in LDL subclass phenotypes or HDL subpopulations even in the presence of abnormalities associated with arteriosclerosis. Similarly, CETP, which is believed to play a role in HDL and LDL particle size distribution, did not change with pravastatin treatment. Further research is needed to determine the pathophysiological basis of abnormal HDL and LDL subclasses in hypercholesterolemia and explore methods of rectifying the abnormalities.

Adult↗
PubMed1993

Lipoprotein heterogeneity in end-stage renal disease.

Fifteen patients on chronic maintenance hemodialysis without any additional known cause for dyslipidemia were arbitrarily divided into two groups based on fasting plasma triglyceride levels. The hypertriglyceridemic patients (plasma triglyceride levels above 170 mg/dl, N = 7) also had decreased high density lipoprotein (HDL) cholesterol levels and decreased post-heparin plasma lipoprotein lipase activity compared to the normotriglyceridemic patients (N = 8). All lipoprotein fractions collected by density gradient ultracentrifugation were triglyceride-enriched in the hypertriglyceridemic patients. Both groups of patients had elevated intermediate density lipoprotein levels, heterogeneity in the distribution of low density lipoproteins (LDL) and apoprotein-specific HDL subpopulations, and abnormalities in the size and composition of both LDL and HDL. The described alterations tended to be more marked in hypertriglyceridemic patients and are not detected by the usual laboratory evaluation of lipoproteins. These lipoprotein abnormalities have been shown to be atherogenic in patients without renal disease and are likely to contribute to the high prevalence of premature atherosclerosis in end-stage renal disease.

Adult↗
PubMed1993

Characterization of apolipoprotein A-I- and A-II-containing lipoproteins in a new case of high density lipoprotein deficiency resembling Tangier disease and their effects on intracellular cholesterol efflux.

A 48-yr-old Caucasian female of central European origin (subject IM) with low plasma cholesterol and normal plasma triglyceride (TG) had extremely low apo A-I (6 mg/dl), A-II (5 mg/dl), and HDL cholesterol (2 mg/dl) levels. She had most of the clinical symptoms typically associated with Tangier disease, including early corneal opacities, yellow-streaked tonsils, hepatomegaly, and variable degrees of peripheral neuropathy, but had no splenomegaly. She had a myocardial infarction at age 46. Since HDL are postulated to be involved in the transport of excess cholesterol from peripheral tissues to the liver for degradation, and the ability of an HDL particle to promote cellular cholesterol efflux appears to be related to its density, size, and apo A-I and A-II contents, we isolated and characterized the HDL particles of this patient and all her first degree relatives (mother, a brother, and two children). The plasma A-I, A-II, and HDL cholesterol levels of all five relatives were either normal or high. Using anti-A-I and anti-A-II immunosorbents, we found three populations of particles in IM: one contained both apo A-I and A-II, Lp(AI w AII); one contained apo A-I but no A-II, Lp(AI w/o AII); and the third (an unusual one) contained apo A-II but no A-I, Lp(AII). Two-thirds of her plasma A-I and A-II existed in separate HDL particles, i.e., in Lp(AI w/o AII) and Lp(AII), respectively. Only Lp(AI w AII) and Lp(AI w/o AII) were present in the plasma of the relatives. All three populations of the patient's HDL particles had a normal core/surface lipid ratio, but the cores were enriched with TG. The apo A-I-containing particles, however, were considerably smaller and contained much less lipid than Lp(AII). Despite these unusual physicochemical characteristics, the apo A-I-containing particles and Lp(AII) were effective suppressors of intracellular cholesterol esterification in cholesterol-loaded human skin fibroblast. The patient's plasma apo D and lecithin cholesterol acyltransferase levels were reduced, with an increased proportion located in non-HDL plasma fractions. These findings are discussed in light of Tangier disease and other known HDL-deficiency cases, and the role of HDL in the maintenance of cell cholesterol homeostasis.

Adolescent↗
PubMed1992

Protein transfer between A-I-containing lipoprotein subpopulations: evidence of non-transferable A-I in particles with A-II.

Transfer of apolipoproteins (apo) between the two subpopulations of apo A-I-containing lipoproteins in human plasma: those with A-II [Lp(AI w AII)] and those without [Lp(AI w/o AII)], were studied by observing the transfer of 125I-apo from a radiolabeled subpopulation to an unlabeled subpopulation in vitro. When Lp(AI w AII) was directly radioiodinated, 50.3 +/- 7.4 and 19.5 +/- 7.7% (n = 6) of the total radioactivity was associated with A-I and A-II, respectively. In radioiodinated Lp(AI w/o AII), 71.5 +/- 6.8% (n = 6) of the total radioactivity was A-I-associated. Time-course studies showed that, while some radiolabeled proteins transferred from one population of HDL particles to another within minutes, at least several hours were necessary for transfer to approach equilibrium. Incubation of the subpopulations at equal A-I mass resulted in the transfer of 51.8 +/- 5.0% (n = 4) of total radioactivity from [125I]Lp(AI w/o AII) to Lp(AI w AII) at 37 degrees C in 24 h. The specific activity (S.A.) of A-I in the two subpopulations after incubation was nearly identical. Under similar incubation conditions, only 13.4 +/- 4.6% (n = 4) of total radioactivity was transferred from [125I]Lp(AI w AII) to Lp(AI w/o AII). The S.A. of A-I after incubation was 2-fold higher in particles with A-II than in particles without A-II. These phenomena were also observed with iodinated high-density lipoproteins (HDL) isolated by ultracentrifugation and subsequently subfractionated by immunoaffinity chromatography. However, when Lp(AI w AII) radiolabeled by in vitro exchange with free [125I]A-I was incubated with unlabeled Lp(AI w/o AII), the S.A. of A-I in particles with and without A-II differed by only 18% after incubation. These data are consistent with the following: (1) in both populations of HDL particles, some radiolabeled proteins transferred rapidly (minutes or less), while others transferred slowly (hours); (2) when Lp(AI w AII) and Lp(AI w/o AII) were directly iodinated, all labeled A-I in particles without A-II were transferable, but some labeled AI in particles with A-II were not; (3) when Lp(AI w AII) were labeled by in vitro exchange with [125I]A-I, considerably more labeled A-I were transferable. These observations suggest the presence of non-transferable A-I in Lp(AI w AII).

Adult↗
PubMed1992

Interaction between high-density lipoprotein subpopulations in apo B-free and abetalipoproteinemic plasma.

Two populations of high-density lipoprotein (HDL) particles exist in human plasma. Both contain apolipoprotein (apo) A-I, but only one contains apo A-II: Lp(AI w AII) and Lp(AI w/o AII). To study the extent of interaction between these particles, apo B-free plasma prepared by the selective removal of apo B-containing lipoproteins (LpB) from the plasma of three normolipidemic (NL) subjects and whole plasma from two patients with abetalipoproteinemia (ABL) were incubated at 37 degrees C for 24 h. Apo B-free plasma samples were used to avoid lipid-exchange between HDL and LpB. Lp(AI w AII) and Lp(AI w/o AII) were isolated from each apo B-free plasma sample before and after incubation and their protein and lipid contents quantified. Before incubation, ABL plasma had reduced levels of Lp(AI w AII) and Lp(AI w/o AII), (40% and 70% of normals, respectively). Compared to the HDL of apo B-free NL plasma, ABL HDL had higher relative contents of free cholesterol, phospholipid and total lipid, and contained more particles with apparent hydrated Stokes diameter in the 9.2-17.0 nm region. These differences were particularly pronounced in particles without apo A-II. Despite their differences, the total cholesterol contents of Lp(AI w AII) increased, while that of Lp(AI w/o AII) decreased in all five plasma samples and the amount of apo A-I in Lp(AI w AII) increased by 6-8 mg/dl in four during the incubation. These compositional changes were accompanied by a relative reduction of particles in the 7.0-8.2 nm Stokes diameter size region and an increase of particles in the 9.2-11.2 nm region. These data are consistent with intravascular modulation between HDL particles with and without apo A-II. The observed increase in apo A-II-associated cholesterol and apo A-I, could involve either the transfer of cholesterol and apo A-I from particles without apo A-II to those with A-II, or the transfer of apo A-II from Lp(AI w AII) to Lp(AI w/o AII). The exact mechanism and direction of the transfer remain to be determined.

Apolipoprotein A-I↗
PubMed1991

A mutation in the human apolipoprotein A-I gene. Dominant effect on the level and characteristics of plasma high density lipoproteins.

Epidemiologic and genetic data suggest an inverse relationship between plasma high density lipoprotein (HDL) cholesterol and the incidence of premature coronary artery disease. Some of the defects leading to low levels of HDL may be a consequence of mutations in the genes coding for HDL apolipoproteins A-I and A-II or for enzymes that modify these particles. A proband with plasma apoA-I and HDL cholesterol that are below 15% of normal levels and with marked bilateral arcus senilis was shown to be heterozygous for a 45-base pair deletion in exon four of the apoA-I gene. This most likely represents a de novo mutation since neither parent carries the mutant allele. The protein product of this allele is predicted to be missing 15 (Glu146-Arg160) of the 22 amino acids comprising the third amphipathic helical domain. The HDL of the proband and his family were studied. Using anti-A-I and anti-A-II immunosorbents we found three populations of HDL particles in the proband. One contained both apoA-I and A-II, Lp(A-I w A-II); one contained apoA-I but no A-II, Lp(A-I w/o A-II); and the third (an unusual one) contained apoA-II but no A-I. Only Lp(A-I w A-II) and (A-I w/o A-II) were present in the plasma of the proband's parents and brother. Analysis of the HDL particles of the proband by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed two protein bands with a molecular mass differing by 6% in the vicinity of 28 kDa whereas the HDL particles of the family members exhibited only a single apoA-I band. The largely dominant effect of this mutant allele (designated apoA-ISeattle) on HDL levels suggests that HDL particles containing any number of mutant apoA-I polypeptides are catabolized rapidly.

Amino Acid Sequence↗
PubMed1991

Altered particle size distribution of apolipoprotein A-I-containing lipoproteins in subjects with coronary artery disease.

Plasma high density lipoproteins (HDL) can be separated into two subpopulations of apolipoprotein A-I-containing particles: those that also contain apoA-II [Lp(AI w AII)] and those that do not [Lp(AI w/o AII)]. These particles were isolated by immunoaffinity chromatography from 17 men (9 normolipidemic (NL), 8 hyperlipidemic (HL) with symptomatic coronary artery disease (CAD), from 17 NL men without any symptoms of CAD (healthy controls), and from 10 NL men with entirely normal coronary arteriograms (CAD-free controls). The distributions of particle size in these two subpopulations were determined by gradient gel electrophoresis and densitometric scanning. Approximately half of the Lp(AI w AII) particles in all subjects were distributed in the 8.2-9.2 nm interval. For patients with CAD, a greater fraction of the particles were small, in the 7.0-8.2 nm interval [33% in CAD vs. 26% in CAD-free controls (P less than 0.01) and 19% in healthy controls (P less than 0.0001)], and a smaller fraction of the particles were in the 9.2-11.2 nm interval (14% in CAD vs. 24% in CAD-free control (P less than 0.002) and healthy control groups (P less than 0.001). The Lp(AI w/o AII) of both control groups were primarily composed of two discrete subpopulations in the 8.2-9.2 nm and the 9.2-11.2 nm intervals. In CAD patients there were fewer particles in the 9.2-11.2 nm size interval (23% in CAD vs. 33% in CAD-free controls (P less than 0.005) and 36% in healthy controls (P less than 0.0001), and more particles in the smallest 7.0-8.2 nm size interval (32% in CAD vs. 23% in CAD-free controls (P less than 0.01) and 18% in healthy controls (P less than 0.001]. Thus, the spectrum of HDL particle sizes in patients with CAD tends to be shifted toward the smaller particle when compared with the two control groups. This was observed in both NL and HL patients with HDL cholesterol (CH) values in the normal range. As a group, CAD patients had lower HDL (42 +/- 7 mg/dl) and HDL2 (6 +/- 4 mg/dl) CH than healthy (HDL: 49 +/- 7, HDL2: 12 +/- 6 mg/dl) and CAD-free (HDL: 51 +/- 9, HDL2: 12 +/- 6 mg/dl) controls. When controls and patients were compared for their frequencies of abnormal HDL CH levels and particle sizes, abnormalities in HDL and HDL2 CH levels were not significantly more frequent (twofold) among CAD patients than among controls.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1990

Apolipoprotein AIMilano. Partial lecithin:cholesterol acyltransferase deficiency due to low levels of a functional enzyme.

The cholesterol esterification process was analyzed in 19 carriers of the apolipoprotein AIMilano (AIM) variant and in 19 age-sex matched controls by measuring lecithin:cholesterol acyltransferase (LCAT) mass, activity (i.e., cholesterol esterification with a standard proteoliposome substrate) and cholesterol esterification rate (i.e., cholesterol esterification in the presence of the endogenous substrate). The AIM subjects had lower LCAT mass (3.30 +/- 0.85 micrograms/ml), activity (71.1 +/- 36.4 nmol/ml per h) and cholesterol esterification rate (23.6 +/- 12.5 nmol/ml per h) compared to controls (5.22 +/- 0.74 micrograms/ml, 121.6 +/- 54.6 nmol/ml per h and 53.6 +/- 29.9 nmol/ml per h, respectively). The specific LCAT activity, i.e., LCAT activity per microgram of LCAT, was similar in the two groups, indicating that the LCAT protein in the AIM carriers is structurally and functionally normal. However, the specific cholesterol esterification rate was 23% lower in the AIM subjects (8.03 +/- 6.01 nmol/h per microgram) compared to controls (10.49 +/- 5.86 nmol/h per microgram; P less than 0.05). The capacity of HDL3, purified from both AIM and control plasma, to act as substrates for cholesterol esterification was similar, thus suggesting that other mechanism(s) may be in play. Carriers with a relative abundance of abnormal, small HDL3b particles had the most altered cholesterol esterification pattern. Upon evaluating all AIM subjects, a complex relationship between HDL structure, plasma lipid-lipoprotein levels and cholesterol esterification emerged, making the AIMilano condition a unique model for the study of the mechanisms regulating the cholesterol esterification-transfer process in man.

Adolescent↗
PubMed1990

cDNA sequence for human erythrocyte ankyrin.

The cDNA for human erythrocyte ankyrin has been isolated from a series of overlapping clones obtained from a reticulocyte cDNA library. The composite cDNA sequence has a large open reading frame of 5636 base pairs (bp) with the complete coding sequence for a polypeptide of 1879 amino acids with a predicted molecular mass of 206 kDa. The derived amino acid sequence contained 194 residues that were identical to those obtained by direct amino acid sequencing of 11 ankyrin proteolytic peptides. The primary sequence contained 23 highly homologous repeat units of 33 amino acids within the 90-kDa band 3 binding domain. Two cDNA clones showed evidence of apparent mRNA processing, resulting in the deletions of 486 bp and 135 bp, respectively. The 486-bp deletion resulted in the removal of a 16-kDa highly acidic peptide, and the smaller deletion had the effect of altering the COOH terminus of the molecule. Radiolabeled ankyrin cDNAs recognized two erythroid message sizes by RNA blot analysis, one of which was predominantly associated with early erythroid cell types. An ankyrin message was also observed in RNA from the human cerebellum by the same method. The ankyrin gene is assigned to chromosome 8 using genomic DNA from a panel of sorted human chromosomes.

Amino Acid Sequence↗
PubMed1989

Secretion of cholesteryl ester transfer protein-lipoprotein complexes by human HepG2 hepatocytes.

We have employed immunoaffinity chromatography to characterize the distribution of cholesteryl ester transfer activity in particles secreted by HepG2 hepatocytes. HepG2-secreted cholesteryl ester transfer activity is associated with apoprotein (apo) A-I (58%) as well as apo A-II (55%), and is not associated with apo B or E. In contrast, our previous studies have shown that most (88%) cholesteryl ester transfer activity in human plasma is associated with apo A-I whereas very little (7%) is associated with apo A-II. Thus, the distribution of cholesteryl ester transfer activity in plasma particles likely reflects active remodeling of nascent particles in the plasma compartment. Further data suggested that HepG2 cells secrete a lipid transfer inhibitor activity which is associated with apo E-containing lipoprotein particles. This inhibitory activity is heat labile.

Apolipoprotein A-I↗