Biomedical subjects

H M Myers

Publications and source records attributed to H M Myers.

At least 19 recordsLinked to original sources

PubMed1998

Identification of a gene encoding an acyl CoA:diacylglycerol acyltransferase, a key enzyme in triacylglycerol synthesis.

Triacylglycerols are quantitatively the most important storage form of energy for eukaryotic cells. Acyl CoA:diacylglycerol acyltransferase (DGAT, EC 2.3.1.20) catalyzes the terminal and only committed step in triacylglycerol synthesis, by using diacylglycerol and fatty acyl CoA as substrates. DGAT plays a fundamental role in the metabolism of cellular diacylglycerol and is important in higher eukaryotes for physiologic processes involving triacylglycerol metabolism such as intestinal fat absorption, lipoprotein assembly, adipose tissue formation, and lactation. DGAT is an integral membrane protein that has never been purified to homogeneity, nor has its gene been cloned. We identified an expressed sequence tag clone that shared regions of similarity with acyl CoA:cholesterol acyltransferase, an enzyme that also uses fatty acyl CoA as a substrate. Expression of a mouse cDNA for this expressed sequence tag in insect cells resulted in high levels of DGAT activity in cell membranes. No other acyltransferase activity was detected when a variety of substrates, including cholesterol, were used as acyl acceptors. The gene was expressed in all tissues examined; during differentiation of NIH 3T3-L1 cells into adipocytes, its expression increased markedly in parallel with increases in DGAT activity. The identification of this cDNA encoding a DGAT will greatly facilitate studies of cellular glycerolipid metabolism and its regulation.

3T3 Cells↗

PubMed1998

ACAT-2, a second mammalian acyl-CoA:cholesterol acyltransferase. Its cloning, expression, and characterization.

The synthesis of cholesterol esters by acyl-CoA:cholesterol acyltransferase (ACAT, EC 2.3.1.26) is an important component of cellular cholesterol homeostasis. Cholesterol ester formation also is hypothesized to be important in several physiologic processes, including intestinal cholesterol absorption, hepatic lipoprotein production, and macrophage foam cell formation in atherosclerotic lesions. Mouse tissue expression studies and the disruption of the mouse ACAT gene (Acact) have indicated that more than one ACAT exists in mammals and specifically that another enzyme is important in mouse liver and intestine. We now describe a second mammalian ACAT enzyme, designated ACAT-2, that is 44% identical to the first cloned mouse ACAT (henceforth designated ACAT-1). Infection of H5 insect cells with an ACAT-2 recombinant baculovirus resulted in expression of a approximately 46-kDa protein in cell membranes that was associated with high levels of cholesterol esterification activity. Both ACAT-1 and ACAT-2 also catalyzed the esterification of the 3beta-hydroxyl group of a variety of oxysterols. Cholesterol esterification activities for ACAT-1 and ACAT-2 exhibited different IC50 values when assayed in the presence of several ACAT-specific inhibitors, demonstrating that ACAT inhibitors can selectively target specific forms of ACAT. ACAT-2 was expressed primarily in mouse liver and small intestine, supporting the hypothesis that ACAT-2 contributes to cholesterol esterification in these tissues. The mouse ACAT-2 gene (Acact2) maps to chromosome 15 in a region containing a quantitative trait locus influencing plasma cholesterol levels. The identification and cloning of ACAT-2 will facilitate molecular approaches to understanding the role of ACAT enzymes in mammalian biology.

Amino Acid Sequence↗

PubMed1998

Adrenocortical lipid depletion gene (ald) in AKR mice is associated with an acyl-CoA:cholesterol acyltransferase (ACAT) mutation.

ald, a recessive allele in AKR inbred mice, is responsible for complete adrenocortical lipid depletion in postpubertal males, which appears to be androgen dependent. Two recent observations (adrenocortical lipid depletion in acyl-CoA:cholesterol acyltransferase-deficient (Acact-/-) mice and the mapping of Acact to a region of chromosome 1 containing the ald locus) prompted us to ask whether adrenocortical lipid depletion in AKR mice results from an Acact mutation. Refined genetic mapping of Acact and ald was consistent with colocalization of these loci. Crossing Acact-/- with AKR (ald/ald) mice yielded postpubertal male offspring characterized by adrenocortical lipid depletion, indicating that these loci are not complementational and are therefore allelic. Immunoblotting of preputial gland homogenates demonstrated that AKR mice had an ACAT protein with a lower molecular mass than other mouse strains. Analysis of Acact cDNA from AKR mice revealed a deletion of the first coding exon and two missense mutations. Despite these coding sequence differences, the ACAT protein from the ald allele catalyzed cholesterol esterification activity at levels similar to that of wild-type protein. We speculate that the adrenocortical lipid depletion resulting from the ald mutation is caused by an altered susceptibility of the mutant protein to modifying factors, such as androgen production at puberty, in an as yet undetermined manner.

Adrenal Cortex↗

PubMed1997

Tissue expression studies on the mouse acyl-CoA: cholesterol acyltransferase gene (Acact): findings supporting the existence of multiple cholesterol esterification enzymes in mice.

Cholesterol esterification is involved in the regulation of cellular cholesterol content and has been hypothesized to play a role in important physiologic processes including intestinal cholesterol absorption, hepatic lipoprotein production, and macrophage foam cell formation in atherosclerotic lesions. Although initial studies of the mouse acyl CoA:cholesterol acyltransferase gene (Acact) suggested that its gene product was responsible for cholesterol esterification in most tissues, we observed recently that Acact-/- mice have only tissue-specific reductions in cholesterol esterification. To better understand the role of Acact in cholesterol esterification, we used in situ hybridization and immunoblotting to perform tissue expression studies in wild-type mice. We found high levels of Acact expression in steroidogenic tissues, sebaceous glands, and atherosclerotic lesions, but not in the liver or the small intestine. These data support the hypothesis that multiple cholesterol esterification enzymes exist in mammals and that another enzyme is likely to be responsible for cholesterol esterification activity in mouse liver and intestine.

Adrenal Cortex↗

PubMed1996

Disruption of the acyl-CoA:cholesterol acyltransferase gene in mice: evidence suggesting multiple cholesterol esterification enzymes in mammals.

The microsomal enzyme acyl-CoA:cholesterol acyltransferase (ACAT; EC 2.3.1.26) catalyzes the esterification of cellular cholesterol with fatty acids to form cholesterol esters. ACAT activity is found in many tissues, including macrophages, the adrenal glands, and the liver. In macrophages, ACAT is thought to participate in foam cell formation and thereby to contribute to atherosclerotic lesion development. Disruption of the gene for ACAT (Acact) in mice resulted in decreased cholesterol esterification in ACAT-deficient fibroblasts and adrenal membranes, and markedly reduced cholesterol ester levels in adrenal glands and peritoneal macrophages; the latter finding will be useful in testing the role of ACAT and macrophage foam cell formation in atherosclerosis. In contrast, the livers of ACAT-deficient mice contained substantial amounts of cholesterol esters and exhibited no reduction in cholesterol esterification activity. These tissue-specific reductions in cholesterol esterification provide evidence that in mammals this process involves more than one form of esterification enzyme.

Adrenal Glands↗

PubMed1987

Structure-activity relationships (SAR) of hydroxyapatite-binding molecules.

Carboxyl-containing molecules can bind to HA with sufficient affinity to prevent the uptake of AZ by this mineral. Structural features that favor binding can be discerned. Isolated carboxyls are inactive; adjacent dicarboxylic functions are marginally active. Crowding of oxygens in the form of vicinal carboxyls or hydroxyls contributes the property of HA binding ability. This property exhibits gradation in magnitude and the variation can be correlated with structural features of the carboxyl-containing molecule. Phospho functions are generally more powerful contributors to HA binding property than are carboxyls.

Adsorption↗

PubMed1983

IR absorption spectrophotometric analysis of the complex formed by tetracycline and synthetic hydroxyapatite.

The infrared (IR) spectra of KBr pellet preparations of tetracycline (TC) complexes with hydroxyapatite (HA) indicated that the binding of the antibiotic to bone mineral can occur independently at each of two ligands. The shifts in the IR spectrum occur for the keto-enol ligand of rings B and C and for the tricarbonylmethane grouping of ring A. Analogs that lack one or the other of these groups are able to form complexes with HA in which the common portion resembles that of the parent molecule.

Chemical Phenomena↗

PubMed1983

Dose-response relationship between water fluoride levels and the category of questionable dental fluorosis.

There is a dose-response relationship between the prevalence of the questionable category of dental fluorosis as reported by various authors and the drinking water fluoride level. While the possibility that chance could have produced this trend cannot be conclusively ruled out, a distinct pattern of increasing prevalence with increasing water fluoride level can be discerned. Such a pattern is not compatible with the concept of a threshold level for the action of fluoride ion on the enamel organ.

Dose-Response Relationship, Drug↗

PubMed1982

Orientation of adsorbed alizarin red S on hydroxyapatite.

Adsorption isotherms of alizarin red S on hydroxyapatite were supplemented with additional data to provide a simple model of adsorption. The model treats the adsorbing surface as a mosaic of unit cell a-c faces which have an area of 65 A2 each. The adsorbate of the model has molecular dimensions consistent with a 1:1 relationship between adsorbate and adsorption site. By comparing slurries of hydroxyapatite which differed by a factor of 4 in surface area of the solid, it was found that the isotherm based on edge-on adsorption was best simulated by the model. A method for compensating for differing degrees of surface coverage is described.

Adsorption↗

PubMed1981