Biomedical subjects

S S Deeb

Publications and source records attributed to S S Deeb.

At least 55 records · Page 3Linked to original sources

PubMed1997

The human hexokinase II gene promoter: functional characterization and detection of variants among patients with NIDDM.

Hexokinase II (HKII) plays an important role in facilitating glucose uptake by skeletal muscle, heart, and adipose tissue in response to insulin. We have cloned and sequenced the proximal promoter region of the human HKII gene, determined the transcription start sites and screened the 2.0 kb of the proximal 5' flanking region for variants in non-insulin-dependent diabetic patients and control subjects. We found three variants in this region, one in the 5' untranslated region (G-->C at +217) and two in the promoter region (T-->G at -1043 and G-->A at -1159). The allele frequencies of these variants did not differ between the diabetic and control subjects and these variants are not associated with insulin resistance. Various segments of the human HKII promoter were tested for driving expression of the luciferase reporter gene. The proximal 500 bp and 400 bp of the promoter were sufficient to drive maximal activity in adipocyte (3T3F442A) and myocyte (C2C12F3) cell lines, respectively. This region of the promoter is GC-rich and contains eight consensus binding sites for the transcription factor Sp-1, five for AP-2, two putative response elements for each of insulin and cyclic AMP. The proximal 175 bases of the promoter retained only 7-15% of maximal activity. Sequence elements located between positions -304 and -215 accounted for approximately 80% of the basal HKII promoter. In addition, the region between -215 and -184 contains a negative regulatory element for expression in 3T3F442A but not in C2C12F3 cells.

Adipocytes↗

PubMed1997

Rayleigh match ranges of red/green color-deficient observers: psychophysical and molecular studies.

Large-field Rayleigh match ranges were measured in 27 red/green color-deficient male observers, using bright, temporally alternating, 3-9 deg annular test fields. The observers' X-linked opsin gene arrays were characterized by molecular genetic techniques, and used to infer the absorption maxima of each observer's L and/or M cone photopigment(s). Measured match ranges decreased rapidly as the inferred separation in pigment absorption maxima increased from 0 to 2-3 nm, and varied irregularly thereafter. Following He & Shevell [(1995) Vision Research, 35, 2579-2588] predicted match ranges were calculated for various pigment separations and assumed values of pigment optical density. The predicted variations in match range encompassed the measured match ranges of most (but not all) of the color-deficient observers. The calculations also showed that differences in pigment optical density, in two cone types containing the same pigment, are sufficient to allow a moderate degree of chromatic discrimination. Such models thus provide a possible account of the fact that some color-deficient observers, with only a single X-linked opsin gene, can make red/green chromatic discriminations.

Adolescent↗

PubMed1997

Visual pigment gene structure and expression in human retinae.

We determined the genotypes of the X-chromosome-linked red/green color vision genes by a novel PCR/SSCP-based method and assessed expression by mRNA analysis in retinae of 51 unselected post mortem eye specimens from Caucasian males of unknown color vision status. All individuals had a single red (long-wave) pigment gene and one or more (an average of two) green (middle-wave) pigment genes. Four males had 5'green-red3' hybrid genes in addition to normal red and green pigment genes. These findings are consistent with earlier studies on human visual pigment gene structure using Southern blotting and with a recent study using pulsed-field electrophoresis. We interpret claims of much larger numbers of red, green and green-red hybrid genes to be technical artifacts. The ratio of expressed red to green pigment retinal mRNA varied widely (1-10 with a mode of 4) and was not correlated with that of red to green pigment genes. In one individual with a green-red hybrid gene in addition to normal red and green pigment genes, the normal red pigment gene and the hybrid gene were both expressed, but the normal green gene was not. This person presumably had deuteranomalous color vision. Two with green-red hybrid genes expressed the normal red and green pigment genes, but not the hybrid genes. These two individuals presumably had normal color vision. We interpret the failure to express their green-red hybrid genes to be caused by their location at a more distal position in the visual pigment gene array.

Color Vision Defects↗

PubMed1996

Two novel apolipoprotein A-IV variants in individuals with familial combined hyperlipidemia and diminished levels of lipoprotein lipase activity.

It has been suggested that apo A-IV may play a role in modulating the activation of lipoprotein lipase (LPL) by apo C-II (Goldberg et al., 1990). Therefore, the role of genetic variation at the apolipoprotein A-IV locus in familial combined hyperlipidemia (FCHL) was investigated. A subset of FCHL patients with half the level of plasma LPL activity was screened by single-strand conformation polymorphism (SSCP) for variants in the apolipoprotein A-IV gene. Two of 20 such individuals were found to be heterozygous carriers of previously undescribed amino acid substitutions: S158L and R 244Q substitutions, designated A-IV-Seattle-1 and A-IV-Seattle-2, respectively. These substitutions were not detected among 20 other FCHL patients with normal LPL levels and among 97 unselected medical students. The finding of these two alleles among only the 20 patients with FCHL with reduced levels of LPL suggests an association with this phenotype. It is hypothesized that these two alleles may contribute, along with alleles of other genes or environmental factors, to the development of FCHL. A third previously undescribed variant (A141S) was observed in four (two homozygotes and two heterozygotes) of the 97 medical students.

Amino Acid Sequence↗

PubMed1996

Sequence and evolutionary history of the length polymorphism in intron 1 of the human red photopigment gene.

The length of intron 1 of the red pigment gene is dimorphic among Africans but not among Caucasians or Asians. This dimorphism was found to result from the presence or absence of a block of 1,284 bp comprised of three Alu elements and 328 bp of intervening unique-sequence DNA. This additional sequence in the "long" intron 1 of the red pigment gene was shown to have inserted into a fourth and older Alu element present in the "short" from of intron 1. Furthermore, the size and sequence of the "short" intron 1 of the red pigment gene is equivalent to that of the adjacent green pigment gene. The block containing the three Alu elements was not found in intron 1 of the red or green pigment genes of Old World monkeys and orangutans but was present in intron 1 of both the green and red pigment genes of gorillas and chimpanzees. The nucleotide sequence of this block in Old World primates and the estimated ages of the three elements suggest that their insertion occurred sequentially in the Old World monkey lineage prior to duplication of the ancestral X-chromosome-linked pigment gene. After gene duplication, deletion of the entire block containing the three Alu elements from one of the genes created the "short" intron variant. Unequal recombination between the adjacent and highly homologous red and green pigment genes may have resulted in the formation of the "short" intron variant of the other gene.

Animals↗

PubMed1996

Molecular genetics of human color vision.

The significant advances in our understanding of color vision has been due to the convergence of information from behavioral and molecular genetic analyses. The molecular biology of the visual pigments; molecular genetic basis of variation in normal and abnormal color vision, and regulation of the genes at the LWS-MWS pigment gene locus are discussed.

Animals↗

PubMed1996

A variation at position -30 of the beta-cell glucokinase gene promoter is associated with reduced beta-cell function in middle-aged Japanese-American men.

We sought to determine whether a G -> A variant at position -30 of the beta-cell promoter of the glucokinase (GCK) gene observed to be present more frequently in Japanese-American men with impaired glucose tolerance (IGT) than in Japanese-American men with normal glucose tolerance (NGT) is associated with impaired beta-cell function. We studied 125 unrelated Japanese-American men (aged 46-74 years; mean 61 +/- 0.5) who were nondiabetic by a 75-g oral glucose tolerance test (OGTT) (65 had NGT and 60 had IGT). The presence of the -30 beta-cell GCK gene promoter variant was determined by single-strand conformation polymorphism analysis. Beta-cell function was assessed using the ratio of the incremental response in immunoreactive insulin (IRI) to that of glucose during the first 30 min of the OGTT (delta IRI[30 min-0 min]/delta glucose[30 min-0 min]) performed at baseline and at 5 years of follow-up. Beta-cell function adjusted for basal IRI ([delta IRI[30 min-0 min]/delta glucose[30 min-0 min]]/basal IRI; the relative insulin response) was also evaluated. At baseline, the -30 beta-cell GCK gene promoter variant was present in 15.4% of subjects with NGT vs. 38.3% of subjects with IGT (P < 0.01). Fasting IRI did not differ between groups. At baseline, delta IRI[30 min-0 min]/delta glucose[30 min-0 min] was significantly lower in subjects with the promoter variant (57 x 10(-9) [35 x 10(-9) to 95 x 10(-9)] vs. 77 x 10(-9) [55 x 10(-9) to 128 x 10(-9)]; median [interquartile range]; P < 0.01) as was the relative insulin response (0.97 [0.70-1.24] vs. 1.37 [0.95-2.03]l/mmol; P < 0.0005). Similarly, at 5 years of follow-up, delta IRI[30 min-0 min]/delta glucose[30 min-0 min] and the relative insulin response were significantly reduced in the group with the variant. In the subgroups of subjects with IGT at baseline, IGT at 5 years, and NGT at 5 years, the relative insulin response was significantly lower in those with the variant. We conclude that the -30 beta-cell GCK gene promoter variant is associated with reduced beta-cell function in middle-aged Japanese-American men and may contribute to the high risk of abnormal glucose tolerance in this population.

Aged↗

PubMed1996

High levels of circulating beta-amyloid peptide do not cause cerebral beta-amyloidosis in transgenic mice.

We have established transgenic mice that constitutively overproduce the signal sequence and the 99-amino-acid carboxyl-terminal region of the human beta-amyloid precursor protein. The transgenic mice strongly expressed the transgene in multiple tissues under the control of a cytomegalovirus enhancer/chick beta-actin promoter. There were exceptionally high levels of beta-amyloid peptides in the plasma (approximately 17 times or more compared with the human plasma level). Although some transgenic mice from one founder line developed amyloidosis in the intestine, no neuropathology was found in transgenic mice up to age 29 months. Given the absence of cerebral beta-amyloidosis despite extremely high levels of circulating beta-amyloid peptides in the transgenic mice, the results suggest that local cerebral metabolism of beta-amyloid precursor protein may play a predominant role in cerebral beta-amyloidosis in transgenic mice. Such transgenic mice may be useful for the investigation of the etiology of the disease and for the establishment of therapeutic strategies.

Amyloid beta-Peptides↗

PubMed1996

Regulatory mutations in the human lipoprotein lipase gene in patients with familial combined hyperlipidemia and coronary artery disease.

We previously reported a compound heterozygote [T(-39)C/T(-93)G] in the human lipoprotein lipase (LPL) gene promoter in one out of 19 patients with familial combined hyperlipidemia (FCHL) and reduced post-heparin plasma LPL levels. The T(-39)C substitution resulted in 85% decrease in LPL promoter activity. Further screening of Caucasian patients with FCHL, coronary artery disease (CAD), and of unselected Caucasian subjects revealed four additional LPL promoter variants. Among the same 19 FCHL patients with reduced LPL levels, we found one heterozygote for a G(-53)C substitution. Among 115 CAD patients, we found five heterozygotes and one homozygote for the T(-93)G substitution and one heterozygote for a CC insertion between +13 and +19 of the 5' untranslated region. In a group of 183 unselected subjects, three heterozygotes with the T(-93)G substitution were found. The G(-53)C substitution led to approximately 70-75% decrease in promoter activity as assayed by transient transfections of THP-1 (macrophage-like) and C2C12 (myotube-like) cells. The T(-93)G substitution resulted in reduction of promoter activity by approximately 40-50%. The CC insertion between +13 and +19 caused a decrease in promoter activity by 20% in THP-1 and 50% in C2C12. Substitutions at -79 and -95, which had no effect on promoter function, were also discovered in the population samples studied. The finding of two promoter mutations (-39 and -53) among 19 FCHL patients with diminished LPL, but not among the other groups of subjects, suggests a potential role of regulatory mutations of the LPL gene in the development of dyslipidemia in FCHL.

Coronary Disease↗

PubMed1995

The mutant Asn291-->Ser human lipoprotein lipase is associated with reduced catalytic activity and does not influence binding to heparin.

Lipoprotein lipase (LPL) plays a central role in triglyceride metabolism, regulating the catabolism of triglyceride-rich lipoprotein particles. LPL performs its hydrolytic action attached to heparan sulfate proteoglycans at the luminal surface of capillary endothelial cells. We have assessed the effect of the Asn291-->Ser (N291S) substitution found in LPL gene from a human hyperlipemic patient. Our results showed that both the wild-type (WT) and N291S hLPL expressed in COS1 cells were secreted to the extracellular medium, and presented similar intracellular distribution patterns. Furthermore, heparin-Sepharose affinity chromatography assays revealed normal heparin affinity of the N291S hLPL. In addition, both the mutant and the WT protein bound to the surface of human fibroblasts and untransfected COS1 cells. Interestingly, diminished LPL specific activity was observed in the extracellular medium from mutant expressing cells. Therefore the lack of normal LPL activity in patients harbouring such a mutation could be the cause of their hyperlipemic disorder.

Base Sequence↗

PubMed1995

A mutation in the promoter of the lipoprotein lipase (LPL) gene in a patient with familial combined hyperlipidemia and low LPL activity.

We have identified a naturally occurring mutation in the promoter of the lipoprotein lipase (LPL) gene. One of 20 patients with familial combined hyperlipidemia (FCHL) and reduced levels of postheparin plasma LPL activity was found to be a heterozygote carrier of this mutation. The mutation, a T-->C substitution at nt -39, occurred in the binding site of the transcription factor Oct-1. As a result, the transcriptional activity of the mutant promoter was < 15% of wild type, as determined by transfection studies in the human macrophage-like cell line THP-1. This decrease in promoter activity was observed in undifferentiated as well as in phorbol ester-differentiated THP-1 cells. Furthermore, the inductive effect of elevating the levels of intracellular cAMP was equally reduced. This mutation was not present among 20 FCHL patients with normal plasma LPL levels nor has it been reported among individuals with familial LPL deficiency. Thus, heterozygosity for LPL promoter mutations may be one of several factors that contribute to the etiology of FCHL.

Base Sequence↗

PubMed1995

Organization of human phospholipid transfer protein gene.

We have determined the exon/intron organization of the human phospholipid transfer protein gene. The gene, which spans approximately 13.3 kilobases, is comprised of 16 exons. The organization of the phospholipid transfer protein gene strikingly resembles that encoding another plasma lipid transfer protein, the human cholesterol ester transfer protein. The exon-intron junctions in these two genes are highly conserved, with eight out of fifteen junctions interrupting the same codons, while the remaining junctions lie within 5 residues of each other. The similarity in gene structure and homology in coding sequences suggests that these two genes most likely evolved from a common ancestral gene.

Amino Acid Sequence↗

PubMed1995

Molecular patterns and sequence polymorphisms in the red and green visual pigment genes of Japanese men.

The red-green pigment gene arrays of 203 (101 from a previous study and 102 from this study) randomly selected men of Japanese ancestry from the Seattle area were screened for the abnormal molecular patterns (deletions and red/green or green/red hybrid genes) that are usually associated with defective color vision. Such molecular patterns were found in approximately 5% of these individuals, which is equivalent to the frequency of phenotypic color vision defects in Japanese males in Japan. Thus, the majority of hybrid genes carried by Japanese males appear to be associated with defective color vision. In contrast, the frequency of hybrid genes among Caucasians and African-Americans is approximately two and five times the frequency of color vision defects in these two ethnic groups, respectively. The coding sequences of 50 males of Japanese ancestry were determined. All the polymorphisms in the red and green pigment genes that were detected in the Japanese sample had been observed in Caucasians and African-Americans. The same polymorphisms of the red pigment gene were present in the green pigment gene, suggesting that gene conversion contributes to sequence homogenization between these pigment genes. As is the case for Caucasians, exon 3 of the red and green pigment genes was observed to be a hot spot for recombination and gene conversion. Fewer polymorphic sites (4 vs 11) and haplotypes (5 vs 14) of the red pigment gene were observed in Japanese than in Caucasians. The Japanese population was more uniform with respect to the red pigment gene, with 70% of individuals having the same haplotype, as compared with the 43% for the Caucasian population. This difference was largely due to the lower degree of polymorphism at position 180 of the red pigment gene in Japanese (84% Ser and 16% Ala vs 62% Ser and 38% Ala.) The number of polymorphic sites and haplotypes in the green pigment gene was similar in the two populations. Nevertheless, the Japanese population was more uniform with 65% having the same haplotype. The difference in the frequency of alleles at position 283 accounted for this difference in haplotype distribution.

Amino Acid Sequence↗

PubMed1995

Polymorphisms of the human hexokinase II gene: lack of association with NIDDM and insulin resistance.

Skeletal muscle and adipose tissue hexokinase II is a promising candidate gene for non-insulin-dependent diabetes mellitus (NIDDM) and insulin resistance. Therefore, we investigated the association of alleles at four polymorphic loci in this gene with NIDDM and insulin resistance in 110 Finnish diabetic patients with NIDDM and in 97 Finnish control subjects with normal glucose tolerance and a negative family history of diabetes. The four polymorphic nucleotide substitutions (silent) in the coding region of the hexokinase II gene were: GAC 251 GAT (exon 7), AAC 692 AAT and CCG 736 CCC (exon 15), and CTG 766 CTA (exon 16). Allele frequencies of each of these polymorphisms did not differ between patients with NIDDM and control subjects. In addition, subjects who were homozygous for the less frequent allele of each of the four polymorphisms had a similar degree of insulin resistance, as determined by the euglycaemic clamp technique, as did the subjects who were homozygous for the common allele in both control subjects and in patients with NIDDM. In conclusion, polymorphisms in the hexokinase II gene are not associated with the risk of NIDDM or insulin resistance in the Finnish population.

Adipose Tissue↗

PubMed1995

Amino acid substitutions in hexokinase II among patients with NIDDM.

Hexokinase (HK) II plays an important role in intracellular glucose metabolism by catalyzing the conversion of glucose to glucose-6-phosphate. HKII is considered to be a promising candidate gene for non-insulin-dependent diabetes mellitus (NIDDM) and insulin resistance. Therefore, we investigated the frequency of variants in the coding region of the HKII gene in patients with NIDDM. Initial screening included a population-based sample of 40 Finnish patients with typical NIDDM, and subsequent screening included an additional 72 patients with NIDDM. By applying single-strand conformation polymorphism analysis and direct sequencing, the following amino acid substitutions were found among the 112 NIDDM patients: Ala314Val in one patient (0.9%), Arg353Cys in three patients (2.7%), and Arg775Gln substitution in three patients (2.7%). We also screened 97 subjects with completely normal glucose tolerance and a negative family history of diabetes for these mutations. The Ala314Val and the Arg353Cys substitutions were not found in control subjects, but the Arg775Gln substitution was found in two (2.1%) control subjects. None of these mutations were located close to the glucose- and ATP-binding sites of HKII. We conclude that mutations of the HKII gene are not a major etiological factor for NIDDM in the Finnish population.

Amino Acid Sequence↗

PubMed1995

Glucokinase gene variants in subjects with late-onset NIDDM and impaired glucose tolerance.

OBJECTIVE: To investigate the frequency of variants of the glucokinase (GCK) gene in subjects with late-onset non-insulin-dependent diabetes mellitus (NIDDM) and in subjects with late-onset impaired glucose tolerance (IGT). RESEARCH DESIGN AND METHODS: The study population included 36 Finnish patients with late-onset NIDDM who were treated with diet for > 8 years or who were newly diagnosed and 40 subjects with late-onset IGT who had low or normal insulin levels when tested by an oral glucose tolerance test. All exons, exon-intron junctions, and islet and liver promotor regions of the GCK gene were amplified with the polymerase chain reaction and screened for mutations using single-strand conformation polymorphism analysis. RESULTS: A silent third-base substitution (TAC: >TAT) in codon 215 of exon 6 was found in 2.8% of NIDDM patients and in 5.0% of IGT subjects. Polymorphisms were found in islet exon 1 at nucleotide 403 (C-->G) in 16.7% of NIDDM patients and in 17.5% of IGT subjects and in the noncoding region of the islet promotor at nucleotide -30 (G-->A) in 13.9% of NIDDM patients and in 25.0% of IGT subjects. Furthermore, in liver intron 1 a variant (C-->T), 12 base pairs upstream from the splice acceptor site, was found in 5.6% of NIDDM patients and in 7.5% of IGT subjects. CONCLUSIONS: These results indicate that the mutations in the coding region of the GCK gene are not likely to play a major role the pathogenesis of late-onset NIDDM or IGT in the Finnish population.

Diabetes Mellitus, Type 2↗

PubMed1995

Absence of N-glycosylation at asparagine 43 in human lipoprotein lipase induces its accumulation in the rough endoplasmic reticulum and alters this cellular compartment.

Lipoprotein lipase (LPL) is the enzyme responsible for the hydrolysis of plasma triglycerides from apolipoprotein C-II-containing lipoproteins at the capillary endothelium and it is synthesized in parenchymal cells of several tissues. Intracellular LPL processing is a major aspect of LPL regulation. The present study aims to determine the intracellular accumulation site of the LPL that is not glycosylated at Asn43. Human LPL (hLPL) cDNA was mutated by site-directed mutagenesis. An Ala residue was substituted for Asn at position 43 of the protein generating N43A hLPL. Wild type hLPL and the mutant hLPL were expressed in COS1 cells. Using immunofluorescence and immunoelectron microscopy we found that wild type hLPL in addition to being secreted into the medium was present in the rough endoplasmic reticulum (ER), Golgi compartments, and vesicles. Neither LPL activity nor protein was found in medium of cells expressing the mutant hLPL and all detectable protein was present exclusively in the ER identified witha specific antibody against the protein disulfide isomerase (PDI), an ER marker. In addition, the intracellular distribution of the ER of the cells that expressed the mutant protein was grossly altered. Treatment of COS1 cells with tunicamycin for 24 h had the same effect on wild type hLPL processing and edoplasmic reticulum distribution. Next, we investigated the influence of the accumulation of mutant hLPL on the intracellular transport of three other proteins that are N-glycosylated before reaching the plasma membrane: the related Bo,+ amino acid transporter (rBAT), the insulin-regulated glucose transporter (GLUT4), and the placental alkaline phosphatase (PLAP) protein. Coexpression of the mutant hLPL (but not wild type) caused the accumulation of rBAT and GLUT4 in the ER while PLAP reached the plasma membrane. Our findings demonstrate that glycosylation of Asn43 of human lipoprotein lipase in the endoplasmic reticulum is essential for its efflux from this compartment and that the retention of the non-glycosylated LPL induces morphological changes in the ER that could also affect its ability to modify the transport of other proteins.

Asparagine↗

PubMed1994

Structure of the human hexokinase II gene.

Mutations in the gene encoding hexokinase II which catalyzes a key step in glycolysis could contribute to the development of peripheral insulin resistance and lead to non-insulin-dependent diabetes mellitus. As a first step towards screening patients for mutations in this gene, we have determined its structure and the sequence of exon-intron junctions. The human HKII gene is composed of 18 exons that span at least 40 kb, and its organization is highly homologous to that of the rat gene. A hexokinase II processed pseudogene was discovered while screening a human genomic library. The coding sequence of this pseudogene is uninterrupted by introns and contains at least one premature stop codon.

Base Sequence↗