Biomedical subjects

M Malkki

Publications and source records attributed to M Malkki.

At least 19 recordsLinked to original sources

PubMed2005

MHC microsatellite diversity and linkage disequilibrium among common HLA-A, HLA-B, DRB1 haplotypes: implications for unrelated donor hematopoietic transplantation and disease association studies.

Twenty-two human major histocompatibility complex (MHC) region microsatellite (Msat) markers were studied for diversity and linkage disequilibrium (LD) with HLA loci in hematopoietic cell transplant recipients and their HLA-A, HLA-B, HLA-C, HLA-DRB1, and HLA-DQB1 allele-matched unrelated donors. These Msats showed highly significant LD over much of the MHC region. The Msat diversity of five common Caucasian haplotypes (HLA-A1-B8-DR3, A3-B7-DR15, A2-B44-DR4, A29-B44-DR7, and A2-B7-DR15) was examined using a new measure called 'haplotype specific heterozygosity' (HSH). Each of the five haplotypes had at least one Msat marker with an HSH value of zero indicating that only one Msat allele was observed for the particular HLA haplotype. In addition, the ability of Msats to predict HLA-A-B-DRB1 haplotypes was studied. Over 90% prediction probability of two common haplotypes (HLA-A1-B8-DR3 and HLA-A3-B7-DR15) was achieved with information from three Msats (D6S265/D6S2787/D6S2894 and D6S510/D6S2810/D6S2876, respectively). We demonstrate how the HSH index can be used in the selection of informative Msats for transplantation and disease association studies. Markers with low HSH values can be used to predict specific HLA haplotypes or multilocus genotypes to supplement the screening of HLA-matched donors for transplantation. Markers with high HSH values will be most informative in studies investigating MHC region disease-susceptibility genes where HLA haplotypic effects are known to exist.

Gene Frequency↗

PubMed2002

Identification of a novel HLA-B07 allele--HLA-B0726.

We describe here, the identification of a novel HLA-B*07 allele named HLA-B*0726. This allele was found in a Caucasian individual serologically typed as HLA-B7, B35. Novel DNA probe patterns for the HLA-B*07 allele were found using HLA-B specific reverse sequence-specific oligonucleotide probe (SSOP) and sequence-specific primer (SSP) typing. DNA sequencing demonstrated the presence of a new HLA-B*07 sequence variant encoding a single nucleotide substitution from a G to a T at nucleotide 539 in exon 3. This results in an amino acid substitution from arginine to leucine at residue 156 in exon 3.

Alleles↗

PubMed2001

Major-histocompatibility-complex class I alleles and antigens in hematopoietic-cell transplantation.

BACKGROUND: Successful engraftment of hematopoietic stem cells from unrelated donors is influenced by disparities between the donor and recipient for HLA-A, B, and C alleles. Disparities between HLA sequence polymorphisms that are serologically detectable are termed antigen mismatches, whereas those that can be identified only by DNA-based typing methods are termed allele mismatches. Whether both kinds of polymorphisms are important in transplantation is not known. We tested the hypothesis that allele mismatches that are detectable only at the DNA level are less immunogenic than those that are serologically detectable and thereby are associated with a lower risk of graft failure after hematopoietic-cell transplantation METHODS: We used DNA sequencing to define the HLA-A, B, and C alleles in 471 patients who received bone marrow from unrelated donors for the treatment of chronic myeloid leukemia after myeloablative conditioning therapy. The odds ratios for graft failure were determined for recipients of transplants from donors with a single class I allele mismatch, a single class I antigen mismatch, or two or more class I mismatches, as compared with those with no mismatch RESULTS: A single HLA allele mismatch did not increase the risk of graft failure, whereas a single antigen mismatch significantly increased the risk. The risk was also increased if the recipient was HLA homozygous at the mismatched class I locus or if the donor had two or more class I mismatches CONCLUSIONS: HLA class I antigen mismatches that are serologically detectable confer an enhanced risk of graft failure after hematopoietic-cell transplantation. Transplants from donors with a single class I allele mismatch that is not serologically detectable may be used without an increased risk of graft failure.

Genes, MHC Class I↗

PubMed2001

Genomics of unrelated-donor hematopoietic cell transplantation.

Unrelated-donor hematopoietic cell transplantation is a proven curative modality for hematologic malignancies. The success of unrelated-donor transplantation has been achieved through a better understanding of the immunobiology of the HLA system and through more precise and comprehensive matching of donors and recipients. The extensive polymorphism of HLA genes confers important biological implications affecting engraftment, graft-versus-host disease and overall survival. Although more-complete HLA identity of the donor and recipient is associated with optimal transplant outcome, new information suggests that not every HLA disparity is functionally relevant. Future advances in unrelated-donor transplantation must include the identification of tolerable HLA mismatches, so that more patients may benefit from this therapeutic modality. Furthermore, the role of cytokine-gene polymorphisms and minor histocompatibility genes in transplant outcome requires investigation. Delineation of the function of these markers as transplantation determinants may provide alternative means for optimizing the results of hematopoietic cell transplantation.

Animals↗

PubMed2001

The biological significance of HLA-DP gene variation in haematopoietic cell transplantation.

Although it has been over 25 years since HLA-DP was mapped to the major histocompatibility complex (MHC), its biological functions remain ill-defined. We sought to test the hypothesis that HLA-DP functions in a manner similar to that of other class II genes by measuring the risk of clinically severe grades III-IV acute graft-vs.-host disease (GVHD) associated with recipient HLA-DP disparity after haematopoietic cell transplantation. HLA-DPB1 exon 2 was sequenced in 205 patients who underwent transplantation from HLA-A, -B, -C, -DRB1 and -DQB1 allele-matched unrelated donors. HLA-DPB1 mismatched recipients experienced a significantly increased risk of acute GVHD compared with HLA-DP-identical transplants. Patients who were mismatched for a single HLA-DPB1 allele had an odds ratio (OR) of 1.0 (0.5, 2.2; P = 0.99) and patients who were mismatched for two alleles had an OR of 2.2 (1.0, 4.9; P = 0.06) for developing acute GVHD. Compared with matched and single-allele mismatched transplants, patients who were mismatched for two DPB1 alleles had an OR of 2.2 (1.2, 4.1; P = 0.01). HLA-DP plays an important role in the alloimmune response. A threshold effect of multiple HLA-DP disparities is evident in determining the risk of acute GVHD after haematopoietic cell transplantation from unrelated donors.

Adolescent↗

PubMed2000

Mouse hexokinase II gene: structure, cDNA, promoter analysis, and expression pattern.

In mammalian tissues, the phosphorylation of intracellular glucose to glucose-6-phosphate (Glu-6-P) is facilitated by four distinct hexokinase (HK) isoenzymes, designated as HKI-IV. Because of the role of HKII as a leading glycolytic enzyme in insulin-sensitive tissues such as skeletal muscle, heart, and adipose tissue, defects in HKII function could contribute to the development of insulin resistance and perhaps Type 2 diabetes. As a first step towards elucidation of the physiological role of HKII in insulin resistance and type 2 diabetes using mouse knock-out models, we determined the genomic structure, sequence of the cDNA and of 4.8 kb of the 5' regulatory region, and tissue-specific expression of the mouse HKII gene. The gene comprises 18 exons that span approximately 50 kb of DNA. Nucleotide sequence of the proximal promoter revealed a number of conserved putative transcription factor binding motifs. We also found numerous repeat elements throughout the mouse HKII gene. The mouse HKII cDNA is approximately 5.5 kb in length and contains an open reading frome of 2751 bp encoding a protein of 917 amino acids. The mouse HKII gene is predominantly expressed in skeletal muscle, heart, and adipose tissue. The transcription initiation and polyadenylation sites for the mouse HKII mRNA were similar to those of the rat and human genes.

Animals↗

PubMed2000

Hypoxia induces hexokinase II gene expression in human lung cell line A549.

During adaptation to hypoxic and hyperoxic conditions, the genes involved in glucose metabolism are upregulated. To probe involvement of the transcription factor hypoxia-induced factor-1 (HIF-1) in hexokinase (HK) II expression in human pulmonary cells, A549 cells and small-airway epithelial cells (SAECs) were exposed to stimuli such as hypoxia, deferoxamine (DFO), and metal ions. The largest increase in HK-II (20-fold for mRNA and 2.5-fold for enzymatic activity) was observed in A549 cells when exposed to DFO. All stimuli selectively increased the 5.5-kb rather than 4-kb transcript in A549 cells. Cycloheximide and actinomycin D inhibited these responses. In addition, cells were transfected with luciferase reporter constructs driven by the full-length HK-II 5'-regulatory region (4.0 kb) or various deletions of that region. A549 cells transfected with the 4.0-kb construct and exposed to hypoxia or DFO increased their luciferase activity 7- and 10-fold, respectively, indicating that HK-II induction is, at least in part, due to increased gene transcription. Sixty percent of the inducible activity of the 4.0-kb construct was shown to reside within the proximal 0.5 kb. Additionally, cotransfection with a stable HIF-1 mutant and the 4.0-kb promoter construct resulted in increased luciferase activity under normoxic conditions. These results strongly suggest that HK-II is selectively regulated in pulmonary cells by a HIF-1-dependent mechanism.

Cell Line↗

PubMed1998

Functional consequences of naturally occurring variants of human hexokinase II.

Hexokinase II (HKII) catalyses a key step in glucose metabolism and can be regarded as a candidate gene for insulin resistance and type 2 (non-insulin-dependent) diabetes mellitus. We observed previously four amino acid substitutions among Finnish type 2 diabetic patients: Gln142His, Ala314Val; 0.9%, Arg353Cys; 2.7% and Arg775Gln; 2.7%. The Arg775Gln mutation was also observed in normal control subjects (2.1%) and the Gln142His substitution was found in both Type II diabetic and normal subjects with similar frequencies (approximately 20%). Since Gln at position 142, Ala at 314 and Arg at 775 are present in human and rat hexokinases and could be important for structure and function of the enzyme, we generated all four substitutions by site-directed mutagenesis and expressed them in E.coli. None of these substitutions had any effect on HKII catalytic activity, K(m) or Vmax for glucose values in vitro. Thus unless these substitutions have an impact on enzyme activity or regulation in vivo, it is unlikely that these substitutions contribute to the aetiology of Type II diabetes.

Animals↗

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↗

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↗

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↗

PubMed1994

Insulin receptor substrate-1 variants in non-insulin-dependent diabetes.

Insulin receptor substrate-1 (IRS-1) plays an important role in insulin-stimulated signaling mechanisms. Therefore, we investigated the frequency and clinical significance of variants in the coding region of this gene in patients with non-insulin-dependent diabetes (NIDDM). Initial screening included a population-based sample of 40 Finnish patients with typical NIDDM. Applying single strand conformation polymorphism analysis the following amino acid substitutions were found among the 40 NIDDM patients: Gly818-Arg, Ser892Gly, and Gly971Arg. The first two variants have not been previously reported. Additional samples of 72 patients with NIDDM and 104 healthy control subjects with completely normal oral glucose tolerance test and a negative family history of diabetes were screened. The most common polymorphism was the Gly971Arg substitution which was found in 11 (9.8%) of 112 NIDDM patients and in 9 (8.7%) of 104 control subjects. The Gly818Arg substitution was found in 2 (1.8%) of NIDDM patients and in 2 (1.9%) of control subjects, and the Ser892Gly substitution was found in 3 (2.7%) NIDDM patients and in 1 (1.0%) control subject. The Gly971Arg substitution was not associated with an impairment in insulin secretion capacity (estimated by insulin responses in an oral glucose tolerance test or by the hyperglycemic clamp) or insulin action (estimated by the euglycemic clamp). Of the three amino acid substitutions observed Ser892Gly is the most interesting one since it abolishes one of the potential serine phosphorylation sites (SPGE) which is located immediately NH2-terminal to the only SH2 binding site of growth factor receptor-bound protein (GRB2), and thus could potentially influence some aspects of signal transduction and metabolic response to insulin.

Aged↗

PubMed1994

Isolated low HDL cholesterol. An insulin-resistant state.

High levels of very-low-density lipoprotein (VLDL) triglycerides (TGs) and low levels of high-density lipoprotein (HDL) cholesterol have been found to be associated with insulin resistance. However, direct evidence that patients with isolated low HDL cholesterol are insulin resistant is still lacking. Therefore, we investigated the degree of insulin resistance and intracellular metabolism of glucose by the euglycemic glucose clamp technique and indirect calorimetry in three groups of subjects with normal glucose tolerance: 17 male control subjects with normolipidemia, 12 male patients with isolated low HDL cholesterol (low HDL group), and 10 male patients with low HDL cholesterol and hypertriglyceridemia (low HDL/high TG group). Fasting, 1-h, and 2-h glucose levels did not differ between the groups in an oral glucose tolerance test (OGTT). In contrast, insulin levels during an OGTT were significantly higher in the low HDL group than in the control group (fasting insulin: 85 +/- 11 vs. 50 +/- 6 pM, P = 0.005; 1-h insulin: 622 +/- 92 vs. 394 +/- 64 pM, P = 0.004; and 2-h insulin: 343 +/- 73 vs. 194 +/- 40 pM, P = 0.006). Similarly, insulin levels were also higher in the low HDL/high TG group than in the control group (fasting insulin: 82 +/- 14 pM, P = 0.037; 1-h insulin: 795 +/- 179 pM, P = 0.063; and 2-h insulin: 488 +/- 145 pM, P = 0.040).(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Glucose↗

PubMed1993

Human hexokinase II: sequence and homology to other hexokinases.

The amino acid sequence of human hexokinase II was deduced from the sequence of cDNA clones isolated from a skeletal muscle library. An open reading frame of 2751 bases encodes a protein of 917 amino acids. The deduced amino acid sequence has 94% identity with rat hexokinase II but only 72% identity with human hexokinase type I. In addition to hexokinase II clones, the human skeletal muscle cDNA library contained at least an equal number of clones of hexokinase I, the isoform reported to be typically found in kidney and brain. Genetic variation in hexokinase II could underlie insulin resistance in peripheral tissues and cause non-insulin-dependent diabetes mellitus. The availability of this sequence would facilitate investigating the role of mutations in the HKII gene in the etiology of this disease.

Adolescent↗

PubMed1993

Obese men with type IIB hyperlipidemia are insulin resistant.

By using the euglycemic clamp technique and indirect calorimetry, we determined the degree of insulin resistance in 12 obese (body mass index > 27.0 kg/m2), normotensive patients with type IIB hyperlipidemia (HLIIB) (total cholesterol > or = 6.5 mmol/L and total triglycerides > or = 2.0 mmol/L) and 17 control subjects (total cholesterol < or = 6.1 mmol/L and total triglycerides < 1.8 mmol/L) who were carefully matched for sex, age, and obesity. Fasting plasma insulin was higher in HLIIB patients than in control subjects (18.4 +/- 4.6 versus 8.9 +/- 1.2 mU/L, respectively; P = .010). The rates of whole-body glucose uptake were significantly lower in HLIIB patients than in control subjects during the last hour of the clamp (42.2 +/- 3.9 versus 54.6 +/- 2.8 mumol/kg per minute, respectively; P = .013). Glucose oxidation during the last 30 minutes of the euglycemic clamp was lower in HLIIB patients than in control subjects (14.6 +/- 0.9 versus 19.0 +/- 1.3 mumol/kg per minute, respectively; P = .017). Nonoxidative glucose disposal during the last 30 minutes of the euglycemic clamp was also lower in HLIIB patients than in control subjects, but the difference was not statistically significant (27.6 +/- 3.3 versus 35.8 +/- 2.8 mumol/kg per minute, respectively; P = .069). Lipid oxidation during the clamp was completely suppressed in control subjects (-0.24 +/- 0.44 mumol/kg per minute) but was significantly less suppressed in the HLIIB patients (0.94 +/- 0.29 mumol/kg per minute, P = .024).(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Glucose↗