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Biomedical subjects

D Shih

Publications and source records attributed to D Shih.

At least 19 recordsLinked to original sources
PubMed2001

HDL and the inflammatory response induced by LDL-derived oxidized phospholipids.

Oxidation of low density lipoprotein (LDL) phospholipids containing arachidonic acid at the sn-2 position occurs when a critical concentration of "seeding molecules" derived from the lipoxygenase pathway is reached in LDL. When this critical concentration is reached, the nonenzymatic oxidation of LDL phospholipids produces a series of biologically active, oxidized phospholipids that mediate the cellular events seen in the developing fatty streak. Normal high density lipoprotein (HDL) contains at least 4 enzymes as well as apolipoproteins that can prevent the formation of the LDL-derived oxidized phospholipids or inactivate them after they are formed. In the sense that normal HDL can prevent the formation of or inactivate these inflammatory LDL-derived oxidized phospholipids, normal HDL is anti-inflammatory. HDL from mice that are genetically predisposed to diet-induced atherosclerosis became proinflammatory when the mice are fed an atherogenic diet, injected with LDL-derived oxidized phospholipids, or infected with influenza A virus. Mice that were genetically engineered to be hyperlipidemic on a chow diet and patients with coronary atherosclerosis, despite normal lipid levels, also had proinflammatory HDL. It is proposed that LDL-derived oxidized phospholipids and HDL may be part of a system of nonspecific innate immunity and that the detection of proinflammatory HDL may be a useful marker of susceptibility to atherosclerosis.

Animals↗
PubMed2000

Pancreatic beta cell-specific transcription of the pdx-1 gene. The role of conserved upstream control regions and their hepatic nuclear factor 3beta sites.

To identify potential transactivators of pdx-1, we sequenced approximately 4.5 kilobases of the 5' promoter region of the human and chicken homologs, assuming that sequences conserved with the mouse gene would contain critical cis-regulatory elements. The sequences associated with hypersensitive site 1 (HSS1) represented the principal area of homology within which three conserved subdomains were apparent: area I (-2694 to -2561 base pairs (bp)), area II (-2139 to -1958 bp), and area III (-1879 to -1799 bp). The identities between the mouse and chicken/human genes are very high, ranging from 78 to 89%, although only areas I and III are present within this region in chicken. Pancreatic beta cell-selective expression was shown to be controlled by mouse and human area I or area II, but not area III, from an analysis of pdx-1-driven reporter activity in transfected beta- and non-beta cells. Mutational and functional analyses of conserved hepatic nuclear factor 3 (HNF3)-like sites located within area I and area II demonstrated that activation by these regions was mediated by HNF3beta. To determine if a similar regulatory relationship might exist within the context of the endogenous gene, pdx-1 expression was measured in embryonic stem cells in which one or both alleles of HNF3beta were inactivated. pdx-1 mRNA levels induced upon differentiation to embryoid bodies were down-regulated in homozygous null HNF3beta cells. Together, these results suggest that the conserved sequences represented by areas I and II define the binding sites for factors such as HNF3beta, which control islet beta cell-selective expression of the pdx-1 gene.

Animals↗
PubMed2000

What benefit specialists think about medical savings account options for large firms.

Currently, tax-preferred medical savings accounts (MSAs) are being offered on a trial basis to employees of small companies. This article reports results of a survey investigating the potential impact of adding an MSA to a medium- or large-sized firm's employee benefit offerings. The variables examined fall into the categories of attitudes toward views on employee benefits in general, the MSA option and issues associated with risk segmentation.

Attitude to Health↗
PubMed1999

Racial differences in survival in an urban peritoneal dialysis program.

We retrospectively evaluated 233 incident patients (61% black, 27% white, and 12% Hispanic/Asian) to our peritoneal dialysis (PD) program from January 1987 to September 1997 to identify any possible racial differences in patient survival. Information collected included clinical features, comorbid conditions, nutritional status, and dialysis dose at initiation of dialysis. The average age was 52 +/- 16 (SD) years, and 49% were men. Diabetes mellitus was present in 41% of patients. Overall follow-up was 31 +/- 24 (median 26) months during which time 21% of patients underwent transplant, 29% of patients transferred to hemodialysis (HD), and 42% of patients died. The Cox proportional hazards analysis, based on intent-to-treat, identified age (RR: 1.03), race (RR: 2.35, white versus black), cardiac disease (RR: 1.97), and serum albumin (RR: 0. 44) to independently predict mortality. Further analysis was performed based on diabetic status, and the analysis identified age (RR: 1.06), race (RR: 2.45, white versus black), and peripheral vascular disease (RR: 2.88) as predictors of mortality in diabetic patients. In nondiabetic patients, age (RR: 1.03), race (RR: 2.24, white versus black), cardiac disease (RR: 2.48), cerebrovascular disease (RR: 3.17), and serum albumin (RR: 0.39) were significant predictors of mortality. The significance of race persisted even after adjusting patients transferring to hemodialysis. The adjusted patient survival at 1, 2, and 5 years was 94%, 87% and 53% for black patients, and 86%, 72%, and 23% for white patients. The adjusted patient survival in diabetics at 1, 2, and 5 years was 92%, 79%, and 37% for black patients, and 82%, 56%, and 9% for white patients. The adjusted patient survival in nondiabetics at 1, 2, and 5 years was 94%, 91%, and 63% for black patients, and 88%, 82%, and 35% for white patients. In conclusion, long-term patient survival is better for black patients than white patients in our peritoneal dialysis program. Peritoneal dialysis should be considered a viable dialytic option for black patients entering an end-stage renal disease program.

Adult↗
PubMed1999

Functional characterization of the MODY1 gene mutations HNF4(R127W), HNF4(V255M), and HNF4(E276Q).

Genetic studies have shown that mutations in the gene encoding hepatocyte nuclear factor (HNF)-4alpha, a member of the steroid/thyroid hormone receptor superfamily, give rise to early-onset type 2 diabetes (MODY1). The functional properties of mutant HNF-4alpha proteins and the molecular mechanisms by which they impair insulin secretion are largely unknown. In the present study, we have investigated transcriptional activation, DNA binding properties, and protein dimerization activity of three HNF-4alpha missense mutations--HNF4(R127W), HNF4(V255M), and HNF4(E276Q)--that have been associated with type 2 diabetes. We demonstrate that HNF4(E276Q) has lost its ability to bind to HNF-4 consensus binding sites and activate transcription. HNF4(E276Q) had no effect on the functional activity of wild-type HNF-4alpha in the pancreatic beta-cell line HIT-T15, but it exhibited weak dominant-negative activity in other cell types. Analysis of HNF4(E276Q) protein showed that it exists in two forms: a full length 54-kDa protein and a 40-kDa COOH-terminal protein lacking the NH2-terminal transactivation domain and the DNA binding domain. Immunoprecipitation experiments indicate that this truncated protein can bind to wild-type HNF-4alpha and may be responsible for the weak dominant-negative effects seen in these cells. In addition, we show that the transcriptional transactivation of HNF4(R127W) and HNF4(V255M) is indistinguishable from that of wild-type HNF-4alpha, suggesting that they are sequence polymorphisms. Our results demonstrate that HNF4(E276Q) is a loss-of-function mutation and that it identifies glutamic acid 276 in alpha-helix 8 of the ligand-binding domain of HNF-4alpha protein as a critical residue for DNA binding, transcriptional activation, and protein stability in vivo.

Animals↗
PubMed1998

Paraoxonase and coronary heart disease.

Paraoxonase (PON1) hydrolyses organophosphate insecticides and nerve gases and is responsible for determining the selective toxicity of these compounds in mammals. Human PON1 has two genetic polymorphisms giving rise to amino-acid substitutions at positions 55 and 192. The 192 polymorphism is the major determinant of the PON1 activity polymorphism towards organophosphates. However, the 55 polymorphism also modulates activity. Ex vivo, the PON1 polymorphisms are important in determining the capacity of HDL to protect LDL against oxidative modification in vitro and this may explain the relationship between the PON1 alleles and coronary heart disease in case-control studies. In recent case-control studies serum PON1 concentration and activity were also found to be decreased in coronary heart disease (CHD) independent of the PON1 polymorphism, and in diabetes serum PON1 specific activity decrease is also independent of the PON1 genetic polymorphism. HDL from transgenic mice lacking PON1 fails to protect LDL against oxidative modification. Thus PON1 may be a determinant of resistance to the development of atherosclerosis by protecting lipoproteins against oxidative modification, perhaps by hydrolysing phospholipid and cholesteryl-ester hydroperoxides.

Animals↗
PubMed1996

An agent cleaving glucose-derived protein crosslinks in vitro and in vivo.

Glucose and other reducing sugars react with proteins by a nonenzymatic, post-translational modification process called nonenzymatic glycosylation or glycation. The sugar-derived carbonyl group adds to a free amine, forming a reversible adduct which over time rearranges to produce a class of products termed advanced-glycation end-products (AGEs). These remain irreversibly bound to macromolecules and can covalently crosslink proximate amino groups. The formation of AGEs on long-lived connective tissue and matrix components accounts largely for the increase in collagen crosslinking that accompanies normal ageing and which occurs at an accelerated rate in diabetes. AGEs can activate cellular receptors and initiate a variety of pathophysiological responses. They modify an appreciable fraction of circulating low-density lipoproteins preventing uptake of these particles by their high-affinity tissue receptors. Advanced glycation has also been implicated in the pathology of Alzheimer's disease. Because AGEs may form by a pathway involving reactive alpha-dicarbonyl intermediates, we investigated a potential pharmacological strategy for selectively cleaving the resultant glucose-derived protein crosslinks. We now describe a prototypic AGE crosslink 'breaker', N-phenacylthiazolium bromide (PTB), which reacts with and cleaves covalent, AGE-derived protein crosslinks. The ability of PTB to break AGE crosslinks in vivo points to the importance of an alpha-dicarbonyl intermediate in the advanced glycation pathway and offers a potential therapeutic approach for the removal of established AGE crosslinks.

Amyloid beta-Peptides↗
PubMed1994

Developmental expression of poly(A) binding protein mRNAs during spermatogenesis in the mouse.

The poly(A) binding protein (PABP), a conserved protein that binds to the 3' poly(A) tail on mRNAs in eukaryotic cells, has been implicated in the regulation of mRNA stability and translation. Two PABP cDNAs with different sequences were isolated from mouse testis cDNA libraries. The predicted amino acid sequence of one, PABP1, is nearly identical (98.9%) to human liver PABP, while 80% of the amino acids of the second, PABPt, are identical to mouse and human PABPs. Northern blots reveal that there is one major PABP mRNA species in liver, muscle, kidney, and brain, two in spleen, and at least four in testis. The levels of PABP mRNA in testis are 5-10-fold higher than in these somatic tissues, but surprisingly the vast majority of all PABP mRNA size variants sediment more slowly than single ribosomes, indicating strong translational repression. Reverse transcriptase-polymerase chain reaction assays demonstrate that PABPt mRNAs are abundant only in testis. Northern blots of RNAs purified from highly enriched spermatogenic cells show that the high levels, multiple sizes of PABP mRNAs, and the PABPt mRNA are present in meiotic and early haploid spermatogenic cells, and are sharply reduced in late haploid cells. Comparison of the binding of PABP1 and PABPt to poly(A) Sepharose in vitro revealed subtle differences, even though PABPt contains substitutions for highly conserved aromatic amino acids that are thought to be necessary for binding to poly(A). The existence of two PABP isoforms in mouse spermatogenic cells could influence cytoplasmic gene expression during spermatogenesis.

Amino Acid Sequence↗
PubMed1992

Sequence of the gene encoding the mitochondrial capsule selenoprotein of mouse sperm: identification of three in-phase TGA selenocysteine codons.

The mitochondrial selenoprotein is a major structural protein of the keratinous mitochondrial capsule in mammalian sperm, a structure that functions in shaping mitochondria into the helical sheath surrounding the flagellum. A cDNA clone (Kleene et al., 1990) was isolated previously encoding a protein whose predicted size and amino acid content of > 20% cysteine and proline closely resembled a selenoprotein in the bull mitochondrial capsule. The sequences of additional cDNAs and genomic DNA reported here reveal that the mouse mitochondrial capsule selenoprotein reading frame begins 54 codons further upstream than previously reported. Significantly, these 54 codons contain three in-phase UGA codons, which normally signify stop but encode selenocysteine in bacterial and mammalian selenoproteins. The coding region of the mitochondrial capsule selenoprotein gene is interrupted by a single intron. S1 mapping and primer extension demonstrate that the vast majority of MCS mRNAs are spliced using consensus 5' and 3' slice junctions in mammalian cells. However, two cDNAs have been identified that apparently represent rare mRNA variants produced by use of cryptic splice sites.

Amino Acid Sequence↗
PubMed1990

Nucleotide sequence of the gene encoding mouse transition protein 2.

The gene encoding the testis-specific basic chromosomal protein, mouse transition protein 2, is split by a single small intron that falls between the first and second nucleotides of a codon. Since the genes encoding protamines 1 and 2 and transition protein 1 in mammals contain a single intron in the same position, protamines and transition proteins appear to be evolutionarily related.

Amino Acid Sequence↗
PubMed1990

Effect of the distal residues on the vibrational modes of the Fe-CO bond in hemoglobin studied by protein engineering.

Using an Escherichia coli gene expression system, we have engineered human hemoglobin (Hb) mutants having the distal histidine (E7) and valine (E11) residues replaced by other amino acids. The interaction between the mutated distal residues and bound carbon monoxide has been studied by Soret-excited resonance Raman spectroscopy. The replacement of Val-E11 by Ala, Leu, Ile, and Met has no effect on the v(C-O), v(Fe-CO) stretching or delta(Fe-C-O) bending frequencies in both the alpha and beta subunits of Hb, although some of these mutations affect the CO affinity as much as 40-fold. The strain imposed on the protein by the binding of CO is not localized in the Fe-CO bond and is probably distributed among many bonds in the globin. The replacement of His-E7 by Val or Gly brings the stretching frequencies v(Fe-CO) and v(C-O) close to those of free heme complexes. In contrast, the substitution of His-E7 by Gln, which is flexible and polar, produces no effects on the resonance Raman spectrum of either alpha- or beta-globin. The replacement of His-E7 of beta-globin by Phe shows the same effect as replacement by Gly or Val. Therefore, the steric bulk of the distal residues is not the primary determinant of the Fe-CO ligand vibrational frequencies. The ability of both histidine and glutamine to alter the v(C-O), v(Fe-CO), or delta(Fe-C-O) frequencies may be attributed to the polar nature of their side chains which can interact with bound CO in a similar manner.

Binding Sites↗
PubMed1989

NMR study of human mutant hemoglobins synthesized in Escherichia coli. Consequences of tyrosine alpha 42 substitutions.

The hydroxyl group of Tyr alpha 42 in human hemoglobin forms a hydrogen bond with the carboxylate of Asp beta 99 which is considered to be one of the most important hydrogen bonds for stabilizing the "T-state." However, no spontaneous mutation at position 42 of the alpha subunit has been reported, and the role of the tyrosine has not been tested experimentally. Two artificial human mutant hemoglobins in which Tyr alpha 42 was replaced by phenylalanine or histidine were synthesized in Escherichia coli, and their proton NMR spectra were studied with particular attention to the hyperfine-shifted and hydrogen-bonded proton resonances. The site-directed mutagenesis of the Tyr alpha 42----Phe removes the hydrogen bond described above and prevents transition to the T-state so that the mutant Hb is rather similar to the "R-state" even when deoxygenated. On the other hand, the mutation from tyrosine to histidine causes less drastic structural changes, and its quaternary and tertiary structures are almost the same as native deoxy-Hb A. This may be attributed to the formation of a new hydrogen bond between His alpha 1(42) and Asp beta 2(99). These observations indicate that the hydrogen bond formed between Tyr alpha 42 and Asp beta 99 is required to convert unliganded Hb to the T-state.

Escherichia coli↗