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G Chu

Publications and source records attributed to G Chu.

At least 19 recordsLinked to original sources
PubMed2006

Recent insights into the role of host innate and acquired immunity responses.

Viral myocarditis can present as dramatic heart failure in the young, and chronic indolent cardiomyopathy in the older adult. The outcome of the disease is still poor, associated with high mortality during long-term follow-up. Enteroviral myocarditis serves as an excellent model to understand virus and host interactions. The virus enters the target cells via collaborating receptors, and this process triggers an inflammatory response in the host. The immune reaction is a two-edged sword, with appropriate activation of the immune system capable of clearing the virus, but excessive activation leads to a chronic inflammatory process that triggers the remodeling of the heart and consequent clinical heart failure. Through genetic dissection strategies, we have identified that the acquired immune system is activated through the T cell receptor and signaling amplification systems, such as the tyrosine kinase p56lck, phosphatase CD45 and downstream ERK1/2, and the family of cytokines. This signaling system not only promotes inflammatory cell clonal expansion but paradoxically also promotes viral proliferation. The innate immune system is now recognized as playing an ever-expanding role in coordinating the host immune response through the Toll-like receptors, triggering downstream signaling adaptors such as MyD88, IRAK, and TRIF/IRFs. These lead to activation of cytokines or interferons, depending on the balance of the signal contributions. The ongoing research in this area should help us to understand the immune response of the heart to viral infection, while identifying potential targets for therapy.

Animals↗
PubMed2003

Embryonic stem-cell research and the moral status of embryos.

Stem-cell research has the potential to significantly advance our knowledge of cell differentiation with the promise of exciting and innovative therapeutic applications for otherwise incurable genetic and degenerative disorders. The issue has been the subject of debate in federal and state parliament as research of embryonic stem cells and their application have come under intense scrutiny. Scientists and medical practitioners are highly skilled in the technical aspects of biomedicine but are decidedly less comfortable with ethics. The place of novel and controversial biomedical technology is commonly left to an ad hoc and complex process whereby social acceptability eventually becomes the final arbiter. Utilitarianism is a popular ethical approach that attempts to weigh all the known and anticipated merits and pitfalls. The scientific background of biomedical professionals, the vast explosion of information, and specialization and subspecialization, have all contributed to a reductionistic view of life and ethics. The 'sanctity of life' doctrine is altogether quite different, as secular and religious advocates appear inflexible and unyielding to the logical propositions of utilitarianism and reductionism or to the consensus of democracy. These four major ethical approaches are discussed with reference to the embryonic stem-cell research debate.

Embryo Research↗
PubMed2001

Occupational transmission of Mycobacterium tuberculosis to health care workers in a university hospital in Lima, Peru.

From November 1996 through March 1997, presumptive active pulmonary tuberculosis (TB) was detected in 44 health care workers (HCWs) at a university hospital in Lima, Peru. To further assess the magnitude of the outbreak and determine risk factors for occupational Mycobacterium tuberculosis transmission, we identified HCWs in whom active pulmonary TB was diagnosed from January 1994 through January 1998, calculated rates by year and hospital work area, and conducted a tuberculin skin test (TST) survey. Thirty-six HCWs had confirmed active pulmonary TB. The rate of TB was significantly higher among the 171 HCWs employed in the laboratory than among HCWs employed in all other areas. In multivariate analysis, the only independent risk factor for HCW M. tuberculosis infection in HWCs employed in the laboratory was the use of common staff areas. Very high rates of active pulmonary TB were detected among HCWs at this hospital, and occupational acquisition in the laboratory was associated with HCW-to-HCW transmission.

Adult↗
PubMed2001

Global analysis of ATM polymorphism reveals significant functional constraint.

ATM, the gene that is mutated in ataxia-telangiectasia, is associated with cerebellar degeneration, abnormal proliferation of small blood vessels, and cancer. These clinically important manifestations have stimulated interest in defining the sequence variation in the ATM gene. Therefore, we undertook a comprehensive survey of sequence variation in ATM in diverse human populations. The protein-encoding exons of the gene (9,168 bp) and the adjacent intron and untranslated sequences (14,661 bp) were analyzed in 93 individuals from seven major human populations. In addition, the coding sequence was analyzed in one chimpanzee, one gorilla, one orangutan, and one Old World monkey. In human ATM, 88 variant sites were discovered by denaturing high-performance liquid chromatography, which is 96%-100% sensitive for detection of DNA sequence variation. ATM was compared to 14 other autosomal genes for nucleotide diversity. The noncoding regions of ATM had diversity values comparable to other genes, but the coding regions had very low diversity, especially in the last 29% of the protein sequence. A test of the neutral evolution hypothesis, through use of the Hudson/Kreitman/Aguadé statistic, revealed that this region of the human ATM gene was significantly constrained relative to that of the orangutan, the Old World monkey, and the mouse, but not relative to that of the chimpanzee or the gorilla. ATM displayed extensive linkage disequilibrium, consistent with suppression of meiotic recombination at this locus. Seven haplotypes were defined. Two haplotypes accounted for 82% of all chromosomes analyzed in all major populations; two others carrying the same D126E missense polymorphism accounted for 33% of chromosomes in Africa but were never observed outside of Africa. The high frequency of this polymorphism may be due either to a population expansion within Africa or to selective pressure.

Africa↗
PubMed2001

Significance analysis of microarrays applied to the ionizing radiation response.

Microarrays can measure the expression of thousands of genes to identify changes in expression between different biological states. Methods are needed to determine the significance of these changes while accounting for the enormous number of genes. We describe a method, Significance Analysis of Microarrays (SAM), that assigns a score to each gene on the basis of change in gene expression relative to the standard deviation of repeated measurements. For genes with scores greater than an adjustable threshold, SAM uses permutations of the repeated measurements to estimate the percentage of genes identified by chance, the false discovery rate (FDR). When the transcriptional response of human cells to ionizing radiation was measured by microarrays, SAM identified 34 genes that changed at least 1.5-fold with an estimated FDR of 12%, compared with FDRs of 60 and 84% by using conventional methods of analysis. Of the 34 genes, 19 were involved in cell cycle regulation and 3 in apoptosis. Surprisingly, four nucleotide excision repair genes were induced, suggesting that this repair pathway for UV-damaged DNA might play a previously unrecognized role in repairing DNA damaged by ionizing radiation.

Apoptosis↗
PubMed2001

Structure and expression of the mouse cardiac calsequestrin gene.

Calsequestrin is a sarcoplasmic reticulum protein, which plays a predominant role in diastolic Ca2+-storage in the mammalian heart. The present study was designed to define the gene structure, developmental and tissue specific expression of the murine, cardiac isoform of calsequestrin. Two sets of genomic libraries (lambda phage and PAC) were screened using the mouse cardiac calsequestrin cDNA, and several overlapping clones were isolated. These clones were characterized using restriction enzyme digestion, Southern blotting and partial sequencing. The cardiac calsequestrin gene consists of 11 exons and its 5' flanking region is characterized by the presence of a TATA-like box, muscle specific promoter elements such as 7 E-boxes, 1 MEF-2, 1 MCBF and 1 Repeat (musS) motifs, as well as several muscle non-specific transcriptional elements (AP-2A, NRE1, NRE2, p53, Spel and TFI-IIA). Expression of the cardiac isoform of calsequestrin was first detected on day 11 pre-birth and approached adult levels by day 4 post-birth. Expression of cardiac calsequestrin was also detected in adult fast-twitch skeletal muscle, thyroid, testis and epididymis tissues. This genomic characterization of cardiac calsequestrin may form the basis for further evaluation of its regulatory role in Ca2+ homeostasis and contractility in the murine heart.

5' Untranslated Regions↗
PubMed2000

A single site (Ser16) phosphorylation in phospholamban is sufficient in mediating its maximal cardiac responses to beta -agonists.

Phospholamban (PLB) can be phosphorylated at Ser(16) by cyclic AMP-dependent protein kinase and at Thr(17) by Ca(2+)-calmodulin-dependent protein kinase during beta-agonist stimulation. A previous study indicated that mutation of S16A in PLB resulted in lack of Thr(17) phosphorylation and attenuation of the beta-agonist stimulatory effects in perfused mouse hearts. To further delineate the functional interplay between dual-site PLB phosphorylation, we generated transgenic mice expressing the T17A mutant PLB in the cardiac compartment of the null background. Lines expressing similar levels of T17A mutant, S16A mutant, or wild-type PLB in the null background were characterized in parallel. Cardiac myocyte basal mechanics and Ca(2+) kinetics were similar among the three groups. Isoproterenol stimulation was associated with phosphorylation of both Ser(16) and Thr(17) in wild-type PLB and Ser(16) phosphorylation in T17A mutant PLB, whereas there was no detectable phosphorylation of S16A mutant PLB. Phosphorylation of Ser(16) alone in T17A mutant PLB resulted in responses of the mechanical and Ca(2+) kinetic parameters to isoproterenol similar to those in wild-type myocytes, which exhibited dual-site PLB phosphorylation. However, those parameters were significantly attenuated in the S16A mutant myocytes. Thus, Ser(16) in PLB can be phosphorylated independently of Thr(17) in vivo, and phosphorylation of Ser(16) is sufficient for mediating the maximal cardiac responses to beta-adrenergic stimulation.

Amino Acid Substitution↗
PubMed2000

Phospholamban decreases the energetic efficiency of the sarcoplasmic reticulum Ca pump.

We tested the hypothesis that increased Sarcoplasmic reticulum (SR) Ca content ([Ca](SRT)) in phospholamban knockout mice (PLB-KO) is because of increased SR Ca pump efficiency defined by the steady-state SR [Ca] gradient. The time course of thapsigargin-sensitive ATP-dependent (45)Ca influx into and efflux out of cardiac SR vesicles from PLB-KO and wild-type (WT) mice was measured at 100 nm free [Ca]. We found that PLB decreased the initial SR Ca uptake rate (0.13 versus 0.31 nmol/mg/s) and decreased steady-state (45)Ca content (0.9 versus 4.1 nmol/mg protein). Furthermore, at similar total SR [Ca], the pump-mediated Ca efflux rate was higher in WT (0.065 versus 0.037 nmol/mg/s). The pump-independent leak rate constant (k(leak)) was also measured at 100 nm free [Ca]. The results indicate that k(leak) was < 1% of pump-mediated backflux and was not different among nonpentameric mutant PLB (PLB-C41F), WT pentameric PLB (same expression level), and PLB-KO. Therefore differences in passive SR Ca leak cannot be the cause of the higher thapsigargin-sensitive Ca efflux from the WT membranes. We conclude that the decreased total SR [Ca] in WT mice is caused by decreased SR Ca influx rate, an increased Ca-pump backflux, and unaltered leak. Based upon both thermodynamic and kinetic analysis, we conclude that PLB decreases the energetic efficiency of the SR Ca pump.

Animals↗
PubMed2000

Activation of DNA-dependent protein kinase by single-stranded DNA ends.

DNA-dependent protein kinase (DNA-PK) is involved in joining DNA double-strand breaks induced by ionizing radiation or V(D)J recombination. The kinase is activated by DNA ends and composed of a DNA binding subunit, Ku, and a catalytic subunit, DNA-PK(CS). To define the DNA structure required for kinase activation, we synthesized a series of DNA molecules and tested their interactions with purified DNA-PK(CS). The addition of unpaired single strands to blunt DNA ends increased binding and activation of the kinase. When single-stranded loops were added to the DNA ends, binding was preserved, but kinase activation was severely reduced. Obstruction of DNA ends by streptavidin reduced both binding and activation of the kinase. Significantly, short single-stranded oligonucleotides of 3-10 bases were capable of activating DNA-PK(CS). Taken together, these data indicate that kinase activation involves a specific interaction with free single-stranded DNA ends. The structure of DNA-PK(CS) contains an open channel large enough for double-stranded DNA and an adjacent enclosed cavity with the dimensions of single-stranded DNA. The data presented here support a model in which duplex DNA binds to the open channel, and a single-stranded DNA end is inserted into the enclosed cavity to activate the kinase.

Antigens, Nuclear↗
PubMed2000

Xeroderma pigmentosum p48 gene enhances global genomic repair and suppresses UV-induced mutagenesis.

UV-damaged DNA-binding activity (UV-DDB) is deficient in some xeroderma pigmentosum group E individuals due to mutation of the p48 gene, but its role in DNA repair has been obscure. We found that UV-DDB is also deficient in cell lines and primary tissues from rodents. Transfection of p48 conferred UV-DDB to hamster cells, and enhanced removal of cyclobutane pyrimidine dimers (CPDs) from genomic DNA and from the nontranscribed strand of an expressed gene. Expression of p48 suppressed UV-induced mutations arising from the nontranscribed strand, but had no effect on cellular UV sensitivity. These results define the role of p48 in DNA repair, demonstrate the importance of CPDs in mutagenesis, and suggest how rodent models can be improved to better reflect cancer susceptibility in humans.

Animals↗
PubMed2000

Phosphorylation of phospholamban and troponin I in beta-adrenergic-induced acceleration of cardiac relaxation.

Activation of cAMP-dependent protein kinase A (PKA) in ventricular myocytes by isoproterenol (Iso) causes phosphorylation of both phospholamban (PLB) and troponin I (TnI) and accelerates relaxation by up to twofold. Because PLB phosphorylation increases sarcoplasmic reticulum (SR) Ca pumping and TnI phosphorylation increases the rate of Ca dissociation from the myofilaments, both factors could contribute to the acceleration of relaxation seen with PKA activation. To compare quantitatively the role of TnI versus PLB phosphorylation, we measured relaxation rates before and after maximal Iso treatment for twitches of matched amplitudes in ventricular myocytes and muscle from wild-type (WT) mice and from mice in which the PLB gene was knocked out (PLB-KO). Because Iso increases contractions, even in the PLB-KO mouse, extracellular [Ca] or sarcomere length was adjusted to obtain matching twitch amplitudes (in the presence and absence of Iso). In PLB-KO myocytes and muscles (which were allowed to shorten), Iso did not alter the time constant (tau) of relaxation ( approximately 29 ms). However, with increasing isometric force development in the PLB-KO muscles, Iso progressively but modestly accelerated relaxation (by 17%). These results contrast with WT myocytes and muscles where Iso greatly reduced tau of cell relaxation and intracellular Ca concentration decline (by 30-50%), independent of mechanical load. The Iso treatment used produced comparable increases in phosphorylation of TnI and PLB in WT. We conclude that the effect of beta-adrenergic activation on relaxation is mediated entirely by PLB phosphorylation in the absence of external load. However, TnI phosphorylation could contribute up to 14-18% of this lusitropic effect in the WT mouse during maximal isometric contractions.

Adrenergic beta-Agonists↗
PubMed2000

[A clinic analysis of 62 male patients with lupus nephritis].

To study the difference between male and female patients with lupus nephritis(LN), we made a retrospective analysis. The clinical characteristics of 62 male patients with LN were compared with 62 female patients with LN. The result indicated the distribution of LN onset ages was different between male and female patients with LN. The incidence of LN was higher in the male than in female patients with SLE. Male patients were often misdiagnosed or diagnosed long after the onset of the disease. Arthritis and positive rate of ANA were less commonly occurred in female patients with LN. Other clinical and pathologic features of LN were similar in male and female patients. The response to treatment and prognosis of male patients with LN was relatively poor. So male patients with LN should be paid more attention to.

Adolescent↗
PubMed1999

Chronic phospholamban-sarcoplasmic reticulum calcium ATPase interaction is the critical calcium cycling defect in dilated cardiomyopathy.

Dilated cardiomyopathy and end-stage heart failure result in multiple defects in cardiac excitation-contraction coupling. Via complementation of a genetically based mouse model of dilated cardiomyopathy, we now provide evidence that progressive chamber dilation and heart failure are dependent on a Ca2+ cycling defect in the cardiac sarcoplasmic reticulum. The ablation of a muscle-specific sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) inhibitor, phospholamban, rescued the spectrum of phenotypes that resemble human heart failure. Inhibition of phospholamban-SERCA2a interaction via in vivo expression of a phospholamban point mutant dominantly activated the contractility of ventricular muscle cells. Thus, interfering with phospholamban-SERCA2a interaction may provide a novel therapeutic approach for preventing the progression of dilated cardiomyopathy.

Animals↗
PubMed1999

Structure of DNA-dependent protein kinase: implications for its regulation by DNA.

DNA double-strand breaks are created by ionizing radiation or during V(D)J recombination, the process that generates immunological diversity. Breaks are repaired by an end-joining reaction that requires DNA-PKCS, the catalytic subunit of DNA-dependent protein kinase. DNA-PKCS is a 460 kDa serine-threonine kinase that is activated by direct interaction with DNA. Here we report its structure at 22 A resolution, as determined by electron crystallography. The structure contains an open channel, similar to those seen in other double-stranded DNA-binding proteins, and an enclosed cavity with three openings large enough to accommodate single-stranded DNA, with one opening adjacent to the open channel. Based on these structural features, we performed biochemical experiments to examine the interactions of DNA-PKCS with different DNA molecules. Efficient kinase activation required DNA longer than 12 bp, the minimal length of the open channel. Competition experiments demonstrated that DNA-PKCS binds to double- and single-stranded DNA via separate but interacting sites. Addition of unpaired single strands to a double-stranded DNA fragment stimulated kinase activation. These results suggest that activation of the kinase involves interactions with both double- and single-stranded DNA, as suggested by the structure. A model for how the kinase is regulated by DNA is described.

Binding Sites↗
PubMed1999

Expression of the p48 xeroderma pigmentosum gene is p53-dependent and is involved in global genomic repair.

In human cells, efficient global genomic repair of DNA damage induced by ultraviolet radiation requires the p53 tumor suppressor, but the mechanism has been unclear. The p48 gene is required for expression of an ultraviolet radiation-damaged DNA binding activity and is disrupted by mutations in the subset of xeroderma pigmentosum group E cells that lack this activity. Here, we show that p48 mRNA levels strongly depend on basal p53 expression and increase further after DNA damage in a p53-dependent manner. Furthermore, like p53(-/-) cells, xeroderma pigmentosum group E cells are deficient in global genomic repair. These results identify p48 as the link between p53 and the nucleotide excision repair apparatus.

DNA Damage↗
PubMed1999

The T allele of the hepatic lipase promoter variant C-480T is associated with increased fasting lipids and HDL and increased preprandial and postprandial LpCIII:B : European Atherosclerosis Research Study (EARS) II.

The common C-480T transition in the hepatic lipase (HL) promoter has been shown to be associated with lower HL activity and increased high density lipoprotein (HDL) cholesterol. We examined the frequency and lipid associations of this HL polymorphism in 385 healthy, young (18- to 28-year-old) men whose fathers had had a premature myocardial infarction (designated cases) and 405 age-matched controls. These individuals were participants in the European Atherosclerosis Research Study II postprandial trial, who had been recruited from 11 European countries in 4 regions (the Baltic; United Kingdom; and central and southern Europe). Overall, the frequency of the T allele was 0.207 in controls and 0.244 in cases (P=0.08). The T allele was associated with higher fasting plasma total cholesterol (P<0.01), triglycerides (P<0.01), and HDL cholesterol (P<0.01). The strongest association was found with apolipoprotein (apo) A-I concentration, which was 10% higher in individuals homozygous for the T allele compared with those homozygous for the C allele (P<0.001). This polymorphism had no effect on the rise in plasma triglyceride levels after a fatty meal. However, before and after the fat load was ingested, levels of particles containing both apoC-III and apoB (LpC-III:B) were higher in carriers of the T allele, with homozygotes having 23% and 27% higher levels preprandially and postprandially, respectively, than those homozygous for the C allele (P<0.05). Thus, our results demonstrate that the C-480T polymorphism in the HL promoter is associated with alterations in plasma lipids and lipoproteins and the accumulation of atherogenic LpC-III:B particles.

Adolescent↗
PubMed1999

Sensitivity and value of digital CT scout radiography for detecting ureteral stones in patients with ureterolithiasis diagnosed on unenhanced CT.

OBJECTIVE: When unenhanced CT reveals ureterolithiasis, some patients will require baseline or follow-up conventional radiography to help guide clinical management. We sought to determine the sensitivity of routinely obtained scout radiographs for revealing stones to determine if the scout view can be used in place of baseline conventional radiography. MATERIALS AND METHODS: We retrospectively reviewed the CT scout radiographs in conjunction with axial CT images in a series of 215 consecutive patients in whom CT revealed a single ureteral stone. On the scout radiographs, stones were classified as definitely visible, definitely not visible, or indeterminate. In addition, a phantom was constructed using fragments of kidney stones to evaluate the effect of the digital scout kilovoltage settings on stone visualization. RESULTS: Forty-nine percent of stones were definitely visible on scout radiography, 47% were definitely not visible, and 4% were indeterminate. Four stones larger than 10 mm that were not visible on scout radiography were composed of uric acid (n = 2) or xanthine (n = 2). Scout radiographs of the phantom determined an optimal kilovoltage setting of 80-100 kVp to visualize stones less than 3 mm, whereas stones greater than or equal to 3 mm were visible at all kilovoltage settings. CONCLUSION: In our series, 49% of ureteral stones were visible on the often-overlooked routine CT scout radiograph. Imaging of phantoms showed that stone visualization can be optimized by using the lowest kilovoltage settings. Therefore, the CT scout view can be used as a baseline study in patients requiring follow-up radiography and for planning treatment of patients requiring lithotripsy or other intervention. Finally, large stones not visible on scout radiographs are likely composed of uric acid or xanthine.

Abdominal Pain↗