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Michael Chang

Publications and source records attributed to Michael Chang.

18 recordsLinked to original sources
PubMed2006

BLAP75/RMI1 promotes the BLM-dependent dissolution of homologous recombination intermediates.

BLM encodes a member of the highly conserved RecQ DNA helicase family, which is essential for the maintenance of genome stability. Homozygous inactivation of BLM gives rise to the cancer predisposition disorder Bloom's syndrome. A common feature of many RecQ helicase mutants is a hyperrecombination phenotype. In Bloom's syndrome, this phenotype manifests as an elevated frequency of sister chromatid exchanges and interhomologue recombination. We have shown previously that BLM, together with its evolutionarily conserved binding partner topoisomerase IIIalpha (hTOPO IIIalpha), can process recombination intermediates that contain double Holliday junctions into noncrossover products by a mechanism termed dissolution. Here we show that a recently identified third component of the human BLM/hTOPO IIIalpha complex, BLAP75/RMI1, promotes dissolution catalyzed by hTOPO IIIalpha. This activity of BLAP75/RMI1 is specific for dissolution catalyzed by hTOPO IIIalpha because it has no effect in reactions containing either Escherichia coli Top1 or Top3, both of which can also catalyze dissolution in a BLM-dependent manner. We present evidence that BLAP75/RMI1 acts by recruiting hTOPO IIIalpha to double Holliday junctions. Implications of the conserved ability of type IA topoisomerases to catalyze dissolution and how the evolution of factors such as BLAP75/RMI1 might confer specificity on the execution of this process are discussed.

Adenosine Triphosphatases↗
PubMed2006

Genomic approaches for identifying DNA damage response pathways in S. cerevisiae.

DNA damage response pathways have been studied extensively in the budding yeast Saccharomyces cerevisiae, yet new genes with roles in the DNA damage response are still being identified. In this chapter we describe the use of functional genomic approaches in the identification of DNA damage response genes and pathways. These techniques take advantage of the S. cerevisiae gene deletion mutant collection, either as an ordered array or as a pool, and can be automated for high throughput.

Base Sequence↗
PubMed2005

Impact of platelet glycoprotein IIb/IIIa Inhibition on the paclitaxel-eluting stent in patients with stable or unstable angina pectoris or provocable myocardial ischemia (a TAXUS IV substudy).

Whether the benefits that glycoprotein IIb/IIIa inhibitors confer in patients who undergo bare metal stent implantation extend to drug-eluting stents is unknown. We performed a prespecified subgroup analysis of the TAXUS IV study population to examine the effect of procedural glycoprotein IIb/IIIa inhibition during paclitaxel-eluting stent implantation on periprocedural creatine kinase-MB (CK-MB) levels. Glycoprotein (GP) IIb/IIIa inhibitors were administered to 57.7% of patients who had been randomized to receive the TAXUS stent and to 56.7% of those who had been randomized to receive the control stent. Among patients who received the TAXUS stent, the rate of CK-MB increases of >3 times the normal level was 2.6-fold higher in those who received a GP IIb/IIIa inhibitor than in those who did not (11.4% vs 4.4%, p = 0.0015). Composite rates of major adverse cardiac events and target vessel failure were also higher at 1 month in the GP IIb/IIIa group. By multivariate analysis, use of GP IIb/IIIa inhibitors during stenting with the TAXUS stent was an independent predictor of CK-MB increases >3 times the normal level. Further studies are warranted.

Abciximab↗
PubMed2005

RMI1/NCE4, a suppressor of genome instability, encodes a member of the RecQ helicase/Topo III complex.

SGS1 encodes a DNA helicase whose homologues in human cells include the BLM, WRN, and RECQ4 genes, mutations in which lead to cancer-predisposition syndromes. Clustering of synthetic genetic interactions identified by large-scale genetic network analysis revealed that the genetic interaction profile of the gene RMI1 (RecQ-mediated genome instability, also known as NCE4 and YPL024W) was highly similar to that of SGS1 and TOP3, suggesting a functional relationship between Rmi1 and the Sgs1/Top3 complex. We show that Rmi1 physically interacts with Sgs1 and Top3 and is a third member of this complex. Cells lacking RMI1 activate the Rad53 checkpoint kinase, undergo a mitotic delay, and display increased relocalization of the recombination repair protein Rad52, indicating the presence of spontaneous DNA damage. Consistent with a role for RMI1 in maintaining genome integrity, rmi1Delta cells exhibit increased recombination frequency and increased frequency of gross chromosomal rearrangements. In addition, rmi1Delta strains fail to fully activate Rad53 upon exposure to DNA-damaging agents, suggesting that Rmi1 is also an important part of the Rad53-dependent DNA damage response.

Adenosine Triphosphatases↗
PubMed2004

Global mapping of the yeast genetic interaction network.

A genetic interaction network containing approximately 1000 genes and approximately 4000 interactions was mapped by crossing mutations in 132 different query genes into a set of approximately 4700 viable gene yeast deletion mutants and scoring the double mutant progeny for fitness defects. Network connectivity was predictive of function because interactions often occurred among functionally related genes, and similar patterns of interactions tended to identify components of the same pathway. The genetic network exhibited dense local neighborhoods; therefore, the position of a gene on a partially mapped network is predictive of other genetic interactions. Because digenic interactions are common in yeast, similar networks may underlie the complex genetics associated with inherited phenotypes in other organisms.

Amino Acid Sequence↗
PubMed2004

Identification of protein complexes required for efficient sister chromatid cohesion.

Ctf8p is a component of Ctf18-RFC, an alternative replication factor C-like complex required for efficient sister chromatid cohesion in Saccharomyces cerevisiae. We performed synthetic genetic array (SGA) analysis with a ctf8 deletion strain as a primary screen to identify other nonessential genes required for efficient sister chromatid cohesion. We then assessed proficiency of cohesion at three chromosomal loci in strains containing deletions of the genes identified in the ctf8 SGA screen. Deletion of seven genes (CHL1, CSM3, BIM1, KAR3, TOF1, CTF4, and VIK1) resulted in defective sister chromatid cohesion. Mass spectrometric analysis of immunoprecipitated complexes identified a physical association between Kar3p and Vik1p and an interaction between Csm3p and Tof1p that we confirmed by coimmunoprecipitation from cell extracts. These data indicate that synthetic genetic array analysis coupled with specific secondary screens can effectively identify protein complexes functionally related to a reference gene. Furthermore, we find that genes involved in mitotic spindle integrity and positioning have a previously unrecognized role in sister chromatid cohesion.

Chromatids↗
PubMed2004

Prevention, early detection, and management of complications after 328 consecutive extrapleural pneumonectomies.

OBJECTIVE: Extrapleural pneumonectomy for therapy of mesothelioma has been associated with significant perioperative mortality and morbidity. Postoperative complications of this procedure require a unique management approach. We developed treatment algorithms for most of the common complications of extrapleural pneumonectomy resulting in reduced mortality and hospital stay. Complications after extrapleural pneumonectomy were further analyzed to elucidate means of prevention, early detection, and treatment. METHODS: A total of 496 patients undergoing extrapleural pneumonectomy were reviewed for mortality rates, with a subset of 328 consecutive patients between 1980 and 2000 who were examined for detailed morbidity data by using a prospective clinical database. RESULTS: Median age was 58 years (range, 28-77 years), with a 10-day (range, 4-101 days) median length of stay. One hundred ninety-eight (60.4%) of 328 patients experienced minor and major complications, and 11 of 328 patients died, for an overall mortality rate of 3.4%. Complications included the following: atrial fibrillation (145 [44.2%]), prolonged intubation (26 [7.9%]), vocal cord paralysis (22 [6.7%]), deep vein thrombosis (21 [6.4%]), technical complications (patch dehiscence, hemorrhage, or both; 20 [6.1%]), tamponade (12 [3.6%]), acute respiratory distress syndrome (12 [3.6%]), cardiac arrest (10 [3%]), constrictive physiology (9 [2.7%]), aspiration (9 [2.7%]), renal failure (9 [2.7%]), empyema (8 [2.4%]), tracheostomy (6 [1.8%]), myocardial infarction (5 [1.5%]), pulmonary embolus (5 [1.5%]), and bronchopleural fistula (2 [0.6%]). Clinical data demonstrated the following: (1) prophylaxis for atrial fibrillation is recommended; (2) early ambulation, aspiration precautions, endoscopic assessment of the vocal cords, and avoidance of fluid overload are crucial; (3) perioperative diagnosis and aggressive management of deep vein thrombosis are important; (4) immediate reoperation and open cardiac massage are essential for relief of cardiac herniation and tamponade from cardiac patch dysfunction; (5) diaphragmatic patch dehiscence, hemorrhage, or both require immediate reoperation; (6) early signs of infection might indicate bronchopleural fistula or empyema and should be treated with thoracoscopic or open drainage and staged removal of patch material; and (7) excessive perioperative mediastinal shift is treated with a catheter placed intraoperatively. CONCLUSION: Complications after extrapleural pneumonectomy require a unique approach to management, and mortality can be minimized by early detection and aggressive treatment.

Adult↗
PubMed2004

An EP overexpression screen for genetic modifiers of Notch pathway function in Drosophila melanogaster.

The Notch pathway comprises a signal transduction cascade required for the proper formation of multiple tissues during metazoan development. Originally described in Drosophila for its role in nervous system formation, the pathway has attracted much wider interest owing to its fundamental roles in a range of developmental and disease-related processes. Despite extensive analysis, Notch signaling is not completely understood and it appears that additional components of the pathway remain to be identified and characterized. Here, we describe a novel genetic strategy to screen for additional Notch pathway genes. The strategy combines partial loss of function for pathway activity with Enhancer-promoter (EP)-induced overexpression of random loci across the dorsoventral wing margin. Mastermind (Mam) is a nuclear component of the Notch signaling cascade. Using a GAL4-UAS-driven dominant-negative form of Mam, we created a genotype that exhibits a completely penetrant dominant wing-nicking phenotype. This phenotype was assayed for enhancement or suppression after outcrossing to several thousand EP lines. The screen identified known components or modifiers of Notch pathway function, as well as several potential new components. Our results suggest that a genetic screen that combines partial loss of function with random gene overexpression might be a useful strategy in the analysis of developmental pathways.

Animals↗
PubMed2004

The origin recognition complex links replication, sister chromatid cohesion and transcriptional silencing in Saccharomyces cerevisiae.

Mutations in genes encoding the origin recognition complex (ORC) of Saccharomyces cerevisiae affect initiation of DNA replication and transcriptional repression at the silent mating-type loci. To explore the function of ORC in more detail, a screen for genetic interactions was undertaken using large-scale synthetic lethal analysis. Combination of orc2-1 and orc5-1 alleles with the complete set of haploid deletion mutants revealed synthetic lethal/sick phenotypes with genes involved in DNA replication, chromatin structure, checkpoints, DNA repair and recombination, and other genes that were unexpected on the basis of previous studies of ORC. Many of these genetic interactions are shared with other genes that are involved in initiation of DNA replication. Strong synthetic interactions were demonstrated with null mutations in genes that contribute to sister chromatid cohesion. A genetic interaction between orc5-1 and the cohesin mutant scc1-73 suggested that ORC function contributes to sister chromatid cohesion. Thus, comprehensive screening for genetic interactions with a replication gene revealed a connection between initiation of DNA replication and sister chromatid cohesion. Further experiments linked sister chromatid cohesion genes to silencing at mating-type loci and telomeres.

DNA Replication↗
PubMed2003

Elg1 forms an alternative RFC complex important for DNA replication and genome integrity.

Genome-wide synthetic genetic interaction screens with mutants in the mus81 and mms4 replication fork-processing genes identified a novel replication factor C (RFC) homolog, Elg1, which forms an alternative RFC complex with Rfc2-5. This complex is distinct from the DNA replication RFC, the DNA damage checkpoint RFC and the sister chromatid cohesion RFC. As expected from its genetic interactions, elg1 mutants are sensitive to DNA damage. Elg1 is redundant with Rad24 in the DNA damage response and contributes to activation of the checkpoint kinase Rad53. We find that elg1 mutants display DNA replication defects and genome instability, including increased recombination and mutation frequencies, and minichromosome maintenance defects. Mutants in elg1 show genetic interactions with pathways required for processing of stalled replication forks, and are defective in recovery from DNA damage during S phase. We propose that Elg1-RFC functions both in normal DNA replication and in the DNA damage response.

Carrier Proteins↗
PubMed2003

Adenovirus-mediated gene transfer of enhanced Herpes simplex virus thymidine kinase mutants improves prodrug-mediated tumor cell killing.

The Herpes simplex virus 1 (HSV) thymidine kinase (tk) suicide gene together with ganciclovir (GCV) have been successfully used for the in vivo treatment of various solid tumors and for the ablation of unwanted transfused stem cells in recent clinical trials. With the aim of improving this therapeutic system, we compared the potential efficacy of adenoviral (Ad) vectors expressing enhanced tk mutants in vitro and in vivo. The previously created HSV-tk mutants dm30 and sr39, created by random sequence mutagenesis, were inserted into a standard Ad.RSV E1(-)E3(-) backbone using homologous recombination. GCV killing of Ad.HSV-tk, Ad.dm30-tk and Ad.sr39-tk was assessed in various tumor cell lines with a cell proliferation assay. Cells expressing the two TK mutants were two-to-five-fold more sensitive to GCV when compared with Ad.HSV-tk transduced cells in all cell lines tested (five human mesotheliomas, one human lung cancer, a human cervical carcinoma, a mouse fibrosarcoma, and a rat glioma line) at equal TK expression levels. Flank tumor models, including cell-mixing studies, assessed the in vivo efficacy of the engineered viruses in BALB/C and SCID mice. In all animal studies, Ad.dm30-tk and Ad.sr39-tk showed more tumor growth inhibition than Ad.HSV-tk when GCV was administered. The use of adenovirus-mediated gene transfer of both tk mutants dm30-tk and sr39-tk for cancer suicide gene therapy should provide a more effective and safer alternative to wild-type HSV-tk.

Adenoviridae↗
PubMed2003

Affinity purification of PSD-95-containing postsynaptic complexes.

A widely used method for the preparation of postsynaptic density (PSD) fractions consists of treatment of synaptosomal membranes with Triton X-100 and further purification by density gradient centrifugation. In the present study, the purity of this preparation was assessed by electron microscopic analysis. Thin-section and rotary shadow immuno-electron microscopy of the Triton X-100-derived PSD fraction shows many PSD-95-positive structures that resemble in situ PSDs in shape and size. However, the fraction also includes contaminants such as CaMKII clusters, spectrin filaments and neurofilaments. We used magnetic beads coated with an antibody against PSD-95 to further purify PSD-95-containing complexes from the Triton-derived PSD fraction. Biochemical analysis of the affinity-purified material shows a substantial reduction in the astrocytic marker glial fibrillary acidic protein and electron microscopic analysis shows mostly individual PSDs attached to magnetic beads. This preparation was used to assess the association of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)-type glutamate receptors with the PSD-95-containing complex. AMPA receptors are demonstrated by immunoblotting to be present in the complex, although they do not co-purify exclusively with PSD-95, suggesting the existence of two pools of receptors, one associated with the PSD-95 scaffold and the other not. Of the AMPA receptor-anchoring proteins tested, SAP-97 is present in the affinity-purified preparation whereas GRIP is found only in trace amounts. These results imply that a subpopulation of AMPA receptors is anchored to the PSD-95-containing scaffold through interaction of GluR1 with SAP-97.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Student leadership in public health advocacy: lessons learned from the hepatitis B initiative.

Increasing hepatitis B vaccination rates for Asian Americans and Pacific Islanders is a priority. Laws requiring vaccination prior to school enrollment have helped, yet many youths remain unvaccinated. The Hepatitis B Initiative (HBI), launched in 1997 and operated by public health and medical school students, provides free screenings and vaccinations to Boston's Asian American/Pacific Islander community, with a focus on youths. By October 2002, 997 HBI patients from Boston's Chinatown had received free hepatitis B screenings. Of these, 384 patients (39%) were deemed susceptible to the hepatitis B virus and provided with free vaccination.

Adolescent↗
PubMed2002

A genome-wide screen for methyl methanesulfonate-sensitive mutants reveals genes required for S phase progression in the presence of DNA damage.

We performed a systematic screen of the set of approximately 5,000 viable Saccharomyces cerevisiae haploid gene deletion mutants and have identified 103 genes whose deletion causes sensitivity to the DNA-damaging agent methyl methanesulfonate (MMS). In total, 40 previously uncharacterized alkylation damage response genes were identified. Comparison with the set of genes known to be transcriptionally induced in response to MMS revealed surprisingly little overlap with those required for MMS resistance, indicating that transcriptional regulation plays little, if any, role in the response to MMS damage. Clustering of the MMS response genes on the basis of their cross-sensitivities to hydroxyurea, UV radiation, and ionizing radiation revealed a DNA damage core of genes required for responses to a broad range of DNA-damaging agents. Of particular significance, we identified a subset of genes that show a specific MMS response, displaying defects in S phase progression only in the presence of MMS. These genes may promote replication fork stability or processivity during encounters between replication forks and DNA damage.

DNA Damage↗
PubMed2002

The vacuum assisted closure device: a method of securing skin grafts and improving graft survival.

HYPOTHESIS: Use of the vacuum assisted closure device (VAC) for securing split-thickness skin grafts (STSGs) is associated with improved wound outcomes compared with bolster dressings. DESIGN: Consecutive case series. PATIENTS AND SETTING: Consecutive patients at a level I trauma center requiring STSG due to traumatic or thermal tissue loss during an 18-month period. MAIN OUTCOME MEASURE: Repeated skin grafting due to failure of the initial graft. Secondary outcome measures included dressing-associated complications, percentage of graft take, and length of hospital stay. RESULTS: Sixty-one patients underwent STSG placement. Indications for STSG were burn injury (n = 32), soft tissue loss (n = 27), and fasciotomy-site coverage (n = 2). Patients were treated with the VAC (n = 34) or the bolster dressing (n = 27). The VAC group required significantly fewer repeated STSGs (1 [3%] vs 5 [19%]; P =.04). Two additional graft failures occurred in the no-VAC group, but repeated STSGs were refused by these patients. No difference was seen between the groups in age, percentage of graft take, or hospital length of stay. The no-VAC group had significantly larger grafts (mean +/- SD, 984 +/- 996 vs 386 +/- 573 cm(2); P =.006). The patients requiring repeated STSGs (n = 6) did not have significantly larger grafts than those not requiring repeated STSGs (mean +/- SD, 617 +/- 717 vs 658 +/- 857 cm(2); P =.62). No dressing-associated complications occurred in the VAC group. CONCLUSIONS: The VAC provides a safe and effective method for securing STSGs and is associated with improved graft survival as measured by a reduction in number of repeated STSGs.

Adult↗
PubMed2002

Adenosine dose should be less when administered through a central line.

A patient with a port-a-cath was given 12 mg of adenosine for paroxysmal supraventricular tachycardia (PSVT), resulting in prolonged (13 s) bradycardia and severe side effects. When the same patient presented 2 weeks later for recurrent PSVT, only 3 mg of adenosine was needed to terminate the episode, without the patient experiencing prolonged bradycardia or severe side effects. The literature suggests that for patients with central venous catheters, a lower dose of adenosine should be used to terminate PSVT.

Adenosine↗
PubMedDate not supplied

Pushrim biomechanics and injury prevention in spinal cord injury: recommendations based on CULP-SCI investigations.

Over 50 percent of manual wheelchair users with spinal cord injury (SCI) are likely to develop upper-limb pain and injury. The majority of studies related to pain have implicated wheelchair propulsion as a cause. This paper draws from a large multisite trial and a long-standing research program to make specific recommendations related to wheelchair propulsion that may decrease the risk of upper-limb injury. The studies include over 60 subjects over 1 yr after a traumatic SCI below the second thoracic level. Specific aspects of the propulsive stroke that may relate to injury include cadence, magnitude of force, and the pattern of the hand during the nonpropulsive part of the stroke. Lower peak forces, slower cadence, and a circular propulsive stroke in which the hand falls below the pushrim during recovery may help prevent injury. In addition, wheelchair users should use the lightest weight adjustable wheelchair possible. Future work should include interventional trials and larger studies that allow for more complex statistical models that can further detail the relationship between wheelchair propulsion, user characteristics, and upper-limb injuries.

Adult↗