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Biomedical subjects

L H Nguyen

Publications and source records attributed to L H Nguyen.

At least 19 recordsLinked to original sources
PubMed2001

The human interferon- and estrogen-regulated ISG20/HEM45 gene product degrades single-stranded RNA and DNA in vitro.

The human ISG20/HEM45 gene was identified independently on the basis of its increased level of expression in response to either interferon or estrogen hormone. Notably, the encoded protein is homologous with members of the 3' to 5' exonuclease superfamily that includes RNases T and D, and the proofreading domain of Escherichia coli DNA polymerase I. We provide here direct biochemical evidence that Isg20 acts as a 3' to 5' exonuclease in vitro. This protein displays a pH optimum of approximately 7.0, prefers Mn2+ as a metal cofactor, and degrades RNA at a rate that is approximately 35-fold higher than its rate for single-stranded DNA. Along with RNase L, Isg20 is the second known RNase regulated by interferon. Previous data showed that Isg20 is located in promyelocytic leukemia (PML) nuclear bodies, known sites of hormone-dependent RNA polymerase II transcription and oncogenic DNA viral transcription and replication. The combined data suggest a potential role for Isg20 in degrading viral RNAs as part of the interferon-regulated antiviral response and/or cellular mRNAs as a regulatory component of interferon and estrogen signaling.

Carrier Proteins↗
PubMed2001

Micrometastasis to in-transit lymph nodes from extremity and truncal malignant melanoma.

BACKGROUND: The sentinel lymph node (SLN) is the first lymph node in the regional nodal basin to receive metastatic cells. In-transit nodes are found between the primary melanoma site and regional nodal basins. To date, this is one of the first reports on micrometastasis to in-transit nodes. METHODS: Retrospective database and medical records were reviewed from October 21, 1993, to November 19. 1999. At the UCSF Melanoma Center, patients with tumor thickness > 1 mm or < 1 mm with high-risk features are managed with preoperative lymphoscintigraphy, selective SLN dissection, and wide local excision. RESULTS: Thirty (5%) out of 557 extremity and truncal melanoma patients had in-transit SLNs. Three patients had positive in-transit SLNs and negative SLNs in the regional nodal basin. Two patients had positive in-transit and regional SLNs. Three patients had negative in-transit SLNs but positive regional SLNs. The remaining 22 patients were negative for in-transit and regional SLNs. CONCLUSIONS: In-transit SLNs may harbor micrometastasis. About 10% of the time, micrometastasis may involve the in-transit and not the regional SLN. Therefore, both in-transit and regional SLNs should be harvested.

Extremities↗
PubMed2001

Promoter recognition and discrimination by EsigmaS RNA polymerase.

Although more than 30 Escherichia coli promoters utilize the RNA polymerase holoenzyme containing sigmaS (EsigmaS), and it is known that there is some overlap between the promoters recognized by EsigmaS and by the major E. coli holoenzyme (Esigma70), the sequence elements responsible for promoter recognition by EsigmaS are not well understood. To define the DNA sequences recognized best by EsigmaS in vitro, we started with random DNA and enriched for EsigmaS promoter sequences by multiple cycles of binding and selection. Surprisingly, the sequences selected by EsigmaS contained the known consensus elements (-10 and -35 hexamers) for recognition by Esigma70. Using genetic and biochemical approaches, we show that EsigmaS and Esigma70 do not achieve specificity through 'best fit' to different consensus promoter hexamers, the way that other forms of holoenzyme limit transcription to discrete sets of promoters. Rather, we suggest that EsigmaS-specific promoters have sequences that differ significantly from the consensus in at least one of the recognition hexamers, and that promoter discrimination against Esigma70 is achieved, at least in part, by the two enzymes tolerating different deviations from consensus. DNA recognition by EsigmaS versus Esigma70 thus presents an alternative solution to the problem of promoter selectivity.

Bacterial Proteins↗
PubMed2001

Evaluation of sentinel lymph node status in spindle cell melanomas.

BACKGROUND: The propensity for spindle cell melanoma to metastasize to the lymph node is relatively low despite its relative thick depth. To date, there are no published reports on the sentinel lymph node (SLN) status in patients diagnosed with spindle cell melanoma and desmoplastic malignant melanoma (DMM). OBJECTIVE: Our purpose was to report our experience on the SLN status in spindle cell melanoma and DMM. METHODS: We undertook a retrospective database and medical record review from Oct 21, 1993 to Sept 29, 1999. At the University of California at San Francisco Melanoma Center, patients with tumor thickness greater than 1 mm or less than 1 mm with high-risk features are managed with preoperative lymphoscintigraphy, selective SLN dissection, and wide excision. RESULTS: Of 29 patients diagnosed with spindle cell melanoma and DMM, 28 had negative SLNs and are free of disease except for one patient who experienced splenic, bony, and brain metastases. The mean follow-up in this population was 16.5 and 11 months, respectively. CONCLUSION: Our preliminary findings show that SLNs from patients diagnosed with spindle cell melanoma and DMM only rarely harbor micrometastasis despite their relative thickness. A larger number of cases from multicenter databases may further define the true biology of SLNs in this melanoma variant.

Adult↗
PubMed2000

The human homolog of Escherichia coli Orn degrades small single-stranded RNA and DNA oligomers.

We report here the identification of human homologues to the essential Escherichia coli Orn protein and the related yeast mitochondrial DNA-escape pathway regulatory factor Ynt20. The human proteins appear to arise from alternatively spliced transcripts, and are thus identical, except the human Ynt20 equivalent contains an NH(2)-terminal extension that possesses a predicted mitochondrial protease cleavage signal. In vitro analysis revealed that the smaller human protein exhibits a 3' to 5' exonuclease activity for small (primarily </=5 nucleotides in length) single-stranded RNA and DNA oligomers. We have named this human protein Sfn for small fragment nuclease to reflect its broad substrate range, and have termed the longer protein hSfnalpha. Sfn prefers Mn(2+) as a metal cofactor and displays a temperature-resistant (to 50 degrees C) nuclease activity. Kinetic analysis indicates that Sfn exhibits a similar affinity for small RNAs and DNAs (K(m) of approximately 1.5 micrometer), but degrades small RNAs approximately 4-fold more efficiently than DNA. Mutation of a conserved aspartate (Asp(136)) to alanine abolishes both nuclease activities of Sfn. Northern blot analysis revealed that a 1-kilobase transcript corresponding to SFN and/or SFNalpha (these mRNAs differ by only two nucleotides) is expressed at varying levels in all fetal and adult human tissues examined. Expressed tag sequence clone analysis found that the two splice variants, SFN to SFNalpha, are present at a ratio of roughly 4 to 1, respectively. The results presented within suggest a role for human Sfn in cellular nucleotide recycling.

14-3-3 Proteins↗
PubMed2000

Mapping the protein-DNA interface and the metal-binding site of the major human apurinic/apyrimidinic endonuclease.

Apurinic/apyrimidinic (AP) endonuclease Ape1 is a key enzyme in the mammalian base excision repair pathway that corrects AP sites in the genome. Ape1 cleaves the phosphodiester bond immediately 5' to AP sites through a hydrolytic reaction involving a divalent metal co-factor. Here, site-directed mutagenesis, chemical footprinting techniques, and molecular dynamics simulations were employed to gain insights into how Ape1 interacts with its metal cation and AP DNA. It was found that Ape1 binds predominantly to the minor groove of AP DNA, and that residues R156 and Y128 contribute to protein-DNA complex stability. Furthermore, the Ape1-AP DNA footprint does not change along its reaction pathway upon active-site coordination of Mg(2+) or in the presence of DNA polymerase beta (polbeta), an interactive protein partner in AP site repair. The DNA region immediately 5' to the abasic residue was determined to be in close proximity to the Ape1 metal-binding site. Experimental evidence is provided that amino acid residues E96, D70, and D308 of Ape1 are involved in metal coordination. Molecular dynamics simulations, starting from the active site of the Ape1 crystal structure, suggest that D70 and E96 bind directly to the metal, while D308 coordinates the cation through the first hydration shell. These studies define the Ape1-AP DNA interface, determine the effect of polbeta on the Ape1-DNA interaction, and reveal new insights into the Ape1 active site and overall protein dynamics.

Amino Acid Substitution↗
PubMed2000

Xanthones and triterpenoids from the bark of Garcinia vilersiana.

The hexane extract of the bark of Garcinia vilersiana from Vietnam contained four triterpenoids (olean-12-ene-3beta,11alpha-diol, lupeol, beta-amyrin and oleanolic acid), and six xanthones (globuxanthone, subelliptenone H, subelliptenone B, 12b-hydroxy-des-D-garcigerrin A, 1-O-methylglobuxanthone and symphoxanthone). The structure of 1-O-methylglobuxanthone, the only novel compound, was determined using 1D and 2D NMR techniques and by correlation with globuxanthone.

Magnetic Resonance Spectroscopy↗
PubMed2000

Computer databases for the sentinel lymph node program.

At the University of California San Francisco Comprehensive Cancer Center, a computer database system was created using the FileMaker Pro database program. The system allows the clinical team to bring together data from all aspects of a multidisciplinary effort toward improving daily clinical management, for research, and ultimately, for the clinical standard of care for melanoma patients. With modest objectives during the initiation of the database, its adaptability has allowed it to become an integral link in all the efforts of the melanoma program. For the future, tapping into the immense potential of the Internet has begun to organize multicenter efforts. Through nationwide collaboration, the Sentinel Lymph Node Working Group will be able to follow, on a larger scale, the successes of the FileMaker pro database at the UCSF Comprehensive Cancer Center.

Aftercare↗
PubMed2000

Dimensionality and reliability of the Civilian Mississippi Scale for PTSD in a postearthquake community.

This study examines psychometric properties of the Civilian Mississippi Scale for posttraumatic stress disorder when administered in a community survey of 656 persons following the 1989 Loma Prieta earthquake. Internal consistency was lower (Cronbach's alpha = .73) than for previous analyses of civilian and combat versions of the Mississippi Scale. The analysis produced one strong factor composed of 25 items with regular wording and a second, weaker factor composed of 10 items with reversed wording. Internal consistency was higher when the 10 reversed items were removed (Cronbach's alpha = .86); the two factors were negatively correlated. Traumatic experiences and psychological distress measures explained more variance in the 25-item factor than in the 35-item scale. Further studies should focus on content analysis and performance of the reversed items.

Adult↗
PubMed1999

Oral acyclovir after penetrating keratoplasty for herpes simplex keratitis.

OBJECTIVE: To determine the efficacy of systemic acyclovir in decreasing complications and improving the outcome of penetrating keratoplasty for herpes simplex virus (HSV) keratitis. METHODS: Retrospective study of 53 primary penetrating keratoplasties for HSV keratitis at an eye hospital from January 1, 1989, through December 31, 1996. Medical records were analyzed for history of HSV keratitis, preoperative neovascularization, and disease activity. Postoperative use of acyclovir, recurrence of HSV keratitis, rejection, uveitis or edema, and graft failure were evaluated. RESULTS: Twenty-four patients (mean +/- SD follow-up, 44.7 +/- 32.6 months) received no acyclovir and were compared with 20 patients, (mean +/- SD follow-up, 28.8 +/- 16.7 months), who received 400 mg acyclovir twice a day for at least 1 year. No patient in the acyclovir group had a recurrence of dendritic keratitis in the first year compared with 5 (21%) of the patients who did not receive acyclovir (P = .03). No patient had graft failure in the acyclovir group compared with 4 (17%) in the group without acyclovir after 1 year of follow-up (P = .06). CONCLUSION: Postoperative systemic acyclovir therapy after penetrating keratoplasty for HSV keratitis is associated with a reduced rate of recurrent HSV dendritic keratitis and possible graft failure at 1 year of follow-up.

Acyclovir↗
PubMed1999

Evidence that a single replication fork proceeds from early to late replicating domains in the IgH locus in a non-B cell line.

In non-B cell lines, like the murine erythroleukemia cell line (MEL), the most distal IgH constant region gene, C alpha, replicates early in S; other heavy chain constant region genes, joining and diversity segments, and the most proximal Vh gene replicate successively later in S in a 3' to 5' direction proportional to their distance from C alpha. In MEL, replication forks detected in the IgH locus also proceed in the same 3' to 5' direction for approximately 400 kb, beginning downstream of the IgH 3' regulatory region and continuing to the D region, as well as within the Vh81X gene. Downstream of the initiation region is an early replicating domain, and upstream of Vh81X is a late replicating domain. Hence, the gradual transition between early and late replicated domains can be achieved by a single replication fork.

Animals↗
PubMed1998

Injuries as a result of California earthquakes in the past decade.

The devastating effects of earthquakes have been demonstrated repeatedly in the past decade, through moderate and major earthquakes such as the October 1987 Whittier Narrows earthquake (5.9 on the Richter scale), the October 1989 Loma Prieta earthquake (7.1) and the January 1994 Northridge earthquake (6.7). While 'official' tallies of injuries and deaths are reported for each event, the numbers vary from report to report. For Northridge, the number of injuries vary between 8,000 and 12,000; the number of deaths from 33 to 73 (Peek-Asa et al., 1997; Durkin, 1996). While official estimates are commonly reported following disasters, the study of actual numbers, types and causes of casualties has not developed. In this paper, we identify the numbers and risk factors for injuries within community-based samples across three earthquakes in urban California. We first report the numbers and types of injuries in each earthquake and then identify risk factors specifically associated with the Northridge earthquake.

Adult↗
PubMed1997

Comparative analysis of the interactions of Escherichia coli sigma S and sigma 70 RNA polymerase holoenzyme with the stationary-phase-specific bolAp1 promoter.

We have investigated the interactions of Escherichia coli sigma 70 and sigma S holoenzyme RNA polymerases (E sigma S and E sigma 70) with the stationary-phase-specific bolAp1 promoter by various footprinting methods in vitro. E sigma S and E sigma 70 have been shown to transcribe the bolApl promoter in vitro. We have determined the effects of salt and holoenzyme concentrations on E sigma S and E sigma 70 open complex formation at the bolAp1 promoter in vitro. We have obtained a high-resolution hydroxyl radical (OH.) footprint of E sigma S and E sigma 70 on the bolApl promoter. The OH. footprinting data show remarkable similarities between the footprints of the heparin-resistant transcription complexes of the two holoenzymes which have the same +1 transcription start site. However, there are distinctive differences in the protection patterns in the region between -20 and -10 of the bolAp1 promoter. KMnO4 reactivity assays reveal that, at 37 degrees C, both holoenzymes produced similar but not identical patterns of reactivities.

Base Sequence↗
PubMed1997

Asthma in a Vietnamese refugee population.

Asians and Pacific Islanders comprise a large and growing minority group in the United States, yet data on health status specific to these populations are scant. We conducted an epidemiologic study of asthma in a Vietnamese refugee population to estimate prevalence, evaluate risk factors, and better understand treatments of asthma among Vietnamese individuals. One hundred twenty-four asthma cases were identified from a population of 2,536 new Vietnamese refugees in San Diego (prevalence = 49 per 1,000; 4.9%). Two nonasthmatic control groups of Vietnamese refugees, matched for age and gender with the asthma cases, were recruited for a case-control study, using a questionnaire administered in Vietnamese. Vietnamese asthmatic individuals used both Western and non-Western therapies. Most subjects used traditional health practices, such as coining, cupping, and oil inhalation. As compared with current-refugee controls, the asthmatic subjects used significantly more bleeding (OR: 3.40; 95% CI: 1.06 to 10.80) and herbal ingestion (OR: 1.87; 95% CI: 1.08 to 3.19). As compared with former-refugee controls, the asthmatic subjects used significantly more oil inhalation (OR: 2.58; 95% CI: 1.45 to 4.85), bleeding (OR: 8.64, 95% CI: 1.02 to 73.70), and herbal ingestion (OR: 1.93; 95% CI: 1.02 to 3.67). The presentation and recognition of asthma among the Vietnamese subjects were similar to those in other populations. This information may be helpful in designing culture-specific health-education programs.

Acculturation↗
PubMed1996

Epitope mapping using histidine-tagged protein fragments: application to Escherichia coli RNA polymerase sigma 70.

We present a simple, rapid, and inexpensive method for mapping epitopes of monoclonal antibodies using His-tagged protein fragments. In essence, four steps are involved: (i) purify overproduced His-tagged protein from inclusion body; (ii) fragment the protein by partial chemical or enzymatic hydrolysis and isolate the His-tagged peptides with a Ni(2+)-chelate column to generate a "ladder" containing a distribution of peptide fragment sizes; (iii) fractionate the isolated peptides by SDS-polyacrylamide gel electrophoresis and probe the ladder by immunoblot analysis; (iv) determine the size of the fragments that do and do not bind the monoclonal antibody using size markers specific to the His-tagged protein being studied. We have applied this method successfully to map the epitope positions of known and new monoclonal antibodies to Escherichia coli sigma 70. We believe this method will find broad application.

Antibodies, Monoclonal↗
PubMed1996

Overproduction and purification of sigmaS, the Escherichia coli stationary phase specific sigma transcription factor.

This paper reports the overproduction and the details of a rapid method to purify active sigmaS monomers from a T7 RNA polymerase-based protein expression system. This 2-day procedure involves solubilizing inclusion bodies in sarkosyl detergent, removal of sarkosyl by dialysis, and a single gel filtration column chromatography step. The final yield of sigmaS is about 9 mg of approximately 92% purity from 0.5 g of wet weight cells. Overproduced sigmaS binds to core RNA polymerase and supports transcription from the bolAp1 promoter, a sigmaS-dependent promoter.

Chromatography, Gel↗