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Biomedical subjects

D H Wong

Publications and source records attributed to D H Wong.

At least 19 recordsLinked to original sources
PubMed2001

Biochemical studies of Zmpste24-deficient mice.

Genetic studies in Saccharomyces cerevisiae identified two genes, STE24 and RCE1, involved in cleaving the three carboxyl-terminal amino acids from isoprenylated proteins that terminate with a CAAX sequence motif. Ste24p cleaves the carboxyl-terminal "-AAX" from the yeast mating pheromone a-factor, whereas Rce1p cleaves the -AAX from both a-factor and Ras2p. Ste24p also cleaves the amino terminus of a-factor. The mouse genome contains orthologues for both yeast RCE1 and STE24. We previously demonstrated, with a gene-knockout experiment, that mouse Rce1 is essential for development and that Rce1 is entirely responsible for the carboxyl-terminal proteolytic processing of the mouse Ras proteins. In this study, we cloned mouse Zmpste24, the orthologue for yeast STE24 and showed that it could promote a-factor production when expressed in yeast. Then, to assess the importance of Zmpste24 in development, we generated Zmpste24-deficient mice. Unlike the Rce1 knockout mice, Zmpste24-deficient mice survived development and were fertile. Since no natural substrates for mammalian Zmpste24 have been identified, yeast a-factor was used as a surrogate substrate to investigate the biochemical activities in membranes from the cells and tissues of Zmpste24-deficient mice. We demonstrate that Zmpste24-deficient mouse membranes, like Ste24p-deficient yeast membranes, have diminished CAAX proteolytic activity and lack the ability to cleave the amino terminus of the a-factor precursor. Thus, both enzymatic activities of yeast Ste24p are conserved in mouse Zmpste24, but these enzymatic activities are not essential for mouse development or for fertility.

Amino Acid Sequence↗
PubMed2000

Studies with recombinant Saccharomyces cerevisiae CaaX prenyl protease Rce1p.

Eukaryotic proteins with carboxyl-terminal CaaX motifs undergo three post-translational processing reactions-protein prenylation, endoproteolysis, and carboxymethylation. Two genes in yeast encoding CaaX endoproteases, AFC1 and RCE1, have been identified. Rce1p is solely responsible for proteolysis of yeast Ras proteins. When proteolysis is blocked, plasma membrane localization of Ras2p is impaired. The mislocalization of undermodified Ras in the cell suggests that Rce1p is an attractive target for cancer therapeutics. Homologous expression of plasmid-encoded Saccharomyces cerevisiae RCE1 under the control of the GAL1 promoter gave a 370-fold increase in endoprotease activity over an uninduced control. Yeast Rce1p was detected by Western blotting with a yRce1p antibody or with an anti-myc antibody to Rce1p bearing a C-terminal myc-epitope. Membrane preparations were examined for their sensitivity to a variety of protease inhibitors, metal ion chelators, and heavy metals. The enzyme was sensitive to cysteine protease inhibitors, Zn(2+), and Ni(2+). The substrate selectivity of yRce1p was determined for a variety of prenylated CaaX peptides including farnesylated and geranylgeranylated forms of human Ha-Ras, Ki-Ras, N-Ras, and yeast Ras2p, a-mating factor, and Rho2p. Six site-directed mutants of conserved polar and ionic amino acids in yRce1p were prepared. Four of the mutants, H194A, E156A, C251A, and H248A, were inactive. Results from the protease inhibition studies and the site-directed mutagenesis suggest that Rce1p is a cysteine protease.

Amino Acid Sequence↗
PubMed1998

Medication errors analysis is an opportunity to improve practice.

The United States Pharmacopeia (USP) Medication Errors Reporting (MER) Program collected and cataloged 2,213 reports between October 1991 and November 1996. Medication errors occur in all health care facilities, involve health care practitioners from all disciplines, and involve drugs from all categories, including neuromuscular blocking agents (38 out of 2,213). This class of drugs is discussed as an example of the program, and we trust will serve the reader as an educational guide about medication errors that occur with drugs in any class. When used inappropriately, they represent a higher morbidity and mortality than many other drug classes analyzed. Reports indicate various causes for the errors, such as similar-appearing products, and include suggestions by practitioners to prevent recurrence of the error. The USP Advisory Panel on Medication Errors has developed recommendations for facilities that are intended to prevent errors with neuromuscular blocking agents (NMB). The USP Medication Errors Reporting Program is presented in cooperation with the Institute for Safe Medication Practices (ISMP).

Adverse Drug Reaction Reporting Systems↗
PubMed1997

Interaction between the small GTPase Ran/Gsp1p and Ntf2p is required for nuclear transport.

Bidirectional movement of proteins and RNAs across the nuclear envelope requires Ran, a Ras-like GTPase. A genetic screen of the yeast Saccharomyces cerevisiae was performed to isolate conditional alleles of GSP1, a gene that encodes a homolog of Ran. Two temperature-sensitive alleles, gsp1-1 and gsp1-2, were isolated. The mutations in these two alleles map to regions that are structurally conserved between different members of the Ras family. Each mutant strain exhibits various nuclear transport defects. Both biochemical and genetic experiments indicate a decreased interaction between Ntf2p, a factor which is required for protein import, and the mutant GSP1 gene products. Overexpression of NTF2 can suppress the temperature sensitive phenotype of gsp1-1 and gsp1-2 and partially rescue nuclear transport defects. However, overexpression of a mutant allele of NTF2 with decreased binding to Gsp1p cannot rescue the temperature sensitivity of gsp1-1 and gsp1-2. Taken together, these data demonstrate that the interaction between Gsp1p and Ntf2p is critical for nuclear transport.

Amino Acid Sequence↗
PubMed1997

A retrospective study on elbow function after internal fixation of intercondylar fracture of adult humerus.

Between 1989 and 1993, 20 intercondylar fractures of the distal humerus were treated by open reduction, internal fixation and early postoperative mobilisation. One patient died on the third postoperative day as a result of multiple injuries, leaving 19 patients for evaluation. The mean follow-up period was 4.1 years (range 2.0 to 6.7 years). According to the Muller system, there were 7 type C1 and 12 type C2 fractures. Using the Jupiter criteria, 6 elbows were rated as excellent, 9 good and 4 fair. Complications included late ulnar neuritis in one patient and wound infection in another patient.

Adolescent↗
PubMed1997

Surgical aspects of autonomic dysreflexia.

Autonomic dysreflexia (AD) is a characteristic syndrome that occurs in spinal cord injury (SCI) patients with lesions above the sympathetic outflow at T6 and rarely in those with lesions below T10. Symptoms are initiated by noxious stimuli below the level of injury which result in massive sympathetic discharges from the isolated cord. These produce what may be called a sympathetic storm manifest by severe life threatening hypertension. Anesthesiologists and surgeons dealing with SCI patients must know how to recognize this syndrome, how to prevent its occurrence and how to manage it aggressively. Choice of anesthesia is frequently difficult and, in particular, it may be difficult to decide which type of anesthesia is best for patients susceptible to the syndrome. Therefore, we have conducted a retrospective study of SCI patients in the Department of Veterans Affairs Medical Center, Long Beach, California, where the Spinal Cord Injury Service is one of the largest in the country.

Adult↗
PubMed1997

A diagnostic dilemma in an elderly patient with bone pains.

A 61-year-old patient presented with multiple bone pains. Biochemical, haematological and radiological investigations initially suggested a diagnosis of osteomalacia because of the presence of hypocalcaemia and looser zones. There were also multiple lytic bone lesions and bone scan showed multiple hot spots suggesting multiple bone secondaries. The key investigation in this case was examination of the bone marrow.

Bone Marrow↗
PubMed1996

Intravenous sedation prior to peribulbar anaesthesia for cataract surgery in elderly patients.

PURPOSE: To investigate if pre-block iv sedation using midazolam, alfentanil, or a midazolam-alfentanil combination minimizes pain, reduces pain recall, and attenuates haemodynamic responses to peribulbar block; and to determine other factors influencing oxygen saturation (SpO2) following iv sedation. METHODS: In a randomized, double-blind, placebo-controlled study, 120 patients, mean age 73 yr, having cataract surgery with peribular anaesthesia, were randomized to receive either normal saline, 1 mg midazolam, 500 micrograms alfentanil, or 0.5 mg midazolam plus 250 micrograms alfentanil. Blood pressure (BP), heart rate (HR) and pulse oximetry readings were recorded before injection of the study drugs, immediately after completion of the peribulbar block, and 10 min after the block. Pain from the anaesthetic block was assessed immediately after the block and after surgery using a visual analog scale, and recall of pain was assessed by telephone on the day after surgery. RESULTS: Pain scores were low in all four groups. Midazolam-alfentanil reduced pain perception, and all iv sedation used reduced pain recall. Midazolam reduced systolic BP; alfentanil +/- midazolam reduced HR. All iv sedation reduced SpO2 more than did saline, but not usually to a clinically important level. Nine patients had a SpO2 < or = 90%; all had received alfentanil with or without midazolam. It was not possible to predict oxygen saturation levels by any factors other than iv sedation and baseline SpO2 levels. CONCLUSION: Intravenous sedation with midazolam or alfentanil or in combination reduced pain perception, pain recall, and haemodynamic responses from peribulbar anaesthesia. Fifteen percent of patients given alfentanil developed clinically important oxygen desaturation. The use of fine gauge needles combined with slow injection of anaesthetic solution causes minimal discomfort, and routine iv sedation may be unnecessary.

Aged↗
PubMed1996

Incidence of perioperative myocardial ischemia in TURP patients.

STUDY OBJECTIVE: To determine the incidence of new episodes of myocardial ischemia in patients undergoing transurethral resection of the prostate (TURP). DESIGN: Prospective, nonrandomized study. SETTING: Veterans Administration medical center. PATIENTS: 39 patients undergoing elective TURP. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Myocardial ischemia was detected with a 3-channel ambulatory ECG recorded. The ambulatory ECG recorder was applied preoperatively and removed when the patient left the recovery room. New myocardial ischemia was defined as a 1 mm or greater ST depression or a 2 mm or greater ST elevation from baseline, lasting for 1 minute or longer in at least one lead at the J point plus 60 msec unless this point fell within the T wave, in which case the J point 40 msec or greater was used. ST changes consistent with myocardial ischemia were confirmed by a cardiologist blinded to the patient's clinical course. Seven of 39 TURP patients (18%) had ST segment changes indicative of new myocardial ischemia. These seven patients had more prostate tissue resected and more blood loss than the 32 patients who did not have any myocardial ischemia (p < 0.05). CONCLUSIONS: Patients undergoing TURP have an 18% incidence of myocardial ischemia. Patients undergoing TURP with more prostate tissue resected and greater blood loss are at increased risk for perioperative myocardial ischemia.

Aged↗
PubMed1996

Dynamic localization of the nuclear import receptor and its interactions with transport factors.

Characterization of the interactions between soluble factors required for nuclear transport is key to understanding the process of nuclear trafficking. Using a synthetic lethal screen with the rna1-1 strain, we have identified a genetic interaction between Rna1p, a GTPase activating protein required for nuclear transport, and yeast importin-beta, a component of the nuclear localization signal receptor. By the use of fusion proteins, we demonstrate that Rna1p physically interacts with importin-beta. Mutants in importin-beta exhibit in vivo nuclear protein import defects, and importin-beta localizes to the nuclear envelope along with other proteins associated with the nuclear pore complex. In addition, we present evidence that importin-alpha, but not importin-beta, mislocalizes to the nucleus in cells where the GTPase Ran is likely to be in the GDP-bound state. We suggest a model of nuclear transport in which Ran-mediated hydrolysis of GTP is necessary for the import of importin-alpha and the nuclear localization signal-bearing substrate into the nucleus, while exchange of GDP for GTP on Ran is required for the export of both mRNA and importin-alpha from the nucleus.

Amino Acid Sequence↗
PubMed1995

Mutants in a yeast Ran binding protein are defective in nuclear transport.

Ran, a Ras-like GTPase, has been implicated in controlling the movement of proteins and RNAs in and out of the nucleus. We have constructed strains of Saccharomyces cerevisiae which produce fusion proteins containing glutathione-S-transferase (GST) fused to Gsp1p, which encodes the essential yeast Ran homolog, and a mutant form of Gsp1p that mimics the GTP-bound state. A major protein with the apparent size of 34 kDa co-purifies with the GTP-bound form of Gsp1p. This protein was identified as Yrb1p (Yeast Ran Binding Protein) and stimulates GTP hydrolysis by Gsp1p in the presence of Rna1p, the Gsp1 GTPase activating protein. Yrb1p is located in the cytoplasm with some concentration at the nuclear periphery. Temperature-sensitive yrb1 mutants are defective in nuclear protein import and RNA export. A mutation in the highly conserved Ran binding region of Yrb1p reduces its ability to interact with Gsp1p. These data indicate that Yrb1p functions with Gsp1p and suggest that together they can control transport of macromolecules across the nuclear envelope.

Amino Acid Sequence↗
PubMed1995

Effect of dopamine on renal blood flow and cardiac output.

OBJECTIVE: To characterize the relationship between changes in renal blood flow and cardiac output induced by dopamine, hypothesizing that at low doses renal blood flow changes more than cardiac output. DESIGN: Anesthetized swine had renal blood flow and cardiac output measured during either continuous dopamine infusions (2 to 8 micrograms/kg per minute) or bolus dosing (1 to 16 micrograms/kg), and increases in both were compared. Two different fluid protocols were compared using constant dopamine infusions. In the constant pulmonary capillary wedge pressure protocol, intravenous fluids were titrated to keep this parameter constant. In the other protocol, fluid therapy was held constant at 10 mL/kg per hour. RESULTS: With infusions, mean increases in renal blood flow and cardiac output were relatively equal. The maximum increase was 35% at 8 micrograms/kg per minute under the constant pulmonary capillary wedge pressure protocol, with no significant differences (P > .1) found between the change in renal blood flow and cardiac output at any dose in either protocol. With bolus dosing, renal blood flow increased significantly more than cardiac output at 1, 4, and 8 micrograms/kg (P < .05). CONCLUSION: Disproportionate increases in renal blood flow compared with cardiac output at low bolus doses show initial renal responses to be independent of cardiac output. The infusion data suggest that renal responses exhibit tachyphylaxis or that cardiac output slowly accommodates to decreased total peripheral resistance.

Animals↗