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Biomedical subjects

J R Bourne

Publications and source records attributed to J R Bourne.

At least 19 recordsLinked to original sources
PubMed1992

GTP-binding mutants of rab1 and rab2 are potent inhibitors of vesicular transport from the endoplasmic reticulum to the Golgi complex.

We have examined the role of ras-related rab proteins in transport from the ER to the Golgi complex in vivo using a vaccinia recombinant T7 RNA polymerase virus to express site-directed rab mutants. These mutations are within highly conserved domains involved in guanine nucleotide binding and hydrolysis found in ras and all members of the ras superfamily. Substitutions in the GTP-binding domains of rab1a and rab1b (equivalent to the ras 17N and 116I mutants) resulted in proteins which were potent trans dominant inhibitors of vesicular stomatitis virus glycoprotein (VSV-G protein) transport between the ER and cis Golgi complex. Immunofluorescence analysis indicated that expression of rab1b121I prevented delivery of VSV-G protein to the Golgi stack, which resulted in VSV-G protein accumulation in pre-Golgi punctate structures. Mutants in guanine nucleotide exchange or hydrolysis of the rab2 protein were also strong trans dominant transport inhibitors. Analogous mutations in rab3a, rab5, rab6, and H-ras did not inhibit processing of VSV-G to the complex, sialic acid containing form diagnostic of transport to the trans Golgi compartment. We suggest that at least three members of the rab family (rab1a, rab1b, and rab2) use GTP hydrolysis to regulate components of the transport machinery involved in vesicle traffic between early compartments of the secretory pathway.

Amino Acid Sequence↗
PubMed1991

Isoprenoid modification of rab proteins terminating in CC or CXC motifs.

Mevalonate starvation of hamster fibroblasts resulted in a shift of rab1b from the membrane to the cytosolic fraction, suggesting that rab1b depends upon an isoprenoid modification for its membrane localization. rab1b and rab3a proteins expressed in insect cells incorporated a product of [3H]mevalonate, and gas chromatography analysis of material released by Raney nickel cleavage demonstrated that rab1b and rab3a are modified by geranylgeranyl groups. Additionally, in vitro prenylation analysis demonstrated farnesyl modification of H-ras but geranylgeranyl modification of five rab proteins (1a, 1b, 2, 3a, and 6). Together, these results suggest that the carboxyl-terminal CC/CXC motifs (X = any amino acid) specifically signal for addition of geranylgeranyl, but not farnesyl, groups. A rab1b mutant protein lacking the two carboxyl-terminal cysteine residues was not prenylated in vitro. However, since a mutant H-ras protein that terminates with tandem cysteine residues was also not modified, the CC motif may be essential, but not sufficient, to signal prenylation of rab1b. Finally, rab1b and rab3a proteins were not efficient substrates for either farnesyl- or geranylgeranyltransferase activities that modify CAAX-containing proteins (A = any aliphatic amino acid). Therefore, rab proteins may be modified by a prenyltransferase(s) distinct from the prenyltransferases that modify carboxyl-terminal CAAX proteins.

Amino Acid Sequence↗
PubMed1991

Rab1b regulates vesicular transport between the endoplasmic reticulum and successive Golgi compartments.

We report an essential role for the ras-related small GTP-binding protein rab1b in vesicular transport in mammalian cells. mAbs detect rab1b in both the ER and Golgi compartments. Using an assay which reconstitutes transport between the ER and the cis-Golgi compartment, we find that rab1b is required during an initial step in export of protein from the ER. In addition, it is also required for transport of protein between successive cis- and medial-Golgi compartments. We suggest that rab1b may provide a common link between upstream and downstream components of the vesicular fission and fusion machinery functioning in early compartments of the secretory pathway.

Animals↗
PubMed1990

Farnesol modification of Kirsten-ras exon 4B protein is essential for transformation.

Oncogenic forms of ras proteins are synthesized in the cytosol and must become membrane associated to cause malignant transformation. Palmitic acid and an isoprenoid (farnesol) intermediate in cholesterol biosynthesis are attached to separate cysteine residues near the C termini of H-ras, N-ras, and Kirsten-ras (K-ras) exon 4A-encoded proteins. These lipid modifications have been suggested to promote or stabilize the association of ras proteins with membranes. Because preventing isoprenylation also prevents palmitoylation, examining the importance of isoprenylation alone has not been possible. However, the oncogenic human [Val12]K-ras 4B protein is not palmitoylated but is isoprenylated, membrane associated, and fully transforming. We therefore constructed mutant [Val12]K-ras 4B proteins that were not isoprenylated to examine the effects of isoprenylation in the absence of palmitoylation. The nonisoprenylated mutant proteins both failed to associate with membranes and did not transform NIH 3T3 cells. In addition, inhibition of isoprenoid and cholesterol synthesis with the drug compactin also decreased [Val12]K-ras 4B protein isoprenylation and membrane association. These results unequivocally demonstrate that isoprenylation, rather than palmitoylation, is essential for ras membrane binding and ras transforming activity. These findings clearly indicate the biological significance of ras protein modification by farnesol and suggest that this modification may be important for facilitating the processing, trafficking, and biological activity of other isoprenylated proteins. Because K-ras is the most frequently activated oncogene in a wide spectrum of human malignancies, study of this pathway could lead to important therapeutic treatments.

Animals↗
PubMed1985

Expert systems in medicine: a biomedical engineering perspective.

Knowledge-based expert systems for medical applications have received considerable attention in recent years. In this review, fundamental terms and notions of artificial intelligence techniques as applied to expert systems are introduced. The most well-known and influential medical expert systems are discussed in detail, and newer efforts are surveyed. A critical comparison of strengths and weaknesses of the systems is made, discussing depth and complexity of knowledge, acquisition of knowledge, user interaction and explanations, knowledge engineering tools, system evaluations, and user resistance. Long- and short-term trends are appraised.

Cholestasis↗
PubMed1983

Computer methods, uremic encephalopathy, and adequacy of dialysis.

It has been recognized for over 30 years that increased renal dysfunction results in increased slow wave activity in the EEG generally prior to the clinical appearance of disabling, dialysis-responsive encephalopathic symptoms of clinical uremia. This paper describes computerized methods that have been used to quantify this slow wave activity and the results of studies that have employed such computerized techniques. Practical information is furnished to guide those who wish to use these methods in their own research and practice. A survey of the limitations and pitfalls inherent in the various techniques is given. A prospectus outlines possible future directions in the field.

Brain Diseases↗
PubMed1982

Identification and labeling of EEG graphic elements using autoregressive spectral estimates.

Syntactic EEG analysis requires descriptive labeling of short (1 s) epochs in an EEG. While discriminant analysis methods are useful for this purpose, significant improvement in label correctness can be achieved using the heuristic method described in this paper. The method is based on the estimation of frequency spectra by autoregressive (AR) modeling. The location of the peak frequencies and the power of these peaks are used to assign labels to 1 s epochs. Artefacts and epochs with exceptionally high or low amplitude and/or frequency values are identified as well. The assignment of labels is accomplished by comparing parameters, extracted from the power spectra estimated for 1 s epochs, with thresholds. These thresholds are automatically adapted to each individual EEG lead. In this paper, the method is outlined and its performance is compared with a discriminant analysis approach and visual labeling.

Computers↗
PubMed1981

Evaluation of a syntactic pattern recognition approach to quantitative electroencephalographic analysis.

This paper reports an experiment designed to evaluate the usefulness of a syntactic pattern recognition approach to quantitative EEG analysis. This approach provides a systematic way of organizing and interpreting spatially and temporally distributed activity in an EEG record. Many automated scoring systems evaluate only background activity, ignoring the significant transient events that may occur in an EEG. In contrast, syntactic methods allow evaluation of background activity in combination with transient events. In this paper, 454 EEGs recorded from a population of renal patients are evaluated using (1) the syntactic approach, and (2) a method based on discriminant analysis. The main finding is that the syntactic approach outperforms the discriminant analysis method when each technique is compared to visual scoring.

Electroencephalography↗
PubMed1981

Assessing the adequacy of dialysis.

In previous work, probes of brain function (quantified EEG and cognitive performance) objectively measured clinical differences patients with chronic renal failure before and after treatment with maintenance haemodialysis or transplantation. This study applied those measures (EEG-discriminant score; choice reaction time, CRT; continuous memory test, CMT; clinical-symptom/self-evaluation questionnaire, CSE) in a prospective experiment to determine whether our standard amount (time) of thrice weekly dialysis could be reduced without inducing some degree of clinical uraemia. In 10 patients a 6 month experimental (E) period was preceded by a 3 month control (CI) and followed by a 3--6 month control (C2) period. During E dialysis time was reduced so that residual renal (Kr) plus dialyser (Kd) urea clearance per week per litre of patients' body water approximated 50--80 percent of the control-level of 3000ml/wk/L. In response average values of all measures worsened; EEG, 54 percent; CRT, 2.5 percent; CMT, 21 percent; and CSE, 11 percent. BUN levels rose slightly, urea generation rates fell, and patients insisted that they felt better as they recorded more severe symptoms (CSE). We conclude: (i) that Kr + Kd = 3000ml/wk/L approximates a minimum level of adequate dialysis; (ii) objective measures which index the neurobehavioural syndrome of clinical uraemia detect inadequate (reduced) dialysis.

Adult↗