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Biomedical subjects

N Li

Publications and source records attributed to N Li.

At least 361 records · Page 20Linked to original sources
PubMed1994

Autophosphorylation mutants of the EGF-receptor signal through auxiliary mechanisms involving SH2 domain proteins.

Many growth factors bind and activate receptors with intrinsic protein tyrosine kinase activity. Once activated these receptors undergo autophosphorylation allowing them to bind src homology 2 (SH2) domain proteins. We mutated or deleted all known autophosphorylation sites of the Epidermal Growth Factor-Receptor (EGF-receptor) and examined the effects of these mutations on gene expression, MAP kinase activation and mitogenesis. We find that the mutant receptors, although unable to bind SH2 domain proteins, are fully competent to activate all these signaling pathways. Our data indicates that these mutant receptors utilize several different compensatory mechanisms to overcome the lack of autophosphorylation sites. One mechanism is the use of tyrosine phosphorylated cellular proteins as surrogates for binding SH2 domain proteins. We find that all these mutant receptors can induce tyrosine phosphorylation of Shc which then acts as a binding site for the Grb2/Sos signaling complex. This data indicates that even though autophosphorylation mutants of the EGF-receptor cannot directly bind SH2 domain proteins, they are able to use auxiliary signals that result in activation of SH2 domain proteins crucial for mitogenesis.

3T3 Cells↗
PubMed1993

BCR-ABL-induced oncogenesis is mediated by direct interaction with the SH2 domain of the GRB-2 adaptor protein.

BCR-ABL is a chimeric oncoprotein that exhibits deregulated tyrosine kinase activity and is implicated in the pathogenesis of Philadelphia chromosome (Ph1)-positive human leukemias. Sequences within the first exon of BCR are required to activate the transforming potential of BCR-ABL. The SH2/SH3 domain-containing GRB-2 protein links tyrosine kinases to Ras signaling. We demonstrate that BCR-ABL exists in a complex with GRB-2 in vivo. Binding of GRB-2 to BCR-ABL is mediated by the direct interaction of the GRB-2 SH2 domain with a phosphorylated tyrosine, Y177, within the BCR first exon. The BCR-ABL-GRB-2 interaction is required for activation of the Ras signaling pathway. Mutation of Y177 to phenylalanine (Y177F) abolishes GRB-2 binding and abrogates BCR-ABL-induced Ras activation. The BCR-ABL (Y177F) mutant is unable to transform primary bone marrow cultures and is impaired in its ability to transform Rat1 fibroblasts. These findings implicate activation of Ras function as an important component in BCR-ABL-mediated transformation and demonstrate that GRB-2 not only functions in normal development and mitogenesis but also plays a role in oncogenesis.

Adaptor Proteins, Signal Transducing↗
PubMed1993

The function of GRB2 in linking the insulin receptor to Ras signaling pathways.

Insulin-induced activation of extracellular signal-regulated kinases [ERKs, also known as mitogen-activated protein (MAP) kinases] is mediated by Ras. Insulin activates Ras primarily by increasing the rate of guanine nucleotide-releasing activity. Here, we show that insulin-induced activation of ERKs was enhanced by stable overexpression of growth factor receptor-bound protein 2 (GRB2) but not by overexpression of GRB2 proteins with point mutations in the Src homology 2 and 3 domains. Moreover, a dominant negative form of Ras (with Ser17 substituted with Asn) blocked insulin-induced activation of ERKs in cells that overexpressed GRB2. GRB2 overexpression led to increased formation of a complex between the guanine nucleotide-releasing factor Sos (the product of the mammalian homolog of son of sevenless gene) and GRB2. In response to insulin stimulation, this complex bound to tyrosine-phosphorylated IRS-1 (insulin receptor substrate-1) and Shc. In contrast to the activated epidermal growth factor receptor that binds the GRB2-Sos complex directly, activation of the insulin receptor results in the interaction of GRB2-Sos with IRS-1 and Shc, thus linking the insulin receptor to Ras signaling pathways.

Adaptor Proteins, Signal Transducing↗
PubMed1993

Guanine-nucleotide-releasing factor hSos1 binds to Grb2 and links receptor tyrosine kinases to Ras signalling.

Many of the actions of receptor tyrosine kinases are mediated by the protein Ras, including the activation of various downstream serine/threonine kinases and the stimulation of growth and differentiation. The human protein Grb2 binds to ligand-activated growth factor receptors and downstream effector proteins through its Src-homology (SH) domains SH2 and SH3, respectively, and like its homologue from Caenorhabditis elegans, Sem-5, apparently forms part of a highly conserved pathway by which these receptors can control Ras activity. Here we show that the SH3 domains of Grb2 bind to the carboxy-terminal part of hSos1, the human homologue of the Drosophila guanine-nucleotide-releasing factor for Ras, which is essential for control of Ras activity by epidermal growth factor receptor and sevenless. Moreover, a synthetic 10-amino-acid peptide containing the sequence PPVPPR specifically blocks the interaction. These results indicate that the Grb2/hSos1 complex couples activated EGF receptor to Ras signalling.

3T3 Cells↗
PubMed1993

Isolation and sequence analysis of variant forms of human transcobalamin II.

Two cDNA clones (1.9 kb and 1.5 kb, respectively) encoding full length human TC II have been isolated from a human endothelial cell cDNA library and sequenced. The differences between the two clones are the length of the 5' end and the 3' end non-coding regions and the codon at position 198 and 219. Both the clones differ from the recently isolated (human endothelial cell) cDNA for TC II (Platica, O., Janecko, R., Quadros, E.V., Regee, A., Romain, R. and Rothenberg, S.P. (1991) J. Biol. Chem. 266, 7860-7863) in codon 259 and 376 and in their calculated pI values. In vitro transcription followed by translation in a reticulocyte lysate system and SDS-PAGE revealed that the isolated cDNA clones encode a protein of 43 kDa. Upon treatment with canine pancreatic microsomes, the molecular mass of the in vitro translated product was reduced to 41.5 kDa, indicating the presence of an approximately 1.5 kDa signal peptide. This translation product was immunoprecipitated with rabbit anti-serum to human TC II and was able to bind to Cbl-Sepharose beads. The amino acid sequence alignment of TC II with that of other Cbl binding proteins (rat intrinsic factor, human transcobalamin I and porcine haptocorrin) revealed only 33% overall homology. However, there were four regions of greater than 80% homology and two regions of about 60% homology. These regions encompass the majority of the hydrophobic areas of the Cbl-binders. Based on these studies, we suggest that structural basis for the expression of different polymorphic forms of TC II may be due to single point mutations and that TC II, like other mammalian Cbl-binders, have evolved from a common ancestral gene. Furthermore, the Cbl-binding functional domain most probably resides in a hydrophobic pocket which is formed by all or some of the six regions of high homology.

Amino Acid Sequence↗
PubMed1993

Importance of pre-existing co-morbidities for prognosis of septicemia in critically ill patients.

OBJECTIVE: To determine admission characteristics associated with the outcome of septicemia in critically ill patients and more specifically assess the prognostic value of pre-existing co-morbidities. DESIGN: 5 year-retrospective cohort study. SETTING: Surgical Intensive Care Unit (ICU-20 beds) in a 1600 bed-tertiary care center. PATIENTS: Among 5457 patients admitted to the ICU between 1984 and 1988, 176 (3.2%) met prospectively-defined criteria for blood culture-proven septicemia (8.77 per 1000 patient-days). Overall septicemic patients had a 5-fold increased risk of death compared to non-septicemic patients (relative risk 5.03, 95% confidence intervals 4.17-6.07, p < 0.0001), and this estimate persisted after stratification according to age, sex, primary diagnosis and conditions of admission to the ICU (emergency/elective). RESULTS: Prognostic factors recorded on admission to ICU that were associated with mortality from septicemia among 173 patients were older age, higher admission Apache II score, gastrointestinal surgery, ultimately and rapidly fatal diseases and the number of co-morbidities in addition to the principal diagnosis (active smoking, alcohol abuse, non-cured malignancy, diabetes mellitus, splenectomy, recent antibiotic therapy, major surgery, or major cardiac event). In the multivariate analysis with logistic regression procedures, Apache II and co-morbidities were identified as the two independent predictors of mortality. CONCLUSIONS: Pre-existing co-morbidities assessed at the admission to the ICU significantly improved the prediction of mortality from septicemia compared to Apache II score alone.

Adult↗
PubMed1993

Association of secondary and polymicrobial nosocomial bloodstream infections with higher mortality.

The objective of this study was to characterize microbiological factors independently associated with higher mortality rates following nosocomial bloodstream infection. All patients admitted to the University of Iowa Hospitals and Clinics between 1 July 1989 and 30 June 1990 who developed a nosocomial bloodstream infection were included. The crude in-house mortality for the 364 patients with nosocomial bloodstream infections was 33%. These deaths accounted for 25% of all in-hospital deaths. Significant risk factors for death from bloodstream infection included diagnoses of cancers and diseases of the cardiovascular and respiratory systems (p < 0.01). Neither previous surgery nor neutropenia was associated with higher mortality rates. Whereas the crude mortality rates associated with gram-negative (33%) and gram-positive (31%) bloodstream infections were similar, that associated with fungemia was higher (54%, p < 0.02). The mortality associated with secondary bloodstream infections (46%) was higher than that associated with primary bloodstream infections (28%, p < 0.001). Furthermore, polymicrobial infections had a worse prognosis than infections from which a single pathogen was isolated (p < 0.05). A multivariate, logistic regression model identified four variables that independently predicted mortality (p = 0.025): age (OR 1.01 per year; CI95 1.00-1.02); cancer (OR 2.35, CI95 1.26-4.37) or diseases of the cardiovascular or respiratory systems (OR 2.20, CI95 1.04-4.67); polymicrobial infection (OR 2.34; CI95 1.21-4.53); and secondary bloodstream infection (OR 2.46; CI95 1.50-4.02). The last variable was the strongest independent predictor. Our study demonstrates the importance of microbiological factors in the outcome of nosocomial bloodstream infections.

Age Factors↗
PubMed1993

The prevalence of coronary heart disease in the multi-ethnic and high diabetes prevalence population of Mauritius.

The prevalence of coronary heart disease (CHD) was determined in a population survey in Mauritius where the prevalence of non-insulin dependent diabetes and mortality from CHD are amongst the highest in the world. Men and women aged 35-74 years of all major ethnic groups were included: Asian Indians (Hindus and Muslims), Creoles and Chinese. ECG abnormalities suggesting either 'probable CHD' or 'possible CHD' were defined using standard criteria. The overall prevalence of probable CHD was 2.7% in men and 0.9% in women, and that of probable or possible CHD together 17.8% in men and 33.3% in women. The prevalence of CHD did not vary significantly between the four ethnic groups. In the multivariate analyses, age and high blood pressure were the most important independent predictors of ECG abnormalities. Neither diabetes nor serum insulin seemed to contribute independently to the prevalence of CHD. This survey confirmed the high ranking of Mauritius in international mortality statistics. The high rates of CHD seen in Asian Indians, African-origin Creoles and Chinese in the rapidly developing country of Mauritius may be a pointer to future problems in their regions of origin.

Adult↗
PubMed1993

Complete nucleotide sequence and molecular characterization of ViaB region encoding Vi antigen in Salmonella typhi.

Plasmid pGBM124, which contains a 14-kb Salmonella typhi chromosomal DNA fragment capable of producing the Vi antigen in Escherichia coli HB101 and ViaB-deleted S. typhi GIFU 10007-3, was studied. We determined the complete nucleotide sequence of this fragment and found 11 open reading frames. Mutagenesis, subcloning, and complementation analysis showed that three genes (vipA, vipB, and vipC) are involved in biosynthesis of the Vi polysaccharide. The putative primary amino acid sequence suggests that both vipA and vipB encode the NAD- or NADP-dependent enzymes to synthesize the nucleotide sugar for the Vi polysaccharide. Five genes (vexA, vexB, vexC, vexD, and vexE) may be involved in translocation of the Vi polysaccharide. Proteins VexA, VexB, VexC, and VexD had moderate similarities to components of group II capsule transporters, and the VexC protein had a putative ATP-binding site. These data indicate that the transport system for the Vi polysaccharide belongs to the ATP-binding cassette transporters. By using the isogenic Vi+ and Vi- strains constructed in this study, we reconfirmed that the Vi antigen is necessary for the serum resistance of S. typhi.

Agglutination Tests↗
PubMed1993

Phosphorylation and ubiquitination of the 26S proteasome complex.

This article reviews recent studies from our laboratory on protein regulators of the proteasome (multicatalytic proteasome complex) in red blood cells. A 240-kD inhibitory component (CF-2) exists in 26S proteasome complexes in a form which is conjugated to ubiquitin. Interestingly, this factor was shown to be identical to delta-aminolevulinic acid dehydratase (ALAD), involved in heme synthesis. A distinct 200-kD inhibitor of the proteasome is not present in the 26S complex. A 32-kD subunit of the 20S proteasome appears to be important for the latency of this core protease. Multiple isoelectric variants of the 32-kD subunit are consistent with phosphorylation. Another 20S proteasome subunit of 30 kD molecular weight is phosphorylated at specific serine residues by copurifying casein kinase II. It is suggested that ubiquitination and phosphorylation may account for at least part of the ATP dependency associated with the 26S proteasome complex. These modifications may play a role in the activity, assembly, translocation and/or turnover of this particle.

Adenosine Triphosphate↗
PubMed1993

An outbreak of hepatitis A among health care workers: risk factors for transmission.

OBJECTIVES: The purpose of this study was to investigate a nosocomial outbreak of hepatitis A that occurred in the burn treatment center of a referral hospital. METHODS: Retrospective cohort and case-control studies were performed to determine acquisition rates and risk factors for transmission. Adjusted infection rates were calculated by week of exposure. A case-control study was conducted to determine potential mechanisms for nosocomial acquisition. Recently infected health care workers were defined as case patients; exposed, serosusceptible health care workers without infection served as controls. RESULTS: The outbreak of hepatitis A affected 11 health care workers and 1 other burn patient (1 secondary patient case). All 11 health care workers became ill after the admission of a man and his 8-month-old son who developed hepatitis A while in the hospital. The cumulative incidence risk ratio was elevated for health care workers caring for either the infant or the father during the same week of exposure. The case-control study implicated the behavior of eating on the hospital ward as the single most important risk factor for infection. CONCLUSION: Inadequate hand-washing and subsequent oral contamination appear responsible for the outbreak. Hospitals may witness other institutional outbreaks if health care workers regularly eat on the wards.

Adult↗
PubMed1993

[Separation and identification of stimulants and their metabolites].

Forty-one stimulant drugs banned by the International Olympic Committee were studied after they were administered to human volunteers. The parent drugs and their metabolites in free or conjugated forms in human urine collected within 24 hours after administration of the drugs were extracted, separated and identified. The separation was performed on a capillary gas chromatograph with nitrogen-phosphorous detector, while the identification was achieved on a capillary gas chromatograph with mass-selective detector. The extract was injected into the gas chromatograph both directly and after derivatization with trifluoroacetic anhydride (TFAA) or N-methyl-N-trimethylsilyl trifluoroacetamide (MSTFA) as well as TFAA and MSTFA combined. The conjugated metabolites were studied after acid hydrolysis of the extract and then selectively derivatized as above. The results are summarized in 4 tables in the text.

Central Nervous System Stimulants↗
PubMed1993

Chronic tonsillitis and IgA nephropathy.

The authors studied the effect of tonsillectomy for IgA nephropathy and the relationship between chronic tonsillitis and IgA nephropathy. Forty-five patients with IgA nephropathy were treated by tonsillectomy in our department. The effective rate of hematuria type IgA nephropathy was 86.2% and that of non-hematuria type 62.5%. We also determined the immunoglobulin composition of the tonsilla tissue in 18 IgA nephropathy patients and compared it with that of 18 chronic tonsillitis patients. The immunoglobin level of the IgA nephropathy group was higher than that of the contrast group, indicating that the disorder of tonsilla immunity may be one of the pathogenic factors for IgA nephropathy. Since no specific method has been available for the treatment of IgA nephropathy, we use tonsillectomy as an effective procedure.

Adolescent↗
PubMed1993

[Proliferating cell nuclear antigen (PCNA/cyclin) in gastric carcinoma in relation to its prognosis].

Expression of proliferating cell nuclear antigen (PCNA/Cyclin) in 73 cases of gastric carcinomas and its relationship to prognosis were semiquantitatively analysed by ABC immunoperoxidase method and its clinical application was explored. PCNA staining located in the nuclei of tumor cells. A semiquantitative PCNA grading showed a significant negative correlation with survival of the gastric carcinomas cases (P < 0.01). Survival analysis also presented that the prognosis of patients with intensive expression of PCNA was poor. Generally speaking, the expression of PCNA showed a significant positive correlation with the differentiation degree of the tumor and nodal metastasis (P < 0.05). However, among these cases, the poorly differentiated adenocarcinomas with a weak grade of PCNA expression generally considered as of a high malignant degree and poor prognosis, survived longer. The facts indicated that the in situ detection of PCNA in gastric carcinoma is more objective and reliable in assessing a proper prognosis than that made on the basis of traditional morphological differentiation grading.

Adenocarcinoma↗
PubMed1993

[The phytohemagglutinins and soybean agglutinin in diagnosis of endometrial adenocarcinoma].

The distribution of PHA and SBA receptors was studied by ABC immunoperoxidase method in 30 cases of endometrial adenocarcinoma (EA), 10 cases of normal endometrium (NE) and 20 cases of cystic glandular hyperplastic endometrium (CGH). The results showed that the positive rate of PHA and SBA in EA was 46.67% and 73.33% respectively, but negative and low in NE and CGH (P < 0.05). PHA and SBA showed a progressive rising tendency along with the changes of NE to CGH and EA (P < 0.01). It is suggested that both PHA and SBA may be used as differentiated markers in EA and may be helpful in clinical diagnosis.

Adenocarcinoma↗
PubMed1993

[Vascular malformation of posterior cerebral artery in supertentorium].

Seventeen cases of vascular malformation of posterior cerebral artery in supertentorium from 1973 to 1991 are reported. These patients accounted for 8.8% of the total supertentorial vascular malformations during the same period. Their ages ranged from ten to forty-eight years with an average of thirty-one years. The vascular malformation was located in the occipital lobe or under the temporal lobe. Its main blood supply was from the basilar artery. Headache and hemorrhage were common clinical manifestations. Some cases had a defect of the visual field. Vertebral angiography is necessary for diagnosis of this disease. All the seventeen cases were operated without any death. The operative approach and experience in seeking for the vascular malformation during the operation are discussed.

Adolescent↗
PubMed1993

Successful segmental small bowel allotransplantation in pigs.

The two step small-bowel transplantation was performed experimentally in pigs. Both ends of heterotopic segmental allografts of 100 cm small bowel were enterostomized during the first operation. After 4-6 weeks, the allograft was interposed in the continuity of the intestine. Rejection was developed in Group I (n = 6) without immunosuppression. The mean survival time of the grafts was 17.7 +/- 7.6 days, and recipients were alive after resection of necrotic grafts. The animals of Group II (n = 6) were treated by cyclosporine concomitantly with azathioprine and methylprednisolone. Two pigs were killed for severe pneumonia on day 92, 97 and the grafts were alive, the other four recipients and their grafts survived for more than 300 days, 270 days, 260 days and 260 days respectively. No GVHD was observed and rejection was the major problem in segmental intestinal transplantation.

Animals↗