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J L Lin

Publications and source records attributed to J L Lin.

At least 163 records · Page 9Linked to original sources
PubMed1992

Glucose binding enhances the papain susceptibility of the intracellular loop of the GLUT1 glucose transporter.

Digestion of human GLUT1 protein in erythrocytes with 5 micrograms/ml papain for 5 min yielded several fragments. By using several site-specific antibodies, two of these fragments containing the intracellular loop domain between M6 and M7 were demonstrated to be further digested by a prolonged incubation with papain. The addition of 0.2 M D-glucose enhanced this digestion between M6 and M7 by approximately 3.5-fold, while the addition of 0.2 M D-sorbitol exhibited no effects. These results strongly suggest that D-glucose binding induces the conformational change of the intracellular loop domain between M6 and M7 of GLUT1 protein. Since the homology of the amino acid sequence was low in this intracellular domain among the five facilitative glucose transporter isoforms, this intracellular loop might contribute to the difference in their Km and Vmax values for glucose uptake.

Erythrocyte Membrane↗
PubMed1992

Two glucose transporter isoforms are sorted differentially and are expressed in distinct cellular compartments.

Rat GLUT4 (adipocyte/muscle-type glucose transporter) was expressed in two fibroblastic cell lines, Chinese hamster ovary (CHO) cells and 3T3-L1 fibroblasts, under the control of the methallothionein I promoter. Although immunoblotting with a GLUT4-specific anti-peptide antibody demonstrated that the amount of GLUT4 expressed was comparable with that in 3T3-L1 adipocytes and rat adipose tissues, no increase in 2-deoxy-D-glucose uptake was observed in the basal state in fibroblasts. Immunocytochemical studies showed that the expressed GLUT4 appeared to be localized in a specific region in the cytoplasm. These results were in marked contrast to those obtained in CHO cells expressing GLUT1 (HepG2/erythrocyte-type glucose transporter) using the same expression vector. In this case the expressed GLUT1 protein appeared to reside mainly on the plasma membranes, and a significant increase in glucose uptake was observed. Although insulin increased glucose uptake in CHO cells and 3T3-L1 fibroblasts as well as in the cells expressing rat GLUT4, an increment due to insulin above basal values was small, at most 2-fold, and no significant differences were observed in insulin-stimulated glucose uptake between transfected and parental cells. In addition, no apparent differences in the subcellular distribution of expressed GLUT4 were observed between the insulin-stimulated and the basal state. These results indicate that in fibroblastic cell lines GLUT1 and GLUT4 proteins are sorted in a different fashion, and the expression of GLUT4 protein per se is not enough to produce a large insulin-induced increase in glucose transport activity such as that observed in rat adipocytes and 3T3-L1 adipocytes. Thus unidentified aspects of the cellular environment which are present in the adipocytes but not in fibroblastic cell lines may be required for a large insulin-induced increase in glucose transport activity to be observed.

Adipose Tissue↗
PubMed1992

Disappearance of immune deposits with EDTA chelation therapy in a case of IgA nephropathy.

In this report, we describe the development of renal function impairment in a 33-year-old patient with mesangial IgA nephropathy and a history of recent gout. Increased body lead burden was identified with a positive EDTA mobilization test. The patient was treated with 1 g of edetate disodium calcium weekly for 2 months until normalization of urinary lead excretion. Improvement of renal function and proteinuria were noted. It was even more interesting to find that both immunofluorescence and electron microscopy studies of the second biopsy specimen revealed the loss of previous mesangial immune deposits. Our case demonstrated that lead may be a nonspecifically damaging factor related to the deterioration of renal function in patients with preexisting renal disease. Moreover, the disappearance of mesangial immune deposits after chelation therapy has not been previously documented. The pathogenetic basis of this observation is unknown, and its causal relationship with lead requires further elucidation.

Adult↗
PubMed1992

Expression of glucose transporter isoforms with aging.

To elucidate the cellular mechanisms for impairment of glucose metabolism associated with aging, the facilitative glucose transporter protein and mRNA were studied in various tissues of young (7-week-old) and aged (20-month-old) rats. GLUT4 glucose transporter protein, a major glucose transporter isoform in the insulin-responsive tissues, was selectively decreased in the epididymal fat tissues of the aged rats compared with the young rats. This decrease is likely to be due to a decrease in protein synthesis rather than in protein stability, since GLUT4 mRNA per unit cellular total RNA was also decreased. GLUT4 mRNA in the skeletal muscle was rather increased in spite of the decreased level of GLUT4 protein in the aged rats, suggesting that the translational efficiency and/or stability of GLUT4 protein is decreased in the skeletal muscle of the aged rats compared with the young rats. In contrast to these alterations in GLUT4 expression, no apparent decrease in the GLUT1 protein amount was observed in the fat tissues, skeletal muscle and brain of the aged rats compared with the young rats. Thus, the tissue and isoform-specific alterations in glucose transporter expression are associated with aging and may contribute to impairment of glucose metabolism observed with aging.

Adipose Tissue↗
PubMed1992

Upregulation of GLUT2 mRNA by glucose, mannose, and fructose in isolated rat hepatocytes.

Previously, demonstrated that GLUT2 mRNA and protein are increased in liver of streptozocin-induced diabetic rats. To examine the mechanisms whereby GLUT2 mRNA is regulated, we cultured isolated hepatocytes in the absence and presence of various concentrations of glucose. Culture of hepatocytes in high glucose concentration (27.8 mM) for 20 h induced a 3.2-fold increase in GLUT2 mRNA levels compared with hepatocytes cultured without D-glucose. Interestingly, D-mannose and D-fructose could substitute for D-glucose to elevate the GLUT2 mRNA level, whereas 3-O-methyl-D-glucose, 2-deoxy-D-glucose, and sucrose, which were not metabolized or taken up by the cells, were without effect. Insulin had no significant effect on GLUT2 mRNA levels in hepatocytes in the presence or absence of D-glucose. Therefore, the regulation of the GLUT2 gene by D-glucose in hepatocytes is contrary to that reported for GLUT1 and GLUT4 genes, which are downregulated by D-glucose. These results also suggest that the elevated GLUT2 mRNA level observed in diabetic rat liver is due to the high blood glucose concentration rather than to insulin deficiency.

3-O-Methylglucose↗
PubMed1992

[Chronic chromate intoxication with renal tubular damage--report of a case].

A 46-year-old male chromium plating worker visited our hospital due to rhinorrhea, sneezing and cough with blood-tinged sputum for more than 10 years. He also had skin ulceration and chronic dermatitis on both hands Medical therapy was inefficient. Physical examinations revealed nasal septum perforation, severe inflammation of the nasopharynx cavity, and eczema of both hands. Laboratory investigations showed significant tubule proteinuria, enzymuria, hypercalciuria, etc. It is evident that renal tube damage was present in this patient. The blood chromium level was 25 ng/mL, and the 24-hour urine chromium excretion level was 2.8 mg/day. A pulmonary function test showed reduced functional residual capacity (FRC), which may be due to either long-term smoking or chromate acid exposure. To our knowledge this is the first case of renal tubal damage induced by chronic chromate intoxication Taiwan. Further evaluation of the occupational safety and health of chromium plating workers is needed on this island.

Chromates↗
PubMed1992

Acute renal failure and severe thrombocytopenia induced by rifampicin: report of a case.

We report on a patient who developed life-threatening thrombocytopenia and acute renal failure after the reinstitution of rifampicin therapy for pulmonary tuberculosis. This combined reaction is rarely reported. Supportive treatment and withdrawal of rifampicin led to complete recovery. The increased incidence of drug-resistant tuberculosis and the need for the reintroduction of rifampicin therapy may lead to more such reactions being observed.

Acute Kidney Injury↗
PubMed1992

[Continuous arteriovenous hemodialysis in critical patients with acute renal failure].

Continuous arteriovenous hemodialysis (CAVHD) offers a modified therapeutic approach for the patient with acute renal failure. The system is modified fron the CAVH write out method by adding two pumps to control the flow rate of the dialysis solution and to reduce the nursing load. The blood flow through the dialyzer is dependent on the net blood pressure gradient. Peritoneal dialysis or bicarbonate dialysate is infused through the dialysate ports utilizing both diffuse and convective transport for an average blood flow rate of 0.9 L/hour. The two pumps control the dialysate inflow and outflow rates. Ten patients with complications and acute renal failure were treated with CAVHD for periods ranging from 10 to 154 hours. Average urea clearance was 9.39 mL/min. Average creatinine clearance was 9.12 mL/min, and in stable patients, the mean BUN was maintained at 60 mg/dL and the mean serum creatinine level was 4.6 mg/dL. The average ultrafiltration rate obtained was 100 mL/hr and was adjusted for the body fluid condition. most patients tolerated CAVHD without further hemodynamic instability and did not develop serious complications. In conclusion, CAVHD is a safe and technically simple procedure, which is particularly suitable for hemodynamically unstable patients requiring fluid removal.

Acute Kidney Injury↗
PubMed1992

Inheritance of hypertrophic cardiomyopathy in Chinese--M-mode and two-dimensional echocardiographic analysis of 28 families.

To determine the mode of inheritance and degree of penetrance of hypertrophic cardiomyopathy (HC) in Chinese, 132 family members of 28 probands with HC were assessed by M-mode and two-dimensional echocardiography. Of these 132, 103 cases were first-degree relatives of the probands. Twenty-seven (20.4%) family members, including 19 cases of first-degree relatives of the probands, had HC. Familial occurrence of HC was noted in 13 (46.4%) families. In 10 families, the affected relatives were identified in successive generations, and the mode of inheritance was most consistent with an autosomal dominant trait. The frequency with which HC was identified in relatives increased significantly with the number of subjects studied and a positive family history of sudden death. Subgroup analysis, using multivariate logistic regression analysis, revealed that increasing age was independently associated with a higher frequency of definite cases in first-degree relatives of the probands. In contrast, by multivariate analysis, there were no significant differences between frequency of definite cases in female and male relatives or in different familial relationships (parent, sibling, offspring) to the probands.

Adolescent↗
PubMed1992

Elevated lead burden in Chinese patients without occupational lead exposure.

Studies were conducted in 10 healthy Chinese controls, 10 patients with chronic renal failure without gout, 8 patients with gout complicated with chronic renal failure and in 6 patients with chronic renal failure who subsequently developed gout. All the subjects had no history of occupational or accidental lead exposure. Total body lead burden was assessed by 24-hour urine collection measurements over a 72-hour period after intravenous administration of 1 g of calcium disodium EDTA. The postinfusion urinary lead excretion of the healthy controls (90.2, range 57.2-161.5 micrograms/3 days/1.73 m2) was higher than the values recently reported for healthy German controls. Similar to earlier studies, we failed to find elevated urinary lead excretion in patients with chronic renal failure without gout. Nevertheless, the EDTA mobilization test identified 2 patients with occult plumbism in this group of patients. Our study also clearly demonstrated that 4 of 6 patients with renal failure who developed gout de novo had underlying plumbism. The high prevalence of increased lead body burden in patients with chronic renal failure, in particular those associated with gout, indicates that lead may contribute to a significant portion of chronic renal disease in our patients. In addition, our data suggest that chronic low-level environmental lead exposure may subtly affect renal function.

Adult↗
PubMed1991

The role of N-glycosylation of GLUT1 for glucose transport activity.

To elucidate a functional role of N-glycosylation in glucose transporters, we introduced oligonucleotide-directed mutagenesis in GLUT1 cDNA to remove the possible site for N-linked glycosylation. The wild-type and the mutated GLUT1 cDNAs which induced a mutation of Asn at residue 45 to Asp, Tyr, or Gln were transfected and stably expressed into Chinese hamster ovary cells. The expressed wild-type and the mutated GLUT1 was demonstrated to be a broad band of a 45-60-kDa form and a sharp band of a 38-kDa form on Western blot analysis, respectively, indicating no glycosylation in the mutated GLUT1. Although the cell surface labeling of the glucose transporters demonstrated the presence of the glycosylation-defective glucose transporters on the cells surface, photoaffinity labeling of glycosylation-defective GLUT1 with [3H] cytochalasin B and a photoreactive mannose derivative, [3H]2-N-4-(1-azi-2,2,2,trifluoroethyl)benzoyl-1,3-bis(D-mannos+ ++-4-yloxy)-2- propylamine in the membranes was observed to be 40-70 and 15-30% of that of the wild-type GLUT1, respectively. The kinetic study of 2-deoxyglucose uptake revealed that the glycosylation-defective GLUT1 had a 2-2.5-fold greater Km value for 2-deoxyglucose uptake compared with the wild-type GLUT1. These observations strongly suggest that 1) N-glycosylation of GLUT1 glucose transporter is only on Asn 45 and 2) N-glycosylation plays an important role in maintaining a structure of glucose transporter with high affinity for glucose, thus, with high transport activity.

Affinity Labels↗
PubMed1991

Characterization of cDNA clones encoding a human fibroblast caldesmon isoform and analysis of caldesmon expression in normal and transformed cells.

Overlapping cDNA clones encoding a low M gamma human nonmuscle caldesmon isoform (HUM 1-CaD) span the entire coding region (538 amino acids) as well as 111 base pairs (bp) of 5'-noncoding and 1249 bp of 3'-noncoding region. Northern blot probes derived from either the coding or 3'-noncoding region hybridized to a 4.3-kilobase mRNA in nonmuscle cells and a 5.2-kilobase mRNA in stomach tissue. Primer extension results indicated that the 5'-noncoding region of the HUM 1-CaD mRNA is approximately 700 bp in length and also suggested that 1-CaD mRNAs with common 5'-noncoding regions are expressed in both liver and fibroblast cells. Comparisons of the human, rat, and chicken 1-CaD amino acids sequences demonstrated that although each isoform has unique characteristics, extensive regions of conservation exist. Amino acids 27-53 and 97-127 are 100% identical in these isoforms while amino acids 297-531 of HUM 1-CaD are 94 and 85% identical to the rat and chicken 1-CaDs, respectively. In addition, the levels of HUM 1-CaD mRNA and protein appeared to be decreased by 2-4 fold in the transformed derivatives of KD and WI38 cell lines as judged by Northern and Western blot analysis. The results suggest that the decrease of 1-CaD protein in these transformed cells is a direct result of decreased 1-CaD mRNA synthesis and/or increased mRNA turnover.

Amino Acid Sequence↗
PubMed1991

Expression of the GLUT1 glucose transporter increases thymidine uptake in Chinese hamster ovary cells at low glucose concentrations.

An increase in expression of the GLUT1 glucose transporter gene has been observed to be associated with an increase in glucose transport activity upon oncogenic transformation of the cells. Increased expression of this glucose transporter isoform has been also observed in fetal tissues. To investigate the consequences of this phenomenon on cellular metabolism and cell growth, an expression vector containing the GLUT1 glucose transporter complementary DNA was transfected into Chinese hamster ovary cells. Overexpression of this glucose transporter isoform resulted in an increase in not only glucose uptake and utilization but also thymidine uptake when cells were exposed to glucose-deficient conditions. This increase in glucose metabolism and DNA synthesis may play an important role on the growth and/or survival of cancer cells and fetal tissues.

3-O-Methylglucose↗
PubMed1991

The glucose transport activity of GLUT1 is markedly decreased by substitution of a single amino acid with a different charge at residue 415.

GLUT1 glucose transporter cDNA was modified to introduce a single amino acid substitution of aspartic acid for asparagine 415, which is conserved among all facilitative glucose transporter isoforms. Although a significant amount of the mutated transporter was expressed into plasma membranes of Chinese hamster ovary cells by transfection with expression vector, almost no increase in glucose transport activity was observed. Analysis of glucose uptake with Lineweaver-Burk plot depicts that the mutation induced a marked decrease (more than 5-fold) in turnover number and a slight increase (1.5-fold) in Km compared with the wild-type GLUT1. Results obtained with cytochalasin B and ethylidene glucose suggested that the inner but not outer glucose binding site was modulated. These results suggest that asparagine 415 is located close to the inner glucose binding site and the putative inner gate of GLUT1 glucose transporter and that an ionic charge in this domain might play an important role in the rate of conformational change between an inward-facing form and an outward-facing form of glucose transporter.

Animals↗