Glucokinase as pancreatic beta cell glucose sensor and diabetes gene

Images

Multiple mechanisms for desensitization of A2a adenosine receptor-mediated cAMP elevation in rat pheochromocytoma PC12 cells

To understand the regulation of A2a adenosine receptor (A2a-R) response, we examined the molecular mechanisms underlying the desensitization of A2a response in rat pheochromocytoma PC12 cells, which possess an A2a-R identical with the A2a receptor we recently cloned from rat brain. Prolonged exposure of PC12 cells to adenosine agonists significantly inhibited the response of the cells to subsequent stimulation with an A2a-selective adenosine agonist (CGS21680). No significant change in the number of binding sites and affinity for CGS21680 was observed in desensitized cells, nor did we find any significant change in the transcript level of A2a-R in cells pretreated with adenosine agonists. However, the basal adenylyl cyclase activity and the cyclase activities stimulated by adenosine agonists, by GTP gamma S, and by forskolin were reduced in desensitized cells. Prolonged exposure of PC12 cells to dibutyryl-cAMP did not significantly change either the basal or the adenosine agonist-evoked adenylyl cyclase activity. Therefore, elevation of cellular cAMP content is by itself not sufficient to produce the observed reductions of adenylyl cyclase activity with A2a desensitization. Inhibition of adenylyl cyclase activity in desensitized cells occurred after short-term (30 min) incubation with CGS21680 and could be blocked by the adenosine antagonist 8-cyclopentyl-1,3-dipropylxanthine. Gs alpha protein levels did not significantly change after a 30-min exposure to CGS21680. In contrast, long-term exposure (12-20 hr) of PC12 cells to adenosine agonists resulted in a slight further reduction of adenylyl cyclase activity and a consistent decline in the Gs alpha protein level. In addition, long-term incubation with adenosine agonists or with forskolin-enhanced phosphodiesterase (PDE) activity in the cytosolic and membrane fractions by 57 +/- 9% and 53 +/- 18%, respectively. Hydrolysis of cAMP was significantly faster in agonist-desensitized cells than in control cells. PDE might therefore play an important role in desensitization of the A2a response in PC12 cells. Polymerase chain reaction-based analysis of the mRNA for A2a-R and A2b-R indicated that both A2a-R and A2b-R were present in PC12 cells; the A2b response was also diminished in A2a-desensitized cells. Our data suggest that inhibition of adenylyl cyclase after short-term agonist treatment, down-regulation of Gs alpha protein level after long-term agonist treatment, and activation of PDE after long-term agonist treatment account for desensitization of the A2a-mediated response in PC12 cells.

Analysis of the c-FOS gene on chromosome 14 and the promoter of the amyloid precursor protein gene in familial Alzheimer's disease

The c-FOS gene product, a putative transacting transcriptional regulator of the amyloid precursor protein (APP) gene, is a candidate locus for the familial Alzheimer's disease (FAD) mutation on chromosome 14 (FAD14). In light of this functional relationship, we investigated the nucleotide sequence and segregation of c-FOS and the nucleotide sequence of the 5' APP promoter. Single-stranded conformational polymorphisms (SSCPs) in the c-FOS gene revealed that c-FOS closely cosegregates with the FAD14 gene but does not show allelic association with FAD. A conservative third-position T-->C mutation was demonstrated in exon 2 (codon 84) of c-FOS, and a C-->G substitution was detected at -209 bp in the 5' promoter of APP. Neither were unique to FAD and are unlikely to be pathogenic or secondary modifiers of the FAD phenotype. We conclude that the c-FOS open reading frame is probably not the site of the FAD14 locus, but we cannot exclude the existence of modifier loci on chromosome 21.

Effects of diethyl spermine analogues in human bladder cancer cell lines in culture

The biochemical and antiproliferative effects of two recently developed N-alkylated analogues of naturally-occurring polyamines, N1,N14-diethylhomospermine (DEHSPM) and N1,N11-diethylnorspermine (DENSPM), were investigated in two human transitional cell carcinoma (TCC) lines, T24 and J82. Parallel studies with the ornithine decarboxylase enzyme inhibitor alpha-difluoromethylornithine (DFMO) were included for comparison. DENSPM displayed greater antiproliferative activity than DEHSPM in both TCC cell lines. Both analogues were strikingly more potent than DFMO. DEHSPM and DENSPM suppressed the activity of the major biosynthetic enzymes, ornithine decarboxylase and S-adenosylmethionine decarboxylase. However, differences in the resulting polyamine depletion suggest that the substantial antiproliferative activity of these analogues may result from mechanisms other than polyamine depletion. The greater polyamine depletion seen with DENSPM is thought to result from its striking induction of spermidine/spermine N1-acetyltransferase. DENSPM is an attractive agent for further preclinical and clinical development, possibly as a chemopreventive agent, in TCC of the bladder.

Femoral version and neck shaft angle

We measured femoral anteversion by the Kingsley-Olmsted method in 24 unpaired, dry femurs. When the head and neck of the same femurs were measured by computed tomography (CT) scan, measurement was 5 degrees less than the Kingsley-Olmsted method, whereas ultrasound of the head and neck was 5 degrees higher. An anterior flat plane was also defined to help measure anteversion in patients with a high neck shaft angle. Physical and ultrasound measurement correlated well with the previous measurement by the Kingsley-Olmsted method and CT scan of anteversion. Although measurement by CT scan and ultrasound are different their results are both reproducible and measure the same parameters; however, ultrasound measurement yields a number approximately 10 degrees higher.

Mutation of the gene for the human lysosomal serine protease cathepsin G is not the cause of aberrant APP processing in familial Alzheimer disease

Recent genetic linkage studies have implicated a gene on chromosome 14 in the pathogenesis of FAD. The identity of this gene remains unknown but it has been speculated that it may be involved in the cellular processing of the amyloid precursor protein (APP). We have analyzed the nucleotide sequence of the entire open reading frame of the cathepsin G gene located on chromosome 14q. No mutations were observed, suggesting that defects in this lysosomal protease are not responsible for aberrant accumulation of proteolytic products of APP in FAD brain tissue.

Surveillance and care of four Chinese hemophiliacs with human immunodeficiency virus (HIV) infection

Four Chinese hemophiliacs with HIV infection have been followed up in Zhejiang Province since 1985. A plan for optimal care of HIV seropositive patients was proposed, including surveillance and care; clinical follow-up and preventive education of asymptomatic HIV seropositive patients; keeping the disease confidential so as not to stir up unnecessary social unease; propaganda and health education about acquired immunodeficiency syndrome (AIDS); treatment with traditional Chinese medicines; and regular surveillance of family members and medical personnel. This plan is regarded as feasible and effective for the prevention and control of AIDS in China.

Genetic evidence for a novel familial Alzheimer's disease locus on chromosome 14

Familial Alzheimer's disease (FAD) has been shown to be genetically heterogeneous, with a very small proportion of early onset pedigrees being associated with mutations in the amyloid precursor protein (APP) gene on chromosome 21, and some late onset pedigrees showing associations with markers on chromosome 19. We now provide evidence for a major early onset FAD locus on the long arm of chromosome 14 near the markers D14S43 and D14S53 (multipoint lod score z = 23.4) and suggest that the inheritance of FAD may be more complex than had initially been suspected.

Visual functions and trace element metabolism in tobacco-toxic optic neuropathy

Visual functions and nutrition metabolic characteristics were studied in 8 subjects (16 eyes) with tobacco-toxic optic neuropathy (TTON). Their visual functions tested by psychophysical and electrophysiologic methods showed that 1: 1. central vision diminished in 16 eyes, 2. dyschromatopsias were found in 14 tested eyes, 3. bilateral symmetrical central or cecocentral scotomas were the visual field characteristics in all cases, 4. PVEP were severe abnormal in 3 spatial frequencies in all cases and 56.3% of 15' checkboard PVEP showed flat responses, which indicated the impairment of optic nerve dominated by the central field. However, the preserved visual responses could be obtained by FVEP test in 14 tested eyes even though their visual acuity were between the range of 0.02-0.2 and flat PVEP responses. The II and III wave latencies of primary stage were more prolonged than those of control group (P < 0.01), which further indicated the preferential demyelination corresponding to the papillomacular bundles, 5. ERG showed slightly attenuated amplitudes in 5 of 8 tested eyes, which indicated the secondary and mild retinal lesion. On the other hand, TTON occurred on a background of long-term, heavy smoking, drinking, emaciation and malnutrition bodies with low serum zinc level.

Expression and function of GLUT-1 and GLUT-2 glucose transporter isoforms in cells of cultured rat pancreatic islets

We have previously investigated glucose induction of glucokinase, glucose usage and insulin release in isolated cultured rat pancreatic islets (Liang, Y., Najafit, H., Smith, R. M., Zimmerman, E. C., Magnuson, M. A., Tal, M., and Mastchinsky, F. M. (1992) Diabetes (1992) 41, 792-806). Here we studied the expression and function of GLUT-1 and GLUT-2 glucose transporter isoforms, using the same system, i.e. isolated pancreatic rat islets immediately after isolation or cultured in the presence of 3 or 30 mM glucose for as long as 10 days. We found by immunofluorescence microscopy and Western and Northern blot analysis of islet extracts that GLUT-1 expression was induced in islet beta-cells in tissue culture both with low or high glucose present. The induction of GLUT-1 was specific to beta-cells but was not present in all beta-cells and was not detected in alpha-cells. GLUT-2 expression was also specific for beta-cells and was not observed in all beta-cells. Some beta-cells in culture coexpressed GLUT-1 and GLUT-2. The expression of the two glucose transporters was regulated in the opposite direction in response to glucose concentration in the culture medium. GLUT-1 was more effectively induced when glucose was low, and GLUT-2 expression was more pronounced when glucose was high in the culture media. Another difference between the two glucose transporters was that GLUT-2 expression was increased while GLUT-1 expression was decreased as culturing continued as long as 7 days. Thus, after 7 days of culture GLUT-2 expression in beta-cells was nearly the same at low and high glucose, whereas GLUT-1 was practically absent no matter what the glucose level was. In attempts to correlate GLUT-1 and GLUT-2 expression to beta-cell function glucose uptake and glucose-stimulated insulin release in fresh and cultured islets were measured. In freshly isolated islet glucose uptake was estimated to be 100-fold in excess of actual glucose use. Glucose uptake was reduced by 7-day culture to about one-third of that observed in freshly isolated islets no matter what the glucose concentration of the culture media. We conclude that in the present experimental system GLUT-1 and GLUT-2 expression and function are not closely associated with glucose usage rates or the secretory function of beta-cells.