Effects of alternate RNA splicing on glucokinase isoform activities in the pancreatic islet, liver, and pituitary

Different glucokinase isoforms are produced by tissue-specific alternative RNA splicing in the liver and pancreatic islet, the only tissues in which glucokinase activity has been detected. To determine whether differences in protein structure brought about by alternative RNA splicing have an effect on glucose phosphorylating activity, we expressed cDNAs encoding four different hepatic and islet glucokinase isoforms and determined the Km and Vmax of each. When the glucokinase B1 and L1 isoforms were expressed in eukaryotic cells, both high Km glucose phosphorylating activity and immunoreactive protein were detected. However, when the glucokinase B2 and L2 isoforms were expressed, both of which differ by deletion of 17 amino acids in a region between the putative glucose and ATP-binding domains, no high Km glucose phosphorylating activity and much less immunoreactive protein were detected. When the glucokinase B1 and B2 isoforms were expressed in Escherichia coli as fusion proteins with glutathione S-transferase, affinity-purified B1 fusion protein was able to phosphorylate glucose whereas the B2 fusion protein was not, thus indicating that the lack of glucose phosphorylating activity from both the B2 and L2 isoforms is due to lack of intrinsic activity in addition to accumulation of less protein. The Km values of the B1 and L1 isoforms, which differ from each other by 15 amino acids at the NH2 terminus, were similar, but the Vmax of the B1 isoform was 2.8-fold higher than that of the L1 isoform. Mutagenesis of the first two potential initiation codons in the glucokinase B1 cDNA from ATG to GTC (methionine to valine) indicated that the first ATG was crucial for activity and is, therefore, the likely translation initiation codon. Messenger RNAs encoding both the B2 and L2 isoforms of glucokinase were detected in islet and liver by polymerase chain reaction amplification of total cDNA, indicating that mRNAs utilizing this weak alternate splice acceptor site in the fourth exon are normally present in both the liver and islet but as minor components. A regulatory role for weak alternate splice acceptor and donor sites in the glucokinase gene was suggested by examining the expression of the gene in the pituitary and in AtT-20 cells. Interestingly, although glucokinase mRNAs of appropriate sizes were detected in both the AtT-20 cells and rat pituitaries, neither exhibited any detectable high Km glucose phosphorylating activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Content of CoA-esters in perifused rat islets stimulated by glucose and other fuels

Fluorometry and high-performance liquid chromatography were used to measure the content of free CoA and the esters of acetate, malonate, succinate, and long-chain fatty acids in isolated perifused rat pancreatic islets exposed to 25 mM glucose or a mixture of fuels (25 mM glucose plus 10 mM glutamine, 10 mM lactate, and 1 mM pyruvate) to assess the role of intermediates of lipid metabolism as candidate metabolic coupling factors in the mechanism of fuel-induced insulin secretion. Insulin secretion was stimulated in a biphasic manner with the fuel mixture, showing twice the potency compared with high glucose alone. Islets perifused for 3 min with high glucose alone or the fuel mixture compared with 2.5 mM glucose showed a significant increase in malonyl-CoA and succinyl-CoA and a decrease in acetyl-CoA. Free CoA and long-chain acyl-CoA levels were unaltered. Perifused islets stimulated with 25 mM glucose for 30 min showed a significant increase in succinyl-CoA and long-chain acyl-CoA and decrease in acetyl-CoA, whereas malonyl-CoA was not affected. However, when islets were stimulated by the fuel mixture for 30 min, malonyl-CoA was maintained at a high level, and the change in succinyl-CoA and long-chain acyl-CoA was similar to that observed in islets stimulated with 25 mM glucose alone. The acetyl-CoA concentration in the islets stimulated with the fuel mixture decreased slightly. These results confirm the viability of the hypothesis that malonyl-CoA and long-chain acyl-CoA serve as metabolic coupling factors in signal transduction when islets are stimulated by high glucose or glucose combined with other fuels.

[Cerebellar infarction and its assistant examination]

The clinical manifestations of cerebellar infarction are often non-particular and it is difficult to make such a diagnosis clinically. Diagnosis was based on pathology previously. Most of the cases were overlooked while still living and the true morbidity was not known. CT scan has made the diagnosis of this disease possible clinically in some patients, but CT is still not an ideal instrument for diagnosing this disease because of the interference by bony artifacts of posterior fossa. The advent of MRI made it possible to distinguish cerebellar infarction safely and easily. It is not the most powerful tool for diagnosing this disease. The authors reported 15 cases of cerebellar infarction diagnosed by clinical manifestation, neuroimages and pathology and pointed out that further knowledge of this disease is needed.

[Immunohistochemical study of extracellular matrices in human glioma and meningioma]

The expression and distribution of the extracellular matrix (ECM) in 37 gliomas and 19 meningiomas were studied immunohistochemically by antibodies to type 3, 4 and 6 collagen, fibronectin and laminin. In gliomas the expression of these antigens was more intense and thicker in the tumor vessel walls, and was positively correlated to the malignant degree of the gliomas. This suggests that the thickening of the vessel walls and the increase of their ECM components in gliomas may be one of the causes why gliomas are extremely rare to metastasize to the outside of the cranium. All the above-cited ECM were positive in the fibroblastic type of meningioma, being just located between the tumor cells; whereas in syncytial type they were negative. This indicates that the immunohistochemistry of ECM may be of advantage in differentiating meningioma type.

Glucose regulates glucokinase activity in cultured islets from rat pancreas

In this study, we have used isolated pancreatic islets cultured for 7 days in 3 or 30 mM glucose to explore whether glucokinase is induced or activated by high glucose concentrations and has related enzyme activity to glucose-stimulated insulin release. Islets cultured in low glucose medium or low glucose medium plus 350 ng/ml insulin did not respond to high glucose stimulation. Islets cultured in medium containing high glucose concentrations showed a high rate of basal insulin secretion when perifused with 5 mM glucose, and the insulin release was greatly augmented in a biphasic secretion profile when the glucose concentration was raised to 16 mM. Islet glucokinase and hexokinase activities were determined by a sensitive and specific fluorometric method. Glucokinase activity was reduced to approximately 50% in islets cultured in low glucose medium with or without insulin present compared to results with fresh islets. However, islets cultured in 30 mM glucose showed that glucokinase activity was elevated to 236% compared to results with fresh islets. It is concluded that (a) glucose is the physiological regulator of glucokinase in the islet of Langerhans and that (b) the activity of glucokinase plays a crucial role in glucose-induced insulin secretion.

[A report of an outbreak of diphtheria in Anshan area]

This paper reports an outbreak of diphtheria and the result of appropriate preventive and therapeutic measures in Anshan area from Dec. 1984 to Dec. 1987. This epidemic of diphtheria occurred mainly in a camp of reform though labour organization and in a spring sanatorium among a population of young adult people with higher level of antibodies. It was proved that the special infection origin was a strain of nontoxic diphtheria bacilli. After a combined management including of injection of a refined diphtheria toxoid and an environment disinfection, the incidence of the disease dropped markedly.

Clinical analysis of four Chinese hemophiliacs with human immunodeficiency virus infection

Human immunodeficiency virus (HIV) is now considered as the causative agent of acquired immunodeficiency syndrome (AIDS). A high risk of AIDS has been reported among patients with hemophilia who received lyophilized commercial factor VIII and IX concentrates of American origin. At a prevalent survey from September to December 1985, HIV antibodies were found in all four patients with hemophilia treated with the batch number W87307, 955 I.U. of American commercial factor VIII concentrate supplied by Armour Pharmaceutical Company, USA. One of the sero-positive patients developed AIDS-related complex (ARC) and died of cerebral hemorrhage. The other three sero-positive patients had abnormalities in cell-mediated immunity. Of them two developed left lumbosacral radiculopathy and hemorrhagic herpes zoster and one remained well so far.

Clinical significance of urine ferritin determination in urologic malignancies

Urine and serum ferritin levels were measured by a double-antibody radio-immunoassay in 96 normal adults and 57 patients with urologic malignancies. In the 96 adults, the urine ferritin levels ranged from 0 to 28 ng/ml. Elevated urine ferritin levels were observed in all 7 patients with renal pelvic carcinoma, 4 of 13 patients with renal carcinoma, 1 of 13 patients with well-differentiated (Grade I) bladder carcinoma, 8 of 19 patients with median-differentiated (Grade II) bladder carcinoma, and all 5 patients with poorly-differentiated (Grades III, IV) bladder carcinoma. These results indicated that urine ferritin assay was helpful in discriminating well-differentiated bladder carcinoma from the poorly-differentiated (P less than 0.01) in addition to differentiating renal pelvic carcinoma from renal carcinoma (P less than 0.05).