Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:6.4.1.1 (pyruvate carboxylase)
 1,516 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Prolactin (PRL) induces beta-cell proliferation and glucose-stimulated insulin secretion (GSIS) and counteracts the effects of glucocorticoids on insulin production. The mechanisms by which PRL up-regulates GSIS are unknown. We used rat islets and insulinoma (INS-1) cells to explore the interactions of PRL, glucose, and dexamethasone (DEX) in the regulation of beta-cell pyruvate carboxylase (PC), pyruvate dehydrogenase (PDH), and the pyruvate dehydrogenase kinases (PDKs), which catalyze the phosphorylation and inactivation of PDH. PRL increased GSIS by 37% (P < 0.001) in rat islets. Glucose at supraphysiological concentrations (11 mm) increased PC mRNA in islets; in contrast, PRL suppressed PC mRNA levels in islets and INS-1 cells, whereas DEX was without effect. Neither PRL nor DEX altered PC protein or activity levels. In INS-1 cells, PRL increased PDH activity 1.4- to 2-fold (P < 0.05-0.001) at glucose concentrations ranging from 2.5-11 mm. DEX reduced PDH activity; this effect was reversed by PRL. PDK1, -2, -3, and -4 mRNAs were detected in both islets and insulinoma cells, but the latter expressed trivial amounts of PDK4. PRL reduced PDK2 mRNA and protein levels in rat islets and INS-1 cells and PDK4 mRNA in islets; DEX increased PDK2 mRNA in islets and INS-1 cells; this effect was reversed by PRL. Our findings suggest that PRL induction of GSIS is mediated by increases in beta-cell PDH activity; this is facilitated by suppression of PDKs. PRL counteracts the effects of DEX on PDH and PDK expression, suggesting novel roles for the lactogens in the defense against diabetes.
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PMID:Regulation of islet beta-cell pyruvate metabolism: interactions of prolactin, glucose, and dexamethasone. 2048 62

l-lactate formation occurs via the reduction of pyruvate catalyzed by lactate dehydrogenase. l-lactate removal takes place via its oxidation into pyruvate, which may be oxidized or converted into glucose. Pyruvate oxidation involves the cooperative effort of pyruvate dehydrogenase, the tricarboxylic acid cycle, and the mitochondrial respiratory chain. Enzymes of the gluconeogenesis pathway sequentially convert pyruvate into glucose. In addition, pyruvate may undergo reversible transamination to alanine by alanine aminotransferase. Enzymes involved in l-lactate metabolism are crucial to diabetes pathophysiology and therapy. Elevated plasma alanine aminotransferase concentration has been associated with insulin resistance. Polymorphisms in the G6PC2 gene have been associated with fasting glucose concentration and insulin secretion. In diabetes patients, pyruvate dehydrogenase is down-regulated and the activity of pyruvate carboxylase is diminished in the pancreatic islets. Inhibitors of fructose 1,6-bisphosphatase are being investigated as potential therapy for type 2 diabetes. In addition, enzymes implicated in l-lactate metabolism have revealed to be important in cancer cell homeostasis. Many human tumors have higher LDH5 levels than normal tissues. The LDHC gene is expressed in a broad range of tumors. The activation of PDH is a potential mediator in the body response that protects against cancer and PDH activation has been observed to reduce glioblastoma growth. The expression of PDK1 may serve as a biomarker of poor prognosis in gastric cancer. Mitochondrial DNA mutations have been detected in a number of human cancers. Genes encoding succinate dehydrogenase have tumor suppressor functions and consequently mutations in these genes may cause a variety of tumors.
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PMID:Enzymes involved in l-lactate metabolism in humans. 2402 12