leptin and Fibrosarcoma

Mice bearing IL-1beta-secreting tumor were used to study the chronic effect of IL-1beta on glucose metabolism. Mice were injected with syngeneic tumor cells transduced with the human IL-1beta gene. Serum IL-1beta levels increased exponentially with time. Secretion of IL-1beta from the developed tumors was associated with decreased food consumption, reduced body weight, and reduced blood glucose levels. Body composition analysis revealed that IL-1beta caused a significant loss in fat tissue without affecting lean body mass and water content. Hepatic phosphoenolpyruvate carboxykinase and glucose-6-phosphatase activities and mRNA levels of these enzymes were reduced, and 2-deoxy-glucose uptake by peripheral tissues was enhanced. mRNA levels of glucose transporters (Gluts) in the liver were determined by real-time PCR analysis. Glut-3 mRNA levels were up-regulated by IL-1beta. Glut-1 and Glut-4 mRNA levels in IL-1beta mice were similar to mRNA levels in pair-fed mice bearing nonsecreting tumor. mRNA level of Glut-2, the major Glut of the liver, was down-regulated by IL-1beta. We concluded that both decreased glucose production by the liver and enhanced glucose disposal lead to the development of hypoglycemia in mice bearing IL-1beta-secreting tumor. The observed changes in expression of hepatic Gluts that are not dependent on insulin may contribute to the increased glucose uptake.

Topics: Animals; Anorexia; Blood Glucose; Body Composition; Body Weight; C-Peptide; Cell Line, Tumor; Eating; Female; Fibrosarcoma; Gluconeogenesis; Glucose; Glucose-6-Phosphatase; Glycogen; Humans; Hypoglycemia; Hypoglycemic Agents; Insulin; Interleukin-1; Leptin; Liver; Mice; Mice, Inbred C57BL; Monosaccharide Transport Proteins; Neoplasm Transplantation; Protein Serine-Threonine Kinases; RNA, Messenger

The induced expression of xanthine-guanine phosphoribosyl transferase (XGPRT) by low concentrations (-2 pg/ml) of interferon-alpha (IFN-alpha) or IFN-beta, in the 2fTPGH cell line caused a 50% cytotoxicity when these cells were grown in medium containing 6-thioguanine. We extended the application of this sensitive, reliable, and easy bioassay to other members of the cytokine family. To activate the IFN signaling pathway, we made receptor chimeras, consisting of the IFN type I receptor intracellular and transmembrane domains, fused to either the interleukin-5 (IL-5) receptors or erythropoietin (Epo) receptor extracellular domains as model systems. 2fTGH cells, stably transfected with these receptor chimeras, responded to very low concentrations of IL-5 or Epo (IC50 values of approximately 15 pg and 3 pg/ml, respectively) and thus can be used as a very sensitive bioassay for both ligands. Background activity of IL-5, Epo, tumor necrosis factor (TNF), IL-6, or leptin on cells that did not carry the receptor chimeras was very low. This methodology can in principle be extended to any ligand that acts via clustering of its receptors.

Topics: Biological Assay; Coloring Agents; Culture Media; Enzyme Induction; Erythropoietin; Fibrosarcoma; Gentian Violet; Humans; Interferon alpha-2; Interferon-alpha; Interferon-beta; Interleukin-5; Interleukin-6; Leptin; Ligands; Membrane Proteins; Neoplasm Proteins; Pentosyltransferases; Receptor Aggregation; Receptor, Interferon alpha-beta; Receptors, Erythropoietin; Receptors, Interferon; Receptors, Interleukin; Receptors, Interleukin-5; Recombinant Fusion Proteins; Recombinant Proteins; Selection, Genetic; Sensitivity and Specificity; Signal Transduction; Thioguanine; Transfection; Tumor Cells, Cultured; Tumor Necrosis Factor-alpha