Down-regulation of TNF-alpha receptors by conophylline in human T-cell leukemia cells.
In the course of our screening for tumor necrosis factor-alpha (TNF-alpha) function inhibitors, conophylline, a vinca alkaloid isolated from the plant Ervatamia microphylla, was found to inhibit TNF-alpha-induced NF-kappaB activation. We studied the effect of conophylline on TNF-alpha-induced NF-kappaB and JNK activations in human T-cell leukemia Jurkat cells. Conophylline inhibited both of these TNF-alpha-induced activations. It also inhibited phosphorylation and degradation of I-kappaB-alpha. Moreover, a receptor binding assay using [125I]-TNF-alpha showed that this inhibitory effect was due to a decrease in the binding of TNF-alpha to the cells. Scatchard analysis of the binding data indicated that conophylline induced only a small change in the affinity of the receptors but a significant change in the receptor number. FACS analysis showed that conophylline reduced the expression of CD120a/TNFR1, the high-affinity receptor for TNF-alpha, on the cell surface. On the other hand, conophylline did not affect the kinetics of internalization and degradation of TNF-alpha/receptor complexes or the half-life of TNF-alpha binding sites. These results indicate that conophylline down-regulates the expression of the TNF-alpha receptors on the cell surface.
Gohda
Jin
J
Division of Cellular and Molecular Biology, Department of Cancer Biology, Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo 108-8639, Japan.
Inoue
Jun-Ichiro
J
Umezawa
Kazuo
K
D015703:Antigens, CD / Q000096:biosynthesis; D001665:Binding Sites; D002462:Cell Membrane / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D002469:Cell Separation; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D004789:Enzyme Activation; D005434:Flow Cytometry; D018922:HL-60 Cells; D006801:Humans; D020672:I-kappa B Proteins / Q000378:metabolism; D019169:Jurkat Cells; D007700:Kinetics; D015458:Leukemia, T-Cell / Q000188:drug therapy* / Q000378:metabolism*; D008956:Models, Chemical; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D018124:Receptors, Tumor Necrosis Factor / Q000096:biosynthesis*; D047888:Receptors, Tumor Necrosis Factor, Type I; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors; D014748:Vinca Alkaloids / Q000494:pharmacology*
D015703:Antigens, CD; D020672:I-kappa B Proteins; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D018124:Receptors, Tumor Necrosis Factor; D047888:Receptors, Tumor Necrosis Factor, Type I; D011994:Recombinant Proteins; D014748:Vinca Alkaloids; C099167:conophylline; D000072000:NF-KappaB Inhibitor alpha