Association between IL-6 and CD40 signaling. IL-6 induces phosphorylation of CD40 receptors.
CD40 mAb at subsaturating doses inhibit the growth of transformants of the M12 murine cell line expressing intact full length CD40 molecules (M12/CD40+ cells) but do not inhibit the growth of two M12 transformants expressing either a mutant CD40 cDNA missing most of the cytoplasmic tail (CD40/tailless) or a mutant cDNA with a substitution at residue 234 (CD40/234A, Ala for Thr). Using these transformants, we tested a panel of cytokines for the ability to mimic CD40 mAb. rIL-6 behaved like CD40 mAb and inhibited the growth of M12/CD40+ cells but not of CD40/tailless or CD40/234A mutants. The effect of IL-6 on M12/CD40+ cells not only required intact CD40 including threonine 234 but also was specific because IL-6 mAb blocked the inhibitory activity. The M12/CD40+ cells responsive to IL-6 expressed greater than 300,000 CD40 molecules/cells but, like M12/CD40-controls, expressed only small numbers (less than 50/cell) of high affinity IL-6R, indicating that CD40 is not a receptor for IL-6. Nevertheless, IL-6 utilizes intact CD40 efficiently when it signals these cells: treatment of M12/CD40+ cells with IL-6 induced increased phosphorylation of CD40. Conversely, triggering CD40 on M12/CD40+ cells leads to IL-6 production. Similar effects were evident in human CD40+ B cells: IL-6 increased the phosphorylation of CD40 in the IL-6-responsive cell line, CESS, and CD40 mAb induced IL-6 production in activated human B cells. Thus, CD40 may function to receive and regulate IL-6-dependent signals in B cells.
Clark
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Department of Microbiology, University of Washington, Seattle 98195.
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D000818:Animals; D000911:Antibodies, Monoclonal; D000944:Antigens, Differentiation, B-Lymphocyte / Q000235:genetics / Q000502:physiology*; D001402:B-Lymphocytes / Q000502:physiology*; D019013:CD40 Antigens; D002460:Cell Line; D003001:Cloning, Molecular; D004252:DNA Mutational Analysis; D006801:Humans; D066298:In Vitro Techniques; D015850:Interleukin-6 / Q000494:pharmacology*; D008213:Lymphocyte Activation; D051379:Mice; D010766:Phosphorylation; D011940:Receptor Aggregation; D011956:Receptors, Cell Surface / Q000502:physiology; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D014162:Transfection
D000911:Antibodies, Monoclonal; D000944:Antigens, Differentiation, B-Lymphocyte; D019013:CD40 Antigens; D015850:Interleukin-6; D011956:Receptors, Cell Surface