CHARACTERIZATION OF AN INTERLEUKIN-6 CYTOKINE FAMILY ANTAGONIST PROTEIN FROM A MARINE SPONGE, CALLYSPONGIA SP

An inhibitor of IL-6 binding to the human hepatoma line HepG2 and myel oma cell line U266 was identified in a saline extract of the marine sp onge, Callyspongia sp. Functional activity, measured through the incre ase in haptoglobin production by HepG2 cells stimulated with IL-6, cou ld be strongly inhibited by the extract. Similarly, IL-6-induced produ ction of IgM by the B cell line SKW6.4 was substantially reduced, In n either cell line was there evidence of toxicity produced by the extrac t. Other sponges of the Callyspongia species were found to contain ana logous activity. The activity was destroyed by trypsin treatment or bo iling of the extract, suggesting that the inhibition is due to a prote in, When the binding of IL-6 to its receptor complex was dissected in. vitro, inhibition of binding of IL-6 to soluble receptor by the extra ct was not detected, but binding of the IL-6 . sIL-6R complex to solub le gp130 was inhibited in a dose-dependent fashion. This was borne out in cellular assays since the extract inhibited activation of HepG2 ce lls stimulated with oncostatin M or leukemia inhibitory factor, cytoki nes which also use gp130 for signal transduction. These results sugges t that the Callyspongia extract contains a protein which blocks the in teraction of the IL-6 family of cytokines with their signal transducti on moiety, gp130, Elucidation of the structure and mode of action of s uch a protein would be helpful in designing gp130 antagonists to inhib it the functions of this cytokine family, overproduction of which has been associated with cancer and pathologies of autoimmune disease and AIDS.