phorbol-12-13-didecanoate and Carcinoma--Hepatocellular

An analysis of the mechanism of generation of the soluble interleukin-6 receptor (IL-6R) has been performed. The membrane-bound receptor is proteolytically cleaved to release a soluble receptor form which retained its ligand binding capacity. Furthermore, the soluble IL-6R is unique in its ability to induce a biological signal in complex with the ligand interleukin-6 (IL-6) on cells which by themselves do not bind IL-6. Shedding of the IL-6R is strongly activated by PMA and can be inhibited by the protein kinase inhibitor staurosporine. The generation of the IL-6R is not dependent on protein synthesis. The inactive PMA analogue 4-alpha-phorbol-12,13-didecanoate fails to induce shedding of the IL-6R. Transfection of a protein kinase C expression plasmid into IL-6R expressing cells leads to enhanced shedding of the receptor. These experiments clearly show that protein kinase C regulates shedding of the IL-6R.

Topics: Alkaloids; Animals; Binding Sites; Carcinoma, Hepatocellular; Cell Line; Cycloheximide; Humans; Interleukin-6; Kinetics; Liver Neoplasms; Macromolecular Substances; Phorbol Esters; Protein Kinase C; Receptors, Immunologic; Receptors, Interleukin-6; Recombinant Proteins; Staurosporine; Transfection; Tumor Cells, Cultured