Binding of manumycin A inhibits IκB kinase β activity

I kappa B kinase (IKK) catalytic subunits play a key role in cytokine-mediated nuclear factor (NF)-kappa B signaling, and a loss of NF-kappa B function appears to inhibit inflammation and oncogenesis. Manumycin A is a potent and selective farnesyltransferase inhibitor with antitumor activity. We found that manumycin A caused a rapid and potent inhibition of IKK activity induced by tumor necrosis factor alpha in a number of cell types. Most unexpectedly, other classes of farnesyltransferase inhibitors had no inhibitory effect. To identify the molecular mechanisms of manumycin A action, cultured human HepG2 hepatoma cells were transiently transfected with various IKK alpha and IKK beta constructs, and a striking difference in manumycin A sensitivity was observed. Furthermore, cells expressing wild-type IKK beta and IKK beta mutated in the activation loop at Cys-179 exhibited covalent homotypic dimerization of IKK beta in response to manumycin A, whereas substitution of Cys-662 and -716 conferred protection against dimer formation. Direct inhibition of IKK activity and formation of stable IKK beta dimers were observed in the presence of manumycin A that could be blocked by dithiothreitol. IKK interaction with the adaptor protein IKK gamma/NEMO was disrupted in manumycin A-treated cells. Most importantly, administration of manumycin A to mice xenografted with murine B16F10 tumors caused potent IKK-suppressive effects. Thus, manumycin A with its epoxyquinoid moieties plays an important regulatory function in IKK signaling through pathways distinct from its role as a protein farnesylation inhibitor.