Binding of manumycin A inhibits IκB kinase β activity

Abstract

IκB kinase (IKK) catalytic subunits play a key role in cytokine-mediated nuclear factor (NF)-κB signaling, and a loss of NF-κB 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 α 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 IKKα and IKKβ constructs, and a striking difference in manumycin A sensitivity was observed. Furthermore, cells expressing wild-type IKKβ and IKKβ mutated in the activation loop at Cys-179 exhibited covalent homotypic dimerization of IKKβ 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 IKKβ dimers were observed in the presence of manumycin A that could be blocked by dithiothreitol. IKK interaction with the adaptor protein IKKγ/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.