Cytochrome c Oxidase Is Required for the Assembly/Stability of Respiratory Complex I in Mouse Fibroblasts

Abstract

Cytochrome c oxidase (COX) biogenesis requires COX10, which encodes a protoheme:heme O farnesyl transferase that participates in the biosynthesis of heme a. We created COX10 knockout mouse cells that lacked cytochrome aa₃, were respiratory deficient, had no detectable complex IV activity, and were unable to assemble COX. Unexpectedly, the levels of respiratory complex I were markedly reduced in COX10 knockout clones. Pharmacological inhibition of COX did not affect the levels of complex I, and transduction of knockout cells with lentivirus expressing wild-type or mutant COX10 (retaining residual activity) restored complex I to normal levels. Pulse-chase experiments could not detect newly assembled complex I, suggesting that either COX is required for assembly of complex I or the latter is quickly degraded. These results suggest that in rapidly dividing cells, complex IV is required for complex I assembly or stability.

We are grateful to Jamey D. Marth (University of California at San Diego) for the targeting construct. We also thank Antoni Barrientos (University of Miami) for help with the cytochrome spectra determination and both A. Barrientos and Sion L. Williams for critical comments.

This work was supported by Public Health Service grants NS041777 and GM55766 to C.T.M. and by a Muscular Dystrophy Association Research Development Grant to F.D. H.F. is a recipient of the Lois Pope LIFE Fellowship.