Subunit specific monoclonal antibodies show different steady-state levels of various cytochrome-c oxidase subunits in chronic progressive external ophthalmoplegia

Monoclonal antibodies recognizing the mitochondrially encoded subunits I and II, and the nuclear-encoded subunits IV, Va, Vb and VIc of human cytochrome-e oxidase were generated. These antibodies are highly specific and allow the assessment of subunit steady-state levels in crude cell extracts and tissue sections. In the experimental human cell line 143B206, which is devoid of mitochondrial DNA, immunovisualization with the antibodies revealed that the nuclear-encoded subunits IV and Va were present in amounts close to that of the parental cell line despite the absence of the mitochondrially encoded subunits. In contrast, the nuclear-encoded subunits Vb and VIc were severely reduced in cell line 143B206, suggesting that unassembled nuclear-encoded subunits are degraded at different rates. In skeletal muscle sections of a patient with chronic progressive external ophthalmoplegia known to harbor the 'common deletion' in a subpopulation of her mitochondrial DNA, most cytochrome-e oxidase activity negative fibers had greatly reduced levels of subunits I, II, Va, Vb and Vie of cytochrome-c oxidase. The steady-state level of subunit IV, however, was less affected. This was particularly evident in cytochrome-c oxidase activity negative fibers with accumulated mitochondria ('ragged-red' fibers) where immunodetection with anti-subunit IV resulted in intense staining. The data presented in this paper demonstrate that the battery of monoclonal antibodies can be employed for diagnostic purposes to analyze steady-state levels of mitochondrially and nuclear-encoded subunits of cytochrome-c oxidase.