GRIM-19, a Cell Death Regulatory Protein, Is Essential for Assembly and Function of Mitochondrial Complex I

Abstract

Mitochondria play essential roles in cellular energy production via the oxidative phosphorylation system (OXPHOS) consisting of five multiprotein complexes and also in the initiation of apoptosis. NADH:ubiquinone oxidoreductase (complex I) is the largest complex that catalyzes the first step of electron transfer in the OXPHOS system. GRIM-19 was originally identified as a nuclear protein with apoptotic nature in interferon (IFN)- and all-trans-retinoic acid (RA)-induced tumor cells. To reveal its biological role, we generated mice deficient in GRIM-19 by gene targeting. Homologous deletion of GRIM-19 causes embryonic lethality at embryonic day 9.5. GRIM-19^−/− blastocysts show retarded growth in vitro and, strikingly, display abnormal mitochondrial structure, morphology, and cellular distribution. We reexamined the cellular localization of GRIM-19 in various cell types and found its primary localization in the mitochondria. Furthermore, GRIM-19 is detected in the native form of mitochondrial complex I. Finally, we show that elimination of GRIM-19 destroys the assembly and electron transfer activity of complex I and also influences the other complexes in the mitochondrial respiratory chain. Our result demonstrates that GRIM-19, a gene product with a specific role in IFN-RA-induced cell death, is a functional component of mitochondrial complex I and is essential for early embryonic development.

This work was supported by the Agency for Science, Technology and Research of Singapore. X. Cao is an adjunct staff member of the Department of Biochemistry, National University of Singapore.

We are grateful to Christopher J. Leaver and Mohammed Sabar for protocols of the mitochondrial complex assays and for valuable suggestions. We thank Baohong Lin and Jie Li for technical assistance. We also thank the staffs in the In Vivo Model System Facility, Histology Unit, and DNA Sequencing and Analysis Facility in our institute and the Electron Microscopy Facility in the Department of Anatomy of the National University of Singapore. We are grateful to Wanjin Hong for valuable comments on the manuscript and Cheh Peng Lim for reading the manuscript critically.