Human Molecular Genetics, 2008, Vol. 17, No. 6 775–788 doi:10.1093/hmg/ddm349 Advance Access published on November 27, 2007 Transcriptional activators HAP/NF-Y rescue a cytochrome c oxidase defect in yeast and human cells
Flavia Fontanesi1, Can Jin3, Alexander Tzagoloff3 and Antoni Barrientos1,2,
1Department of Neurology and 2Department of Biochemistry & Molecular Biology, The John T. MacDonald Foundation Center for Medical Genetics, University of Miami Miller School of Medicine, Miami, FL, USA and Downloaded from https://academic.oup.com/hmg/article/17/6/775/600424 by guest on 29 September 2021 3Department of Biological Sciences, Columbia University, New York, NY, USA
Received October 29, 2007; Revised and Accepted November 26, 2007
Cell survival and energy production requires a functional mitochondrial respiratory chain. Biogenesis of cytochrome c oxidase (COX), the last enzyme of the mitochondrial respiratory chain, is a very complicated process and requires the assistance of a large number of accessory factors. Defects in COX assembly alter cellular respiration and produce severe human encephalomyopathies. Mutations in SURF1, a COX assembly factor of exact unknown function, produce Leigh’s syndrome (LS), the most frequent cause of COX deficiency in infants. In the yeast Saccharomyces cerevisiae, deletion of the SURF1 homologue SHY1 results in a similar COX deficiency. In order to identify genetic modifiers of the shy1 mutant phenotype, we have explored for genetic interactions involving SHY1. Here we report that overexpression of Hap4p, the catalytic subunit of the CCAAT binding transcriptional activator Hap2/3/4/5p complex, suppresses the respiratory defect of yeast shy1 mutants by increasing the expression of nuclear-encoded COX subunits that interact with the mitochondrially encoded Cox1p. Analogously, overexpression of the Hap complex human homologue NF-YA/B/C transcription complex in SURF1-deficient fibroblasts from an LS patient effi- ciently rescues their COX deficiency.
INTRODUCTION The subunits composing COX are thought to be matured and inserted into the nascent complex in an ordered fashion. Eukaryotic cytochrome c oxidase (COX), the terminal enzyme At least four COX assembly intermediates (or subcomplexes) of the respiratory chain, catalyzes electron transfer from cyto- can be detected in human mitochondria, which represent major chrome c to molecular oxygen. COX is located in the mito- steps in the COX assembly process (1,2). Although more dif- chondrial inner membrane and is made up of some dozen ficult to detect, COX subassemblies have also been described different subunits encoded by both mitochondrial and in some yeast mutants (3,4). Shy1p is an important COX nuclear DNA. The catalytic core of the enzyme consists of assembly factor which functions early in the assembly three subunits (Cox1p, 2p and 3p) all of which are mitochon- pathway (5,6). Identifying the precise function of this drial gene products. Cox1p contains two redox centers, one protein is of considerable interest because mutations in its formed by a low-spin heme a and the other by a binuclear human homologue, SURF1, are responsible for most diag- center consisting of a high-spin heme a3 and CuB. A third nosed cases of Leigh’s syndrome (LS) presenting a COX redox center is formed by the two copper ions present in the deficiency, a devastating early-onset encephalomyopathy CuA site of Cox2p. The 8 (yeast) or 10 (mammalian) (7,8). Unlike other assembly-defective strains of yeast that nuclear encoded subunits act as a protective shield surround- display a complete absence of COX, shy1 mutants produce ing the catalytic core. 10–15% fully assembled and functional COX (9), similar to