Transcriptional regulation of human nuclear encoded mitochondrial genes

University dissertation from Stockholm : Stockholm University

Abstract: Biogenesis of mammalian mitochondria requires the participation of both nuclear and mitochondrial genes. This thesis presents studies that characterize the common features of several nuclear encoded mitochondrial promoter genes and proposes the identity of factors regulating the transcription and responsible for coordinated, constitutive expression of diverse mammalian oxidative phosphorylation (OXPHOS) genes.As a model, we chose to study the promoters of four nuclear-encoded OXPHOS genes, all which are constitutively expressed, but, in addition, exhibit different responses to hormone and/or growth-activation. They also represent functionally different OXPHOS complexes. These promoters are from the human cytochrome c1, the mitochondrial transcription factor, mtTFA, the F1-ATPase b-subunit, and the adenine nucleotide translocator isoform 2 (ANT2) genes. The results presented in this thesis can be summarized as follows:The General transcription factor Sp1 can activate and repress different mammalian OXPHOS genes. Sp1 binding elements (GC boxes) are present in most, if not all, OXPHOS promoter, which suggest that Sp1 may have a general role in regulating the expression of nuclear encoded mitochondrial genes. (b) Sp1-mediated repression and activation from the ANT2 promoter require the D transactivation domain of Sp1 bound to the Cbox. (c) Sp1-mediated repression from the ANT2 promoter is not due to steric interference with the assembly of the transcription machinery. Sp1 bound to the Cbox, under certain conditions, activates the ANT2 promoter (d) Different Sp family members (Sp2, Sp3 and Sp4) differentially affect transcription of the OXPHOS promoters studied. (e) AP-2 enhances Sp1-dependent transactivation of the ANT2 promoter gene. (f) Sp3, but not Sp4, can repress the ANT2 promoter via the Cbox, suggesting that different members of the Sp family can have different roles when they bind to the ANT2 Cbox. (g) Thyroid hormone activates reporter gene expression driven from the ANT2 and cytochrome c1 promoters, which suggests that thyroid hormone induction of some OXPHOS genes is at the transcriptional level.