Synergism and Antagonism of Two Distinct, but Confused, Nrf1 Factors in Integral Regulation of the Nuclear-to-Mitochondrial Respiratory and Antioxidant Transcription Networks

Figure 7

Transcriptional regulation of TFAM by Nfe2l1, Nfe2l2, and Pitx2. (a) Two similar α-helical structural wheels were formed by successive mitochondria-targeting sequences MTS1 (aa 1-18) and MTS2 (aa 21-38). Basic arginine and lysine residues were placed on blue backgrounds; nucleophilic serine and threonine residues are on purple backgrounds; an unamiable proline residue was on a green background, and all other hydrophobic amino acids were on yellow backgrounds, except for small alanine and glycine on grey backgrounds. The lower panel shows an alignment of three amino-acid sequences of human TFAM (NP_003192) and mouse TFAMs (NP_033386 and XP_017169407), in which, MTS1, MTS2, nuclear localization signal (NLS), and DNA-binding MHG-box were indicated. (b) The putative consensus ARE sites and other cis-regulatory binding sites for Pitx2, α-Pal^NRF1, or GABP within the human TFAM gene promoter region were indicated. (c) Four distinct ARE-driven (i.e., ARE1-luc to ARE4-luc) and another Pitx2RE-luc reporters were constructed into the pGL3-Promoter vector. (d) HepG2 cells were cotransfected with PitxRE-luc and pRL-TK, plus a Pitx2 expression plasmid or an empty pcDNA3.1, and then allowed for 24 h recovery before the luciferase activity was measured. The data are shown as () with significant increase ($, ). (e) HepG2 cells were cotransfected with each of ARE1-luc to ARE4-luc, together with pRL-TK plus an expression construct for Nfe2l1, Nfe2l2, or an empty pcDNA3.1, and then allowed for 24 h recovery, before such ARE-driven activity was detected. The resultant data are shown as () with significant increases ($, ) or decreases (). (f) A model is proposed to explain the transcriptional regulation of TFAM by Nfe2l1, Nfe2l2, Pitx2, and α-Pal^NRF1 in HepG2 cells.

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