Synergism and antagonism of two distinct, but confused, Nrf1 factors in integral regulation of the nuclear-to-mitochondrial respiratory and antioxidant transcription networks

Abstract

There is hitherto no literature available for explaining two distinct, but confused Nrf1 transcription factors, because they shared the same abbreviations from nuclear factor erythroid 2-related factor 1 (also called Nfe2l1) and nuclear respiratory factor (originally designated -Pal). Thus, we have here identified that Nfe2l1 Nrf1 and -Pal NRF1 exert synergistic and antagonistic roles in integrative regulation of the nuclear-to-mitochondrial respiratory and antioxidant transcription profiles. In mouse embryonic fibroblasts (MEFs), knockout of Nfe2l1 / leads to substantial decreases in expression levels of -Pal NRF1 and Nfe2l2, together with TFAM (mitochondrial transcription factor A) and other target genes. Similar inhibitory results were determined in Nfe2l2 / MEFs, with an exception that GSTa1 and Aldh1a1 were distinguishably up-regulated in Nfe2l1 / MEFs. Such synergistic contributions of Nfe2l1 and Nfe2l2 to the positive regulation of -Pal NRF1 and TFAM were validated in Keap1 / MEFs. However, human -Pal NRF1 expression was unaltered by hNfe2l1 / , hNfe2l2 /TA or even hNfe2l1 / +siNrf2, albeit TFAM was activated by Nfe2l1 but inhibited by Nfe2l2; such an antagonism occured in HepG2 cells. Conversely, almost all of mouse Nfe2l1, Nfe2l2 and co-target genes were down-expressed in -Pal NRF1/ MEFs. On the contrary, up-regulation of human Nfe2l1, Nfe2l2 and relevant reporter genes took place after silencing of -Pal NRF1 , but their down-regulation occurred upon ectopic expression of -Pal NRF1 .Furtherly, Pitx2 (pituitary homeobox 2) was also identified as a direct upstream regulator of Nfe2l1 and TFAM, besides -Pal NRF1 . Overall, these across-talks amongst Nfe2l1, Nfe2l2 and -Pal NRF1 , along with Pitx2, are integrated from the endoplasmic reticulum to the nuclear-to-mitochondrial communication for targeting TFAM, in order to finely tune the cellular respiratory and antioxidant gene transcription networks, albeit they differ between the mouse and the human. Keywords: Nfe2l1/Nrf1, Nfe2l2/Nrf2, -Pal NRF1 , TFAM, Pitx2, cap'n'collar (CNC), antioxidant response element (ARE), nuclear-to-mitochondrial respiratory system, and ER-nuclear-mitochondrial (ENUM) communication Running title: Two distinct Nrf1 factors responsible for cellular antioxidant and respiration.

Loss of Nrf1 rather than Nrf2 leads to inflammatory accumulation of lipids and reactive oxygen species (ROS) in human hepatoma cells, which is alleviated by 2-bromopalmitate

“…In the present study, we have provided the evidence unraveling different or even opposite contributions of Nrf1 and Nrf2 have been made in human lipid metabolism, in addition to our previously-reported glucose metabolism (14,23), protein homeostasis (proteostasis) (12,24), redox balance and signaling control (25,26). It is of crucial significance to note that the experimental cell model of Nrf1α -/- with pathophysiological phenotypes appears to largely resemble those manifested by the liver-specific Nrf1 knockout mice.…”

Commentary on Distinct, but Previously Confused, Nrf1 Transcription Factors and Their Functions in Redox Regulation

“…While consensus a-Pal NRF1 -binding sites (5 0 -TG CGCATGCGCA-3 0 ) are only present in the SOD1 gene promoter, the regulatory regions of Mt1, Gsta1, and Aldha1a are characterized by potential non-canonical binding sites, which await further functional analysis. Recent results from Zhang et al (2020) with mouse embryonic fibroblasts show altered expression of some antioxidant genes as a function of regulation by a-Pal NRF1 . Importantly, Nfe2l1 Nrf1 , which regulates antioxidant gene expression through ARE sites in their promoters, was not examined in L'honoré et al Regulatory Crosstalk between Nfe2l1 Nrf1 and a-Pal NRF1 : To gain insight into the function of the three transcription factors Nfe2l1 Nrf1 , Nfe2l2 Nrf2 , and a-Pal NRF1 , new experimental evidence has been provided by Zhang et al, 2020), in an attempt to further clarify the previously confusing view of these three Nrf1/2 factors.…”

“…Recent results from Zhang et al (2020) with mouse embryonic fibroblasts show altered expression of some antioxidant genes as a function of regulation by a-Pal NRF1 . Importantly, Nfe2l1 Nrf1 , which regulates antioxidant gene expression through ARE sites in their promoters, was not examined in L'honoré et al Regulatory Crosstalk between Nfe2l1 Nrf1 and a-Pal NRF1 : To gain insight into the function of the three transcription factors Nfe2l1 Nrf1 , Nfe2l2 Nrf2 , and a-Pal NRF1 , new experimental evidence has been provided by Zhang et al, 2020), in an attempt to further clarify the previously confusing view of these three Nrf1/2 factors. This manuscript identifies varying levels of inter-regulatory crosstalk between Nfe2l1 Nrf1 , Nfe2l2 Nrf2 , and a-Pal NRF1 (Zhang et al, 2020).…”

“…The confusion generated by these similarly named proteins, all involved in redox regulation, is the impetus for our joint letter, which aims to clarify the nomenclature and biological roles of these transcription factors. More detailed examination of this can be found in Zhang et al (2020).…”

“…Importantly, Nfe2l1 Nrf1 , which regulates antioxidant gene expression through ARE sites in their promoters, was not examined in L'honoré et al Regulatory Crosstalk between Nfe2l1 Nrf1 and a-Pal NRF1 : To gain insight into the function of the three transcription factors Nfe2l1 Nrf1 , Nfe2l2 Nrf2 , and a-Pal NRF1 , new experimental evidence has been provided by Zhang et al, 2020), in an attempt to further clarify the previously confusing view of these three Nrf1/2 factors. This manuscript identifies varying levels of inter-regulatory crosstalk between Nfe2l1 Nrf1 , Nfe2l2 Nrf2 , and a-Pal NRF1 (Zhang et al, 2020). Figure S1C presents a proposed model based on experimental ll data obtained from distinct genotypes of mouse Nfe2l1 À/À , Nfe2l2 À/À , Keap1 À/À , and a-Pal NRF1+/À embryonic fibroblasts.…”