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Transcription factor Nrf2 (nuclear factor, erythroid 2-like 2, encoded by Nfe2l2) has been accepted as a key player in redox regulatory responses to oxidative or reductive stresses. However, relatively little is known about the potential role of Nrf1 (nuclear factor, erythroid 2-like 1, encoded by Nfe2l1) in the redox responses, particularly to reductive stress, although this ‘fossil-like’ factor is indispensable for cell homeostasis and organ integrity during the life process. Herein, we examine distinct roles of Nrf1 and Nrf2 in monitoring the defense response to 1,4–dithiothreitol (DTT, serving as a reductive stressor), concomitantly with unfolded protein response being induced by this chemical (also defined as an endoplasmic reticulum stressor). The results revealed that intracellular reactive oxygen species (ROS) were modestly increased in DTT-treated wild-type (WT) and Nrf1α−/− cell lines, but almost unaltered in Nrf2−/−ΔTA or caNrf2ΔN cell lines (with a genetic loss of transactivation or N-terminal Keap1-binding domains, respectively). This chemical treatment also enabled the rate of oxidized to reduced glutathione (i.e., GSSG to GSH) to be amplified in WT and Nrf2−/−ΔTA cells, but diminished in Nrf1α−/− cells, along with to or less extents changes in caNrf2ΔN cells. Consequently, Nrf1α−/−, but not Nrf2−/−ΔTA or caNrf2ΔN, cell viability was reinforced by DTT against its cytotoxicity, as accompanied by decreased apoptosis. Further experiments unraveled that Nrf1 and Nrf2 differentially, and also synergistically, regulated DTT-inducible expression of critical genes for defending against redox stress and endoplasmic reticulum stress. In addition, we also identified that Cys342 and Cys640 of Nrf1 (as redox-sensing sites within its N-glycodomain and DNA-binding domain, respectively) are required for its protein stability and transcription activity.

Among multiple distinct isoforms, Nrf1D is synthesized from a de novo translation of an alternatively-spliced transcript of Nrf1 mRNA, as accompanied by a naturally-occurring deletion of its stop codon-flanking 1466 nucleotides. This molecular event leads to the generation of a reading frameshift mutation, which results in a constitutive substitution of the intact Nrf1’s C-terminal 72 amino acids (aa, covering the second half of the leucine zipper motif to C-terminal Neh3L domain) by an additional extended 80-aa stretch to generate a unique variant Nrf1D. The C-terminal extra 80-aa region of Nrf1D was herein identified to be folded into a redox-sensitive transmembrane domain, enabling it to be tightly integrated within the endoplasmic reticulum (ER) membranes. Notably, the salient feature of Nrf1D enables it to be distinguishable from prototypic Nrf1, such that Nrf1D is endowed with a lesser ability than wild-type Nrf1 to mediate target gene expression. Further evidence has also been presented revealing that both mRNA and protein levels of Nrf1D, together with other isoforms similar to those of Nrf1, were detected to varying extents in hemopoietic and somatic tissues. Surprisingly, we found the existence of Nrf1D-derived isoforms in blood plasma, implying that it is a candidate secretory transcription factor, albeit its precursor acts as an integral transmembrane-bound CNC-bZIP protein that entails dynamic topologies across membranes, before being unleashed from the ER to enter the blood.

BackgroundThe dysfunction of neuregulin 1 (NRG1) is one of the plausible hypotheses for the pathogenesis of schizophrenia. The neuregulin 1 (NRG1) is located on chromosome 8p, as suggested by multiple linkage studies. The aim of this study is to clarify the contribution of polymorphisms of the neuregulin 1 (NRG1) with schizophreniaMethodsAfter informed consent was obtained, 100 schizophrenia patients and 100 control subjects were enrolled in this study. All subjects were administered the Diagnostic Interview for Genetic Studies (DIGS) (National Institute of Mental Health-Molecular Genetics Initiative, 1992; Nurnberger et al., 1994) by a research assistant with extensive training in this interview. Blood samples were collected in anonymously identified 10-ml Vacutainer tubes (Becton Dickinson). DNA was prepared by a modified SDS/Proteinase K procedure (Gusells et al., 1979). We genotyped polymorphism neuregulin 1 (NRG1) with the PCR-RFLP methods. The PCR products were digested by restricted enzyme.ResultsWe observed a significant association between the polymorphism neuregulin 1 (NRG1) and the schizophrenia (Chi-Square Test P= 0.0449).DiscussionThe NRG1gene was originally identified as a susceptibility gene for schizophrenia by using a combination of a linkage and association approaches based on microsatellite markers and then using SNPs after microsatellite at risk haplotypes were identified. We found there is the frequency of the polymorphism of neuregulin 1 (NRG1) was significantly increased in schizophrenia patients. This allelic association suggests that the functional polymorphism neuregulin 1 (NRG1) may play a role in susceptibility to schizophrenia. Further study with larger sample sizes is required.

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