Characterization of Nrf1b, a Novel Isoform of the Nuclear Factor-Erythroid-2 Related Transcription Factor-1 That Activates Antioxidant Response Element-Regulated Genes

Nuclear factor E2-related factor 1 (Nrf1) is a basic leucine zipper transcription factor that plays an important role in the activation of cytoprotective genes through the antioxidant response elements. The previously characterized long isoform of Nrf1 (Nrf1a) is targeted to the endoplasmic reticulum and accumulates in the nucleus in response to activating signals. Here we characterized a novel Nrf1 protein isoform (Nrf1b) generated through an alternative promoter and first exon that lacks the ER targeting domain of Nrf1a. The 5'-flanking region of Nrf1b directed high levels of luciferase reporter expression in cells. RT-PCR and Western blotting showed Nrf1b is widely expressed in various cell lines and mouse tissues. Immunoblot analysis of subcellular fractions and imaging of green fluorescence protein (GFP)-tagged Nrf1b demonstrate Nrf1b is constitutively localized to the nucleus. Nrf1b can activate GAL4-dependent transcription when fused to the heterologous GAL4 DNA-binding domain. Gel-shift and coimmunoprecipitation experiments demonstrate that Nrf1b forms a complex with MafG, and expression of Nrf1b activates the expression of antioxidant response element containing reporters and genes in cells. These results suggest Nrf1b is targeted to the nucleus where it activates ARE-driven genes and may play a role in modulating antioxidant response elements

Nrf1b expression is widely distributed.

<p>Nrf1a and Nrf1b mRNA expression patterns were analyzed by RT-PCR in various cell lines (<b>A</b>) and mouse tissues (<b>B</b>)<b>.</b> Nrf1a and Nrf1b cDNA was amplified by PCR for 30 cycles and 18S was amplified for 20 cycles. Histograms show relative Nrf1a and Nrf1b expression normalized against 18S. (<b>C</b>)<b>.</b> Western blot of different mouse tissues probed with Nrf1 antibody. HEK293 cells transfected with pEF1-Nrf1a (lane 1), and pEF1-Nrf1b (lane 2) were used as controls for detection of the Nrf1a and Nrf1b isoforms by the Nrf1 antibody. Beta-actin was used as a loading control.</p

Nrf1b activates ARE-driven genes.

<p>Luciferase reporter bearing 3 copies of ARE (<b>A</b>)<b>,</b> or GCLM-luciferase reporter (<b>B</b>) was co-transfected with either Nrf1a or Nrf1b expression plasmid. Luciferase activities were normalized to <i>Renilla</i> luciferase from pRL-TK. Results are expressed relative to luciferase activities observed with vector alone. Histograms show the means of three separate experiments ± SD carried out in triplicates. *P<0.05 (<b>C</b>) Induction of endogenous ARE target genes. NIH3T3 cells were transfected with the indicated plasmids, and mRNA was harvested and analyzed 2 days after transfection by qRT-PCR. Histograms show mean ± SD (n = 4).</p

Nrf1b is derived by alternative promoter usage.

<p>(<b>A</b>)<b>.</b> Nucleotide sequence and identification of putative cis-acting elements in the 5′-flanking region of Nrf1b exon 1. Numbering is relative to the first nucleotide of the initiation codon (ATG) designated as +1. Vertical arrow represents the transcription start site identified by primer extension analysis, and coding region is underlined. The cis-acting elements containing consensus sequences are boxed. (<b>B</b>)<b>.</b> Primer extension result with NIH3T3 mRNA. The peak corresponding to a 108-bp elongation product (FAM-labeled cDNA) is indicated by an arrow. Labeled cDNA was aligned with the sequence electropherogram to identify the base at which transcription starts for Nrf1b. Nucleotides are indicated on the x-axis. (<b>C</b>)<b>.</b> Relative luciferase activities of the mouse Nrf1b promoter construct in HEK293 and Hepa1c1c7 cells. Negative control consisted of the pGL3-Basic control. Luciferase activities were normalized to <i>Renilla</i> luciferase from pRL-TK. Histograms show mean ± SD of three independent experiments with triplicate samples per experiment. *P<0.05.</p

Nrf1b-MafG complex binds the ARE.

<p>(<b>A</b>) EMSA studies were performed with Nrf1b and MafG proteins generated by in vitro transcription and translation, and biotinylated DNA probe containing a consensus antioxidant response element described in Materials and Methods. Rabbit anti-Nrf1, anti-MafG, and IgG were used for super-shifts. Chevrons and arrows indicate shifted and super-shifted bands, respectively. (<b>B</b>) HEK293 cells transfected with Nrf1b-V5 were harvested 48 h after, and lysates were immunoprecipitated with anti-V5 antibody. Immunoprecipitates were then subjected to immunoblotting with anti-V5 or anti-MafG antibodies.</p

Nrf1b protein is localized in the nucleus.

<p>(<b>A</b>)<b>.</b> Epifluorescent micrographs showing COS7 cells transfected with Nrf1b-EGFP. (<b>B</b>) Quantitative analysis of the results in (B). The subcellular localization of EGFP and Nrf1b-EGFP was scored as follows: N>C, predominantly nuclear; N  =  C, evenly distributed between the nucleus and cytoplasm; NC)<b>.</b> Distribution of Nrf1b-V5 in cells. V5-tagged Nrf1b was harvested from HEK293 cells 48hr after transfection as described in the methods section, and analyzed by Western blot. The antibodies used for Western blotting are indicated on the right. Pyruvate kinase was used as a cytoplasmic marker, calnexin as an ER membrane marker, and lamina-associated polypeptide 2α (LAP2α) as a nuclear marker.</p

Risk Factors for Gastrointestinal Leak after Bariatric Surgery: MBASQIP Analysis.

BACKGROUND:Gastrointestinal leak remains one of the most dreaded complications in bariatric surgery. We aimed to evaluate risk factors and the impact of common perioperative interventions on the development of leak in patients who underwent laparoscopic bariatric surgery. STUDY DESIGN:Using the 2015 database of accredited centers, data were analyzed for patients who underwent laparoscopic sleeve gastrectomy or Roux-en-Y gastric bypass (LRYGB). Emergent, revisional, and converted cases were excluded. Multivariate logistic regression was used to analyze risk factors for leak, including provocative testing of anastomosis, surgical drain placement, and use of postoperative swallow study. RESULTS:Data from 133,478 patients who underwent laparoscopic sleeve gastrectomy (n&nbsp;= 92,495 [69.3%]) and LRYGB (n&nbsp;= 40,983 [30.7%]) were analyzed. Overall leak rate was 0.7% (938 of 133,478). Factors associated with increased risk for leak were oxygen dependency (adjusted odds ratio [AOR] 1.97), hypoalbuminemia (AOR 1.66), sleep apnea (AOR 1.52), hypertension (AOR 1.36), and diabetes (AOR 1.18). Compared with LRYGB, laparoscopic sleeve gastrectomy was associated with a lower risk of leak (AOR 0.52; 95% CI 0.44 to 0.61; p &lt; 0.01). Intraoperative provocative test was performed in 81.9% of cases and the leak rate was higher in patients with vs without a provocative test (0.8% vs 0.4%, respectively; p &lt; 0.01). A surgical drain was placed in 24.5% of cases and the leak rate was higher in patients with vs without a surgical drain placed (1.6% vs 0.4%, respectively; p &lt; 0.01). A swallow study was performed in 41% of cases and the leak rate was similar between patients with vs without swallow study (0.7% vs 0.7%; p&nbsp;= 0.50). CONCLUSIONS:The overall rate of gastrointestinal leak in bariatric surgery is low. Certain preoperative factors, procedural type (LRYGB), and interventions (intraoperative provocative test and surgical drain placement) were associated with a higher risk for leaks

Characterization of Nrf1b, a Novel Isoform of the Nuclear Factor-Erythroid-2 Related Transcription Factor-1 That Activates Antioxidant Response Element-Regulated Genes

Nuclear factor E2-related factor 1 (Nrf1) is a basic leucine zipper transcription factor that plays an important role in the activation of cytoprotective genes through the antioxidant response elements. The previously characterized long isoform of Nrf1 (Nrf1a) is targeted to the endoplasmic reticulum and accumulates in the nucleus in response to activating signals. Here we characterized a novel Nrf1 protein isoform (Nrf1b) generated through an alternative promoter and first exon that lacks the ER targeting domain of Nrf1a. The 5′-flanking region of Nrf1b directed high levels of luciferase reporter expression in cells. RT-PCR and Western blotting showed Nrf1b is widely expressed in various cell lines and mouse tissues. Immunoblot analysis of subcellular fractions and imaging of green fluorescence protein (GFP)-tagged Nrf1b demonstrate Nrf1b is constitutively localized to the nucleus. Nrf1b can activate GAL4-dependent transcription when fused to the heterologous GAL4 DNA-binding domain. Gel-shift and coimmunoprecipitation experiments demonstrate that Nrf1b forms a complex with MafG, and expression of Nrf1b activates the expression of antioxidant response element containing reporters and genes in cells. These results suggest Nrf1b is targeted to the nucleus where it activates ARE-driven genes and may play a role in modulating antioxidant response elements