Endoplasmic Reticulum–Localized Transcription Factors and Mitochondrial Retrograde Regulation

AbstractTranscription factors (TFs) are known to be involved in regulating the expression of several classes of genes during folliculogenesis. However, the regulatory role of TFs during oxidative stress (OS) is not fully understood. The current study was aimed to investigate the regulation of the TFs in bovine granulosa cells (bGCs) during exposure to OS induced by H2O2 in vitro. For this, bGCs derived from ovarian follicles were cultured in vitro till their confluency and then treated with H2O2 for 40 min. Twenty-four hours later, cells were subjected to various phenotypic and gene expression analyses for genes related to TFs, endoplasmic reticulum stress, apoptosis, cell proliferation, and differentiation markers. The bGCs exhibited higher reactive oxygen species accumulation, DNA fragmentation, and endoplasmic reticulum stress accompanied by reduction of mitochondrial activity after exposure to OS. In addition, higher lipid accumulation and lower cell proliferation were noticed in H2O2-challenged cells. The mRNA level of TFs including NRF2, E2F1, KLF6, KLF9, FOS, SREBF1, SREBF2, and NOTCH1 was increased in H2O2-treated cells compared with non-treated controls. However, the expression level of KLF4 and its downstream gene, CCNB1, were downregulated in the H2O2-challenged group. Moreover, targeted inhibition of NRF2 using small interference RNA resulted in reduced expression of KLF9, FOS, SREBF2, and NOTCH1 genes, while the expression of KLF4 was upregulated. Taken together, bovine granulosa cells exposed to OS exhibited differential expression of various transcription factors, which are mediated by the NRF2 signaling pathway.

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Unification of Opposites between Two Antioxidant Transcription Factors Nrf1 and Nrf2 in Mediating Distinct Cellular Responses to the Endoplasmic Reticulum Stressor Tunicamycin

Antioxidants ◽

10.3390/antiox9010004 ◽

2019 ◽

Vol 9 (1) ◽

pp. 4 ◽

Cited By ~ 11

Author(s):

Yu-ping Zhu ◽

Ze Zheng ◽

Shaofan Hu ◽

Xufang Ru ◽

Zhuo Fan ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Transcription Factor ◽

Transcription Factors ◽

Er Stress ◽

Target Genes ◽

Cellular Responses ◽

Water Soluble ◽

Heme Oxygenase 1 ◽

Nuclear Factor ◽

Activating Transcription Factor

The water-soluble Nrf2 (nuclear factor, erythroid 2-like 2, also called Nfe2l2) is accepted as a master regulator of antioxidant responses to cellular stress, and it was also identified as a direct target of the endoplasmic reticulum (ER)-anchored PERK (protein kinase RNA-like endoplasmic reticulum kinase). However, the membrane-bound Nrf1 (nuclear factor, erythroid 2-like 1, also called Nfe2l1) response to ER stress remains elusive. Herein, we report a unity of opposites between these two antioxidant transcription factors, Nrf1 and Nrf2, in coordinating distinct cellular responses to the ER stressor tunicamycin (TU). The TU-inducible transcription of Nrf1 and Nrf2, as well as GCLM (glutamate cysteine ligase modifier subunit) and HO-1 (heme oxygenase 1), was accompanied by activation of ER stress signaling networks. Notably, the unfolded protein response (UPR) mediated by ATF6 (activating transcription factor 6), IRE1 (inositol requiring enzyme 1) and PERK was significantly suppressed by Nrf1α-specific knockout, but hyper-expression of Nrf2 and its target genes GCLM and HO-1 has retained in Nrf1α−/− cells. By contrast, Nrf2−/−ΔTA cells with genomic deletion of its transactivation (TA) domain resulted in significant decreases of GCLM, HO-1 and Nrf1; this was accompanied by partial decreases of IRE1 and ATF6, rather than PERK, but with an increase of ATF4 (activating transcription factor 4). Interestingly, Nrf1 glycosylation and its trans-activity to mediate the transcriptional expression of the 26S proteasomal subunits, were repressed by TU. This inhibitory effect was enhanced by Nrf1α−/− and Nrf2−/−ΔTA, but not by a constitutive activator caNrf2ΔN (that increased abundances of the non-glycosylated and processed Nrf1). Furthermore, caNrf2ΔN also enhanced induction of PERK and IRE1 by TU, but reduced expression of ATF4 and HO-1. Thus, it is inferred that such distinct roles of Nrf1 and Nrf2 are unified to maintain cell homeostasis by a series of coordinated ER-to-nuclear signaling responses to TU. Nrf1α (i.e., a full-length form) acts in a cell-autonomous manner to determine the transcription of most of UPR-target genes, albeit Nrf2 is also partially involved in this process. Consistently, transactivation of ARE (antioxidant response element)-driven BIP (binding immunoglobulin protein)-, PERK- and XBP1 (X-box binding protein 1)-Luc reporter genes was mediated directly by Nrf1 and/or Nrf2. Interestingly, Nrf1α is more potent than Nrf2 at mediating the cytoprotective responses against the cytotoxicity of TU alone or plus tBHQ (tert-butylhydroquinone). This is also further supported by the evidence that the intracellular reactive oxygen species (ROS) levels are increased in Nrf1α−/− cells, but rather are, to our surprise, decreased in Nrf2−/−ΔTA cells.

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Altered activity patterns of transcription factors induced by endoplasmic reticulum stress

BMC Biochemistry ◽

10.1186/s12858-016-0060-2 ◽

2016 ◽

Vol 17 (1) ◽

Cited By ~ 11

Author(s):

Sheena Jiang ◽

Eric Zhang ◽

Rachel Zhang ◽

Xianqiang Li

Keyword(s):

Endoplasmic Reticulum ◽

Transcription Factors ◽

Endoplasmic Reticulum Stress ◽

Activity Patterns

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Activation of the Endoplasmic Reticulum (ER) Unfolded Protein Response (UPR) in Aggressive B-Cell Lymphomas.

Blood ◽

10.1182/blood.v108.11.2038.2038 ◽

2006 ◽

Vol 108 (11) ◽

pp. 2038-2038

Author(s):

Olga Balague ◽

Luis Colomo ◽

Armando Lopez-Guillermo ◽

Elias Campo ◽

Antonio Martinez

Keyword(s):

Endoplasmic Reticulum ◽

Transcription Factors ◽

Western Blot ◽

Er Stress ◽

B Cell ◽

Cell Lines ◽

Plasma Cell ◽

Plasma Cells ◽

Lymphoid Tissues ◽

B Cell Lymphomas

Abstract BACKGROUND The UPR is a prosurvival pathway activated in cells under ER stress induced by the accumulation of unfolded proteins. UPR activation in B cells normally occurs during the differentiation to antibody secreting plasma cells and requires XBP1activation. XBP-1 is a member of the TREB family of transcription factors that exists in the endoplasmic reticulum (ER) as a 33kDa protein, and in the nucleus as an active 50kDa transcription factor. The UPR stimulates two different ER proteins, ATF-6 and Ire-1, to increase XBP-1 transcription and XBP-1 mRNA splicing resulting in the accumulation of the active 50kDa nuclear protein. Moreover XBP1 is a target of proteosome inhibitors and is related to the aggressive behaviour of some carcinomas. The role of the activation of XBP-1 in lymphomas is still unknown. DESIGN: Reactive lymphoid tissues and 25 neoplastic human B-cell lines representing different stages of B-cell development were studied for XBP-1 expression by western blot and XBP-1, PAX-5, Blimp-1/prdm1, MUM-1/IRF-4 and ICSBP1/IRF-8 by immunohistochemistry. XBP-1 activation was assessed in 225 B-cell lymphomas from the archives of the laboratory of pathology by western blot, RT-PCR and immunohistochemistry . To further evaluate whether XBP-1 activation was related to the plasmacytic program or to ER stress signals we analyzed the cell lines by Western blot for XBP-1 and ATF-6 expression. RESULTS We characterize XBP-1 expression in reactive lymphoid tissues, 25 human cell lines and 225 B-cell tumors. In nearly all tonsillar lymphoid cells XBP-1 was detected as a cytoplasmic protein with a paranuclear dot pattern. Nuclear positivity was observed only in scattered centrocytes in the light zone of the germinal centers and in plasma cells, always coexpressed with plasma cell related transcription factors as MUM-1/IRF-4 and Blimp1/prdm1. Active p50XBP-1 was found in 24/25 cell lines by western blot regardless ATF-6 expression and confirmed by immunohistochemistry . Moreover p50XBP1 was found in 27/31(87%) plasmacytomas, 36/64(56%) DLBCL-ABC and in 3/10(30%) DLBCL-GCB and 22/43(51%) plasmablastic lymphomas. Intriguingly, p50XBP1 was detected also in 2/11(18%)BL and 4/25(16%)MCL with blastic features. CONCLUSIONS.XBP-1 is activated in a subset of follicular centre cells committed to plasma cell differentiation and in plasma cells.UPR prosurvival pathways in the neoplastic cell lines are activated independently of the extent of the ATF-6 activation.p50XBP1 is mostly activated in aggressive B-cell lymphomas regardless to the plasmacytic differentiation of the tumours. Thus, p50XBP-1 may be a new molecular target in the treatment of aggressive B-cell malignancies.

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Liver gene expression analysis reveals endoplasmic reticulum stress and metabolic dysfunction in SCD1-deficient mice fed a very low-fat diet

Physiological Genomics ◽

10.1152/physiolgenomics.00139.2007 ◽

2008 ◽

Vol 33 (3) ◽

pp. 361-372 ◽

Cited By ~ 57

Author(s):

Matthew T. Flowers ◽

Mark P. Keller ◽

YounJeong Choi ◽

Hong Lan ◽

Christina Kendziorski ◽

...

Keyword(s):

Gene Expression ◽

Endoplasmic Reticulum ◽

Transcription Factors ◽

Fatty Acid ◽

Er Stress ◽

Acid Synthesis ◽

Nutrient Sensing ◽

Metabolic Dysfunction ◽

Low Fat ◽

Unsaturated Fat

We previously reported that mice deficient in stearoyl-CoA desaturase-1 ( Scd1) and maintained on a very low-fat (VLF) diet for 10 days developed severe loss of body weight, hypoglycemia, hypercholesterolemia, and many cholestasis-like phenotypes. To better understand the metabolic changes associated with these phenotypes, we performed microarray analysis of hepatic gene expression in chow- and VLF-fed female Scd1+/+ and Scd1−/− mice. We identified an extraordinary number of differentially expressed genes (>4,000 probe sets) in the VLF Scd1−/− relative to both VLF Scd1+/+ and chow Scd1−/− mice. Transcript levels were reduced for genes involved in detoxification and several facets of fatty acid metabolism including biosynthesis, elongation, desaturation, oxidation, transport, and ketogenesis. This pattern is attributable to the decreased mRNA abundance of several genes encoding key transcription factors, including LXRα, RXRα, FXR, PPARα, PGC-1β, SREBP1c, ChREBP, CAR, DBP, TEF, and HLF. A robust induction of endoplasmic reticulum (ER) stress is indicated by enhanced splicing of XBP1, increased expression of the stress-induced transcription factors CHOP and ATF3, and elevated expression of several genes involved in the integrated stress and unfolded protein response pathways. The gene expression profile is also consistent with induction of an acute inflammatory response and macrophage recruitment. These results highlight the importance of monounsaturated fatty acid synthesis for maintaining metabolic homeostasis in the absence of sufficient dietary unsaturated fat and point to a novel cellular nutrient-sensing mechanism linking fatty acid availability and/or composition to the ER stress response.

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Calcium-dependent Nr4a1 expression in mouse Leydig cells requires distinct AP1/CRE and MEF2 elements

Journal of Molecular Endocrinology ◽

10.1530/jme-15-0202 ◽

2016 ◽

Vol 56 (3) ◽

pp. 151-161 ◽

Cited By ~ 9

Author(s):

Houssein S Abdou ◽

Nicholas M Robert ◽

Jacques J Tremblay

Keyword(s):

Gene Expression ◽

Endoplasmic Reticulum ◽

Transcription Factors ◽

Signaling Pathway ◽

Binding Sites ◽

Leydig Cells ◽

Sex Differentiation ◽

Calcium Dependent ◽

Male Sex ◽

Camp Levels

The nuclear receptor NR4A1 is expressed in steroidogenic Leydig cells where it plays pivotal roles by regulating the expression of several genes involved in steroidogenesis and male sex differentiation including Star, HSD3B2, and Insl3. Activation of the cAMP and Ca2+ signaling pathways in response to LH stimulation leads to a rapid and robust activation of Nr4a1 gene expression that requires the Ca2+/CAMKI pathway. However, the downstream transcription factor(s) have yet to be characterized. To identify potential Ca2+/CaM effectors responsible for hormone-induced Nr4a1 expression, MA-10 Leydig cells were treated with forskolin to increase endogenous cAMP levels, dantrolene to inhibit endoplasmic reticulum Ca2+ release, and W7 to inhibit CaM activity. We identified Ca2+-responsive elements located in the discrete regions of the Nr4a1 promoter, which contain binding sites for several transcription factors such as AP1, CREB, and MEF2. We found that one of the three AP1/CRE sites located at –255 bp is the most responsive to the Ca2+ signaling pathway as are the two MEF2 binding sites at –315 and –285 bp. Furthermore, we found that the hormone-induced recruitment of phospho-CREB and of the co-activator p300 to the Nr4a1 promoter requires the Ca2+ pathway. Lastly, siRNA-mediated knockdown of CREB impaired NR4A1 expression and steroidogenesis. Together, our data indicate that the Ca2+ signaling pathway increases Nr4a1 expression in MA-10 Leydig cells, at least in part, by enhancing the recruitment of coactivator most likely through the MEF2, AP1, and CREB transcription factors thus demonstrating an important interplay between the Ca2+ and cAMP pathways in regulating Nr4a1 expression.

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