Insights from the crystal structure of the chicken CREB3 bZIP suggest that members of the CREB3 subfamily transcription factors may be activated in response to oxidative stress

CREB3L4 promotes hepatocellular carcinoma progression and decreases sorafenib chemosensitivity by promoting RHEB-mTORC1 signaling pathway

This study was designed to explore the roles of CREB3L4 in the pathogenesis and drug resistance of hepatocellular carcinoma (HCC). The proliferation of HCC lines was determined in the presence of CREB3L4 over-expression and silencing. Chromatin immunoprecipitation (ChIP) assay and dual-luciferase reporter assay were performed to screen the potential target of CREB3L4 on mTORC1. Xenografted tumor model was established to define the regulatory effects of CREB3L4 in the tumorigenesis. Then we evaluated the roles of CREB3L4 in chemosensitivity to sorafenib treatment. CREB3L4 significantly induced the HCC cell proliferation by modulating the activation of mTROC1-S6K1 signaling pathway via binding with RHEB promoter. Moreover, CREB3L4 dramatically inhibited the chemosensitivity to sorafenib treatment via up-regulating RHEB-mTORC1 signaling. CREB3L4 promoted HCC progression and decreased its chemosensitivity to sorafenib through up-regulating RHEB-mTORC1 signaling pathway, indicating a potential treatment strategy for HCC through targeting CREB3L4.

bZIP transcription factor FabR: Redox-dependent mechanism controlling docosahexaenoic acid biosynthesis and H2O2 stress response in Schizochytrium sp

Schizochytrium sp. is an important industrial strain for commercial production of docosahexaenoic acid (DHA), which plays essential physiological roles in infant development and human health. The regulatory network for DHA biosynthesis and lipid accumulation in Schizochytrium remains poorly understood. FabR (fatty acid biosynthesis repressor), a basic leucine zipper (bZIP) transcription factor, was transcriptionally downregulated under low-nitrogen condition. Deletion of fabR gene (mutant ΔfabR) increased production of total lipids and DHA by 30.1% and 46.5%, respectively. ΔfabR displayed H2O2 stress resistance higher than that of parental strain or complementation strain CfabR. FabR bound specifically to 7-bp pseudo-palindromic sequence 5'-ATTSAAT-3' in upstream regions and repressed transcription of fatty acid biosynthesis genes (acl, fas, pfa) and antioxidant defense genes (cat, sod1, sod2, gpx). DNA binding activity of FabR was regulated in a redox-dependent manner. Under oxidative condition, FabR forms intermolecular disulfide bonds between two Cys46 residues of dimers; its DNA binding activity is thereby lost, and the transcription of its target genes is enhanced through derepression. Our findings clarify the redox-dependent mechanism that modulates FabR activity governing lipid and DHA biosynthesis and H2O2 stress response in Schizochytrium.

ER stress-associated transcription factor CREB3 is essential for normal Ca2+, ATP, and ROS homeostasis

In mammalian cells, mitochondrial respiration produces reactive oxygen species (ROS) such as superoxide (O₂^-), which is then converted by the SOD1 enzyme into hydrogen peroxide (H₂O₂), the predominant form of cytosolic ROS. ROS at high levels can be toxic, but below this threshold are important for physiological processes acting as a second messenger similar to Ca²⁺. Mitochondrial Ca²⁺ influx from the ER increases ATP and ROS production, while ATP and ROS can regulate Ca²⁺ homeostasis, leading to an intricate interplay between Ca²⁺, ROS, and ATP synthesis. The Unfolded Protein Response (UPR) proteins ATF6α and XBP1 contribute to protection from oxidative stress through upregulation of Sod1 and Catalase genes. Here, UPR-associated protein CREB3 is shown to play a role in balancing Ca²⁺, ROS, and ATP homeostasis. Creb3-deficient mouse embryonic fibroblast cells (MEF^-/-) were susceptible to H₂O₂-induced oxidative stress while having a functioning antioxidant gene expression response compared to MEF^+/+. MEF^-/- cells also contained elevated basal cytosolic ROS levels, which was attributed to drastically increased basal mitochondrial respiration and spare respiratory capacity relative to MEF^+/+. MEF^-/- cells also showed an increase in endoplasmic reticulum Ca²⁺ release and mitochondrial Ca²⁺ levels hinting at a potential cause for MEF^-/- cell mitochondrial dysfunction. These results suggest that CREB3 is essential for maintaining proper Ca²⁺, ATP, and ROS homeostasis in mammalian cells.

Genome-Wide Identification and Expression Analysis of the Basic Leucine Zipper (bZIP) Transcription Factor Gene Family in Fusarium graminearum

The basic leucine zipper (bZIP) is a widely found transcription factor family that plays regulatory roles in a variety of cellular processes including cell growth and development and various stress responses. However, the bZIP gene family has not been well studied at a genome-wide scale in Fusarium graminearum (Fg), a potent pathogen of cereal grains. In the present study, we conducted a genome-wide identification, characterization, and expression profiling of 22 F. graminearum bZIP (FgbZIP) genes at different developmental stages and under various abiotic stresses. All identified FgbZIPs were categorized into nine groups based on their sequence similarity and phylogenetic tree analysis. Furthermore, the gene structure analysis, conserved motif analysis, chromosomal localization, protein network studies, and synteny analysis were performed. The symmetry of the exon and intron varied with the phylogenetic groups. The post-translational modifications (PTMs) analysis also predicted several phosphorylation sites in FgbZIPs, indicating their functional diversity in cellular processes. The evolutionary study identified many orthogroups among eight species and also predicted several gene duplication events in F. graminearum. The protein modeling indicated the presence of a higher number of α-helices and random coils in their structures. The expression patterns of FgbZIP genes showed that 5 FgbZIP genes, including FgbZIP_1.1, FgbZIP_1.3, FgbZIP_2.6 FgbZIP_3.1 and FgbZIP_4.3, had high expression at different growth and conidiogenesis stages. Similarly, eight genes including FgbZIP_1.1, FgbZIP_1.6, FgbZIP_2.3, FgbZIP_2.4, FgbZIP_4.1, FgbZIP_4.2, FgbZIP_4.3 and FgbZIP_4.6 demonstrated their putative role in response to various abiotic stresses. In summary, these results provided basic information regarding FgbZIPs which are helpful for further functional analysis.