Stress-induced Transcription Factor Research Articles

ATF4/NUPR1 axis promotes cancer cell survival and mediates immunosuppression in clear cell renal cell carcinoma

Cancer cells encounter unavoidable stress during tumor growth. The stress-induced transcription factor, activating transcription factor 4 (ATF4), has been reported to upregulate various adaptive genes involved in salvage pathways to alleviate stress and promote tumor progression. However, this effect is unknown in clear cell renal cell carcinoma (ccRCC). In this study, we found that ATF4 expression was remarkably upregulated in tumor tissues and associated with poor ccRCC outcomes. ATF4 depletion significantly impaired ccRCC cell proliferation, migration, and invasion in vitro and in vivo by inhibiting the AKT/mTOR and epithelial–mesenchymal transition (EMT)-related signaling pathway. RNA sequencing and functional studies identified nuclear protein 1 (NUPR1) as a key downstream target of ATF4 for repressing ferroptosis and promoting ccRCC cell survival. In addition, targeting ATF4 or pharmacological inhibition using NUPR1 inhibitor ZZW115 promoted antitumor immunity in syngeneic graft mouse models, represented by increased infiltration of CD4+ and CD8+ T cells. Furthermore, ZZW115 could improve the response to the PD-1 immune checkpoint blockade. The results demonstrate that the ATF4/NUPR1 signaling axis promotes ccRCC survival and facilitates tumor-mediated immunosuppression, providing a set of potential targets and prognostic indicators for ccRCC patients.Graphical abstract

Activation of ATF3 via the integrated stress response pathway regulates innate immune response to restrict Zika virus.

Zika virus (ZIKV) is a re-emerging mosquito-borne flavivirus that co-opts cellular mechanisms to support viral processes that can reprogram the host transcriptional profile. Such viral-directed transcriptional changes and the pro- or anti-viral outcomes remain understudied. We previously showed that ATF3, a stress-induced transcription factor, is significantly upregulated in ZIKV-infected mammalian cells, along with other cellular and immune response genes. We now define the intracellular pathway responsible for ATF3 activation and elucidate the impact of ATF3 expression on ZIKV infection. We show that during ZIKV infection, the integrated stress response pathway stimulates ATF3 which enhances the innate immune response to antagonize ZIKV infection. This study establishes a link between viral-induced stress response and transcriptional regulation of host defense pathways and thus expands our knowledge of virus-mediated transcriptional mechanisms and transcriptional control of interferon-stimulated genes during ZIKV infection.

Abstract B084: Comparative functional analysis of TP53 alleles in pancreatic ductal adenocarcinoma in vivo

Abstract TP53 is the second most mutated gene in pancreatic ductal adenocarcinoma (PDAC), bearing both truncal loss-of-function and missense point mutations. TP53 encodes a stress-induced transcription factor (p53) capable of activating tumor suppressive pathways mediating cell cycle arrest, apoptosis, senescence, and metabolic reprogramming. Despite high mutational frequency, how TP53 mutants function to suppress pancreatic tumorigenesis in vivo remains unclear. Previous studies indicate that the most frequent point mutations observed in human PDAC (TP53 R175H and R273H; mouse homologues Trp53 R172H and R270H) exhibit both dominant-negative (e.g., response to radiation in leukemia cells) and gain-of-function (e.g., increased liver metastasis in advanced PDAC models) roles compared to p53 null cells in various contexts. To rigorously explore the differential functions of p53 point and deletion mutants in PDAC progression, we performed an isogenic comparative analysis of Trp53 alleles in vivo using Mosaic Analysis with Double Markers (MADM) in mice. MADM uses stochastic mitotic recombination to induce two genotypically distinct daughter cells – created at 1-to-1 ratios – expressing different Trp53 variants dependent on the genotype of the mouse (+/+ vs. -/-, R172H/R172H vs. +/+, R172H/R172H vs. -/-, R270H/R270H vs. +/+, R270H/R270H vs. -/-) and simultaneously label them with unique genetically encoded fluorescent markers (TdTomato vs. GFP). We integrated MADM into a faithful Kras-driven model of pancreatic tumorigenesis (KC: Kras LSL-G12D/+ ; Pdx1-Cre) and used fluorescence microscopy to trace subclonal populations with various Trp53 alleles within the same mouse. By analyzing the ratio of TdTomato+ to GFP+ cells, we studied the functional differences between alleles in driving tumor initiation and expansion at various stages of progression. Strikingly, we found that Trp53 -/- cells exhibited greater expansion in preinvasive pancreatic intraepithelial neoplasias (PanINs) compared to not only Trp53 +/+ cells but also cells harboring either point mutation (Trp53 R172H/R172H or Trp53 R270H/R270H ). While Trp53 R270H/R270H cells predominated over Trp53 +/+ in PanINs, Trp53 R172H/R172H cells were surprisingly indistinguishable from Trp53 +/+ cells, suggesting that p53R172H retains tumor suppressive properties in early PDAC progression. Conversely, both Trp53 R172H/R172H and Trp53 R270H/R270H cells progressed to advanced PDAC with comparable PDAC incidence and survival as Trp53 -/- , arguing that Trp53 R172H is a separation-of-function mutant concordant with a distinct transcriptional profile relative to Trp53 -/- tumor cells. Together, these studies offer the strongest evidence to date for stage-specific functional differences between TP53 mutant variants in cancer progression in vivo and provide a faithful MADM-based PDAC model to define molecular mechanisms (through ongoing transcriptomic, epigenomic, and metabolomic studies) that govern functional differences amongst these diverse alleles. Citation Format: Sherry S. Agabiti, Andy Tang, Timothy Nottoli, Mandar D. Muzumdar. Comparative functional analysis of TP53 alleles in pancreatic ductal adenocarcinoma in vivo [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B084.

Krüppel-like factor 2 is an endoprotective transcription factor in diabetic kidney disease.

Diabetic kidney disease (DKD) is a microvascular complication of diabetes, and glomerular endothelial cell (GEC) dysfunction is a key driver of DKD pathogenesis. Krüppel-like factor 2 (KLF2), a shear stress-induced transcription factor, is among the highly regulated genes in early DKD. In the kidney, KLF2 expression is mostly restricted to endothelial cells, but its expression is also found in immune cell subsets. KLF2 expression is upregulated in response to increased shear stress by the activation of mechanosensory receptors but suppressed by inflammatory cytokines, both of which characterize the early diabetic kidney milieu. KLF2 expression is reduced in progressive DKD and hypertensive nephropathy in humans and mice, likely due to high glucose and inflammatory cytokines such as TNF-α. However, KLF2 expression is increased in glomerular hyperfiltration-induced shear stress without metabolic dysregulation, such as in settings of unilateral nephrectomy. Lower KLF2 expression is associated with CKD progression in patients with unilateral nephrectomy, consistent with its endoprotective role. KLF2 confers endoprotection by inhibition of inflammation, thrombotic activation, and angiogenesis, and thus KLF2 is considered a protective factor for cardiovascular disease (CVD). Based on similar mechanisms, KLF2 also exhibits renoprotection, and its reduced expression in endothelial cells worsens glomerular injury and albuminuria in settings of diabetes or unilateral nephrectomy. Thus KLF2 confers endoprotective effects in both CVD and DKD, and its activators could potentially be developed as a novel class of drugs for cardiorenal protection in diabetic patients.

Activation of ATF3 via the Integrated Stress Response Pathway Regulates Innate Immune Response to Restrict Zika Virus.

Zika virus (ZIKV) is a re-emerging mosquito-borne flavivirus that can have devastating health consequences. The developmental and neurological effects from a ZIKV infection arise in part from the virus triggering cellular stress pathways and perturbing transcriptional programs. To date, the underlying mechanisms of transcriptional control directing viral restriction and virus-host interaction are understudied. Activating Transcription Factor 3 (ATF3) is a stress-induced transcriptional effector that modulates the expression of genes involved in a myriad of cellular processes, including inflammation and antiviral responses, to restore cellular homeostasis. While ATF3 is known to be upregulated during ZIKV infection, the mode by which ATF3 is activated and the specific role of ATF3 during ZIKV infection is unknown. In this study, we show via inhibitor and RNA interference approaches that ZIKV infection initiates the integrated stress response pathway to activate ATF4 which in turn induces ATF3 expression. Additionally, by using CRISPR-Cas9 system to delete ATF3, we found that ATF3 acts to limit ZIKV gene expression in A549 cells. We also determined that ATF3 enhances the expression of antiviral genes such as STAT1 and other components in the innate immunity pathway to induce an ATF3-dependent anti-ZIKV response. Our study reveals crosstalk between the integrated stress response and innate immune response pathways and highlights an important role for ATF3 in establishing an antiviral effect during ZIKV infection.

Erratum to: Prediction and analysis of stress-inducible ICE transcription factors in Deschampsia antarctica

Erratum to: Prediction and analysis of stress-inducible ICE transcription factors in Deschampsia antarctica

Upregulation of ATF4 mediates the cellular adaptation to pharmacologic inhibition of amino acid transporter LAT1 in pancreatic ductal adenocarcinoma cells

L-type amino acid transporter 1 (LAT1) is recognized as a promising target for cancer therapy; however, the cellular adaptive response to its pharmacological inhibition remains largely unexplored. This study examined the adaptive response to LAT1 inhibition using nanvuranlat, a high-affinity LAT1 inhibitor. Proteomic analysis revealed the activation of a stress-induced transcription factor ATF4 following LAT1 inhibition, aligning with the known cellular responses to amino acid deprivation. This activation was linked to the GCN2-eIF2α pathway which regulates translation initiation. Our results show that ATF4 upregulation counteracts the suppressive effect of nanvuranlat on cell proliferation in pancreatic ductal adenocarcinoma cell lines, suggesting a role for ATF4 in cellular adaptation to LAT1 inhibition. Importantly, dual targeting of LAT1 and ATF4 exhibited more substantial anti-proliferative effects in vitro than individual treatments. This study underscores the potential of combining LAT1 and ATF4 inhibition as a therapeutic strategy in cancer treatment.

XBP1-mediated transcriptional regulation of SLC5A1 in human epithelial cells in disease conditions

BackgroundSodium-Glucose cotransporter 1 and 2 (SGLT1/2) belong to the family of glucose transporters, encoded by SLC5A1 and SLC5A2, respectively. SGLT2 is almost exclusively expressed in the renal proximal convoluted tubule cells. SGLT1 is expressed in the kidneys but also in other organs throughout the body. Many SGLT inhibitor drugs have been developed based on the mechanism of blocking glucose (re)absorption mediated by SGLT1/2, and several have gained major regulatory agencies’ approval for treating diabetes. Intriguingly these drugs are also effective in treating diseases beyond diabetes, for example heart failure and chronic kidney disease. We recently discovered that SGLT1 is upregulated in the airway epithelial cells derived from patients of cystic fibrosis (CF), a devastating genetic disease affecting greater than 70,000 worldwide.ResultsIn the present work, we show that the SGLT1 upregulation is coupled with elevated endoplasmic reticulum (ER) stress response, indicated by activation of the primary ER stress senor inositol-requiring protein 1α (IRE1α) and the ER stress-induced transcription factor X-box binding protein 1 (XBP1), in CF epithelial cells, and in epithelial cells of other stress conditions. Through biochemistry experiments, we demonstrated that the spliced form of XBP1 (XBP1s) acts as a transcription factor for SLC5A1 by directly binding to its promoter region. Targeting this ER stress → SLC5A1 axis by either the ER stress inhibitor Rapamycin or the SGLT1 inhibitor Sotagliflozin was effective in attenuating the ER stress response and reducing the SGLT1 level in these cellular model systems.ConclusionsThe present work establishes a causal relationship between ER stress and SGLT1 upregulation and provides a mechanistic explanation why SGLT inhibitor drugs benefit diseases beyond diabetes.

ATF4 in cellular stress, ferroptosis, and cancer.

Activating transcription factor 4 (ATF4), a member of the ATF/cAMP response element-binding (CREB) family, plays a critical role as a stress-induced transcription factor. It orchestrates cellular responses, particularly in the management of endoplasmic reticulum stress, amino acid deprivation, and oxidative challenges. ATF4's primary function lies in regulating gene expression to ensure cell survival during stressful conditions. However, when considering its involvement in ferroptosis, characterized by severe lipid peroxidation and pronounced endoplasmic reticulum stress, the ATF4 pathway can either inhibit or promote ferroptosis. This intricate relationship underscores the complexity of cellular responses to varying stress levels. Understanding the connections between ATF4, ferroptosis, and endoplasmic reticulum stress holds promise for innovative cancer therapies, especially in addressing apoptosis-resistant cells. In this review, we provide an overview of ATF4, including its structure, modifications, and functions, and delve into its dual role in both ferroptosis and cancer.

Early Atf4 activity drives airway club and goblet cell differentiation.

Activating transcription factor 4 (Atf4), which is modulated by the protein kinase RNA-like ER kinase (PERK), is a stress-induced transcription factor responsible for controlling the expression of a wide range of adaptive genes, enabling cells to withstand stressful conditions. However, the impact of the Atf4 signaling pathway on airway regeneration remains poorly understood. In this study, we used mouse airway epithelial cell culture models to investigate the role of PERK/Atf4 in respiratory tract differentiation. Through pharmacological inhibition and silencing of ATF4, we uncovered the crucial involvement of PERK/Atf4 in the differentiation of basal stem cells, leading to a reduction in the number of secretory cells. ChIP-seq analysis revealed direct binding of ATF4 to regulatory elements of genes associated with osteoblast differentiation and secretory cell function. Our findings provide valuable insights into the role of ATF4 in airway epithelial differentiation and its potential involvement in innate immune responses and cellular adaptation to stress.

Molecular cloning, expression and Insilco analysis of drought stress inducible MYB transcription factor encoding gene from C4 plant Eleusine coracana

Drought is one of the key abiotic stresses that critically influences the crops by restraining their growth and yield potential. Being sessile, plant tackle the detrimental effects of drought stress by modulating the cellular state by changing the gene expression. The transcriptional syndicate essentially drives such alteration of gene expression. Transcription factors (TF) are the key regulatory protein that controls the expression of their target gene by binding to the cis-regulatory elements present in the promoter region. Myb-TF, ubiquitously present in all eukaryotes belong to one of the largest TF family, and play a wide array of biological functions in plants, including anthocyanin biosynthesis, vasculature system, cell signalling, seed maturation and abiotc stress responses. The present performed isolation and molecular cloning of full length Myb TF from Eleusine corocana. The isolated full-length coding sequence has 1053 bp and 350 aa was submitted to NCBI (Accession number MT312253). The transcript level of EcMYB increases under different abiotic stress treatments including dehydration, salinity, and high-temperature stress. The promoter region of EcMyb1 was found to be enriched in stress-responsive cis-regulatory elements such as DRE, HSE, ABRE etc. In phylogenetic analysis, EcMyb1 appeared to have high homology with its monocot orthologs particularly Sateria italica, Hordeum vulgare, Saccharum barberi and Oryza sativa. The three-dimension protein structure was generated based on homology modeling and structural aspects were discussed. Further, Insilco analysis was conducted to explore the physiological properties, subcellular localization, potential posttranslational modification sites (phosphorylation and glycosylation sites), and molecular and biological function of the full-length protein. Overall, the expression profiling and Insilco analysis of EcMyb1 strongly indicated its potential role in abiotic stress response in Eleusine corocana.

O-GlcNAc regulates the mitochondrial integrated stress response by regulating ATF4.

Accumulation of mitochondrial dysfunctional is a hallmark of age-related neurodegeneration including Alzheimer's disease (AD). Impairment of mitochondrial quality control mechanisms leading to the accumulation of damaged mitochondria and increasing neuronal stress. Therefore, investigating the basic mechanisms of how mitochondrial homeostasis is regulated is essential. Herein, we investigate the role of O-GlcNAcylation, a single sugar post-translational modification, in controlling mitochondrial stress-induced transcription factor Activating Transcription Factor 4 (ATF4). Mitochondrial dysfunction triggers the integrated stress response (ISRmt), in which the phosphorylation of eukaryotic translation initiation factor 2α results in the translation of ATF4. We used patient-derived induced pluripotent stem cells, a transgenic mouse model of AD, SH-SY5Y neuroblastoma and HeLa cell-lines to examine the effect of sustained O-GlcNAcase inhibition by Thiamet-G (TMG) on ISRmt using biochemical analyses. We show that TMG elevates ATF4 protein levels upon mitochondrial stress in SH-SY5Y neuroblastoma and HeLa cell-lines. An indirect downstream target of ATF4 mitochondrial chaperone glucose-regulated protein 75 (GRP75) is significantly elevated. Interestingly, knock-down of O-GlcNAc transferase (OGT), the enzyme that adds O-GlcNAc, in SH-SY5Y increases ATF4 protein and mRNA expression. Additionally, ATF4 target gene Activating Transcription Factor 5 (ATF5) is significantly elevated at both the protein and mRNA level. Brains isolated from TMG treated mice show elevated levels of ATF4 and GRP75. Importantly, ATF4 occupancy increases at the ATF5 promoter site in brains isolated from TMG treated mice suggesting that O-GlcNAc is regulating ATF4 targeted gene expression. Interestingly, ATF4 and GRP75 are not induced in TMG treated familial Alzheimer's Disease mice model. The same results are seen in a human in vitro model of AD. Together, these results indicate that in healthy conditions, O-GlcNAc regulates the ISRmt through regulating ATF4, while manipulating O-GlcNAc in AD has no effect on ISRmt.

Stress Induced Activation of LTR Retrotransposons in the Drosophila melanogaster Genome.

Background: Retrotransposons with long terminal repeats (LTR retrotransposons) are widespread in all groups of eukaryotes and are often both the cause of new mutations and the source of new sequences. Apart from their high activity in generative and differentiation-stage tissues, LTR retrotransposons also become more active in response to different stressors. The precise causes of LTR retrotransposons' activation in response to stress, however, have not yet been thoroughly investigated. Methods: We used RT-PCR to investigate the transcriptional profile of LTR retrotransposons and piRNA clusters in response to oxidative and chronic heat stresses. We used Oxford Nanopore sequencing to investigate the genomic environment of new insertions of the retrotransposons. We used bioinformatics methods to find the stress-induced transcription factor binding sites in LTR retrotransposons. Results: We studied the transposition activity and transcription level of LTR retrotransposons in response to oxidative and chronic heat stress and assessed the contribution of various factors that can affect the increase in their expression under stress conditions: the state of the piRNA-interference system, the influence of the genomic environment on individual copies, and the presence of the stress-induced transcription factor binding sites in retrotransposon sequences. Conclusions: The main reason for the activation of LTR retrotransposons under stress conditions is the presence of transcription factor binding sites in their regulatory sequences, which are triggered in response to stress and are necessary for tissue regeneration processes. Stress-induced transposable element activation can function as a trigger mechanism, triggering multiple signal pathways and resulting in a polyvariant cell response.

Impaired glucocorticoid receptor function attenuates herpes simplex virus 1 production during explant-induced reactivation from latency in female mice.

A correlation exists between stress and increased episodes of human alpha-herpes virus 1 reactivation from latency. Stress increases corticosteroid levels; consequently, the glucocorticoid receptor (GR) is activated. Recent studies concluded that a GR agonist, but not an antagonist, accelerates productive infection and reactivation from latency. Furthermore, GR and certain stress-induced transcription factors cooperatively transactivate promoters that drive the expression of infected cell protein 0 (ICP0), ICP4, and VP16. This study revealed female mice expressing a GR containing a serine to alanine mutation at position 229 (GRS229A) shed significantly lower levels of infectious virus during explant-induced reactivation compared to male GRS229A or wild-type parental C57BL/6 mice. Furthermore, female GRS229A mice contained fewer VP16 + TG neurons compared to male GRS229A mice or wild-type mice during the early stages of explant-induced reactivation from latency. Collectively, these studies revealed that GR transcriptional activity has female-specific effects, whereas male mice can compensate for the loss of GR transcriptional activation.

Cloning and functional characterization of FtWRKY29, a low phosphorus stress-inducible transcription factor in Tartary buckwheat

The regulation of the expression of genes related to abiotic stress in plants is significantly influenced by the binding of the transcription factor (TF) WRKY to the W-box elements in their promoters. The findings of this study have confirmed that the ability of Tartary buckwheat (Fagopyrum tataricum Gaertn.) to tolerate phosphorus (P) deficiency is regulated by FtWRKY29, which is classified as a member of group II of the WRKY family. The roots predominantly exhibited an enhanced expression of FtWRKY29, which was significantly upregulated in response to low-P-induced stress. The W-box motif was bound to by FtWRKY29 which enhanced the transcription of genes and was localized to the nucleus. The overexpression of FtWRKY29 in Arabidopsis thaliana produced transgenic lines that exhibited phenotypes typical of diminished sensitivity to low-P-induced stress by promoting root growth, increasing P-uptake, and regulating the accumulation of anthocyanin. The low-P-responsive genes, PHT1;1, PHT1;4, and PHO1 were significantly up-regulated in these lines. In addition, the overexpression of FtWRKY29 restored the P-absorption ability of the wrky75 mutant to a certain extent. Moreover, the binding of FtWRKY29 to the promoter of PHT1;1 activated its expression in tobacco. It was also observed that FtWRKY29 interacts with AtMPK3, AtMPK6, FtMPK3, and FtMPK7. This study provides preliminary evidence that FtWRKY29 improved the tolerance of transgenic A. thaliana plants to low-P-induced stress and deepened the understanding of the regulatory mechanism behind the same in Tartary buckwheat.

The effect of feeding with different protein levels on internal organ weight and gene expression of MEF2A and ATF3 in crossbred local chicken using RT-PCR

BackgroundMyogenic enhancer transcription factor 2A (MEF2A) is a transcription factor known for its role in controlling skeletal muscle regeneration and metabolic processes, while activating transcription factor 3 (ATF3) is a stress-induced transcription factor that plays a role in modulating metabolic processes, immunity, and oncogenesis. Environmental factors, such as dietary protein, can influence gene expression levels. Insufficient protein intake can negatively affect the metabolic performance of internal organs, leading to the abnormal weight of internal organs. A total of 192 non-sexing crossbred local chickens day-old-chick (DOC) with a completely randomized design (CRD) method of 3 treatments and 8 replicates. Real-time polymerase chain reaction (RT-PCR) is used to measure the gene expression levels. This study aimed to determine the effect of feeding with various protein levels on internal organ weight and gene expression of MEF2A and ATF3 in crossbred local chickens. ResultThe analysis of treatment revealed that the results were not significantly different (P > 0.05) on gizzard weight and spleen weight. However, it shows a significantly different result (P < 0.05) on heart weight and a highly significantly different result (P < 0.01) on pancreas weight. These findings suggest that protein levels in the diet had a significant impact on heart and pancreas weights. In terms of gene expression, the increased utilization of protein did not result in an elevation of MEF2A gene expression in both muscle tissue and liver tissue. Specifically, in muscle tissue, MEF2A gene expression was highly expressed at 18% protein feed for the starter phase and 16% for the finisher phase. Conversely, in liver tissue, MEF2A gene expression was highly expressed at 22% protein feed for the starter phase and 20% for the finisher phase. Moreover, ATF3 gene expression in muscle tissue exhibited a negative correlation with increasing feed protein levels. ConclusionThe results indicate that varying protein levels did not lead to abnormal weights in the liver, kidney, heart, and spleen organs. Additionally, the differential gene expression patterns of MEF2A and ATF3 in muscle tissue and liver tissue suggest that these genes respond differently to varying protein-feeding treatments. These findings provide insights into the complex regulatory mechanisms of MEF2A and ATF3 genes in relation to protein levels and organ-specific responses in crossbred local chickens.

Prediction and analysis of stress-inducible ICE transcription factors in Deschampsia antarctica

Prediction and analysis of stress-inducible ICE transcription factors in Deschampsia antarctica

SPOTTED-LEAF7 targets the gene encoding β-Galactosidase9, which functions in rice growth and stress responses.

β-Galactosidases (Bgals) remove terminal β-D-galactosyl residues from the non-reducing ends of β-D-galactosides and oligosaccharides. Bgals are present in bacteria, fungi, animals, and plants and have various functions. Despite many studies on the evolution of BGALs in plants, their functions remain obscure. Here, we identified rice (Oryza sativa) β-galactosidase9 (OsBGAL9) as a direct target of the heat stress-induced transcription factor SPOTTED-LEAF7 (OsSPL7), as demonstrated by protoplast transactivation analysis and yeast one-hybrid and electrophoretic mobility shift assays. Knockout plants for OsBGAL9 (Osbgal9) showed short stature and growth retardation. Histochemical ß-glucuronidase (GUS) analysis of transgenic lines harboring an OsBGAL9pro:GUS reporter construct revealed that OsBGAL9 is mainly expressed in internodes at the mature stage. OsBGAL9 expression was barely detectable in seedlings under normal conditions but increased in response to biotic and abiotic stresses. Ectopic expression of OsBGAL9 enhanced resistance to the rice pathogens Magnaporthe oryzae and Xanthomonas oryzae pv. oryzae, as well as tolerance to cold and heat stress, while Osbgal9 mutant plants showed the opposite phenotypes. OsBGAL9 localized to the cell wall, suggesting that OsBGAL9 and its plant putative orthologs likely evolved functions distinct from those of its closely related animal enzymes. Enzyme activity assays and analysis of the cell wall composition of OsBGAL9 overexpression and mutant plants indicated that OsBGAL9 has activity toward galactose residues of arabinogalactan proteins (AGPs). Our study clearly demonstrates a role for a member of the BGAL family in AGP processing during plant development and stress responses.

The KEAP1–NRF2 pathway regulates TFEB/TFE3-dependent lysosomal biogenesis

The maintenance of redox and metabolic homeostasis is integral to embryonic development. Nuclear factor erythroid 2-related factor 2 (NRF2) is a stress-induced transcription factor that plays a central role in the regulation of redox balance and cellular metabolism. Under homeostatic conditions, NRF2 is repressed by Kelch-like ECH-associated protein 1(KEAP1). Here, we demonstrate that Keap1 deficiency induces Nrf2 activation and postdevelopmental lethality. Loss of viability is preceded by severe liver abnormalities characterized by an accumulation of lysosomes. Mechanistically, we demonstrate that loss of Keap1 promotes aberrant activation of transcription factor EB(TFEB)/transcription factor binding to IGHM Enhancer 3(TFE3)-dependent lysosomal biogenesis. Importantly, we find that NRF2-dependent regulation of lysosomal biogenesis is cell autonomous and evolutionarily conserved. These studies identify a role for the KEAP1-NRF2 pathway in the regulation of lysosomal biogenesis and suggest that maintenance of lysosomal homeostasis is required during embryonic development.

Abstract LB234: Activation of the integrated stress response by the developmental HSF1 pathway inhibitor NXP800

Abstract HSF1 is a stress-inducible transcription factor that regulates the eukaryotic heat shock response (HSR). HSF1 activation induces the expression of multiple proteins needed for cellular recovery from stress. HSF1 also plays a key role in tumorigenesis and regulates the expression of a cancer-specific gene signature which is unique to malignant cells and distinct from that activated during the HSR. We discovered NXP800, the first-in-class orally active HSF1 pathway inhibitor which is now undergoing Phase 1 clinical trial, based on a phenotypic pathway screen. Here we employed various techniques to investigate the mechanism of action of NXP800. Using RNAseq in a panel of human carcinoma cell lines, we identified overlapping gene expression changes in response to NXP800. These included genes regulated by HSF1 and interestingly also genes associated with activation of the integrated stress response (ISR). In contrast, we found no evidence for activation of the unfolded protein response. Consistent with the observed NXP800-induced phosphorylation of eIF2α which is a critical regulator of the ISR, NXP800 increased the protein expression of downstream ISR markers ATF4, CHOP and CHAC1, both in human tumor cells in vitro and in human tumor xenograft models in vivo. Induction of the ISR is controlled by four stress-activated protein kinases (PKs) that phosphorylate eIF2α. To further explore these kinases in the mechanism of action of NXP800 we used genetic knockdown by siRNA and inhibition by small-molecule tool compounds. Silencing each of the ISR-regulatory PKs revealed that GCN2 was required for ISR activation by NXP800. This was confirmed using two GCN2 inhibitors from different chemical series. Global phospho-proteome analysis showed that altered protein phosphorylation following NXP800 exposure was reversed upon co-treatment with a GCN2 inhibitor. We also demonstrated that activation of the ISR caused inhibition of HSF1 activation when stimulated with an HSF1 activator, thus confirming the link between ISR induction and inhibition of HSF1 activation. Activation of GCN2 and the ISR can occur in response to a variety of stimuli including amino acid deprivation. However, we did not detect a difference in the uptake of amino acids following exposure to NXP800, indicating that NXP800 does not directly impair amino acid uptake. Using an siRNA approach to determine if activation of the ISR components was contributing to growth inhibition following NXP800 exposure, we found that blocking the induction of ATF4 reduced the response of NXP800-sensitive SK-OV-3 human ovarian carcinoma cells to NXP800 treatment. In summary, NXP800 acts on cancer cells to induce activation of the ISR pathway via GCN2, which then leads to inhibition of HSF1 activation. Further studies are underway to determine the precise molecular target of NXP800 and the mechanism of HSF1 pathway inhibition. Citation Format: Marissa V. Powers, Swee Y. Sharp, Eirini-Maria Lampraki, Toby Roe, Loredana Pellegrino, Maria Taskinen, Robert te Poele, Florence Raynaud, Suzanne Eccles, Matthew Cheeseman, Keith Jones, Paul A. Clarke, Paul Workman. Activation of the integrated stress response by the developmental HSF1 pathway inhibitor NXP800 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB234.