CREB is activated by ER stress and modulates the unfolded protein response by regulating the expression of IRE1α and PERK

cAMP response element-binding protein: A credible cancer drug target

Despite advancements in radiotherapy, chemotherapy, endocrine therapy, targeted therapy, and immunotherapy, resistance to therapy remains a pervasive challenge in oncology, in part owing to tumor heterogeneity. Identifying new therapeutic targets is key to addressing this challenge because it can both diversify and enhance existing treatment options, particularly through combination regimens. The cAMP response element-binding protein (CREB) is a transcription factor involved in various biological processes. It is aberrantly activated in several aggressive cancer types, including breast cancer. Clinically, high CREB expression is associated with increased breast tumor aggressiveness and poor prognosis. Functionally, CREB promotes breast cancer cell proliferation, survival, invasion, metastasis, as well as therapy resistance by deregulating genes related to apoptosis, cell cycle, and metabolism. Targeting CREB with small molecule inhibitors has demonstrated promise in preclinical studies. This review summarizes the current understanding of CREB mechanisms and their potential as a therapeutic target. SIGNIFICANCE STATEMENT: cAMP response element-binding protein (CREB) is a master regulator of multiple biological processes, including neurodevelopment, metabolic regulation, and immune response. CREB is a putative proto-oncogene in breast cancer that regulates the cell cycle, apoptosis, and cellular migration. Preclinical development of CREB-targeting small molecules is underway.

A stress paradox: the dual role of the unfolded protein response in the placenta

The placenta is a temporary organ that forms during pregnancy and is essential for fetal development and maternal health. As an endocrine organ, proper placental function requires continual production, folding, and transport of proteins and lipids. Central to these processes is the endoplasmic reticulum (ER), a dynamic organelle responsible for maintaining cellular protein and lipid synthesis and processing. ER stress occurs when there is an accumulation of unfolded or misfolded proteins, which triggers the activation of cellular pathways collectively called the unfolded protein response. Unfolded protein response pathways act to alleviate the misfolded protein burden and restore ER homeostasis, or if unresolved, initiate cell death. While prolonged ER stress has been linked to deficient placental function and adverse pregnancy outcomes, basal activation of unfolded protein response pathways is required for placental development and function. This review explores the importance of ER homeostasis in placental development and function, examining how disruptions in ER stress responses may contribute to adverse pregnancy outcomes.

Promotion of endoplasmic reticulum retrotranslocation by overexpression of E3 ubiquitin-protein ligase synoviolin 1 reduces endoplasmic reticulum stress and preserves cone photoreceptors in cyclic nucleotide-gated channel deficiency

Cone photoreceptor cyclic nucleotide-gated (CNG) channels play an essential role in phototransduction and cellular Ca2+ homeostasis. Mutations in genes encoding the channel subunits CNGA3 and CNGB3 are associated with achromatopsia, progressive cone dystrophy, and early-onset macular degeneration. Cone loss in patients with achromatopsia and cone dystrophy associated with CNG channel mutations has been documented by optical coherence tomography and in mouse models of CNG channel deficiency. Cone death in CNG channel-deficient retinas involves endoplasmic reticulum (ER) stress-associated apoptosis, dysregulation of cellular/ER Ca2+ homeostasis, impaired protein folding/processing, and impaired ER-associated degradation (ERAD). The E3 ubiquitin-protein ligase synoviolin 1 (SYVN1) is the primary component of the SYVN1/SEL1L ER retrotranslocon responsible for ERAD. Previous studies have shown that manipulations that protect cones and reduce ER stress/cone death in CNG channel deficiency, such as increasing ER Ca2+ preservation or treatment with an ER chaperone, increase the expression of SYVN1 and other components of the ER retrotranslocon. The present work investigated the effects of SYVN1 overexpression. Intraocular injection of AAV5-IRBP/GNAT2-Syvn1 resulted in overexpression of SYVN1 in cones of CNG channel-deficient mice. Following treatment, cone density in Cnga3-/- mice was significantly increased, compared with untreated controls, outer segment localization of cone opsin was improved, and ER stress/apoptotic cell death was reduced. Overexpression of SYVN1 also led to increased expression levels of the retrotranslocon components, degradation in ER protein 1 (DERL1), ERAD E3 ligase adaptor subunit (SEL1L), and homocysteine inducible ER protein with ubiquitin-like domain 1 (HERPUD1). Moreover, overexpression of SYVN1 likely enhanced protein ubiquitination/proteasome degradation in CNG channel-deficient retinas. This study demonstrates the role of SYVN1/ERAD in cone preservation in CNG channel deficiency and supports the strategy of promoting ERAD for cone protection.

Evidence for ~12-h ultradian gene programs in humans

Mice and many marine organisms exhibit ~12-h ultradian rhythms, however, direct evidence of ~12-h ultradian rhythms in humans is lacking. Here, we performed prospective, temporal transcriptome profiling of peripheral white blood cells from three healthy humans. All three participants independently exhibited robust ~12-h transcriptional rhythms in molecular programs involved in RNA and protein metabolism, with strong homology to circatidal gene programs previously identified in Cnidarian marine species.

Adipose Tissue Hypoxia in Obesity: Clinical Reappraisal of Hypoxia Hypothesis

Obese subjects exhibit lower adipose tissue oxygen consumption in accordance with the lower adipose tissue blood flow. Thereby, compared to lean subjects, obese individuals have almost half lower capillary density and more than half lower vascular endothelial growth factor (VEGF). The VEGF expression together with hypoxia-inducible transcription factor-1 alpha (HIF-1α) activity also requires phosphatidylinositol 3-kinase (PI3K) and mammalian target of rapamycin (mTOR)-mediated signaling. Especially HIF-1α is an important signaling molecule for hypoxia to induce the inflammatory responses. Hypoxia contributes to several biological functions, such as angiogenesis, cell proliferation, apoptosis, inflammation, and insulin resistance (IR). Pathogenesis of obesity-related comorbidities is attributed to intermittent hypoxia (IH), which is mostly observed in visceral obesity. Proinflammatory phenotype of the adipose tissue is a crucial link between IH and the development of IR. Inhibition of adaptive unfolded protein response (UPR) in hypoxia increases β cell death. Moreover, deletion of HIF-1α worsens β cell function. Oxidative stress, as well as the release of proinflammatory cytokines/adipokines in obesity, is proportional to the severity of IH. Reactive oxygen species (ROS) generation at mitochondria is responsible for propagation of the hypoxic signal; however, mitochondrial ROS production is required for hypoxic HIF-1α protein stabilization. Alterations in oxygen availability of adipose tissue directly affect the macrophage polarization and are responsible for the dysregulated adipocytokines production in obesity. Hypoxia both inhibits adipocyte differentiation from preadipocytes and macrophage migration from the hypoxic adipose tissue. Upon reaching a hypertrophic threshold beyond the adipocyte fat loading capacity, excess extracellular matrix (ECM) components are deposited, causing fibrosis. HIF-1α initiates the whole pathological process of fibrosis and inflammation in the obese adipose tissue. In addition to stressed adipocytes, hypoxia contributes to immune cell migration and activation which further aggravates adipose tissue fibrosis. Therefore, targeting HIF-1α might be an efficient way to suppress hypoxia-induced pathological changes in the ECM. The fibrosis score of adipose tissue correlates negatively with the body mass index and metabolic parameters. Inducers of browning/beiging adipocytes and adipokines, as well as modulations of matrix remodeling enzyme inhibitors, and associated gene regulators, are potential pharmacological targets for treating obesity.

GRP78 acts as a cAMP/PKA signaling modulator through the MC4R pathway in porcine embryonic development

Glucose-regulated protein 78 (GRP78) binds to and stabilizes melanocortin 4 receptor (MC4R), which activates protein kinase A (PKA) by regulating G proteins. GRP78 is primarily used as a marker for endoplasmic reticulum stress; however, its other functions have not been well studied. Therefore, in this study, we aimed to investigate the function of GRP78 during porcine embryonic development. The developmental quality of porcine embryos, expression of cell cycle proteins, and function of mitochondria were evaluated by inhibiting the function of GRP78. Porcine oocytes were activated to undergo parthenogenesis, and blastocysts were obtained after 7 days of in vitro culture. GRP78 function was inhibited by adding 20 μM HA15 to the in vitro culture medium. The inhibition in GRP78 function led to a decrease in G proteins release, which subsequently downregulated the cyclic adenosine monophosphate (cAMP)/PKA pathway. Ultimately, inhibition of GRP78 function induced the inhibition of CDK1 and cyclin B expression and disruption of the cell cycle. In addition, inhibition of GRP78 function regulated DRP1 and SIRT1 expression, resulting in mitochondrial dysfunction. This study provides new insights into the role of GRP78 in porcine embryonic development, particularly its involvement in the regulation of the MC4R pathway and downstream cAMP/PKA signaling. The results suggest that the inhibition of GRP78 function in porcine embryos by HA15 treatment may have negative effects on embryo quality and development. This study also demonstrated that GRP78 plays a crucial role in the functioning of MC4R, which releases the G protein during porcine embryonic development.

Regulation of the unfolded protein response during dehydration stress in African clawed frogs, Xenopus laevis

The unfolded protein response (UPR) is a wide-ranging cellular response to accumulation of malfolded proteins in the endoplasmic reticulum (ER) and acts as a quality control mechanism to halt protein processing and repair/destroy malfolded proteins under stress conditions of many kinds. Among vertebrate species, amphibians experience the greatest challenges in maintaining water and osmotic balance, the high permeability of their skin making them very susceptible to dehydration and challenging their ability to maintain cellular homeostasis. The present study evaluates the involvement of the UPR in dealing with dehydration-mediated disruption of protein processing in the tissues of African clawed frogs, Xenopus laevis. This primarily aquatic frog must deal with seasonal drought conditions in its native southern Africa environment. Key markers of cellular stress that impact protein processing were identified in six tissues of frogs that had lost 28% of total body water, as compared with fully hydrated controls. This included upregulation of glucose-regulated proteins (GRPs) that are resident chaperones in the ER, particularly 2-ninefold increases in GRP58, GRP75, and/or GRP94 in the lung and skin. Activating transcription factors (ATF3, ATF4, ATF6) that mediate UPR responses also responded to dehydration stress, particularly in skeletal muscle where both ATF3 and ATF4 rose strongly in the nucleus. Other protein markers of the UPR including GADD34, GADD153, EDEM, and XBP-1 also showed selective upregulation in frog tissues in response to dehydration and nuclear levels of the transcription factors XBP-1 and P-CREB rose indicating up-regulation of genes under their control.

Sustained overexpression of spliced X-box-binding protein-1 in neurons leads to spontaneous seizures and sudden death in mice

The underlying etiologies of seizures are highly heterogeneous and remain incompletely understood. While studying the unfolded protein response (UPR) pathways in the brain, we unexpectedly discovered that transgenic mice (XBP1s-TG) expressing spliced X-box-binding protein-1 (Xbp1s), a key effector of UPR signaling, in forebrain excitatory neurons, rapidly develop neurologic deficits, most notably recurrent spontaneous seizures. This seizure phenotype begins around 8 days after Xbp1s transgene expression is induced in XBP1s-TG mice, and by approximately 14 days post induction, the seizures evolve into status epilepticus with nearly continuous seizure activity followed by sudden death. Animal death is likely due to severe seizures because the anticonvulsant valproic acid could significantly prolong the lives of XBP1s-TG mice. Mechanistically, our gene profiling analysis indicates that compared to control mice, XBP1s-TG mice exhibit 591 differentially regulated genes (mostly upregulated) in the brain, including several GABAA receptor genes that are notably downregulated. Finally, whole-cell patch clamp analysis reveals a significant reduction in both spontaneous and tonic GABAergic inhibitory responses in Xbp1s-expressing neurons. Taken together, our findings unravel a link between XBP1s signaling and seizure occurrence.

Aorta- and liver-generated TMAO enhances trained immunity for increased inflammation via ER stress/mitochondrial ROS/glycolysis pathways

We determined whether gut microbiota-produced trimethylamine (TMA) is oxidized into trimethylamine N-oxide (TMAO) in nonliver tissues and whether TMAO promotes inflammation via trained immunity (TI). We found that endoplasmic reticulum (ER) stress genes were coupregulated with MitoCarta genes in chronic kidney diseases (CKD); TMAO upregulated 190 genes in human aortic endothelial cells (HAECs); TMAO synthesis enzyme flavin-containing monooxygenase 3 (FMO3) was expressed in human and mouse aortas; TMAO transdifferentiated HAECs into innate immune cells; TMAO phosphorylated 12 kinases in cytosol via its receptor PERK and CREB, and integrated with PERK pathways; and PERK inhibitors suppressed TMAO-induced ICAM-1. TMAO upregulated 3 mitochondrial genes, downregulated inflammation inhibitor DARS2, and induced mitoROS, and mitoTEMPO inhibited TMAO-induced ICAM-1. β-Glucan priming, followed by TMAO restimulation, upregulated TNF-α by inducing metabolic reprogramming, and glycolysis inhibitor suppressed TMAO-induced ICAM-1. Our results have provided potentially novel insights regarding TMAO roles in inducing EC activation and innate immune transdifferentiation and inducing metabolic reprogramming and TI for enhanced vascular inflammation, and they have provided new therapeutic targets for treating cardiovascular diseases (CVD), CKD-promoted CVD, inflammation, transplantation, aging, and cancer.

Gut metabolite trimethylamine N-oxide induces aging-associated phenotype of midbrain organoids for the induced pluripotent stem cell-based modeling of late-onset disease

Brain organoids are valuable research models for human development and disease since they mimic the various cell compositions and structures of the human brain; however, they have challenges in presenting aging phenotypes for degenerative diseases. This study analyzed the association between aging and the gut metabolite trimethylamine N-oxide (TMAO), which is highly found in the midbrain of elderly and Parkinson’s disease (PD) patients. TMAO treatment in midbrain organoid induced aging-associated molecular changes, including increased senescence marker expression (P21, P16), p53 accumulation, and epigenetic alterations. In addition, TMAO-treated midbrain organoids have shown parts of neurodegeneration phenotypes, including impaired brain-derived neurotrophic factor (BDNF) signaling, loss of dopaminergic neurons, astrocyte activation, and neuromelanin accumulation. Moreover, we found TMAO treatment-induced pathophysiological phosphorylation of α-synuclein protein at Ser-129 residues and Tau protein at Ser202/Thr205. These results suggest a role of TMAO in the aging and pathogenesis of the midbrain and provide insight into how intestinal dysfunction increases the risk of PD. Furthermore, this system can be utilized as a novel aging model for induced pluripotent stem cell (iPSC)-based modeling of late-onset diseases.

Large-scale mapping of positional changes of hypoxia-responsive genes upon activation

Chromosome structure and nuclear organization are important factors in the regulation of gene expression. Transcription of a gene is influenced by local and global chromosome features such as chromatin condensation status. The relationship between the 3D position of a gene in the nucleus and its activity is less clear. Here we used high-throughput imaging to perform a large-scale analysis of the spatial location of nearly 100 hypoxia-responsive genes to determine whether their location and activity state are correlated. Radial distance analysis demonstrated that the majority of Hypoxia-Inducible Factor (HIF)- and CREB-dependent hypoxia-responsive genes are located in the intermediate region of the nucleus, and some of them changed their radial position in hypoxia. Analysis of the relative distances among a subset of HIF target genes revealed that some gene pairs altered their relative location to each other on hypoxic treatment, suggesting higher-order chromatin rearrangements. While these changes in location occurred in response to hypoxic activation of the target genes, they did not correlate with the extent of their activation. These results suggest that induction of the hypoxia-responsive gene expression program is accompanied by spatial alterations of the genome, but that radial and relative gene positions are not directly related to gene activity.

Endoplasmic Reticulum Stress of Gut Enterocyte and Intestinal Diseases

The endoplasmic reticulum, a vast reticular membranous network from the nuclear envelope to the plasma membrane responsible for the synthesis, maturation, and trafficking of a wide range of proteins, is considerably sensitive to changes in its luminal homeostasis. The loss of ER luminal homeostasis leads to abnormalities referred to as endoplasmic reticulum (ER) stress. Thus, the cell activates an adaptive response known as the unfolded protein response (UPR), a mechanism to stabilize ER homeostasis under severe environmental conditions. ER stress has recently been postulated as a disease research breakthrough due to its significant role in multiple vital cellular functions. This has caused numerous reports that ER stress-induced cell dysfunction has been implicated as an essential contributor to the occurrence and development of many diseases, resulting in them targeting the relief of ER stress. This review aims to outline the multiple molecular mechanisms of ER stress that can elucidate ER as an expansive, membrane-enclosed organelle playing a crucial role in numerous cellular functions with evident changes of several cells encountering ER stress. Alongside, we mainly focused on the therapeutic potential of ER stress inhibition in gastrointestinal diseases such as inflammatory bowel disease (IBD) and colorectal cancer. To conclude, we reviewed advanced research and highlighted future treatment strategies of ER stress-associated conditions.

Tacrine Induces Endoplasmic Reticulum-Stressed Apoptosis via Disrupting the Proper Assembly of Oligomeric Acetylcholinesterase in Cultured Neuronal Cells

Acetylcholinesterase inhibitors (AChEIs), the most developed treatment strategies for Alzheimer's disease (AD), will be used in clinic for, at least, the next decades. Their side effects are in highly variable from drug to drug with mechanisms remaining to be fully established. The withdrawal of tacrine (Cognex) in the market makes it as an interesting case study. Here, we found tacrine could disrupt the proper trafficking of proline-rich membrane anchor-linked tetrameric acetylcholinesterase (AChE) in the endoplasmic reticulum (ER). The exposure of tacrine in cells expressing AChE, e.g., neurons, caused an accumulation of the misfolded AChE in the ER. This misfolded enzyme was not able to transport to the Golgi/plasma membrane, which subsequently induced ER stress and its downstream signaling cascade of unfolded protein response. Once the stress was overwhelming, the cooperation of ER with mitochondria increased the loss of mitochondrial membrane potential. Eventually, the tacrine-exposed cells lost homeostasis and underwent apoptosis. The ER stress and apoptosis, induced by tacrine, were proportional to the amount of AChE. Other AChEIs (rivastigmine, bis(3)-cognitin, daurisoline, and dauricine) could cause the same problem as tacrine by inducing ER stress in neuronal cells. The results provide guidance for the drug design and discovery of AChEIs for AD treatment. SIGNIFICANCE STATEMENT: Acetylcholinesterase inhibitors (AChEIs) are the most developed treatment strategies for Alzheimer's disease (AD) and will be used in clinic for at least the next decades. This study reports that tacrine and other AChEIs disrupt the proper trafficking of acetylcholinesterase in the endoplasmic reticulum. Eventually, the apoptosis of neurons and other cells are induced. The results provide guidance for drug design and discovery of AChEIs for AD treatment.

Cas9-mediated genome editing reveals a significant contribution of calcium signaling pathways to anhydrobiosis in Pv11 cells

Pv11 is an insect cell line established from the midge Polypedilum vanderplanki, whose larval form exhibits an extreme desiccation tolerance known as anhydrobiosis. Pv11 itself is also capable of anhydrobiosis, which is induced by trehalose treatment. Here we report the successful construction of a genome editing system for Pv11 cells and its application to the identification of signaling pathways involved in anhydrobiosis. Using the Cas9-mediated gene knock-in system, we established Pv11 cells that stably expressed GCaMP3 to monitor intracellular Ca2+ mobilization. Intriguingly, trehalose treatment evoked a transient increase in cytosolic Ca2+ concentration, and further experiments revealed that the calmodulin-calcineurin-NFAT pathway contributes to tolerance of trehalose treatment as well as desiccation tolerance, while the calmodulin-calmodulin kinase-CREB pathway conferred only desiccation tolerance on Pv11 cells. Thus, our results show a critical contribution of the trehalose-induced Ca2+ surge to anhydrobiosis and demonstrate temporally different roles for each signaling pathway.

Hinokitiol-induced decreases of tyrosinase and microphthalmia-associated transcription factor are mediated by the endoplasmic reticulum-associated degradation pathway in human melanoma cells

Tyrosinase (TYR) is a key enzyme for melanin production. We previously showed that hinokitiol, a naturally occurring seven-membered ring terpenoid, potently inhibits human TYR activity. Interestingly, hinokitiol was recently reported to decrease expression of TYR and microphthalmia-associated transcription factor (MITF), which is a main transcription factor of the TYR gene, in murine melanoma cells. However, the mechanisms by which hinokitiol decreases the intracellular levels of TYR and MITF have not been fully elucidated. Here, we investigated the underlying mechanisms of the decreases using cultured human melanoma cells. As a result, hinokitiol treatment decreased TYR protein level in a time- and dose-dependent manner in G361 human melanoma cells, while MITF protein level was decreased only at higher concentrations after 3 days treatment. Notably, the mRNA levels of TYR and MITF were slightly increased by hinokitiol treatment. Therefore, we focused on the degradation of TYR and MITF in endoplasmic reticulum (ER)-associated protein degradation (ERAD) pathway. Importantly, co-treatment of ERAD inhibitor with hinokitiol restored the protein levels of TYR and MITF to approximately 30% and 20% of total those in untreated control cells, respectively. Hinokitiol affected the ER homeostasis as well as degradation of TYR and MITF in two human melanoma cell lines, G361 and HT-144, but the changes of ER-stress markers under the hinokitiol treatment were different in the two human melanoma cell lines. Taken together, these observations indicate that hinokitiol may induce ER stress and trigger the degradation of unfolded newly synthesizing TYR and MITF via the ERAD pathway.

Preservation of endoplasmic reticulum (ER) Ca2+ stores by deletion of inositol-1,4,5-trisphosphate receptor type 1 promotes ER retrotranslocation, proteostasis, and protein outer segment localization in cyclic nucleotide-gated channel-deficient cone photoreceptors

Endoplasmic reticulum (ER) Ca²⁺ homeostasis relies on an appropriate balance between efflux- and influx-channel activity responding to dynamic changes of intracellular Ca²⁺ levels. Dysregulation of this complex signaling network has been shown to contribute to neuronal and photoreceptor death in neuro- and retinal degenerative diseases, respectively. In mice with cone cyclic nucleotide-gated (CNG) channel deficiency, a model of achromatopsia/cone dystrophy, cones display early-onset ER stress-associated apoptosis and protein mislocalization. Cones in these mice also show reduced cytosolic Ca²⁺ level and subsequent elevation in the ER Ca²⁺ -efflux-channel activity, specifically the inositol-1,4,5-trisphosphate receptor type 1 (IP₃ R1), and deletion of IP₃ R1 results in preservation of cones. This work investigated how preservation of ER Ca²⁺ stores leads to cone protection. We examined the effects of cone specific deletion of IP₃ R1 on ER stress responses/cone death, protein localization, and ER proteostasis/ER-associated degradation. We demonstrated that deletion of IP₃ R1 improves trafficking of cone-specific proteins M-/S-opsin and phosphodiesterase 6C to cone outer segments and reduces localization to cone inner segments. Consistent with the improved protein localization, deletion of IP₃ R1 results in increased ER retrotranslocation protein expression, reduced proteasome subunit expression, reduced ER stress/cone death, and reduced retinal remodeling. We also observed the enhanced ER retrotranslocation in mice that have been treated with a chemical chaperone, supporting the connection between improved ER retrotranslocation/proteostasis and alleviation of ER stress. Findings from this work demonstrate the importance of ER Ca²⁺ stores in ER proteostasis and protein trafficking/localization in photoreceptors, strengthen the link between dysregulation of ER Ca²⁺ homeostasis and ER stress/cone degeneration, and support an involvement of improved ER proteostasis in ER Ca²⁺ preservation-induced cone protection; thereby identifying IP₃ R1 as a critical mediator of ER stress and protein mislocalization and as a potential target to preserve cones in CNG channel deficiency.

Links between the unfolded protein response and the DNA damage response in hypoxia: a systematic review

Hypoxia is a feature of most solid tumours and predicts for poor prognosis. In radiobiological hypoxia (<0.1% O₂) cells become up to three times more resistant to radiation. The biological response to radiobiological hypoxia is one of few physiologically relevant stresses that activates both the unfolded protein and DNA damage responses (UPR and DDR). Links between these pathways have been identified in studies carried out in normoxia. Based in part on these previous studies and recent work from our laboratory, we hypothesised that the biological response to hypoxia likely includes overlap between the DDR and UPR. While inhibition of the DDR is a recognised strategy for improving radiation response, the possibility of achieving this through targeting the UPR has not been realised. We carried out a systematic review to identify links between the DDR and UPR, in human cell lines exposed to <2% O₂. Following PRISMA guidance, literature from January 2010 to October 2020 were retrieved via Ovid MEDLINE and evaluated. A total of 202 studies were included. LAMP3, ULK1, TRIB3, CHOP, NOXA, NORAD, SIAH1/2, DYRK2, HIPK2, CREB, NUPR1, JMJD2B, NRF2, GSK-3B, GADD45a, GADD45b, STAU1, C-SRC, HK2, CAV1, CypB, CLU, IGFBP-3 and SP1 were highlighted as potential links between the hypoxic DDR and UPR. Overall, we identified very few studies which demonstrate a molecular link between the DDR and UPR in hypoxia, however, it is clear that many of the molecules highlighted warrant further investigation under radiobiological hypoxia as these may include novel therapeutic targets to improve radiotherapy response.

Extracellular α-Synuclein Modulates Iron Metabolism Related Proteins via Endoplasmic Reticulum Stress in MES23.5 Dopaminergic Cells

Alpha-synuclein plays a vital role in the pathology of Parkinson's disease (PD). Spreading of α-synuclein in neighboring cells was believed to contribute to progression in PD. How α-synuclein transmission affects adjacent cells is not full elucidated. Here, we used recombinant α-synuclein to mimic intercellular transmitted α-synuclein in MES23.5 dopaminergic cells, to investigate whether and how it could modulate iron metabolism. The results showed that α-synuclein treatment up-regulated divalent metal transporter 1 (DMT1) and down-regulated iron transporter (FPN), also up-regulated iron regulatory protein 1 (IRP1) protein levels and hepcidin mRNA levels. Endocytosis inhibitor dynasore pretreatment completely abolished and even reversed the upregulation of DMT1 and IRP1 induced by α-synuclein, however, FPN down-regulation was partially blocked by dynasore. Autophagy-inducing agent rapamycin reversed DMT1 up-regulation and FPN down-regulation, and fully blocked the upregulation of IRP1. Elevated hepcidin levels induced by α-synuclein was fully blocked by dynasore pretreatment, however, even higher with rapamycin pretreatment. Alpha-synuclein treatment triggered endoplasmic reticulum (ER) stress. ER stress inducer thapsigargin induced similar responses elicited by α-synuclein. ER stress inhibitor salubrinal blocked the up-regulation of IRP1 and hepcidin, as well as DMT1 up-regulation and FPN down-regulation, also dramatically abolished cAMP-response elements binding protein phosphorylation induced by α-synuclein. Taken together, these finding indicated that extracellular α-synuclein could regulate cellular iron metabolism, probably mediated by ER stress. It provides novel evidence to elucidate the relationships between transmitted α-synuclein and iron metabolism disturbance in PD.

What turns CREB on? And off? And why does it matter?

Altered expression and function of the transcription factor cyclic AMP response-binding protein (CREB) has been identified to play an important role in cancer and is associated with the overall survival and therapy response of tumor patients. This review focuses on the expression and activation of CREB under physiologic conditions and in tumors of distinct origin as well as the underlying mechanisms of CREB regulation by diverse stimuli and inhibitors. In addition, the clinical relevance of CREB is summarized, including its use as a prognostic and/or predictive marker as well as a therapeutic target.

Activated α2-macroglobulin binding to cell surface GRP78 induces trophoblastic cell fusion

The villous cytotrophoblastic cells have the ability to fuse and differentiate, forming the syncytiotrophoblast (STB). The syncytialisation process is essential for placentation. Nevertheless, the mechanisms involved in cell fusion and differentiation are yet to be fully elucidated. It has been suggested that cell surface glucose-regulated protein 78 (GRP78) was involved in this process. In multiple cancer cells, cell membrane-located GRP78 has been reported to act as a receptor binding to the active form of α₂-macroglobulin (α₂M*), activating thus several cellular signalling pathways implicated in cell growth and survival. We hypothesised that GRP78 interaction with α₂M* may also activate signalling pathways in trophoblastic cells, which, in turn, may promote cell fusion. Here, we observed that α₂M mRNA is highly expressed in trophoblastic cells, whereas it is not expressed in the choriocarcinoma cell line BeWo. We thus took advantage of forskolin-induced syncytialisation of BeWo cells to study the effect of exogenous α₂M* on syncytialisation. We first demonstrated that α₂M* induced trophoblastic cell fusion. This effect is dependent on α₂M*-GRP78 interaction, ERK1/2 and CREB phosphorylation, and unfolded protein response (UPR) activation. Overall, these data provide novel insights into the signalling molecules and mechanisms regulating trophoblastic cell fusion.

Potential contribution of ryanodine receptor 2 upregulation to cGMP/PKG signaling-induced cone degeneration in cyclic nucleotide-gated channel deficiency

Photoreceptor cyclic nucleotide-gated (CNG) channels regulate Ca2+ influx in rod and cone photoreceptors. Mutations in cone CNG channel subunits CNGA3 and CNGB3 are associated with achromatopsia and cone dystrophies. Mice lacking functional cone CNG channel show endoplasmic reticulum (ER) stress-associated cone degeneration. The elevated cyclic guanosine monophosphate (cGMP)/cGMP-dependent protein kinase (PKG) signaling and upregulation of the ER Ca2+ channel ryanodine receptor 2 (RyR2) have been implicated in cone degeneration. This work investigates the potential contribution of RyR2 to cGMP/PKG signaling-induced ER stress and cone degeneration. We demonstrated that the expression and activity of RyR2 were highly regulated by cGMP/PKG signaling. Depletion of cGMP by deleting retinal guanylate cyclase 1 or inhibition of PKG using chemical inhibitors suppressed the upregulation of RyR2 in CNG channel deficiency. Depletion of cGMP or deletion of Ryr2 equivalently inhibited unfolded protein response/ER stress, activation of the CCAAT-enhancer-binding protein homologous protein, and activation of the cyclic adenosine monophosphate response element-binding protein, leading to early-onset cone protection. In addition, treatment with cGMP significantly enhanced Ryr2 expression in cultured photoreceptor-derived Weri-Rb1 cells. Findings from this work demonstrate the regulation of cGMP/PKG signaling on RyR2 in the retina and support the role of RyR2 upregulation in cGMP/PKG signaling-induced ER stress and photoreceptor degeneration.

Splice switching an oncogenic ratio of SmgGDS isoforms as a strategy to diminish malignancy

The chaperone protein SmgGDS promotes cell-cycle progression and tumorigenesis in human breast and nonsmall cell lung cancer. Splice variants of SmgGDS, named SmgGDS-607 and SmgGDS-558, facilitate the activation of oncogenic members of the Ras and Rho families of small GTPases through membrane trafficking via regulation of the prenylation pathway. SmgGDS-607 interacts with newly synthesized preprenylated small GTPases, while SmgGDS-558 interacts with prenylated small GTPases. We determined that cancer cells have a high ratio of SmgGDS-607:SmgGDS-558 (607:558 ratio), and this elevated ratio is associated with reduced survival of breast cancer patients. These discoveries suggest that targeting SmgGDS splicing to lower the 607:558 ratio may be an effective strategy to inhibit the malignant phenotype generated by small GTPases. Here we report the development of a splice-switching oligonucleotide, named SSO Ex5, that lowers the 607:558 ratio by altering exon 5 inclusion in SmgGDS pre-mRNA (messenger RNA). Our results indicate that SSO Ex5 suppresses the prenylation of multiple small GTPases in the Ras, Rho, and Rab families and inhibits ERK activity, resulting in endoplasmic reticulum (ER) stress, the unfolded protein response, and ultimately apoptotic cell death in breast and lung cancer cell lines. Furthermore, intraperitoneal (i.p.) delivery of SSO Ex5 in MMTV-PyMT mice redirects SmgGDS splicing in the mammary gland and slows tumorigenesis in this aggressive model of breast cancer. Taken together, our results suggest that the high 607:558 ratio is required for optimal small GTPase prenylation, and validate this innovative approach of targeting SmgGDS splicing to diminish malignancy in breast and lung cancer.

Nuclear factor erythroid 2 - related factor 2 and its relationship with cellular response in nickel exposure: a systems biology analysis

Background

Nickel and nickel-containing compounds (NCC) are known human carcinogens. However, the precise molecular mechanisms of nickel-induced malignant transformation remain unknown. Proposed mechanisms suggest that nickel and NCC may participate in the dual activation/inactivation of enzymatic pathways involved in cell defenses against oxidative damage, where Nuclear factor-erythroid 2 related factor 2 (Nrf2) plays a central role.

Methods

For assessing the potential role of proteins involved in the Nrf2-mediated response to nickel and NCC exposure, we designed an interactome network using the STITCH search engine version 5.0 and the STRING software 10.0. The major NCC-protein interactome (NCPI) generated was analyzed using the MCODE plugin, version 1.5.1 for the detection of interaction modules or subnetworks. Main centralities of the NCPI were determined with the CentiScape 2.2 plugin of Cytoscape 3.4.0 and main biological processes associated with each cluster were assessed using the BiNGO plugin of Cytoscape 3.4.0.

Results

Water-soluble NiSO₄ and insoluble Ni₃S₂ were the most connected to proteins involved in the NCPI network. Nfr2 was detected as one of the most relevant proteins in the network, participating in several multifunctional protein complexes in clusters 1, 2, 3 and 5. Ontological analysis of cluster 3 revealed several processes related to unfolded protein response (UPR) and response to endoplasmic reticulum (ER) stress.

Conclusions

Cellular response to NCC exposure was very comparable, particularly concerning oxidative stress response, inflammation, cell cycle/proliferation, and apoptosis. In this cellular response, Nfr2 was highly centralized and participated in several multifunctional protein complexes, including several related to ER-stress. These results add evidence on the possible Ni²⁺ induced – ER stress mainly associated with insoluble NCC. In this scenario, we also show how protein degradation mediated by ubiquitination seems to play key roles in cellular responses to Ni.

Regulation of Gene Expression under Hypoxic Conditions

Eukaryotes are often subjected to different kinds of stress. In order to adjust to such circumstances, eukaryotes activate stress–response pathways and regulate gene expression. Eukaryotic gene expression consists of many different steps, including transcription, RNA processing, RNA transport, and translation. In this review article, we focus on both transcriptional and post-transcriptional regulations of gene expression under hypoxic conditions. In the first part of the review, transcriptional regulations mediated by various transcription factors including Hypoxia-Inducible Factors (HIFs) are described. In the second part, we present RNA splicing regulations under hypoxic conditions, which are mediated by splicing factors and their kinases. This work summarizes and discusses the emerging studies of those two gene expression machineries under hypoxic conditions.

ER Stress, CREB, and Memory: A Tangled Emerging Link in Disease

The brain undergoes several changes at structural, molecular, and cellular levels leading to alteration in its functions and these processes are primarily maintained by proteostasis in cells. However, an imbalance in proteostasis due to the abnormal accumulation of protein aggregates induces endoplasmic reticulum (ER) stress. This event, in turn, activate the unfolded protein response; however, in most neurodegenerative conditions and brain injury, an uncontrolled unfolded protein response elicits memory dysfunction. Although the underlying signaling mechanism for impairment of memory function following induction of ER stress remains elusive, recent studies have highlighted that inactivation of a transcription factor, CREB, which is essential for synaptic function and memory formation, plays an essential role for ER stress-induced synaptic and memory dysfunction. In this review, current studies and most updated view on how ER stress affects memory function in both physiological and pathological conditions will be highlighted.

CREB element is essential for unfolded protein response (UPR) mediating the Cu-induced changes of hepatic lipogenic metabolism in Chinese yellow catfish (Pelteobagrus fulvidraco)

The present study was conducted to explore the underlying mechanism of unfolded protein response (UPR) mediating the Cu-induced changes of hepatic lipogenic metabolism in a low vertebrate, freshwater teleost yellow catfish Pelteobagrus fulvidraco. To this end, three experiments were conducted. In Exp. 1, we cloned the regions of grp78, perk, ire-1α and atf-6α promoters, and found that multiple cAMP-response element binding protein (CREB) binding sites were identified in their promoter regions. Furthermore, these CREB binding sites played crucial role in transcriptional regulation of UPR. In Exp. 2, the involvement of perk, ire-1α and atf-6α in Cu-induced changes of hepatic lipid metabolism was confirmed by specific miRNA. In Exp. 3, the regulatory mechanism of CREB underlying UPR mediating Cu-induced hepatic lipogenic metabolism were investigated. Cu induced UPR via the activation of CREB binding sites in the promoter regions of grp78, perk, ire-1α and atf-6α. In addition, the inhibition of CREB markedly attenuated the Cu-induced up-regulation of hepatic lipogenic metabolism in hepatocytes. This conclusion was further supported by the results from the trial of CREB over-expression. Taken together, the present study indicated that CREB was essential for UPR mediating Cu-induced lipogenic metabolism, supporting a mechanistic link among CREB, UPR and Cu-induced changes of lipid metabolism.

Sequence homology in eukaryotes (SHOE): interactive visual tool for promoter analysis

Background

Microarray and DNA-sequencing based technologies continue to produce enormous amounts of data on gene expression. This data has great potential to illuminate our understanding of biology and medicine, but the data alone is of limited value without computational tools to allow human investigators to visualize and interpret it in the context of their problem of interest.

Results

We created a web server called SHOE that provides an interactive, visual presentation of the available evidence of transcriptional regulation and gene co-expression to facilitate its exploration and interpretation. SHOE predicts the likely transcription factor binding sites in orthologous promoters of humans, mice, and rats using the combined information of 1) transcription factor binding preferences (position-specific scoring matrix (PSSM) libraries such as Transfac32, Jaspar, HOCOMOCO, ChIP-seq, SELEX, PBM, and iPS-reprogramming factor), 2) evolutionary conservation of putative binding sites in orthologous promoters, and 3) co-expression tendencies of gene pairs based on 1,714 normal human cells selected from the Gene Expression Omnibus Database.

Conclusion

SHOE enables users to explore potential interactions between transcription factors and target genes via multiple data views, discover transcription factor binding motifs on top of gene co-expression, and visualize genes as a network of gene and transcription factors on its native gadget GeneViz, the CellDesigner pathway analyzer, and the Reactome database to search the pathways involved. As we demonstrate here when using the CREB1 and Nf-κB datasets, SHOE can reliably identify experimentally verified interactions and predict plausible novel ones, yielding new biological insights into the gene regulatory mechanisms involved. SHOE comes with a manual describing how to run it on a local PC or via the Garuda platform (www.garuda-alliance.org), where it joins other popular gadgets such as the CellDesigner pathway analyzer and the Reactome database, as part of analysis workflows to meet the growing needs of molecular biologists and medical researchers. SHOE is available from the following URL http://ec2-54-150-223-65.ap-northeast-1.compute.amazonaws.com

A video demonstration of SHOE can be found here: https://www.youtube.com/watch?v=qARinNb9NtE

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5101-3) contains supplementary material, which is available to authorized users.

Supra-pharmacological concentration of capsaicin stimulates brown adipogenesis through induction of endoplasmic reticulum stress

We previously showed that brown (pre)adipocytes express Trpv1, a capsaicin receptor, and that capsaicin stimulates differentiation of brown preadipocytes in the late stages of brown adipogenesis. The present study revealed that treatment with 100 μM capsaicin stimulates brown adipogenesis by inducing endoplasmic reticulum (ER) stress. Treatment with capsaicin (100 μM) during brown adipogenesis enhanced lipid accumulation and the expression of Ucp1, a gene selectively expressed in brown adipocytes. Capsaicin treatment also caused an increase in the cytosolic calcium concentration even when extracellular calcium was removed. I-RTX, a Trpv1 inhibitor, did not modulate the increase in cytosolic calcium concentration, lipid accumulation or Ucp1 expression. Previous studies revealed that the release of calcium from the ER induces ER stress, leading to the conversion of X-box binding protein 1 (Xbp1) pre-mRNA to spliced Xbp1 (sXbp1) as well as the up-regulation of Chop expression. Capsaicin treatment increased the expression of sXbp1 and Chop in brown preadipocytes and did not enhance lipid accumulation or Ucp1 expression in Xbp1 knockdown cells. The present results describe a novel mechanism of brown adipogenesis regulation via ER stress that is induced by a supra-pharmacological concentration of capsaicin.

Glucose availability controls ATF4-mediated MITF suppression to drive melanoma cell growth

It is well know that cancer cells have adopted an altered metabolism and that glucose is a major source of energy for these cells. In melanoma, enhanced glucose usage is favoured through the hyper-activated MAPK pathway, which suppresses OXPHOS and stimulates glycolysis. However, it has not been addressed how glucose availability impacts on melanoma specific signaling pathways that drive melanoma cell proliferation. Here we show that melanoma cells are dependent on high glucose levels for efficient growth. Thereby, glucose metabolism controls the expression of the melanoma fate transcription factor MITF, a master regulator of melanoma cell survival and proliferation, invasion and therapy resistance. Restriction of glucose availability to physiological concentrations induces the production of reactive oxygen species (ROS). Increased ROS levels lead to the up-regulation of AFT4, which in turn suppresses MITF expression by competing with CREB, an otherwise potent inducer of the MITF promoter. Our data give new insight into the complex regulation of MITF, a key regulator of melanoma biology, and support previous findings that link metabolic disorders such as hyperglycemia and diabetes with increased melanoma risk.

Tat-haFGF14-154 Upregulates ADAM10 to Attenuate the Alzheimer Phenotype of APP/PS1 Mice through the PI3K-CREB-IRE1α/XBP1 Pathway

Acid fibroblast growth factor (aFGF) has shown neuroprotection in Alzheimer’s disease (AD) models in previous studies, yet its mechanism is still uncertain. Here we report that the efficacy of Tat-haFGF_14–154 is markedly increased when loaded cationic liposomes for intranasal delivery are intranasally administered to APP/PS1 mice. Our results demonstrated that liposomal Tat-haFGF_14–154 treatment significantly ameliorated behavioral deficits, relieved brain Aβ burden, and increased the expression and activity of disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) in the brain. Tat-haFGF_14–154 antagonized Aβ_1–42-induced cell death and structural damage in rat primary neurons in an ADAM10-dependent manner, which, in turn, was promoted by the activation of XBP1 splicing and modulated by the PI3K-CREB pathway. Both knockdown of ADAM10 and inhibition of PI3K (LY294002) negated Tat-haFGF_14–154 rescue. Thus, Tat-haFGF_14–154 activates the IRE1α/XBP1 pathway of the unfolded protein response (UPR) against the endoplasmic reticulum (ER) stress induced by Aβ, and, subsequently, the nuclear translocation of spliced XBP1 (XBP1s) promotes transcription of ADAM10. These results highlight the important role of ADAM10 and its activation through the PI3K-CREB-IRE1α/XBP1 pathway as a key factor in the mechanism of neuroprotection for Tat-haFGF_14–154.

Oxidative protein modification alters proteostasis under acute hypobaric hypoxia in skeletal muscles: a comprehensive in vivo study

While numerous maladies are associated with hypobaric hypoxia, muscle protein loss is an important under studied topic. Hence, the present study was designed to investigate the mechanism of muscle protein loss at HH. SD rats were divided into normoxic rats, while remaining rats were exposed to simulated hypoxia equivalent to 282-torr pressure (equal to an altitude of 7620 m, 8% oxygen), at 25 °C for 6, 12, and 24 h. Post-exposure rats were sacrificed and analysis was performed. Ergo, muscle loss-related changes were observed at 12 and 24 h post-HH exposure. An increased reactive oxygen species production and decreased thiol content was observed in HH-exposed rats. This disturbance caused substantial protein oxidative modification in the form of protein carbonyl content and advanced oxidation protein products. The analysis showed increase levels of bityrosine, oxidized tryptophan, lysine conjugate, lysine conjugate with MDA, protein hydroperoxide, and protein-MDA product. These changes were also in agreement with increase in lipid hydroperoxides and MDA content. HSP-70 and HSP-60 were upregulated significantly, and this finding is corroborated with increase in ER stress biomarker, GRP-78. Overloading of cells with misfolded proteins further activated degradative machinery. Consequently, pro-apoptotic signaling cascade, caspase-3, and C/EBP homologous protein were also activated in 24-h HH exposure. Release of tryptophan and tyrosine was also increased with 24-h HH exposure, indicated protein degradation. Elevation in resting intracellular calcium ion, [Ca2+]i, was also observed at 12- and 24-h HH exposure. The present study provides a detailed mechanistic representation of muscle protein loss during HH exposure.

Adipose Tissue Hypoxia in Obesity and Its Impact on Preadipocytes and Macrophages: Hypoxia Hypothesis

Obese subjects exhibit lower adipose tissue oxygen consumption in accordance with the lower adipose tissue blood flow. Thus, compared with lean subjects, obese subjects have 44% lower capillary density and 58% lower vascular endothelial growth factor (VEGF). The VEGF expression together with hypoxia-inducible transcription factor-1 (HIF-1) activity also requires phosphatidylinositol 3-kinase (PI3K)- and target of rapamycin (TOR)-mediated signaling. HIF-1alpha is an important signaling molecule for hypoxia to induce the inflammatory responses. Hypoxia affects a number of biological functions, such as angiogenesis, cell proliferation, apoptosis, inflammation and insulin resistance. Additionally, reactive oxygen radical (ROS) generation at mitochondria is responsible for propagation of the hypoxic signal. Actually mitochondrial ROS (mtROS) production, but not oxygen consumption is required for hypoxic HIF-1alpha protein stabilization. Adipocyte mitochondrial oxidative capacity is reduced in obese compared with non-obese adults. In this respect, mitochondrial dysfunction of adipocyte is associated with the overall adiposity. Furthermore, hypoxia also inhibits macrophage migration from the hypoxic adipose tissue. Alterations in oxygen availability of adipose tissue directly affect the macrophage polarization and are responsible from dysregulated adipocytokines production in obesity. Hypoxia also inhibits adipocyte differentiation from preadipocytes. In addition to stressed adipocytes, hypoxia contributes to immune cell immigration and activation which further aggravates adipose tissue fibrosis. Fibrosis is initiated in response to adipocyte hypertrophy in obesity.

Autophagy gene ATG7 regulates ultraviolet radiation-induced inflammation and skin tumorigenesis

Macroautophagy (hereafter autophagy) is a cellular "self-eating" process that is implicated in many human cancers, where it can act to either promote or suppress tumorigenesis. However, the role of autophagy in regulation of inflammation during tumorigenesis remains unclear. Here we show that autophagy is induced in the epidermis by ultraviolet (UV) irradiation and autophagy gene Atg7 promoted UV-induced inflammation and skin tumorigenesis. Atg7 regulated UV-induced cytokine expression and secretion, and promoted Ptgs2/Cox-2 expression through both a CREB1/CREB-dependent cell autonomous mechanism and an IL1B/IL1β-dependent non-cell autonomous mechanism. Adding PGE2 increased UV-induced skin inflammation and tumorigenesis, reversing the epidermal phenotype in mice with Atg7 deletion in keratinocytes. Similar to ATG7 knockdown in human keratinocytes, ATG5 knockdown inhibited UVB-induced expression of PTGS2 and cytokines. Furthermore, ATG7 loss increased the activation of the AMPK pathway and the phosphorylation of CRTC1, and led to endoplasmic reticulum (ER) accumulation and reduction of ER stress. Inducing ER stress and inhibiting calcium influx into the ER by thapsigargin reverses the inflammation and tumorigenesis phenotype in mice with epidermal Atg7 deletion. Taken together, these findings demonstrate that deleting autophagy gene Atg7 leads to a suppression of carcinogen-induced protumorigenic inflammatory microenvironment and tumorigenesis of the epithelium.

Heat Shock Enhances the Expression of the Human T Cell Leukemia Virus Type-I (HTLV-I) Trans-Activator (Tax) Antigen in Human HTLV-I Infected Primary and Cultured T Cells

The environmental factors that lead to the reactivation of human T cell leukemia virus type-1 (HTLV-I) in latently infected T cells in vivo remain unknown. It has been previously shown that heat shock (HS) is a potent inducer of HTLV-I viral protein expression in long-term cultured cell lines. However, the precise HTLV-I protein(s) and mechanisms by which HS induces its effect remain ill-defined. We initiated these studies by first monitoring the levels of the trans-activator (Tax) protein induced by exposure of the HTLV-I infected cell line to HS. HS treatment at 43 °C for 30 min for 24 h led to marked increases in the level of Tax antigen expression in all HTLV-I-infected T cell lines tested including a number of HTLV-I-naturally infected T cell lines. HS also increased the expression of functional HTLV-I envelope gp46 antigen, as shown by increased syncytium formation activity. Interestingly, the enhancing effect of HS was partially inhibited by the addition of the heat shock protein 70 (HSP70)-inhibitor pifithlin-μ (PFT). In contrast, the HSP 70-inducer zerumbone (ZER) enhanced Tax expression in the absence of HS. These data suggest that HSP 70 is at least partially involved in HS-mediated stimulation of Tax expression. As expected, HS resulted in enhanced expression of the Tax-inducible host antigens, such as CD83 and OX40. Finally, we confirmed that HS enhanced the levels of Tax and gp46 antigen expression in primary human CD4⁺ T cells isolated from HTLV-I-infected humanized NOD/SCID/γc null (NOG) mice and HTLV-I carriers. In summary, the data presented herein indicate that HS is one of the environmental factors involved in the reactivation of HTLV-I in vivo via enhanced Tax expression, which may favor HTLV-I expansion in vivo.

Protein Kinase A Activation Promotes Cancer Cell Resistance to Glucose Starvation and Anoikis

Cancer cells often rely on glycolysis to obtain energy and support anabolic growth. Several studies showed that glycolytic cells are susceptible to cell death when subjected to low glucose availability or to lack of glucose. However, some cancer cells, including glycolytic ones, can efficiently acquire higher tolerance to glucose depletion, leading to their survival and aggressiveness. Although increased resistance to glucose starvation has been shown to be a consequence of signaling pathways and compensatory metabolic routes activation, the full repertoire of the underlying molecular alterations remain elusive. Using omics and computational analyses, we found that cyclic adenosine monophosphate-Protein Kinase A (cAMP-PKA) axis activation is fundamental for cancer cell resistance to glucose starvation and anoikis. Notably, here we show that such a PKA-dependent survival is mediated by parallel activation of autophagy and glutamine utilization that in concert concur to attenuate the endoplasmic reticulum (ER) stress and to sustain cell anabolism. Indeed, the inhibition of PKA-mediated autophagy or glutamine metabolism increased the level of cell death, suggesting that the induction of autophagy and metabolic rewiring by PKA is important for cancer cellular survival under glucose starvation. Importantly, both processes actively participate to cancer cell survival mediated by suspension-activated PKA as well. In addition we identify also a PKA/Src mechanism capable to protect cancer cells from anoikis. Our results reveal for the first time the role of the versatile PKA in cancer cells survival under chronic glucose starvation and anoikis and may be a novel potential target for cancer treatment.

Tumor heterogeneity exists in many human cancers, and it has been shown that it can play a role in tumor progression. Indeed, cell diversity may be critically important when tumors experience selective pressures, like nutrient deprivation, hypoxia, chemotherapy. PKA, through incompletely understood mechanisms, controls several cellular processes like cell growth, cell differentiation, cell metabolism, cell migration and, as more recently observed, also cancer progression. In this work, we show that activation of PKA induces the ability of a cancer cell sub-population to survive under strong stress conditions namely nutrient deprivation and cell detachment. Indeed, PKA activation in these cells results in autophagy induction, and at the same time, in activation of glutamine metabolism and Src kinase. Importantly, blocking directly the PKA pathway, as well as the autophagy, the glutamine metabolism or the Src pathway by inhibitory drugs, almost completely prevents cell growth of this sub-population of resistant cancer cells. These results suggest that drugs, targeting especially PKA pathway as well as downstream processes like autophagy, glutamine metabolism and Src signaling, may specifically inhibit cancer cells ability to survive under selective pressure favoring cancer resistance.