NF-kappaB/Egr-1/Gadd45 are sequentially activated upon UVB irradiation to mediate epidermal cell death

Multifaceted regulatory mechanisms of the EGR family in tumours and prospects for therapeutic applications (Review)

The early growth response (EGR) family comprises four zinc finger transcription factors: EGR1, EGR2, EGR3 and EGR4. These transcription factors belong to the Cys2‑His2‑type zinc finger protein family and are essential in cell differentiation, proliferation, apoptosis and stress response. Initially, EGR1 was recognised for its essential regulatory role in tumourigenesis. Recent studies have identified similarities between other members of the EGR family and EGR1 in tumour regulation and the multifaceted regulatory mechanism employed by the EGR family to affect tumours. Therefore, the present review describes the dual roles of the EGR family in tumours and their regulatory mechanisms in immunity, metabolism and differentiation. Additionally, the present review offers a new perspective on relevant tumour therapeutic studies based on current EGR targeting.

Growth arrest and DNA damage-inducible 45: a new player on inflammatory diseases

Growth arrest and DNA damage-inducible 45 (GADD45) proteins are critical stress sensors rapidly induced in response to genotoxic/physiological stress and regulate many cellular functions. Even though the primary function of the proteins is to block the cell cycle, inhibit cell proliferation, promote cell apoptosis, and repair DNA damage to cope with the damage caused by internal and external stress on the body, evidence has shown that GADD45 also has the function to modulate innate and adaptive immunity and plays a broader role in inflammatory and autoimmune diseases. In this review, we focus on the immunomodulatory role of GADD45 in inflammatory and autoimmune diseases. First, we describe the regulatory factors that affect the expression of GADD45. Then, we introduce its immunoregulatory roles on immune cells and the critical signaling pathways mediated by GADD45. Finally, we discuss its immunomodulatory effects in various inflammatory and autoimmune diseases.

Recombinant collagen for the repair of skin wounds and photo-aging damage

The skin, being the body's primary defense mechanism, is susceptible to various injuries such as epidermal wounds, natural aging, and ultraviolet-induced damage. As a result, there is growing interest in researching skin repair methods. Traditional animal-derived collagen, widely available on the market, poses risks due to its immunogenicity and potential for viral contamination. In contrast, recombinant collagen sourced from human genes offers a safer alternative. To investigate the potential of human recombinant collagen in skin repair, our research team applied two types, type I human collagen (Col I) and CF-1552(I), to two different skin injury models: a wound-healing model and a photo-aging model. Our findings indicate that both Col I and CF-1552(I) effectively enhance wound healing and repair skin damaged by ultraviolet exposure. Notably, CF-1552(I) showed effects comparable to Col I in promoting cell proliferation in the wound-healing model and increasing malondialdehyde content in the photo-aging model, suggesting that CF-1552(I) may offer greater potential for skin repair compared to the larger Col I molecule.

Soluble klotho induces the heat shock factor 1 through EGR1 expression

Klotho is an antiaging protein that has multiple functions. The purpose of this study is to investigate whether soluble klotho plays a role in cellular stress response pathways. We found that klotho deficiency (kl-/-) largely decreased HSF1 levels and impaired heat shock protein expression. Interestingly, recombinant soluble klotho-induced HSF1 and HSPs such as HSP90, HSP70, and HSP27 in kl-/- mouse embryonic fibroblasts (MEFs). Soluble Klotho treatment also induced cell proliferation and HSF1 promoter activity in MEF kl-/- cells in a concentration-dependent manner. Furthermore, using point mutagenesis, we identified regulatory/binding sites of transcription factors EGR1 regulated by soluble klotho in the HSF1 promoter. Taken together, our findings unravel the molecular basis of klotho and provide molecular evidence supporting a direct interaction between soluble klotho and HSF1-mediated stress response pathway.

GADD45A: With or without you

The growth arrest and DNA damage inducible (GADD)45 family includes three small and ubiquitously distributed proteins (GADD45A, GADD45B, and GADD45G) that regulate numerous cellular processes associated with stress signaling and injury response. Here, we provide a comprehensive review of the current literature investigating GADD45A, the first discovered member of the family. We first depict how its levels are regulated by a myriad of genotoxic and non-genotoxic stressors, and through the combined action of intricate transcriptional, posttranscriptional, and even, posttranslational mechanisms. GADD45A is a recognized tumor suppressor and, for this reason, we next summarize its role in cancer, as well as the different mechanisms by which it regulates cell cycle, DNA repair, and apoptosis. Beyond these most well-known actions, GADD45A may also influence catabolic and anabolic pathways in the liver, adipose tissue and skeletal muscle, among others. Not surprisingly, GADD45A may trigger AMP-activated protein kinase activity, a master regulator of metabolism, and is known to act as a transcriptional coregulator of numerous nuclear receptors. GADD45A has also been reported to display a cytoprotective role by regulating inflammation, fibrosis and oxidative stress in several organs and tissues, and is regarded an important contributor for the development of heart failure. Overall data point to that GADD45A may play an important role in metabolic, neurodegenerative and cardiovascular diseases, and also autoimmune-related disorders. Thus, the potential mechanisms by which dysregulation of GADD45A activity may contribute to the progression of these diseases are also reviewed below.

The chemotherapeutic agent doxorubicin induces brain senescence, with modulation by APOE genotype

Many cancer patients experience serious cognitive problems related to their treatment, which can greatly affect their quality of life. The molecular mechanisms of this cancer chemotherapy-induced cognitive impairment (CICI) are unknown, thus slowing the development of preventative approaches. We hypothesized that cancer chemotherapies could induce cellular senescence in the brain, creating a pro-inflammatory environment and damaging normal brain communication. We tested this hypothesis using the common chemotherapeutic agent doxorubicin in two independent mouse models. In the first model, we used mice that express tdTomato under the pdkn2a (p16) promoter; p16 is a regulator of cellular senescence, and its upregulation is denoted by the presence of fluorescently tagged cells. Two weeks after exposure to three doses of 5 mg/kg doxorubicin, the number of tdTomato positive cells were increased nearly three-fold in both the cerebral cortex and the hippocampus. tdTomato staining co-localized with neurons, microglia, oligodendrocyte precursor cells, and endothelial cells, but not astrocytes. In the second model, we used APOE knock-in mice, since the APOE4 allele is a risk factor for CICI in humans and mouse models. We isolated RNA from the cerebral cortex of APOE3 and APOE4 mice from one to 21 days after a single dose of 10 mg/kg doxorubicin. Using NanoString analysis of over 700 genes related to neuroinflammation and RT-qPCR analysis of cerebral cortex transcripts, we found two-fold induction of four senescence-related genes at three weeks in the APOE4 mice compared to the APOE3 control mice: p21(cdkn1a), p16, Gadd45a, and Egr1. We conclude that doxorubicin promotes cellular senescence pathways in the brain, supporting the hypothesis that drugs to eliminate senescent cells could be useful in preventing CICI.

Chitotriose Enhanced Antitumor Activity of Doxorubicin through Egr1 Upregulation in MDA-MB-231 Cells

Dietary supplementation is proposed as a strategy to reduce the side effects of conventional chemotherapy for triple-negative breast cancer (TNBC). Chitosan oligosaccharides (COS), a functional carbohydrate, have been identified to potentially inhibit cancer cell proliferation. However, a detailed investigation is required to fully understand its exact influence, particularly in terms of COS composition. The antitumor activities of COS oligomers and its monomer of glucosamine, when combined with doxorubicin separately, were evaluated in MDA-MB-231 cells. Chitotriose was identified to have the most significant synergistic effect. Preincubation with chitotriose was observed to promote the entry of doxorubicin into the cell nuclei and induce morphological changes in the cells. Mechanism analysis at the transcriptional level revealed that the early growth response 1 (Egr1) gene was a key regulator in enhancing the suppressive effect. This gene was found to modulate the activity of its downstream gene, growth arrest, and DNA damage-inducible alpha (Gadd45a). The role of Egr1 was confirmed through a small interfering RNA test and function assay. These findings provide insight into the effect and underlying mechanism of chitotriose supplementation for TNBC therapy.

Characterization of Novel α-Mangostin and Paeonol Derivatives With Cancer-Selective Cytotoxicity

α-Mangostin (aMan) and Paeonol (Pae) have shown anticancer and anti-inflammatory properties. However, these two natural compounds have no clinical value because of their low solubility and low membrane permeability. In this study, we screened chemically synthesized derivatives from these two natural compounds as potential novel chemicals that increase cancer cell cytotoxicity over nontransformed human cells. We found that two derivative compounds, named α-Mangostin-1 (aMan1) and Paeonol-1 (Pae1) more efficiently and more specifically induced cytotoxicity in HCT116, HT29, and SW48 colorectal cancer cell lines than the parental compounds. Both aMan1 and Pae1 arrested HCT116 cells in the G₁ phase and HT29 and SW48 cells in the G₂-M phase of the cell cycle. Both aMan1 and Pae1 induced apoptosis in human colorectal cancer cells, through a caspase-dependent mechanism. aMan1 and Pae1 induced selective transcriptional responses in colorectal cancer cells involving genes related to metabolic stress and DNA damage response signaling pathways. Finally, experiments on primary colon organoids showed that both derivatives were able to kill cancer-derived organoids without affecting the viability of organoids derived from healthy tissue, where the parental compounds and the currently used chemotherapeutic drug irinotecan failed. In conclusion, our findings expand the knowledge of natural compound derivatives as anticancer agents and open new avenues of research in the derivation of lead compounds aimed at developing novel chemotherapeutic drugs for colorectal cancer treatment that selectively target cancer, but not healthy cells.

Therapeutic wavelengths of ultraviolet B radiation activate apoptotic, circadian rhythm, redox signalling and key canonical pathways in psoriatic epidermis

Ultraviolet B radiation (UVB) exerts pleiotropic effects on human skin. DNA damage response and repair pathways are activated by UVB; if damage cannot be repaired, apoptosis ensues. Although cumulative UVB exposure predisposes to skin cancer, UVB phototherapy is widely used as an effective treatment for psoriasis. Previous studies defined the therapeutic action spectrum of UVB and showed that psoriasis is resistant to apoptosis. This study aimed to investigate early molecular responses within psoriasis plaques following irradiation with single equi-erythemogenic doses of clinically-effective (311 nm, narrow-band) compared to clinically-ineffective (290 nm) UVB. Forty-eight micro-dissected epidermal samples from 20 psoriatic patients were analyzed using microarrays. Our bioinformatic analysis compared gene expression between 311 nm irradiated, 290 nm irradiated and control psoriasis epidermis to specifically identify 311 nm UVB differentially expressed genes (DEGs) and their upstream regulatory pathways. Key DEGs and pathways were validated by immunohistochemical analysis. There was a dynamic induction and repression of 311 nm UVB DEGs between 6 h and 18 h, only a limited number of DEGs maintained their designated expression status between time-points. Key disease and function pathways included apoptosis, cell death, cell migration and leucocyte chemotaxis. DNA damage response pathways, NRF2-mediated oxidative stress response and P53 signalling were key nodes, interconnecting apoptosis and cell cycle arrest. Interferon signalling, dendritic cell maturation, granulocyte adhesion and atherosclerotic pathways were also differentially regulated. Consistent with these findings, top transcriptional regulators of 311 nm UVB DEGs related to: a) apoptosis, DNA damage response and cell cycle control; b) innate/acquired immune regulation and inflammation; c) hypoxia/redox response and angiogenesis; d) circadian rhythmicity; f) EGR/AP1 signalling and keratinocyte differentiation; and g) mitochondrial biogenesis. This research provides important insights into the molecular targets of 311 nm UVB, underscoring key roles for apoptosis and cell death. These and the other key pathways delineated may be central to the therapeutic effects of 311 nm in psoriasis.

ENTPD1 (CD39) Expression Inhibits UVR-Induced DNA Damage Repair through Purinergic Signaling and Is Associated with Metastasis in Human Cutaneous Squamous Cell Carcinoma

UVR and immunosuppression are major risk factors for cutaneous squamous cell carcinoma (cSCC). Regulatory T cells promote cSCC carcinogenesis, and in other solid tumors, infiltrating regulatory T cells and CD8⁺ T cells express ectonucleoside triphosphate diphosphohydrolase 1 (ENTPD1) (also known as CD39), an ectoenzyme that catalyzes the rate-limiting step in converting extracellular adenosine triphosphate (ATP) to extracellular adenosine (ADO). We previously showed that extracellular purine nucleotides influence DNA damage repair. In this study, we investigate whether DNA damage repair is modulated through purinergic signaling in cSCC. We found increased ENTPD1 expression on T cells within cSCCs when compared with the expression on T cells from blood or nonlesional skin, and accordingly, concentrations of derivative extracellular adenosine diphosphate (ADP), adenosine monophosphate (AMP), and ADO are increased in tumors compared with those in normal skin. Importantly, ENTPD1 expression is significantly higher in human cSCCs that metastasize than in those that are nonmetastatic. We also identify in a mouse model that ENTPD1 expression is induced by UVR in an IL-27-dependent manner. Finally, increased extracellular ADO is shown to downregulate the expression of NAP1L2, a nucleosome assembly protein we show to be important for DNA damage repair secondary to UVR. Together, these data suggest a role for ENTPD1 expression on skin-resident T cells to regulate DNA damage repair through purinergic signaling to promote skin carcinogenesis and metastasis.

EGR-1 plays a protective role in AMPK inhibitor compound C-induced apoptosis through ROS-induced ERK activation in skin cancer cells

Skin cancer is caused by abnormal proliferation, gene regulation and mutation of epidermis cells. Compound C is commonly used as an inhibitor of AMP-activated protein kinase (AMPK), which serves as an energy sensor in cells. Recently, compound C has been reported to induce apoptotic and autophagic death in various skin cancer cell lines via an AMPK-independent pathway. However, the signaling pathways activated in compound C-treated cancer cells remain unclear. The present oligodeoxynucleotide-based microarray screening assay showed that the mRNA expression of the zinc-finger transcription factor early growth response-1 (EGR-1), which helps regulate cell cycle progression and cell survival, was significantly upregulated in compound C-treated skin cancer cells. Compound C was demonstrated to induce EGR-1 mRNA and protein expression in a time and dose-dependent manner. Confocal imaging showed that compound C-induced EGR-1 protein expression was localized in the nucleus. Compound C was demonstrated to activate extracellular signal-regulated kinase (ERK) phosphorylation. Inhibition of this compound C-induced ERK phosphorylation downregulated the mRNA and protein expression of EGR-1. In addition, removal of compound C-induced reactive oxygen species (ROS) not only decreased ERK phosphorylation, but also inhibited compound C-induced EGR-1 expression. A functional assay showed that knock down of EGR-1 expression in cancer cells decreased the survival rate while also increasing caspase-3 activity and apoptotic marker expression after compound C treatment. However, no difference in autophagy marker light chain 3-II protein expression was observed between compound C-treated control cells and EGR-1-knockdown cells. Thus, it was concluded that that EGR-1 may antagonize compound C-induced apoptosis but not compound C-induced autophagy through the ROS-mediated ERK activation pathway.

EGR1/GADD45α Activation by ROS of Non-Thermal Plasma Mediates Cell Death in Thyroid Carcinoma

Simple Summary

Recent studies have identified new anti-cancer mechanisms of nonthermal plasma (NTP) in several cancers. However, the molecular mechanisms underlying its therapeutic effect on thyroid cancer have not been elucidated. The objective of this study was to understand the anticancer effects of NTP-activated medium (NTPAM) on thyroid cancer cells and elucidate the signaling mechanisms responsible for NTPAM-induced thyroid cancer cell death.

Abstract

(1) Background: Nonthermal plasma (NTP) induces cell death in various types of cancer cells, providing a promising alternative treatment strategy. Although recent studies have identified new mechanisms of NTP in several cancers, the molecular mechanisms underlying its therapeutic effect on thyroid cancer (THCA) have not been elucidated. (2) Methods: To investigate the mechanism of NTP-induced cell death, THCA cell lines were treated with NTP-activated medium -(NTPAM), and gene expression profiles were evaluated using RNA sequencing. (3) Results: NTPAM upregulated the gene expression of early growth response 1 (EGR1). NTPAM-induced THCA cell death was enhanced by EGR1 overexpression, whereas EGR1 small interfering RNA had the opposite effect. NTPAM-derived reactive oxygen species (ROS) affected EGR1 expression and apoptotic cell death in THCA. NTPAM also induced the gene expression of growth arrest and regulation of DNA damage-inducible 45α (GADD45A) gene, and EGR1 regulated GADD45A through direct binding to its promoter. In xenograft in vivo tumor models, NTPAM inhibited tumor progression of THCA by increasing EGR1 levels. (4) Conclusions: Our findings suggest that NTPAM induces apoptotic cell death in THCA through a novel mechanism by which NTPAM-induced ROS activates EGR1/GADD45α signaling. Furthermore, our data provide evidence that the regulation of the EGR1/GADD45α axis can be a novel strategy for the treatment of THCA.

Inhibiting calpain 1 and 2 in cyclin G associated kinase-knockout mice mitigates podocyte injury

Evidence for reduced expression of cyclin G associated kinase (GAK) in glomeruli of patients with chronic kidney disease was observed in the Nephroseq human database, and GAK was found to be associated with the decline in kidney function. To examine the role of GAK, a protein that functions to uncoat clathrin during endocytosis, we generated podocyte-specific Gak-knockout mice (Gak-KO), which developed progressive proteinuria and kidney failure with global glomerulosclerosis. We isolated glomeruli from the mice carrying the mutation to perform messenger RNA profiling and unearthed evidence for dysregulated podocyte calpain protease activity as an important contributor to progressive podocyte damage. Treatment with calpain inhibitor III specifically inhibited calpain-1/-2 activities, mitigated the degree of proteinuria and glomerulosclerosis, and led to a striking increase in survival in the Gak-KO mice. Podocyte-specific deletion of Capns1, essential for calpain-1 and calpain-2 activities, also improved proteinuria and glomerulosclerosis in Gak-KO mice. Increased podocyte calpain activity-mediated proteolysis of IκBα resulted in increased NF-κB p65-induced expression of growth arrest and DNA-damage-inducible 45 beta in the Gak-KO mice. Our results suggest that loss of podocyte-associated Gak induces glomerular injury secondary to calcium dysregulation and aberrant calpain activation, which when inhibited, can provide a protective role.

EZH2 overexpression dampens tumor-suppressive signals via an EGR1 silencer to drive breast tumorigenesis

The mechanism underlying EZH2 overexpression in breast cancer and its involvement in tumorigenesis remain poorly understood. In this study, we developed an approach to systematically identify the trans-acting factors regulating the EZH2 expression, and identified more than 20 such factors. We revealed reciprocal regulation of early growth response 1 (EGR1) and EZH2: EGR1 activates the expression of EZH2, and EZH2 represses EGR1 expression. Using CRISPR-mediated genome/epigenome editing, we demonstrated that EHZ2 represses EGR1 expression through a silencer downstream of the EGR1 gene. Deletion of the EGR1 silencer resulted in reduced cell growth, invasion, tumorigenicity of breast cancer cells, and extensive changes in gene expression, such as upregulation of GADD45, DDIT3, and RND1; and downregulation of genes encoding cholesterol biosynthesis pathway enzymes. We hypothesize that EZH2/PRC2 acts as a "brake" for EGR1 expression by targeting the EGR1 silencer, and EZH2 overexpression dampens tumor-suppressive signals mediated by EGR1 to drive breast tumorigenesis.

Nuclear Factor Kappa B Signaling Complexes in Acute Inflammation

Significance: Nuclear factor kappa B (NF-κB) is a master regulator of the inflammatory response and represents a key regulatory node in the complex inflammatory signaling network. In addition, selective NF-κB transcriptional activity on specific target genes occurs through the control of redox-sensitive NF-κB interactions. Recent Advances: The selective NF-κB response is mediated by redox-modulated NF-κB complexes with ribosomal protein S3 (RPS3), Pirin (PIR). cAMP response element-binding (CREB)-binding protein (CBP)/p300, peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α), activator protein-1 (AP-1), signal transducer and activator of transcription 3 (STAT3), early growth response protein 1 (EGR-1), and SP-1. NF-κB is cooperatively coactivated with AP-1, STAT3, EGR-1, and SP-1 during the inflammatory process, whereas NF-κB complexes with CBP/p300 and PGC-1α regulate the expression of antioxidant genes. PGC-1α may act as selective repressor of phospho-p65 toward interleukin-6 (IL-6) in acute inflammation. p65 and nuclear factor erythroid 2-related factor 2 (NRF2) compete for binding to coactivator CBP/p300 playing opposite roles in the regulation of inflammatory genes. S-nitrosylation or tyrosine nitration favors the recruitment of specific NF-κB subunits to κB sites. Critical Issues: NF-κB is a redox-sensitive transcription factor that forms specific signaling complexes to regulate selectively the expression of target genes in acute inflammation. Protein-protein interactions with coregulatory proteins, other transcription factors, and chromatin-remodeling proteins provide transcriptional specificity to NF-κB. Furthermore, different NF-κB subunits may form distinct redox-sensitive homo- and heterodimers with distinct affinities for κB sites. Future Directions: Further research is required to elucidate the whole NF-κB interactome to fully characterize the complex NF-κB signaling network in redox signaling, inflammation, and cancer.

EGR1 Transcription Factor is a Multifaceted Regulator of Matrix Production in Tendons and Other Connective Tissues

Although the transcription factor EGR1 is known as NGF1-A, TIS8, Krox24, zif/268, and ZENK, it still has many fewer names than biological functions. A broad range of signals induce Egr1 gene expression via numerous regulatory elements identified in the Egr1 promoter. EGR1 is also the target of multiple post-translational modifications, which modulate EGR1 transcriptional activity. Despite the myriad regulators of Egr1 transcription and translation, and the numerous biological functions identified for EGR1, the literature reveals a recurring theme of EGR1 transcriptional activity in connective tissues, regulating genes related to the extracellular matrix. Egr1 is expressed in different connective tissues, such as tendon (a dense connective tissue), cartilage and bone (supportive connective tissues), and adipose tissue (a loose connective tissue). Egr1 is involved in the development, homeostasis, and healing processes of these tissues, mainly via the regulation of extracellular matrix. In addition, Egr1 is often involved in the abnormal production of extracellular matrix in fibrotic conditions, and Egr1 deletion is seen as a target for therapeutic strategies to fight fibrotic conditions. This generic EGR1 function in matrix regulation has little-explored implications but is potentially important for tendon repair.

Dose and time effects of solar-simulated ultraviolet radiation on the in vivo human skin transcriptome

Background

Terrestrial ultraviolet (UV) radiation causes erythema, oxidative stress, DNA mutations and skin cancer. Skin can adapt to these adverse effects by DNA repair, apoptosis, keratinization and tanning.

Objectives

To investigate the transcriptional response to fluorescent solar‐simulated radiation (FSSR) in sun‐sensitive human skin in vivo.

Methods

Seven healthy male volunteers were exposed to 0, 3 and 6 standard erythemal doses (SED). Skin biopsies were taken at 6 h and 24 h after exposure. Gene and microRNA expression were quantified with next generation sequencing. A set of candidate genes was validated by quantitative polymerase chain reaction (qPCR); and wavelength dependence was examined in other volunteers through microarrays.

Results

The number of differentially expressed genes increased with FSSR dose and decreased between 6 and 24 h. Six hours after 6 SED, 4071 genes were differentially expressed, but only 16 genes were affected at 24 h after 3 SED. Genes for apoptosis and keratinization were prominent at 6 h, whereas inflammation and immunoregulation genes were predominant at 24 h. Validation by qPCR confirmed the altered expression of nine genes detected under all conditions; genes related to DNA repair and apoptosis; immunity and inflammation; pigmentation; and vitamin D synthesis. In general, candidate genes also responded to UVA1 (340–400 nm) and/or UVB (300 nm), but with variations in wavelength dependence and peak expression time. Only four microRNAs were differentially expressed by FSSR.

Conclusions

The UV radiation doses of this acute study are readily achieved daily during holidays in the sun, suggesting that the skin transcriptional profile of ‘typical’ holiday makers is markedly deregulated.

What's already known about this topic?

The skin's transcriptional profile underpins its adverse (i.e. inflammation) and adaptive molecular, cellular and clinical responses (i.e. tanning, hyperkeratosis) to solar ultraviolet radiation.

Few studies have assessed microRNA and gene expression in vivo in humans, and there is a lack of information on dose, time and waveband effects.

What does this study add?

Acute doses of fluorescent solar‐simulated radiation (FSSR), of similar magnitude to those received daily in holiday situations, markedly altered the skin's transcriptional profiles.

The number of differentially expressed genes was FSSR‐dose‐dependent, reached a peak at 6 h and returned to baseline at 24 h.

The initial transcriptional response involved apoptosis and keratinization, followed by inflammation and immune modulation. In these conditions, microRNA expression was less affected than gene expression.

Linked Comment:Hart. Br J Dermatol 2020; 182:1328–1329.

Plain language summary available online

Respond to this article

Protein inhibitor of activated STAT1 Ser503 phosphorylation-mediated Elk-1 SUMOylation promotes neuronal survival in APP/PS1 mice

BACKGROUND AND PURPOSE

Protein inhibitor of activated STAT1 (PIAS1) is phosphorylated by IKKα at Ser⁹⁰ in a PIAS1 E3 ligase activity-dependent manner. Whether PIAS1 is also phosphorylated at other residues and the functional significance of these additional phosphorylation events are not known. The transcription factor Elk-1 remains SUMOylated under basal conditions, but the role of Elk-1 SUMOylation in brain is unknown. Here, we examined the functional significance of PIAS1-mediated Elk-1 SUMOylation in Alzheimer's disease (AD) using the APP/PS1 mouse model of AD and amyloid β (Aβ) microinjections in vivo.

EXPERIMENTAL APPROACH

Novel phosphorylation site(s) on PIAS1 were identified by LC-MS/MS, and MAPK/ERK-mediated phosphorylation of Elk-1 demonstrated using in vitro kinase assays. Elk-1 SUMOylation by PIAS1 in brain was determined using in vitro SUMOylation assays. Apoptosis in hippocampus was assessed by measuring GADD45α expression by western blotting, and apoptosis of hippocampal neurons in APP/PS1 mice was assessed by TUNEL assay.

KEY RESULTS

Using LC-MS/MS, we identified a novel MAPK/ERK-mediated phosphorylation site on PIAS1 at Ser⁵⁰³ and showed this phosphorylation determines PIAS1 E3 ligase activity. In rat brain, Elk-1 was SUMOylated by PIAS1, which decreased Elk-1 phosphorylation and down-regulated GADD45α expression. Moreover, lentiviral-mediated transduction of Elk-1-SUMO1 reduced the number of hippocampal apoptotic neurons in APP/PS1 mice.

CONCLUSIONS AND IMPLICATIONS

MAPK/ERK-mediated phosphorylation of PIAS1 at Ser⁵⁰³ determines PIAS1 E3 ligase activity. Moreover, PIAS1 mediates SUMOylation of Elk-1, which functions as an endogenous defence mechanism against Aβ toxicity in vivo. Targeting Elk-1 SUMOylation could be considered a novel therapeutic strategy against AD.

Chronic adolescent stress sex-specifically alters central and peripheral neuro-immune reactivity in rats

Adversity during development is a reliable predictor of psychiatric disorders such as depression and anxiety which are increasingly recognized to have an immune component. We have previously demonstrated that chronic adolescent stress (CAS) in rats leads to depressive-like behavior in adulthood along with long-lasting changes to the hypothalamic-pituitary-adrenal axis and pro-inflammatory cytokine induction in the hippocampus. However, the mechanisms by which CAS promotes hippocampal inflammation are not yet defined. Here we tested the hypothesis that a history of CAS exaggerates induction of the pro-inflammatory NFκB pathway in the adult rat hippocampus without compromising the peripheral immune response. We also assessed potential sex differences because it is unclear whether females, who are twice as likely to suffer from mood disorders as males, are disproportionally affected by stress-primed inflammation. Male and female adolescent rats underwent a CAS paradigm or received no stress. Six weeks following the last stressor, all rats received a single systemic injection of either lipopolysaccharide or vehicle to unmask possible immune-priming effects of CAS. An NFκB signaling PCR array demonstrated that CAS exaggerated the expression of NFκB-related genes in the hippocampus of both males and females. Interestingly, targeted qPCR demonstrated that CAS potentiated the induction of hippocampal IL1B and REL mRNA in female rats only, suggesting that some immune effects of CAS are indeed sex-specific. In contrast to the hippocampal findings, indices of peripheral inflammation such as NFκB activity in the spleen, plasma IL-1β, IL-6, TNF-α, and corticosterone were not impacted by CAS in female rats. Despite showing no pro-inflammatory changes to hippocampal mRNA, male CAS rats displayed lower plasma corticosterone response to LPS at 2 h after injection followed by an exaggerated plasma IL-1β response at 4 h. This potentially blunted corticosterone response coupled with excessive innate immune signaling in the periphery is consistent with possible glucocorticoid resistance in males. In contrast, the effects of CAS manifested as excessive hippocampal immune reactivity in females. We conclude that while a history of exposure to chronic adolescent stress enhances adult immune reactivity in both males and females, the mechanism and manifestation of such alterations are sex-specific.

EGR-mediated control of STIM expression and function

Ca²⁺ is a ubiquitous, dynamic and pluripotent second messenger with highly context-dependent roles in complex cellular processes such as differentiation, proliferation, and cell death. These Ca²⁺ signals are generated by Ca²⁺-permeable channels located on the plasma membrane (PM) and endoplasmic reticulum (ER) and shaped by PM- and ER-localized pumps and transporters. Differences in the expression of these Ca²⁺ homeostasis proteins contribute to cell and context-dependent differences in the spatiotemporal organization of Ca²⁺ signals and, ultimately, cell fate. This review focuses on the Early Growth Response (EGR) family of zinc finger transcription factors and their role in the transcriptional regulation of Stromal Interaction Molecule (STIM1), a critical regulator of Ca²⁺ entry in both excitable and non-excitable cells.

Mechanistic Insights into CpG DNA and IL-15 Synergy in Promoting B Cell Chronic Lymphocytic Leukemia Clonal Expansion

Malignant cell growth within patients with B cell chronic lymphocytic leukemia (B-CLL) is largely restricted to lymphoid tissues, particularly lymph nodes. The recent in vitro finding that TLR-9 ligand (oligodeoxynucleotide [ODN]) and IL-15 exhibit strong synergy in promoting B-CLL growth may be particularly relevant to growth in these sites. This study shows IL-15-producing cells are prevalent within B-CLL-infiltrated lymph nodes and, using purified B-CLL cells from blood, investigates the mechanism for ODN and IL-15 synergy in driving B-CLL growth. ODN boosts baseline levels of phospho-RelA(S529) in B-CLL and promotes NF-κB-driven increases in IL15RA and IL2RB mRNA, followed by elevated IL-15Rα and IL-2/IL-15Rβ (CD122) protein. IL-15→CD122 signaling during a critical interval, 20 to 36-48 h following initial ODN exposure, is required for optimal induction of the cycling process. Furthermore, experiments with neutralizing anti-IL-15 and anti-CD122 mAbs indicate that clonal expansion requires continued IL-15/CD122 signaling during cycling. The latter is consistent with evidence of heightened IL2RB mRNA in the fraction of recently proliferated B-CLL cells within patient peripheral blood. Compromised ODN+IL-15 growth with limited cell density is consistent with a role for upregulated IL-15Rα in facilitating homotypic trans IL-15 signaling, although there may be other explanations. Together, the findings show that ODN and IL-15 elicit temporally distinct signals that function in a coordinated manner to drive B-CLL clonal expansion.

The Role of the Nuclear Factor κB Pathway in the Cellular Response to Low and High Linear Energy Transfer Radiation

Astronauts are exposed to considerable doses of space radiation during long-term space missions. As complete shielding of the highly energetic particles is impracticable, the cellular response to space-relevant radiation qualities has to be understood in order to develop countermeasures and to reduce radiation risk uncertainties. The transcription factor Nuclear Factor κB (NF-κB) plays a fundamental role in the immune response and in the pathogenesis of many diseases. We have previously shown that heavy ions with a linear energy transfer (LET) of 100–300 keV/µm have a nine times higher potential to activate NF-κB compared to low-LET X-rays. Here, chemical inhibitor studies using human embryonic kidney cells (HEK) showed that the DNA damage sensor Ataxia telangiectasia mutated (ATM) and the proteasome were essential for NF-κB activation in response to X-rays and heavy ions. NF-κB’s role in cellular radiation response was determined by stable knock-down of the NF-κB subunit RelA. Transfection of a RelA short-hairpin RNA plasmid resulted in higher sensitivity towards X-rays, but not towards heavy ions. Reverse Transcriptase real-time quantitative PCR (RT-qPCR) showed that after exposure to X-rays and heavy ions, NF-κB predominantly upregulates genes involved in intercellular communication processes. This process is strictly NF-κB dependent as the response is completely absent in RelA knock-down cells. NF-κB’s role in the cellular radiation response depends on the radiation quality.

NF-κB at the Crossroads of Normal Mammary Gland Biology and the Pathogenesis and Prevention of BRCA1-Mutated Breast Cancer

Recent studies have shown that progesterone receptor (PR)-expressing cells respond to progesterone in part through the induction of the receptor activator of NF-κB ligand (RANKL), which acts in a paracrine manner to induce expansion of a RANK-expressing luminal progenitor cell population. The RANK⁺ population in human breast tissue from carriers of BRCA1 mutations (BRCA1^mut/+) as well as the luminal progenitor population in Brca1-deficient mouse mammary glands is abnormally amplified. Remarkably, mouse Brca1^+/- and human BRCA1^mut/+ progenitor cells are able to form colonies in vitro in the absence of progesterone, demonstrating a hormone-independent proliferative capacity. Our research has demonstrated that proliferation in BRCA1-deficient cells results in a DNA damage response (DDR) that activates a persistent NF-κB signal, which supplants progesterone/RANKL signaling for an extended time period. Thus, the transcriptional targets normally activated by RANKL that promote a proliferative response in luminal progenitors can contribute to the susceptibility of mammary epithelial cells to BRCA1-mutated breast cancers as a consequence of DDR-induced NF-κB. Together, these latest findings mark substantial progress in uncovering the mechanisms driving high rates of breast tumorigenesis in BRCA1 mutation carriers and ultimately reveal possibilities for nonsurgical prevention strategies. Cancer Prev Res; 11(2); 69-80. ©2017 AACR.

Egr-1 regulates RTA transcription through a cooperative involvement of transcriptional regulators

Kaposi's sarcoma associated herpesvirus (KSHV) regulates the host cellular environment to establish life-long persistent infection by manipulating cellular signaling pathways, with approximately 1- 5% of cells undergoing lytic reactivation during the course of infection. Egr-1 (Early Growth Response Factor-1) is one such cellular transcription factor, which gets phosphorylated during the lytic phase of viral life cycle to perpetrate its function. This study demonstrates the mechanism of how Egr-1 mediates transcription of the immediate early gene, RTA (Replication and transcription activator), which is the lytic switch gene of KSHV. Egr-1 depleted KSHV infected cells exhibited reduced expression of RTA. Also, an increase in Egr-1 phosphorylation led to a higher virion production, which was suppressed in the presence of p38 and Raf inhibitors. Reporter assays showed that coexpression of Egr-1 and CBP (CREB-binding protein) enhances RTA promoter activity as compared to the expression of either Egr-1 or CBP alone. Binding of Egr-1 and CBP at RTA promoter was analyzed by chromatin immunoprecipitation assay (ChIP), which showed an enhanced accumulation during viral reactivation. Mutation in Egr-1 binding site of the RTA promoter eliminated Egr-1 response on promoter activation. Furthermore, de novo infection of THP-1 (monocytic) and HUVECs (endothelial) cells showed an upregulation of Egr-1 phosphorylation, whereas depletion of Egr-1 reduced the mRNA levels of RTA during primary infection. Together, these results demonstrate a cooperative role of Egr-1 and CBP in mediating RTA transcription, which significantly improves our understanding of the involvement of cellular factors controlling RTA transcription in KSHV pathogenesis.

Activating transcription factor 3 is crucial for antitumor activity and to strengthen the antiviral properties of Onconase

Onconase is a ribonuclease that presents both antitumor and antiviral properties linked to its ribonucleolytic activity and represents a new class of RNA-damaging drugs. It has reached clinical trials for the treatment of several cancers and human papilloma virus warts. Onconase targets different RNAs in the cell cytosol but Onconase-treated cells present features that are different from a simple arrest of protein synthesis. We have used microarray-derived transcriptional profiling to identify Onconase-regulated genes in two ovarian cancer cell lines (NCI/ADR-RES and OVCAR-8). RT-qPCR analyses have confirmed the microarray findings. We have identified a network of up-regulated genes implicated in different signaling pathways that may explain the cytotoxic effects exerted by Onconase. Among these genes, activating transcription factor 3 (ATF3) plays a central role in the key events triggered by Onconase in treated cancer cells that finally lead to apoptosis. This mechanism, mediated by ATF3, is cell-type independent. Up-regulation of ATF3 may also explain the antiviral properties of this ribonuclease because this factor is involved in halting viral genome replication, keeping virus latency or preventing viral oncogenesis. Finally, Onconase-regulated genes are different from those affected by nuclear-directed ribonucleases.

Regulation and action of early growth response 1 in bovine granulosa cells

Fibroblast growth factors (FGF) modify cell proliferation and differentiation through receptor tyrosine kinases, which stimulate the expression of transcription factors including members of the early growth response (EGR) family. In ovarian granulosa cells, most FGFs activate typical response genes, although the role of EGR proteins has not been described. In the present study, we determined the regulation of EGR mRNA by FGFs and explored the role of EGR1 in the regulation of FGF-response genes. Addition of FGF1, FGF2, FGF4 or FGF8b increased EGR1 and EGR3 mRNA levels, whereas FGF18 increased only EGR1 mRNA abundance. No mRNA encoding EGR2 or EGR4 was detected. Overexpression of EGR1 increased EGR3 mRNA levels as well as the FGF-response genes SPRY2, NR4A1 and FOSL1 and also increased the phosphorylation of MAPK3/1. Knockdown of EGR3 did not alter the ability of FGF8b to stimulate SPRY2 mRNA levels. These data demonstrate the regulation of EGR1 and EGR3 mRNA abundance by FGFs in granulosa cells and suggest that EGR1 is likely an upstream component of FGF signaling in granulosa cells.

HTLV-1 Tax upregulates early growth response protein 1 through nuclear factor-κB signaling

Human T cell leukemia virus type 1 (HTLV-1) is a complex retrovirus that causes adult T cell leukemia (ATL) in susceptible individuals. The HTLV-1-encoded oncoprotein Tax induces persistent activation of the nuclear factor-κB (NF-κB) pathway. Early growth response protein 1 (EGR1) is overexpressed in HTLV-1-infected T cell lines and ATL cells. Here, we showed that both Tax expression and HTLV-1 infection promoted EGR1 overexpression. Loss of the NF-κB binding site in the EGR1 promotor or inhibition of NF-κB activation reduced Tax-induced EGR1 upregulation. Tax mutants unable to activate NF-κB induced only slight EGR1 upregulation as compared with wild-type Tax, confirming NF-κB pathway involvement in EGR1 regulation. Tax also directly interacted with the EGR1 protein and increased endogenous EGR1 stability. Elevated EGR1 in turn promoted p65 nuclear translocation and increased NF-κB activation. These results demonstrate a positive feedback loop between EGR1 expression and NF-κB activation in HTLV-1-infected and Tax-expressing cells. Both NF-κB activation and Tax-induced EGR1 stability upregulated EGR1, which in turn enhanced constitutive NF-κB activation and facilitated ATL progression in HTLV-1-infected cells. These findings suggest EGR1 may be an effective anti-ATL therapeutic target.

Caffeic acid attenuated acetaminophen-induced hepatotoxicity by inhibiting ERK1/2-mediated early growth response-1 transcriptional activation

Caffeic acid (CA) is a natural compound abundant in fruits, coffee and plants. This study aims to investigate the involved mechanism of the therapeutic detoxification of CA against acetaminophen (APAP)-induced hepatotoxicity. CA (10, 30 mg/kg) was orally given to mice at 1 h after mice were pre-administrated with APAP (300 mg/kg). The therapeutic detoxification of CA against APAP-induced hepatotoxicity was observed by detecting serum aminotransferases, liver malondialdehyde (MDA) amount and liver histological evaluation in vivo. CA reduced APAP-induced increase in the mRNA expression of early growth response 1 (Egr1) in hepatocytes, and inhibited APAP-induced Egr1 transcriptional activation in vitro and in vivo. CA reduced the increased expression of growth arrest and DNA-damage-inducible protein (Gadd45)α induced by APAP in hepatocytes. Moreover, Egr1 siRNA reduced Gadd45α expression and reversed APAP-induced cytotoxicity in hepatocytes. Further results showed that CA blocked APAP-induced activation of extracellular-regulated protein kinase (ERK1/2) signaling cascade in vivo and in vitro. In addition, the application of ERK1/2 inhibitors (PD98059 and U0126) abrogated the nuclear translocation of Egr1 induced by APAP in hepatocytes. In conclusion, this study demonstrated the therapeutic detoxification of CA against APAP-induced liver injury, and the inhibition of CA on ERK1/2-mediated Egr1 transcriptional activation was involved in this process.

NF-kappaΒ-inducing kinase regulates stem cell phenotype in breast cancer

Breast cancer stem cells (BCSCs) overexpress components of the Nuclear factor-kappa B (NF-κB) signaling cascade and consequently display high NF-κB activity levels. Breast cancer cell lines with high proportion of CSCs exhibit high NF-κB-inducing kinase (NIK) expression. The role of NIK in the phenotype of cancer stem cell regulation is poorly understood. Expression of NIK was analyzed by quantitative RT-PCR in BCSCs. NIK levels were manipulated through transfection of specific shRNAs or an expression vector. The effect of NIK in the cancer stem cell properties was assessed by mammosphere formation, mice xenografts and stem markers expression. BCSCs expressed higher levels of NIK and its inhibition through small hairpin (shRNA), reduced the expression of CSC markers and impaired clonogenicity and tumorigenesis. Genome-wide expression analyses suggested that NIK acts on ERK1/2 pathway to exert its activity. In addition, forced expression of NIK increased the BCSC population and enhanced breast cancer cell tumorigenicity. The in vivo relevance of these results is further supported by a tissue microarray of breast cancer samples in which we observed correlated expression of Aldehyde dehydrogenase (ALDH) and NIK protein. Our results support the essential involvement of NIK in BCSC phenotypic regulation via ERK1/2 and NF-κB.

A Positive Feed-forward Loop Associating EGR1 and PDGFA Promotes Proliferation and Self-renewal in Glioblastoma Stem Cells

Glioblastomas are the most common primary brain tumors, highly vascularized, infiltrating, and resistant to current therapies. This cancer leads to a fatal outcome in less than 18 months. The aggressive behavior of glioblastomas, including resistance to current treatments and tumor recurrence, has been attributed to glioma stemlike/progenitor cells. The transcription factor EGR1 (early growth response 1), a member of a zinc finger transcription factor family, has been described as tumor suppressor in gliomas when ectopically overexpressed. Although EGR1 expression in human glioblastomas has been associated with patient survival, its precise location in tumor territories as well as its contribution to glioblastoma progression remain elusive. In the present study, we show that EGR1-expressing cells are more frequent in high grade gliomas where the nuclear expression of EGR1 is restricted to proliferating/progenitor cells. We show in primary cultures of glioma stemlike cells that EGR1 contributes to stemness marker expression and proliferation by orchestrating a PDGFA-dependent growth-stimulatory loop. In addition, we demonstrate that EGR1 acts as a positive regulator of several important genes, including SHH, GLI1, GLI2, and PDGFA, previously linked to the maintenance and proliferation of glioma stemlike cells.

4EBP1/c-MYC/PUMA and NF-κB/EGR1/BIM pathways underlie cytotoxicity of mTOR dual inhibitors in malignant lymphoid cells

The mammalian target of rapamycin (mTOR), a kinase that regulates proliferation and apoptosis, has been extensively evaluated as a therapeutic target in multiple malignancies. Rapamycin analogs, which partially inhibit mTOR complex 1 (mTORC1), exhibit immunosuppressive and limited antitumor activity, but sometimes activate survival pathways through feedback mechanisms involving mTORC2. Thus, attention has turned to agents targeting both mTOR complexes by binding the mTOR active site. Here we show that disruption of either mTOR-containing complex is toxic to acute lymphocytic leukemia (ALL) cells and identify 2 previously unrecognized pathways leading to this cell death. Inhibition of mTORC1-mediated 4EBP1 phosphorylation leads to decreased expression of c-MYC and subsequent upregulation of the proapoptotic BCL2 family member PUMA, whereas inhibition of mTORC2 results in nuclear factor-κB-mediated expression of the Early Growth Response 1 (EGR1) gene, which encodes a transcription factor that binds and transactivates the proapoptotic BCL2L11 locus encoding BIM. Importantly, 1 or both pathways contribute to death of malignant lymphoid cells after treatment with dual mTORC1/mTORC2 inhibitors. Collectively, these observations not only provide new insight into the survival roles of mTOR in lymphoid malignancies, but also identify alterations that potentially modulate the action of mTOR dual inhibitors in ALL.

Sex-specific molecular genetic response to UVB exposure in Xiphophorus maculatus skin

In both Xiphophorus fishes and humans, males are reported to have a higher incidence of melanoma than females. To better understand sex-specific differences in the molecular genetic response to UVB, we performed RNA-Seq experiments in skin of female and male Xiphophorus maculatus Jp 163 B following UVB doses of 8 or 16kJ/m(2) exposure. Male X. maculatus differentially express a significantly larger number of transcripts following exposure to 16kJ/m(2) UVB (1293 genes) compared to 8kJ/m(2) UVB (324 genes). Female skin showed differential gene expression in a larger number of transcripts following 8kJ/m(2) UVB (765) than did males; however, both females and males showed similar numbers of differentially expressed genes at 16kJ/m(2) UVB (1167 and1293, respectively). Although most modulated transcripts after UVB exposure represented the same dominant pathways in both females and males (e.g., DNA repair, circadian rhythm, and fatty acid biosynthesis), we identified genes in several pathways that exhibited opposite modulation in female vs. male skin (e.g., synaptic development, cell differentiation, wound healing, and glucose metabolism). The oppositely modulated genes appear related through uncoupling protein 3 (UCP3) that is involved with the regulation of fatty acid oxidation and serves to balance glucose and lipid metabolism. Overall, these results identify gender-specific differences in UVB-induced genetic profiles in the skin of females and males and show female and male X. maculatus respond to UVB differently through pathways involved in reactive oxygen species, wound healing, and energy homeostasis.

Regulatory circuit of PKM2/NF-κB/miR-148a/152-modulated tumor angiogenesis and cancer progression

Upregulation of the embryonic M2 isoform of pyruvate kinase (PKM2) emerges as a critical player in the cancer development and metabolism, yet the underlying mechanism of PKM2 overexpression remains to be elucidated. Here we demonstrate that IGF-1/IGF-IR regulates PKM2 expression by enhancing HIF-1α-p65 complex binding to PKM2 promoter. PKM2 expression is regulated by miR-148a/152 suppression. PKM2 directly interacts with NF-κB p65 subunit to promote EGR1 expression for regulating miR-148a/152 feedback circuit in normal cells, but not in cancer cells because of the DNA hypermethylation of miR-148a and miR-152 gene promoters. The silencing of miR-148a/152 contributes to the overexpression of PKM2, NF-κB or/and IGF-IR in some cancer cells. We show that disruption of PKM2/NF-κB/miR-148a/152 feedback loop can regulate cancer cell growth and angiogenesis, and is also associated with triple-negative breast cancer (TNBC) phenotype, which may have clinical implication for providing novel biomarker(s) of TNBC and potential therapeutic target(s) in the future.

NF-κB transcription factor role in consolidation and reconsolidation of persistent memories

Transcriptional regulation is an important molecular process required for long-term neural plasticity and long-term memory (LTM) formation. Thus, one main interest in molecular neuroscience in the last decades has been the identification of transcription factors that are involved in memory processes. Among them, the nuclear factor κB (NF-κB) family of transcription factors has gained interest due to a significant body of evidence that supports a key role of these proteins in synaptic plasticity and memory. In recent years, the interest was particularly reinforced because NF-κB was characterized as an important regulator of synaptogenesis. This function may be explained by its participation in synapse to nucleus communication, as well as a possible local role at the synapse. This review provides an overview of experimental work obtained in the last years, showing the essential role of this transcription factor in memory processes in different learning tasks in mammals. We focus the review on the consolidation and reconsolidation memory phases as well as on the regulation of immediate-early and late genes by epigenetic mechanisms that determine enduring forms of memories.

CArG-driven GADD45α activated by resveratrol inhibits lung cancer cells

We report anticarcinogenic effects of suicide gene therapy that relies on the use of resveratrol-responsive CArG elements from the Egr-1 promoter to induce GADD45α. In A549 lung cancer cells, endogenous GADD45α was not induced upon resveratrol treatment. Therefore, induction of exogenous GADD45α resulted in growth inhibition. Resveratrol transiently induced Egr-1 through ERK/JNK-ElK-1. Hence, we cloned natural or synthetic Egr-1 promoter upstream of GADD45α cDNA to create a suicide gene therapy vector. Since natural promoter may have antagonized effects, we tested synthetic promoter that contains either five, six or nine repeats of CArG elements essential in the Egr-1 promoter to drive the expression of GADD45α upon resveratrol treatment. Further analysis confirmed that both synthetic promoter and natural Egr-1 promoter were able to “turn on” the expression of GADD45α when combined with resveratrol, and subsequently led to suppression of cell proliferation and apoptosis.

Sequential activation of Elk-1/Egr-1/GADD45α by arsenic

Long-term exposure to arsenic, an environmental contaminant, leads to increased risks of cancers. In the present study, we investigated the sequential regulation of Elk-1 and Egr-1 on As³⁺-induced GADD45α, an effector of G2/M checkpoint. We found that As3+ transcriptionally induced both Elk-1 and Egr-1, and NF-κB binding site was necessary for As³⁺-induced Egr-1 promoter activity. However, specific inhibition of JNK, ERK, and Elk-1 inhibited Egr-1 induction. Furthermore, silencing of Egr-1 downregulated As³⁺-induced expression of GADD45α and ChIP assay confirmed the direct binding of Egr-1 to GADD45α promoter. Taken together, our data indicated that the increase of GADD45α in response to As³⁺ was mediated sequentially by Elk-1 and Egr-1.

Activation of Toll-like receptors by intestinal microflora reduces radiation-induced DNA damage in mice

Activation of Toll-like receptors (TLRs) signaling by intestinal microflora-derived bacterial products plays a key role in injury defence for the host. We investigated the role of TLRs activated by intestinal microflora in radiation-induced DNA damage in mice. We analyzed DNA damage induced by 2Gy γ-ray radiation in an intestinal commensal bacteria-depleted mouse model (CD group), in which TLRs (TLR2/6, TLR4 and TLR5) ligand levels in serum were reduced. Chromosomal aberrations were measured in bone marrow cells and peripheral blood leukocyte comet assays were performed. DNA damage was increased in the CD group compared with the control group. Treatment of mice with TLR agonists (CBLB502, LPS and lipopeptide) 1h before radiation resulted in a significant decrease in DNA damage. Genes induced by TLR5 activation were analyzed; activation of TLRs regulated the expression of Gadd45b, Sod2, and Rad21, which are involved in DNA damage repair. In summary, our data indicate that TLRs activation by intestinal microflora reduces DNA damage induced by radiation and regulates expression of several DNA repair genes.

A genotoxic stress-responsive miRNA, miR-574-3p, delays cell growth by suppressing the enhancer of rudimentary homolog gene in vitro

MicroRNA (miRNA) is a type of non-coding RNA that regulates the expression of its target genes by interacting with the complementary sequence of the target mRNA molecules. Recent evidence has shown that genotoxic stress induces miRNA expression, but the target genes involved and role in cellular responses remain unclear. We examined the role of miRNA in the cellular response to X-ray irradiation by studying the expression profiles of radio-responsive miRNAs and their target genes in cultured human cell lines. We found that expression of miR-574-3p was induced in the lung cancer cell line A549 by X-ray irradiation. Overexpression of miR-574-3p caused delayed growth in A549 cells. A predicted target site was detected in the 3′-untranslated region of the enhancer of the rudimentary homolog (ERH) gene, and transfected cells showed an interaction between the luciferase reporter containing the target sequences and miR-574-3p. Overexpression of miR-574-3p suppressed ERH protein production and delayed cell growth. This delay was confirmed by knockdown of ERH expression. Our study suggests that miR-574-3p may contribute to the regulation of the cell cycle in response to X-ray irradiation via suppression of ERH protein production.

Shikonin induces cell cycle arrest in human gastric cancer (AGS) by early growth response 1 (Egr1)-mediated p21 gene expression

ETHNOPHARMACOLOGICAL RELEVANCE

Lithospermum erythrorhizon, a naphthoquinone compound derived from a shikonin, has long been used as traditional Chinese medicine for treatment of various diseases, including cancer. To evaluate the cytotoxic effects of shikonin on AGS gastric cancer cells via induction of cell cycle arrest.

MATERIALS AND METHODS

We observed the effects of 12.5-100 ng/mL dosage of shikonin treatment on AGS cancer cell line with the incubation time of 6h. Cytotoxic effects were assessed by measuring the changes in the intracellular ROS, appearance of senescence phenotype, cell cycle progression, CDK and cyclins expression levels upon shikonin treatment. We also examined upon the activation of Egr1-mediated p21 expression, by siRNA transfection, Luciferase assay, and ChIP assay.

RESULTS

In this study, we found that shikonin inhibits cell proliferation by arresting cell cycle progression at the G2/M phase via modulation of p21 in AGS cells. Also, our results revealed that the p21 gene was transactivated by early growth response1 (Egr1) in response to the shikonin treatment. Transient Egr1 expression enhanced shikonin-induced p21 promoter activity, whereas the suppression of Egr1 expression by small interfering RNA attenuated the ability of shikonin to induce p21 promoter activity.

CONCLUSION

Our results suggested that the anti-proliferative activity of shikonin was due to its ability to induce cell cycle arrest via Egr1-p21 signaling pathway. Thus, the work stated here validates the traditional use of shikonin in the treatment of cancer.

The transcription factor Zif268/Egr1, brain plasticity, and memory

The capacity to remember our past experiences and organize our future draws on a number of cognitive processes that allow our brain to form and store neural representations that can be recalled and updated at will. In the brain, these processes require mechanisms of neural plasticity in the activated circuits, brought about by cellular and molecular changes within the neurons activated during learning. At the cellular level, a wealth of experimental data accumulated in recent years provides evidence that signaling from synapses to nucleus and the rapid regulation of the expression of immediate early genes encoding inducible, regulatory transcription factors is a key step in the mechanisms underlying synaptic plasticity and the modification of neural networks required for the laying down of memories. In the activated neurons, these transcriptional events are thought to mediate the activation of selective gene programs and subsequent synthesis of proteins, leading to stable functional and structural remodeling of the activated networks, so that the memory can later be reactivated upon recall. Over the past few decades, novel insights have been gained in identifying key transcriptional regulators that can control the genomic response of synaptically activated neurons. Here, as an example of this approach, we focus on one such activity-dependent transcription factor, Zif268, known to be implicated in neuronal plasticity and memory formation. We summarize current knowledge about the regulation and function of Zif268 in different types of brain plasticity and memory processes.

Novel regulatory action of ribosomal inactivation on epithelial Nod2-linked proinflammatory signals in two convergent ATF3-associated pathways

In response to excessive nucleotide-binding oligomerization domain-containing protein 2 (Nod2) stimulation caused by mucosal bacterial components, gut epithelia need to activate regulatory machinery to maintain epithelial homeostasis. Activating transcription factor 3 (ATF3) is a representative regulator in the negative feedback loop that modulates TLR-associated inflammatory responses. In the current study, the regulatory effects of ribosomal stress-induced ATF3 on Nod2-stimulated proinflammatory signals were assessed. Ribosomal inactivation caused persistent ATF3 expression that in turn suppressed proinflammatory chemokine production facilitated by Nod2. Decreased chemokine production was due to attenuation of Nod2-activated NF-κB and early growth response protein 1 (EGR-1) signals by ATF3. However, the underlying molecular mechanisms involve two convergent regulatory pathways. Although ATF3 induced by ribosomal inactivation regulated Nod2-induced EGR-1 expression epigenetically through the recruitment of histone deacetylase 1, NF-κB regulation was associated with posttranscriptional regulation by ATF3 rather than epigenetic modification. ATF3 induced by ribosomal inactivation led to the destabilization of p65 mRNA caused by nuclear entrapment of transcript-stabilizing human Ag R protein via direct interaction with ATF3. These findings demonstrate that ribosomal stress-induced ATF3 is a critical regulator in the convergent pathways between EGR-1 and NF-κB, which contributes to the suppression of Nod2-activated proinflammatory gene expression.

Dolastatin, along with Celecoxib, stimulates apoptosis by a mechanism involving oxidative stress, membrane potential change and PI3-K/AKT pathway down regulation

BACKGROUND

Phosphoinositide 3-kinase (PI3-K) is an important regulator of oncogenesis and apoptosis in various types of cancers including colon cancer. A combinatorial strategy of using Cyclooxygenase-2 inhibitor, Celecoxib and Dolastatin, a linear peptide from marine mollusks of Indian Ocean origin has shown anti-neoplastic effects in colon cancer in a rat model.

METHODS

The signal transduction pathway of PI3-K/AKT and the downstream signaling proteins had been studied in an early stage of colon carcinogenesis (DMH induced) by gene and protein expression, apoptotic studies by colonocyte apoptotic bleb assay, intracellular calcium level by fluorescence spectrometry, mitochondrial membrane potential by Rhodamine 123 flow cytometry and Reactive oxygen species measurement. Molecular docking analysis was employed to study the interaction of oncogenic proteins and the ligand, Celecoxib and Dolastatin.

RESULTS

Apoptotic cell index was lowered with DMH while both the drugs increased it and inhibited PI3-K and AKT expression. Docking studies revealed both the proteins targeted by the drugs via an ATP binding site. An increased expression of GSK-3β, pro-apoptotic protein Bad, transcription factor Egr-1, tumor suppressor protein PTEN while a downregulation of G1-associated cell cycle protein, Cyclin D1 and increased intracellular calcium as well as reactive oxygen species were observed. Also, the number of cells having a higher mitochondrial membrane potential was lowered.

CONCLUSION

Celecoxib and Dolastatin inhibited the tumor development through regulation of the PI3-K/AKT pathway which can act as a novel target for these drugs.

GENERAL SIGNIFICANCE

The anti-cancer properties of Dolastatin, a peptide isolated from marine mollusks in colorectal cancer is shown.

The mechanism of DAB2IP in chemoresistance of prostate cancer cells

PURPOSE

The docetaxel-based chemotherapy is the standard of care for castration-resistant prostate cancer (CRPC), inevitably, patients develop resistance and decease. Until now, the mechanism and predictive marker for chemoresistance are poorly understood.

EXPERIMENTAL DESIGN

Immortalized normal prostate and cancer cell lines stably manipulated with different DAB2IP expression levels were used and treated with chemotherapeutic drugs commonly used in prostate cancer therapy. Cell proliferation was measured using MTT assay; Western blot, quantitative PCR, and luciferase reporter assays were used to analyze Clusterin gene regulation by DAB2IP. Immunohistochemical analysis was conducted for evaluating DAB2IP, Clusterin and Egr-1 expression in human prostate cancer tissue.

RESULTS

DAB2IP Knockdown (KD) cells exhibited resistance to several chemotherapeutic drugs, whereas increased DAB2IP in C4-2 cells restored the drug sensitivity. Parallel, DAB2IP KD cells exhibited higher expression of Clusterin, an antiapoptotic factor, whereas elevated DAB2IP in C4-2 cells decreased Clusterin expression. Functionally, knocking down Clusterin by short-hairpin RNA or antisense oligonucleotide OGX-011 decreased drug resistance, whereas overexpressing Clusterin in C4-2 D2 enhanced drug resistance. Mechanistically, DAB2IP blocked the cross-talk between Wnt/β-catenin and IGF-I signaling, leading to the suppression of Egr-1 that is responsible for Clusterin expression. A similar result was observed in the prostate of DAB2IP knockout animals. In addition, we observed a significantly inverse correlation between DAB2IP and Egr-1 or Clusterin expression from clinical tissue microarray.

CONCLUSIONS

This study unveils a new regulation of the Egr-1/Clusterin signaling network by DAB2IP. Loss of DAB2IP expression in CRPC cells signifies their chemoresistance. Clusterin is a key target for developing more effective CRPC therapy.

Egr-1 regulates the transcription of the BRCA1 gene by etoposide

The breast cancer susceptibility gene BRCA1 encodes a nuclear protein, which functions as a tumor suppressor and is involved in gene transcription and DNA repair processes. Many families with inherited breast and ovarian cancers have mutations in the BRCA1 gene. However, only a few studies have reported on the mechanism underlying the regulation of BRCA1 expression in humans. In this study, we investigated the transcriptional regulation of BRCA1 in HeLa cells treated with etoposide. We found that three Egr-1-binding sequences (EBSs) were located at -1031, -1005, and -385 within the enhancer region of the BRCA1 gene. Forced expression of Egr-1 stimulated the BRCA1 promoter activity. EMSA data showed that Egr-1 bound directly to the EBS within the BRCA1 gene. Knockdown of Egr-1 through the expression of a small hairpin RNA (shRNA) attenuated etoposide-induced BRCA1 promoter activity. We conclude that Egr-1 targets the BRCA1 gene in HeLa cells exposed to etoposide.

Silibinin inhibits ultraviolet B radiation-induced DNA-damage and apoptosis by enhancing interleukin-12 expression in JB6 cells and SKH-1 hairless mouse skin

Recent studies have demonstrated silibinin efficacy against ultraviolet B (UVB)-induced skin carcinogenesis via different mechanisms in cell lines and animal models; however, its role in regulating interleukin-12 (IL-12), an immunomodulatory cytokine that reduces UVB-induced DNA damage and apoptosis, is not known. Here, we report that UVB irradiation causes caspase 3 and PARP cleavage and apoptosis, and addition of recombinant IL-12 or silibinin immediately after UVB significantly protects UVB-induced apoptosis in JB6 cells. IL-12 antibody-mediated blocking of IL-12 activity compromised the protective effects of both IL-12 and silibinin. Both silibinin and IL-12 also accelerated the repair of UVB-caused cyclobutane-pyrimidine dimers (CPDs) in JB6 cells. Additional studies confirmed that indeed silibinin causes a significant increase in IL-12 levels in UVB-irradiated JB6 cells as well as in mouse skin epidermis, and that similar to cell-culture findings, silibinin topical application immediately after UVB exposure causes a strong protection against UVB-induced TUNEL positive cells in epidermis possibly through a significantly accelerated repair of UVB-caused CPDs. Together, these findings for the first time provide an important insight regarding the pharmacological mechanism wherein silibinin induces endogenous IL-12 in its efficacy against UVB-caused skin damages. In view of the fact that an enhanced endogenous IL-12 level could effectively remove UVB-caused DNA damage and associated skin cancer, our findings suggest that the use of silibinin in UVB-damaged human skin would also be a practical and translational strategy to manage solar radiation-caused skin damages as well as skin cancer.