c-Abl regulates early growth response protein (EGR1) in response to oxidative stress

Regulatory mechanism of downregulation of SOD1 expression on cardiomyocyte function

BACKGROUND

Many diseases are clinically related to oxidative stress. Obstructive sleep apnea (OSA) is a common disease with oxidative stress in clinical practice, which is mostly associated with cardio-cerebrovascular diseases. It has been shown that the level of oxidative stress increases and the level of antioxidant copper zinc superoxide dismutase (SOD1) decreases in intermittent hypoxia (IH). SOD1 is one of the key antioxidant enzymes in organisms, and it can also be used as a signal transmission controller. Its abnormal expression further affects organ functions, but the specific mechanism is not yet fully clear.

METHODS

We downregulated the SOD1 gene in H9C2 cell line, using high-throughput RNA sequencing (RNA-seq) to find differentially expressed genes (DEGs) related to cardiomyocyte function by using GO and KEGG databases to annotate, enrich and analyze the metabolic pathways of DEGs.

RESULTS

Through the analysis of these functional gene changes, we can understand the regulation of SOD1 downregulation on cardiomyocyte function. The results found 213 DEGs, of which 135 genes were upregulated and 78 genes were downregulated. The upregulated DEGs were mainly enriched in biological processes such as transcriptional regulation and metabolism. The expression levels of EGR1 and NR1D1 exceeded 1 in the samples. EGR1 was reported to be involved in oxidative stress and cardiac hypertrophy, and NR1D1 played an important regulatory role in regulating inflammatory responses and reducing ROS production. The biological processes involved in downregulated DEGs mainly involve metabolism and redox processes. Among them, SCD1 and CCL2 genes were highly expressed among the genes involved in the redox process involved in SOD1. SCD1 is an important player in the regulation of cardiometabolic processes; downregulation of CCL2 reduces atherosclerosis. We found that the TNF signaling pathway, NOD-like receptor signaling pathway, and chemokine signaling pathway, which were enriched in KEGG analysis, were all associated with inflammation, and the CXCL1 and CCL7 genes are all related to inflammation.

CONCLUSION

The gene and signaling pathways involved in oxidative stress and inflammatory response process regulated by SOD1 were demonstrated. SOD1 may affect the function of the heart by affecting myocardial contraction, inflammation, lipid metabolism, and other pathways. It is inferred that they may also play a role in the process of OSA-related myocardial injury, which is worthy of attention and further study.

Amino acid restriction induces a long non-coding RNA UBA6-AS1 to regulate GCN2-mediated integrated stress response in breast cancer

Oncogene activation, massive proliferation, and increased nutrient demands often result in nutrient and oxygen deprivation in solid tumors including breast cancer (BC), leading to the induction of oxidative stress and endoplasmic reticulum (ER) stress, and subsequently triggering integrated stress response (ISR). To elucidate the role of long non-coding RNAs (lncRNAs) in the ISR of BC, we performed transcriptome analyses and identified a lncRNA, UBA6-AS1, which was upregulated upon amino acid deprivation and ER stress. UBA6-AS1 was preferentially induced in triple-negative BC (TNBC) cells deprived of arginine or glutamine, two critical amino acids required for cancer cell growth, or treated with ER stress inducers. Mechanistically, UBA6-AS1 was regulated through the GCN2/eIF2α/ATF4 pathway, one of the major routes mediating ISR in amino acid sensing. In addition, both in vitro and in vivo assays indicated that UBA6-AS1 promoted TNBC cell survival when cells encountered metabolic stress, implicating a regulatory role of UBA6-AS1 in response to intratumoral metabolic stress during tumor progression. Moreover, PARP1 expression and activity were positively regulated by the GCN2/UBA6-AS1 axis upon amino acid deprivation. In conclusion, our data suggest that UBA6-AS1 is a novel lncRNA regulating ISR upon metabolic stress induction to promote TNBC cell survival. Furthermore, the GCN2-ATF4 axis is important for UBA6-AS1 induction to enhance PARP1 activity and could serve as a marker for the susceptibility of PARP inhibitors in TNBC.

Canady Helios Cold Plasma Induces Breast Cancer Cell Death by Oxidation of Histone mRNA

Breast cancer is the most common cancer among women worldwide. Its molecular receptor marker status and mutational subtypes complicate clinical therapies. Cold atmospheric plasma is a promising adjuvant therapy to selectively combat many cancers, including breast cancer, but not normal tissue; however, the underlying mechanisms remain unexplored. Here, four breast cancer cell lines with different marker status were treated with Canady Helios Cold Plasma™ (CHCP) at various dosages and their differential progress of apoptosis was monitored. Inhibition of cell proliferation, induction of apoptosis, and disruption of the cell cycle were observed. At least 16 histone mRNA types were oxidized and degraded immediately after CHCP treatment by 8-oxoguanine (8-oxoG) modification. The expression of DNA damage response genes was up-regulated 12 h post-treatment, indicating that 8-oxoG modification and degradation of histone mRNA during the early S phase of the cell cycle, rather than DNA damage, is the primary cause of cancer cell death induced by CHCP. Our report demonstrates for the first time that CHCP effectively induces cell death in breast cancer regardless of subtyping, through histone mRNA oxidation and degradation during the early S phase of the cell cycle.

Microglial Activation Is Associated With Vasoprotection in a Rat Model of Inflammatory Retinal Vasoregression

Vascular dysfunction and vasoregression are hallmarks of a variety of inflammatory central nervous system disorders and inflammation-related retinal diseases like diabetic retinopathy. Activation of microglia and the humoral innate immune system are contributing factors. Anti-inflammatory approaches have been proposed as therapies for neurovascular diseases, which include the modulation of microglial activation. The present study aimed at investigating the effects of microglial activation by clodronate-coated liposomes on vasoregression in a model of retinal degeneration. Clodronate treatment over 5 weeks led to an increase in activated CD74⁺ microglia and completely prevented acellular capillaries and pericyte loss. Gene expression analyses indicated that vasoprotection was due to the induction of vasoprotective factors such as Egr1, Stat3, and Ahr while expression of pro-inflammatory genes remained unchanged. We concluded that activated microglia led to a shift toward induction of pleiotropic protective pathways supporting vasoprotection in neurovascular retinal diseases.

Environmental Epigenetics of Diesel Particulate Matter Toxicogenomics

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by disruptions in social communication and behavioral flexibility. Both genetic and environmental factors contribute to ASD risk. Epidemiologic studies indicate that roadway vehicle exhaust and in utero exposure to diesel particulate matter (DPM) are associated with ASD. Using the Comparative Toxicogenomics Database (CTD), we identified genes connected to DPM exposure and ASD, extracted the known enhancers/promoters of the identified genes, and integrated this with Assay for Transposase Accessible Chromatin (ATAC-seq) data from DPM-exposed human neural progenitor cells. Enhancer/promoter elements with significantly different chromosome accessibility revealed enriched DNA sequence motifs with transcription factor binding sites for EGR1. Variant extraction for linkage disequilibrium blocks of these regions followed by analysis through Genome Wide Association Studies (GWAS) revealed multiple neurological trait associations including exploratory eye movement and brain volume measurement. This approach highlights the effects of pollution on the regulatory regions of genes implicated in ASD by genetic studies, indicating convergence of genetic and environmental factors on molecular networks that contribute to ASD. Integration of publicly available data from the CTD, cell culture exposure studies, and phenotypic genetics synergize extensive evidence of chemical exposures on gene regulation for altered brain development.

Identifying functions and prognostic biomarkers of network motifs marked by diverse chromatin states in human cell lines

Epigenetic modifications play critical roles in modulating gene expression, yet their roles in regulatory networks in human cell lines remain poorly characterized. We integrated multiomics data to construct directed regulatory networks with nodes and edges labeled with chromatin states in human cell lines. We observed extensive association of diverse chromatin states and network motifs. The gene expression analysis showed that diverse chromatin states of coherent type-1 feedforward loop (C1-FFL) and incoherent type-1 feedforward loops (I1-FFL) contributed to the dynamic expression patterns of targets. Notably, diverse chromatin state compositions could help C1- or I1-FFL to control a large number of distinct biological functions in human cell lines, such as four different types of chromatin state compositions cooperating with K562-associated C1-FFLs controlling “regulation of cytokinesis,” “G1/S transition of mitotic cell cycle,” “DNA recombination,” and “telomere maintenance,” respectively. Remarkably, we identified six chromatin state-marked C1-FFL instances (HCFC1-NFYA-ABL1, THAP1-USF1-BRCA2, ZNF263-USF1-UBA52, MYC-ATF1-UBA52, ELK1-EGR1-CCT4, and YY1-EGR1-INO80C) could act as prognostic biomarkers of acute myelogenous leukemia though influencing cancer-related biological functions, such as cell proliferation, telomere maintenance, and DNA recombination. Our results will provide novel insight for better understanding of chromatin state-mediated gene regulation and facilitate the identification of novel diagnostic and therapeutic biomarkers of human cancers.

The photosensitizer verteporfin has light-independent anti-leukemic activity for Ph-positive acute lymphoblastic leukemia and synergistically works with dasatinib

Cell lines have been used for drug discovery as useful models of cancers; however, they do not recapitulate cancers faithfully, particularly from the viewpoints of microenvironmental independence. Patient-derived xenografts (PDX) are established by the transfer of primary tumor cells directly from patients into immunodeficient mice and can provide primary-like tumor cells of the amount needed at the desired time. We developed a high-throughput drug screening system using PDX cells and performed drug screening using the PDX cells of Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph⁺ ALL). We established four Ph⁺ ALL PDX mice and performed high-throughput screening of 3440 compounds using leukemia cells from the PDX mice (PDX-cell screening). The profiles of drugs selected by PDX-cell screening were markedly different from those by screening using the Ph⁺ ALL cell line. We found that verteporfin, an FDA-approved drug, exhibited strong PDX cell-specific cytotoxicity. In the validation assay, its GI₅₀ was 228 nM, 395 nM, and 538 nM in three PDX cells and 3.93 μM, 2.11 μM, and 5.61 μM in three cell lines. Although verteporfin is a photosensitizer activated by photoirradiation, its cytotoxic effects were mediated by the light-independent production of reactive oxygen species; therefore, its anti-leukemic effects were also exerted in vivo without photoirradiation. Furthermore, it exhibited synergistic effects with dasatinib, an ABL kinase inhibitor. These results indicated the potential of verteporfin as a new anti-leukemic reagent.

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.

Neurotransmission systems in Parkinson’s disease

Parkinson’s disease (PD) is histologically characterized by the accumulation of α-synuclein particles, known as Lewy bodies. The second most common neurodegenerative disorder, PD is widely known because of the typical motor manifestations of active tremor, rigidity, and postural instability, while several prodromal non-motor symptoms including REM sleep behavior disorders, depression, autonomic disturbances, and cognitive decline are being more extensively recognized. Motor symptoms most commonly arise from synucleinopathy of nigrostriatal pathway. Glutamatergic, γ-aminobutyric acid (GABA)ergic, cholinergic, serotoninergic, and endocannabinoid neurotransmission systems are not spared from the global cerebral neurodegenerative assault. Wide intrabasal and extrabasal of the basal ganglia provide enough justification to evaluate network circuits disturbance of these neurotransmission systems in PD. In this comprehensive review, English literature in PubMed, Science direct, EMBASE, and Web of Science databases were perused. Characteristics of dopaminergic and non-dopaminergic systems, disturbance of these neurotransmitter systems in the pathophysiology of PD, and their treatment applications are discussed.

Involvement of c-Abl Kinase in Microglial Activation of NLRP3 Inflammasome and Impairment in Autolysosomal System

A growing body of evidence suggests that excessive microglial activation and pesticide exposure may be linked to the etiology of PD; however, the mechanisms involved remain elusive. Emerging evidence indicates that intracellular inflammasome complex namely NLRP3 complex is involved in the recognition and execution of host inflammatory response. Thus, in the present study, we investigated the hypothesis that NLRP3 inflammasome activation is linked to rotenone (ROT)-induced microglial activation which is dependent upon a priming stimulus by a pathogen-associated molecular pattern (PAMP) or damage associated molecular pattern (DAMP), respectively. Herein using both BV2 cells and primary microglial cells, we show that LPS priming and subsequent ROT stimulation enhanced NLRP3 inflammasome activation, c-Abl and PKCδ activation, mitochondrial dysfunction, NF-κB activation, and autophagic markers, while TFEB levels were decreased dramatically. Mechanistic studies revealed c-Abl acts as a proximal signal that exacerbated the activation of the afore mentioned markers. Intriguingly, siRNA-mediated depletion or pharmacological inhibition of c-Abl via dasatinib abrogated LPS and ROT-induced microglial activation response via attenuation of NLRP3 inflammasome activation, mitochondrial oxidative stress, and ALS dysfunction. Moreover, mitoTEMPO, a mitochondrial antioxidant, attenuated NLRP3 inflammasome activation effects via blockade of c-Abl and PKCδ activation. In LPS treated mice, dasatinib attenuated NLRP3 inflammasome activation, c-Abl and PKCδ activation; and sickness behavior. Together our findings identify an exaggerated ROS/c-Abl/NLRP3 signaling axis in the heightened microglial activation response evidenced in LPS-primed ROT-stimulated microglial cells and suggest that targeting c-Abl-regulated NLRP3 inflammasome signaling offers a novel therapeutic strategy for PD treatment. Graphical Abstract ᅟ.

Silica nanoparticles induced metabolic stress through EGR1, CCND, and E2F1 genes in human mesenchymal stem cells

The SiO2 synthesized in bulk form, adopting the conventional methods for application in food industry applications, may also contain nano-sized particles. On account of the unique physico-chemical properties, the SiO2 particulates, such as size and shape, cause metabolic toxicity in cells. Poor understanding of the molecular level nanotoxicity resulting from high-volume synthetic SiO2 exposures in humans is a serious issue, since these particles may also contribute to metabolic stress-mediated chronic diseases. In the present study, we examined the structural characteristics of these nano-sized silica particles adopting SEM and dynamic light scattering (DLS) and assessed the alterations in the cell cycle induced by these silica particles in human mesenchymal stem cells (hMSCs) adopting 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell viability assay, morphological changes in the cells adopting fluorescent microscopy, cell cycle analysis adopting flow cytometry, and the expression of genes linked to cell cycle (i.e., proliferating cell nuclear antigen (PCNA), early growth response protein (EGR1), E2F transcription factor (E2F1), cyclin D1, cyclin C, and cyclin D3) adopting qPCR. The SEM and DLS studies indicated that the commercial grade SiO2-NPs were in the nano-scale range. Alterations in the cytoplasmic organization, nuclear morphology, cell cycle progression, and expression of genes linked to cell cycle-dependent metabolic stress through EGR1, CCND, and E2F1 genes were the primary indicators of metabolic stress. Overall, the results of this study demonstrate that synthetic SiO2 acutely affects hMSC through cell cycle-dependent oxidative stress gene network. The toxicity mechanisms (both acute and chronic) of food grade silica should be investigated in greater depth with special reference to food safety.

A phosphotyrosine switch determines the antitumor activity of ERβ

Estrogen receptors ERα and ERβ share considerable sequence homology yet exert opposite effects on breast cancer cell proliferation. While the proliferative role of ERα in breast tumors is well characterized, it is not clear whether the antitumor activity of ERβ can be mobilized in breast cancer cells. Here, we have shown that phosphorylation of a tyrosine residue (Y36) present in ERβ, but not in ERα, dictates ERβ-specific activation of transcription and is required for ERβ-dependent inhibition of cancer cell growth in culture and in murine xenografts. Additionally, the c-ABL tyrosine kinase and EYA2 phosphatase directly and diametrically controlled the phosphorylation status of Y36 and subsequent ERβ function. A nonphosphorylatable, transcriptionally active ERβ mutant retained antitumor activity but circumvented control by upstream regulators. Phosphorylation of Y36 was required for ERβ-mediated coactivator recruitment to ERβ target promoters. In human breast cancer samples, elevated phosphorylation of Y36 in ERβ correlated with high levels of c-ABL but low EYA2 levels. Furthermore, compared with total ERβ, the presence of phosphorylated Y36-specific ERβ was strongly associated with both disease-free and overall survival in patients with stage II and III disease. Together, these data identify a signaling circuitry that regulates ERβ-specific antitumor activity and has potential as both a prognostic tool and a molecular target for cancer therapy.

c-Abl phosphorylates α-synuclein and regulates its degradation: implication for α-synuclein clearance and contribution to the pathogenesis of Parkinson's disease

Increasing evidence suggests that the c-Abl protein tyrosine kinase could play a role in the pathogenesis of Parkinson's disease (PD) and other neurodegenerative disorders. c-Abl has been shown to regulate the degradation of two proteins implicated in the pathogenesis of PD, parkin and α-synuclein (α-syn). The inhibition of parkin's neuroprotective functions is regulated by c-Abl-mediated phosphorylation of parkin. However, the molecular mechanisms by which c-Abl activity regulates α-syn toxicity and clearance remain unknown. Herein, using NMR spectroscopy, mass spectrometry, in vitro enzymatic assays and cell-based studies, we established that α-syn is a bona fide substrate for c-Abl. In vitro studies demonstrate that c-Abl directly interacts with α-syn and catalyzes its phosphorylation mainly at tyrosine 39 (pY39) and to a lesser extent at tyrosine 125 (pY125). Analysis of human brain tissues showed that pY39 α-syn is detected in the brains of healthy individuals and those with PD. However, only c-Abl protein levels were found to be upregulated in PD brains. Interestingly, nilotinib, a specific inhibitor of c-Abl kinase activity, induces α-syn protein degradation via the autophagy and proteasome pathways, whereas the overexpression of α-syn in the rat midbrains enhances c-Abl expression. Together, these data suggest that changes in c-Abl expression, activation and/or c-Abl-mediated phosphorylation of Y39 play a role in regulating α-syn clearance and contribute to the pathogenesis of PD.

Decreased c-Abl activity in PC-3 and LNCaP prostate cancer cells overexpressing the early growth response-1 protein

Early growth response-1 (Egr-1) and the non-receptor protein tyrosine kinase (c-Abl) are 2 response genes that can act as regulators of cell growth and apoptosis in response to stress. Both Egr-1 and c-Abl regulate cell proliferation and survival in different types of cancer cells. To study the effect of overexpression of EGR-1 on the activity of c-Abl in prostate cancer cells, human PC-3 and LNCaP cells were transfected with a control vector or a vector containing the murine Egr-1 cDNA and assessed for the expression of the c-Abl gene. Cells overexpressing Egr-1 were studied with respect to apoptosis (Annexin V)/DEVDase activity, Egr-1/c-Abl activation (western blotting) and cell proliferation (MTT assay). The cells were exposed to tumor necrosis factor α (TNF-α), a known inductor of Egr-1, to c-Abl inhibitor STI-571 and to small interfering RNA (siRNA)-Egr-1, respectively. The results from our studies strongly suggest that overexpression of Egr-1 decreased c-Abl activity independent of endogenous Egr-1 inhibition by siRNA-Egr-1.

Early growth response protein 1 upregulation and nuclear translocation by 2'-benzoyloxycinnamaldehyde induces prostate cancer cell death

2'-Benzoyloxycinnamaldehyde (BCA) induces apoptosis in human cancer cells through ROS generation. BCA upregulates proapoptotic genes such as activating transcription factor 3 (ATF3), NSAID-activated gene 1 protein (NAG-1), and growth arrest and DNA-damage-inducible protein alpha (GADD45A) in prostate cancer cells. These genes are known to be induced by transcription factor early growth response protein 1 (EGR1). BCA induces significant EGR1 upregulation, while EGR1 knockdown decreases the induction of these genes with concurrent alleviation of cell death by BCA. Antioxidant glutathione pretreatment with BCA removes EGR1 expression increase, suggesting that EGR1 upregulation is dependent on oxidative stress generated by BCA. In prostate cancer cells, EGR1 localizes in the cytoplasm; however, BCA remarkably upregulates EGR1 nuclear translocalization, suggesting its possible effect as a transcriptional activator. BCA induces transient upregulation of importin-7 (IPO7) which is critical for EGR1 nuclear translocation, and IPO7 knockdown led to a significant decrease in chemosensitivity to BCA. Taken together, our findings suggest that BCA induces prostate cancer cell death via EGR1 upregulation and nuclear translocalization, followed by activation of proapoptotic target genes.

Disease progression mediated by egr-1 associated signaling in response to oxidative stress

When cellular reducing enzymes fail to shield the cell from increased amounts of reactive oxygen species (ROS), oxidative stress arises. The redox state is misbalanced, DNA and proteins are damaged and cellular transcription networks are activated. This condition can lead to the initiation and/or to the progression of atherosclerosis, tumors or pulmonary hypertension; diseases that are decisively furthered by the presence of oxidizing agents. Redox sensitive genes, like the zinc finger transcription factor early growth response 1 (Egr-1), play a pivotal role in the pathophysiology of these diseases. Apart from inducing apoptosis, signaling partners like the MEK/ERK pathway or the protein kinase C (PKC) can activate salvage programs such as cell proliferation that do not ameliorate, but rather worsen their outcome. Here, we review the currently available data on Egr-1 related signal transduction cascades in response to oxidative stress in the progression of epidemiologically significant diseases. Knowing the molecular pathways behind the pathology will greatly enhance our ability to identify possible targets for the development of new therapeutic strategies.

A molecular signature of proteinuria in glomerulonephritis

Proteinuria is the most important predictor of outcome in glomerulonephritis and experimental data suggest that the tubular cell response to proteinuria is an important determinant of progressive fibrosis in the kidney. However, it is unclear whether proteinuria is a marker of disease severity or has a direct effect on tubular cells in the kidneys of patients with glomerulonephritis. Accordingly we studied an in vitro model of proteinuria, and identified 231 “albumin-regulated genes” differentially expressed by primary human kidney tubular epithelial cells exposed to albumin. We translated these findings to human disease by studying mRNA levels of these genes in the tubulo-interstitial compartment of kidney biopsies from patients with IgA nephropathy using microarrays. Biopsies from patients with IgAN (n = 25) could be distinguished from those of control subjects (n = 6) based solely upon the expression of these 231 “albumin-regulated genes.” The expression of an 11-transcript subset related to the degree of proteinuria, and this 11-mRNA subset was also sufficient to distinguish biopsies of subjects with IgAN from control biopsies. We tested if these findings could be extrapolated to other proteinuric diseases beyond IgAN and found that all forms of primary glomerulonephritis (n = 33) can be distinguished from controls (n = 21) based solely on the expression levels of these 11 genes derived from our in vitro proteinuria model. Pathway analysis suggests common regulatory elements shared by these 11 transcripts. In conclusion, we have identified an albumin-regulated 11-gene signature shared between all forms of primary glomerulonephritis. Our findings support the hypothesis that albuminuria may directly promote injury in the tubulo-interstitial compartment of the kidney in patients with glomerulonephritis.

Low-dose radiation-induced senescent stromal fibroblasts render nearby breast cancer cells radioresistant

In addition to cell cycle arrest, DNA repair or/and apoptosis, ionizing radiation can also induce premature senescence, which could lead to very different biological consequences depending on the cell type. We show in this report that low-dose radiation-induced senescent stromal fibroblasts stimulate proliferation of cocultured breast carcinoma cells. Such effects of senescent fibroblasts appear to result from their ability to induce the expression in carcinoma cells of mitotic genes and subsequent mitotic division. The elevated proliferation of breast carcinoma cells correlates with resistance to radiation as well as to adriamycin. Of interest is the observation that exposure to lower doses (<20 cGy) augments the ability of senescent fibroblasts to promote the survival of cocultured breast carcinoma cells. The resistance appears to be mediated partially by the Akt pathway, because expression of a dominant negative Akt mutant in breast carcinoma cells results in a partial reversal of the radioresistance. The ability of fibroblasts to modulate the radiosensitivity of nearby carcinoma cells implicates the importance of targeting the stroma during therapy.

A non-Smad mechanism of fibroblast activation by transforming growth factor-beta via c-Abl and Egr-1: selective modulation by imatinib mesylate

The nonreceptor protein tyrosine kinase c-Abl regulates cell proliferation and survival. Recent studies provide evidence that implicate c-Abl as a mediator for fibrotic responses induced by transforming growth factor-beta (TGF-beta), but the precise mechanisms underlying this novel oncogene function are unknown. Here, we report that when expressed in normal fibroblasts, a constitutively active mutant of Abl that causes chronic myelogenous leukemia (CML) stimulated the expression and transcriptional activity of the early growth response factor 1 (Egr-1). Mouse embryonic fibroblasts (MEFs), lacking c-Abl, were resistant to TGF-beta stimulation. Responsiveness of these MEFs to TGF-beta could be rescued by wild-type c-Abl, but not by a kinase-deficient mutant form of c-Abl. Furthermore, Abl kinase activity was necessary for the induction of Egr-1 by TGF-beta in normal fibroblasts, and Egr-1 was required for stimulation of collagen by Bcr-Abl. Lesional skin fibroblasts in mice with bleomycin-induced fibrosis of skin displayed evidence of c-Abl activation in situ, and elevated phospho-c-Abl correlated with increased local expression of Egr-1. Collectively, these results position Egr-1 downstream of c-Abl in the fibrotic response, delineate a novel Egr-1-dependent intracellular signaling mechanism that underlies the involvement of c-Abl in certain TGF-beta responses, and identify Egr-1 as a target of inhibition by imatinib. Furthermore, the findings show in situ activation of c-Abl paralleling the upregulated tissue expression of Egr-1 that accompanies fibrosis. Pharmacological targeting of c-Abl and its downstream effector pathways may, therefore, represent a novel therapeutic approach to blocking TGF-beta-dependent fibrotic processes.

The cinnamon-derived Michael acceptor cinnamic aldehyde impairs melanoma cell proliferation, invasiveness, and tumor growth

Redox dysregulation in cancer cells represents a chemical vulnerability that can be targeted by pro-oxidant redox intervention. Dietary constituents that contain an electrophilic Michael acceptor pharmacophore may therefore display promising chemopreventive and chemotherapeutic anti-cancer activity. Here, we demonstrate that the cinnamon-derived dietary Michael acceptor trans-cinnamic aldehyde (CA) impairs melanoma cell proliferation and tumor growth. Feasibility of therapeutic intervention using high doses of CA (120 mg/kg, po, daily, 10 days) was demonstrated in a human A375 melanoma SCID mouse xenograft model. Low-micromolar concentrations (IC(50)< 10 microM) of CA, but not closely related CA derivatives devoid of Michael acceptor activity, suppressed proliferation of human metastatic melanoma cell lines (A375, G361, LOX) with G1 cell-cycle arrest, elevated intracellular ROS, and impaired invasiveness. Expression array analysis revealed that CA induced an oxidative stress response in A375 cells, up-regulating heme oxygenase 1, sulfiredoxin 1 homolog, thioredoxin reductase 1, and other genes, including the cell-cycle regulator and stress-responsive tumor suppressor gene cyclin-dependent kinase inhibitor 1A, a key mediator of G1-phase arrest. CA, but not Michael-inactive derivatives, inhibited NF-kappaB transcriptional activity and TNFalpha-induced IL-8 production in A375 cells. These findings support a previously unrecognized role of CA as a dietary Michael acceptor with potential anti-cancer activity.

Oxidative stress promotes transcriptional up-regulation of Fyn in BCR-ABL1-expressing cells

Signaling initiated by the BCR-ABL1 kinase causes chronic myelogenous leukemia (CML). Recently, we reported that expression of Fyn, a Src kinase, is heightened in CML cells and patient specimens and confers in vitro and in vivo proliferative advantages. Fyn is regulated by redox, and because BCR-ABL1 raises intracellular oxidant levels, which have been implicated in CML progression, we explored the molecular regulation of Fyn. Here we identify the transcription factors that drive redox- and BCR-ABL1-dependent Fyn expression. Promoter deletion analysis in 293T, BaF3, BaF3-p210, and K562 cells identified the region essential for basal transcriptional activity. Mutation of Sp1 and Egr1 binding sites within the essential region diminished Fyn promoter activity and identified Egr1 as conferring redox sensitivity. Gel shift and chromatin immunoprecipitation assays confirmed the binding of Sp1 and Egr1 to the promoter fragments. Importantly, knockdown of Sp1 or Egr1 with small interference RNA or inhibition of Sp1 binding by mithramycin A repressed Fyn protein expression. Our work is the first to define transcription factors that are responsible for endogenous, oxidative stress-dependent and BCR-ABL1-dependent Fyn expression.

Suppression of inflammatory signaling in monocytes from patients with coronary artery disease

Monocytes and T-cells play an important role in the development of atherosclerotic coronary artery disease (CAD). Transcriptome analysis of circulating mononuclear cells from carefully matched atherosclerotic and control patients will potentially provide insights into the pathophysiology of atherosclerosis and supply biomarkers for diagnostic purposes. From patients undergoing coronary angiography because of anginal symptoms, we carefully matched 18 patients with severe triple-vessel CAD to 13 control patients without angiographic signs of CAD. All patients were on statin and aspirin treatment. Elevated soluble-ICAM levels demonstrated increased vascular inflammation in atherosclerotic patients. RNA from circulating CD4+ T-cells, CD14+ monocytes, lipopolysaccharide-stimulated monocytes, and macrophages was subjected to genome-wide expression analysis. In CD14+ monocytes, few inflammatory genes were overexpressed in control patients, while atherosclerotic patients showed overexpression of a group of Krüppel-associated box - containing transcription factors involved in negative regulation of gene expression. These differences disappeared upon LPS-stimulation or differentiation towards macrophages. No consistent changes in T cell transcriptomes were detected. Large inter-individual variability prevented the use of single differentially expressed genes as biomarkers, while monocyte gene expression signature predicted patient status with an accuracy of 84%. In this comprehensive analysis of circulating cell transcriptomes in atherosclerotic CAD, cautious patient matching revealed only small differences in transcriptional activity in different mononuclear cell types. Only an indication of a negative feedback to inflammatory gene expression was detected in atherosclerotic patients. Transcriptome differences of circulating cells possibly play less of a role than hitherto thought in the individual patient's susceptibility to atherosclerotic CAD, when appropriately matched for clinical symptoms and medication taken.

Smad-independent transforming growth factor-beta regulation of early growth response-1 and sustained expression in fibrosis: implications for scleroderma

Transforming growth factor-beta (TGF-beta) plays a key role in scleroderma pathogenesis. The transcription factor early growth response-1 (Egr-1) mediates the stimulation of collagen transcription elicited by TGF-beta and is necessary for the development of pulmonary fibrosis in mice. Here, we report that TGF-beta causes a time- and dose-dependent increase in Egr-1 protein and mRNA levels and enhanced transcription of the Egr-1 gene via serum response elements in normal fibroblasts. The ability of TGF-beta to stimulate Egr-1 was preserved in Smad3-null mice and in explanted Smad3-null fibroblasts. The response was blocked by a specific mitogen-activated protein kinase kinase 1 (MEK1) inhibitor but not by an ALK5 kinase inhibitor. Furthermore, MEK1 was phosphorylated by TGF-beta, which was sufficient to drive Egr-1 transactivation. Stimulation by TGF-beta enhanced the transcriptional activity of Elk-1 via the MEK-extracellular signal-regulated kinase 1/2 pathway. Bleomycin-induced scleroderma in the mouse was accompanied by increased Egr-1 accumulation in lesional fibroblasts. Furthermore, biopsies of lesional skin and lung from patients with scleroderma showed increased Egr-1 levels, which were highest in early diffuse disease. Moreover, both Egr-1 mRNA and protein were elevated in explanted scleroderma skin fibroblasts in vitro. Together, these findings define a Smad-independent TGF-beta signal transduction mechanism that underlies the stimulation of Egr-1, demonstrate for the first time sustained Egr-1 up-regulation in fibrotic lesions and suggests that Egr-1 has a role in the induction and progression of fibrosis.

The chemokine interleukin-8 and the surface activation protein CD69 are markers for Bcr-Abl activity in chronic myeloid leukemia

We have identified differentially regulated genes in chronic myeloid leukemia (CML) cells upon short treatment with the broad-spectrum Bcr-Abl inhibitor dasatinib. The highly specific Bcr-Abl inhibitor nilotinib caused a very similar gene expression signature, validating the identified differentially regulated genes as a read-out of Bcr-Abl activity and implying that Bcr-Abl is the functionally central target of dasatinib in CML cells. Among the strongest downregulated genes, we have further validated the activation marker CD69 and the chemokine interleukin (IL)-8. Expression of both proteins is upregulated upon Bcr-Abl expression and inhibited by dasatinib and nilotinib. IL-8 may thus be a useful marker for the monitoring of CML inhibitor efficacy and play a potential pathophysiological role in CML.

Cooperative roles of c-Abl and Cdk5 in regulation of p53 in response to oxidative stress

The p53 tumor suppressor protein, a critical modulator of cellular stress responses, is activated through diverse mechanisms that result in its stabilization and transcriptional activation. p53 activity is controlled by transcriptional, translational, and post-translational regulation. The major mechanisms of p53 regulation occur primarily through interactions with HDM2, an E3 ubiquitin ligase that leads to p53 nuclear export and degradation. Here, we demonstrate that hydrogen peroxide-induced oxidative stress elicits down-regulation of HDM2. c-Abl mediates down-regulation of HDM2, leading to an increase of p53 level. Moreover, Cdk5 (cyclin-dependent kinase 5), a proline-directed Ser/Thr kinase, additionally increases p53 stability via post-translational modification of p53 in response to hydrogen peroxide. The p53 protein stabilized by c-Abl and Cdk5 is transcriptionally active; however, transcription of its target gene is differentially regulated with selective binding of p53 on promoter regions of its target genes by c-Abl. In addition, c-Abl modulates Cdk5 activity via phosphorylation of tyrosine 15 in cooperation with cleavage of p35 to p25. Our results show that c-Abl and Cdk5 cooperatively regulate maximal activation of p53, resulting in neuronal death in response to oxidative stress by hydrogen peroxide. These findings aid in clarifying the mechanism underlying the occurrence of neuronal apoptosis as a result of c-Abl and Cdk5-mediated p53 stabilization and transcriptional activation.

Cascade of transcriptional induction and repression during IL-2 deprivation-induced apoptosis

Apoptosis of mature T lymphocytes is an essential process for maintaining immune system homeostasis. However, the details of the molecular signaling pathways leading to T cell apoptosis are poorly understood. We used cDNA microarrays containing 15,630 murine genes to study the gene expression profile in T lymphocytes at different time points of IL-2 withdrawal. Comparison of the gene expression profiles revealed that 2% of the genes were affected by cytokine starvation. Interestingly, the apoptotic program rather seems to activate gene expression in the early phase of cell death. On the contrary, transcription was strongly repressed in later stages of apoptosis. Self-organizing map clustering of the 270 differentially expressed transcripts revealed specific temporal expression patterns supporting the idea that IL-2 deprivation triggers a tightly regulated transcriptional program to induce cell death. To validate microarray results, changes in gene expression following IL-2 deprivation were confirmed for selected genes by Northern blot. In addition, the signaling pathways created can explain the molecular events leading to T cell apoptosis, even if the T cell line used in this study might not reflect individual T cell subpopulations expressing different level of IL-2 receptor or IL-2 dependence. Taken together, these results provide novel insights into the temporal regulation of gene expression during T lymphocyte death.

Expression of the protein phosphatase 1 inhibitor KEPI is downregulated in breast cancer cell lines and tissues and involved in the regulation of the tumor suppressor EGR1 via the MEK-ERK pathway

KEPI is a protein kinase C-potentiated inhibitory protein for type 1 Ser/Thr protein phosphatases. We found no or reduced expression of KEPI in breast cancer cell lines, breast tumors and metastases in comparison to normal breast cell lines and tissues, respectively. KEPI protein expression and ubiquitous localization was detected with a newly generated antibody. Ectopic KEPI expression in MCF7 breast cancer cells induced differential expression of 95 genes, including the up-regulation of the tumor suppressors EGR1 (early growth response 1) and PTEN (phosphatase and tensin homolog), which is regulated by EGR1. We further show that the up-regulation of EGR1 in MCF7/KEPI cells is mediated by MEK-ERK signaling. The inhibition of this pathway by the MEK inhibitor UO126 led to a strong decrease in EGR1 expression in MCF7/KEPI cells. These results reveal a novel role for KEPI in the regulation of the tumor suppressor gene EGR1 via activation of the MEK-ERK MAPK pathway.

A network of p73, p53 and Egr1 is required for efficient apoptosis in tumor cells

p73, a transcription factor rarely mutated in cancer, regulates a subset of p53 target genes that cause cells to respond to genotoxic stress by growth arrest and apoptosis. p73 is produced in two main forms; only TAp73 reiterates the roles of p53, while DeltaNp73 can be oncogenic in character. We show that the TAp73 form produced by TP73 P1 promoter has five distinct Egr1-binding sites, each contributing to the transcriptional upregulation of TAp73 by Egr1 in several cell types. In contrast, TP73 P2 promoter transcribes DeltaNp73, is not induced by Egr1, but is induced by TAp73 and p53. Induction of TAp73 by genotoxic stress requires Egr1 in mouse in vivo. Newly discovered non-consensus p53-binding sites in p73, p53 and Egr1 promoters reveal inter-regulating networks and sustained expression by feedback loops in response to stress, resulting in prolonged expression of the p53 family of genes and efficient apoptosis.