Ionizing radiation down-regulates p53 protein in primary Egr-1-/- mouse embryonic fibroblast cells causing enhanced resistance to apoptosis

FOCAD/miR-491-5p, downregulated by EGR1, function as tumor suppressor by inhibiting the proliferation and migration of gastric cancer cells

Gastric cancer is a common malignant tumor in China; however, its carcinogenesis remains unknown. Focadhesin (FOCAD) is a tumor suppressor gene in gliomas, its expression, role, and mechanism in gastric cancer have not been defined. The aim of the present study was to explore the expression pattern of FOCAD in human normal tissues and cancer tissues and elucidate the role and regulatory mechanism of Early Growth Response 1 (EGR1) in FOCAD and its intron, miR-491-5p, in gastric cancer. Immuno histochemical staining revealed that FOCAD is widely and highly expressed in normal gastric mucosa, but is absent in gastric cancer tissue. Based on an association analysis FOCAD expression was found to be negatively associated with lymph node metastasis (P = 0.004); higher FOCAD levels were associated with longer survival in patients with gastric cancer (P = 0.001). MTT, colony, Transwell chamber, and flow cytometry assays revealed that siFOCAD promoted cell proliferation, growth, and migration, and inhibited apoptosis. Furthermore, bioinformatic analysis, Fluorescence reporter gene and chromatin immunoprecipitation analyses confirmed that EGR1 binds to the promoter and negatively regulates FOCAD and miR-491-5p at the transcriptional level. The overexpression of EGR1 was also found to promote cell proliferation, growth, and migration, and inhibit apoptosis. Overall, FOCAD is specifically overexpressed in the gastric mucosa and is significantly downregulated in gastric cancer. To our knowledge, this is the first study to demonstrate that FOCAD is a tumor suppressor, higher FOCAD levels might be a better prognostic marker of gastric cancer, and FOCAD/miR-491-5p may be negatively regulated by EGR1.

EGR1 Haploinsufficiency Confers a Fitness Advantage to Hematopoietic Stem Cells Following Chemotherapy

Therapy-related myeloid neoplasms (t-MNs) share many clinical and molecular characteristics with AML de novo in the elderly. One common factor is that they arise in the setting of chronic inflammation, likely because of advanced age or chemotherapy-induced senescence. Here, we examined the effect of haploinsufficient loss of the del(5q) tumor suppressor gene, EGR1, commonly deleted in high-risk MNs. In mice, under the exogenous stress of either serial transplant or successive doses of the alkylating agent N-ethyl-nitrosourea (ENU), Egr1-haploinsufficient hematopoietic stem cells (HSCs) exhibit a clonal advantage. Complete loss of EGR1 function is incompatible with transformation; mutations of EGR1 are rare and are not observed in the remaining allele in del(5q) patients, and complete knockout of Egr1 in mice leads to HSC exhaustion. Using chromatin immunoprecipitation sequencing (ChIP-seq), we identified EGR1 binding sites in human CD34+ cord blood-derived stem and progenitor cells (HSPCs) and found that EGR1 binds genes critical for stem cell differentiation, inflammatory signaling, and the DNA damage response. Notably, in the chromosome 5 sequences frequently deleted in patients, there is a significant enrichment of innate and inflammatory genes, which may confer a fitness advantage in an inflammatory environment. Short hairpin RNA (shRNA)-mediated silencing of EGR1 biases HSPCs toward a self-renewal transcriptional signature. In the absence of EGR1, HSPCs are characterized by upregulated MYC-driven proliferative signals, downregulated CDKN1A (p21), disrupted DNA damage response, and downregulated inflammation-adaptations anticipated to confer a relative fitness advantage for stem cells especially in an environment of chronic inflammation.

New Insights on the Regulatory Gene Network Disturbed in Central Areolar Choroidal Dystrophy-Beyond Classical Gene Candidates

Central areolar choroidal dystrophy (CACD) is a rare hereditary disease that mainly affects the macula, resulting in progressive and usually profound visual loss. Being part of congenital retinal dystrophies, it may have an autosomal dominant or recessive inheritance and, until now, has no effective treatment. Given the shortage of genotypic information about the disease, this work systematically reviews the literature for CACD-causing genes. Three independent researchers selected 33 articles after carefully searching and filtering the Scielo, Pubmed, Lilacs, Web of Science, Scopus, and Embase databases. Mutations of six genes (PRPH2, GUCA1A, GUCY2D, CDHR1, ABCA4, and TTLL5) are implicated in the monogenic dominant inheritance of CACD. They are functionally related to photoreceptors (either in the phototransduction process, as in the case of GUCY2D, or the recovery of retinal photodegradation in photoreceptors for GUCA1A, or the formation and maintenance of specific structures within photoreceptors for PRPH2). The identified genetic variants do not explain all observed clinical features, calling for further whole-genome and functional studies for this disease. A network analysis with the CACD-related genes identified in the systematic review resulted in the identification of another 20 genes that may influence CACD onset and symptoms. Furthermore, an enrichment analysis allowed the identification of 13 transcription factors and 4 long noncoding RNAs interacting with the products of the previously mentioned genes. If mutated or dysregulated, they may be directly involved in CACD development and related disorders. More than half of the genes identified by bioinformatic tools do not appear in commercial gene panels, calling for more studies about their role in the maintenance of the retina and phototransduction process, as well as for a timely update of these gene panels.

The Role of the Transcription Factor EGR1 in Cancer

Early growth response factor 1 (EGR1) is a transcription factor that is mainly involved in the processes of tissue injury, immune responses, and fibrosis. Recent studies have shown that EGR1 is closely related to the initiation and progression of cancer and may participate in tumor cell proliferation, invasion, and metastasis and in tumor angiogenesis. Nonetheless, the specific mechanism whereby EGR1 modulates these processes remains to be elucidated. This review article summarizes possible mechanisms of action of EGR1 in tumorigenesis and tumor progression and may serve as a reference for clinical efficacy predictions and for the discovery of new therapeutic targets.

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.

Suprabasin-derived bioactive peptides identified by plasma peptidomics

Identification of low-abundance, low-molecular-weight native peptides using non-tryptic plasma has long remained an unmet challenge, leaving potential bioactive/biomarker peptides undiscovered. We have succeeded in efficiently removing high-abundance plasma proteins to enrich and comprehensively identify low-molecular-weight native peptides using mass spectrometry. Native peptide sequences were chemically synthesized and subsequent functional analyses resulted in the discovery of three novel bioactive polypeptides derived from an epidermal differentiation marker protein, suprabasin. SBSN_HUMAN[279-295] potently suppressed food/water intake and induced locomotor activity when injected intraperitoneally, while SBSN_HUMAN[225-237] and SBSN_HUMAN[243-259] stimulated the expression of proinflammatory cytokines via activation of NF-κB signaling in vascular cells. SBSN_HUMAN[225-237] and SBSN_HUMAN[279-295] immunoreactivities were present in almost all human organs analyzed, while immunoreactive SBSN_HUMAN[243-259] was abundant in the liver and pancreas. Human macrophages expressed the three suprabasin-derived peptides. This study illustrates a new approach for discovering unknown bioactive peptides in plasma via the generation of peptide libraries using a novel peptidomic strategy.

Egr1 mediates retinal vascular dysfunction in diabetes mellitus via promoting p53 transcription

Objectives

This study focused on investigating the expression and underlying molecular mechanism of early growth response 1 (Egr1) in diabetic retinopathy.

Methods

A microarray assay was applied to examine differentially expressed genes in the retina tissues of normal rats, as well as in those of streptozotocin‐induced diabetic rats. Human retinal vascular endothelial cells (HRVECs) transfected with sh‐NC, sh‐Egr1 or sh‐Egr1+ pVax1‐p53 were cultured under high‐glucose conditions and then used to explore the role of Egr1 in vitro. The effect of Egr1 on retinal vascular dysfunction caused by diabetes was examined by sh‐Egr1 administration in vivo

Results

Early growth response 1 was found to be up‐regulated in the retinas of diabetic rats compared to those of normal rats. Down‐regulation of Egr1 in HRVECs under high‐glucose conditions inhibited the apoptosis, migration and tube formation in vitro. Moreover, sh‐Egr1 partially reduced the injurious effects of hyperglycaemia on retinal vascular function by decreasing apoptotic cells and microvascular formation in vivo. The reduction of Egr1 evidently down‐regulated the p53 expression. Overexpression of p53 rescued the inhibition of sh‐Egr1 in HRVECs under high‐glucose concentration on apoptosis, migration and tube formation in vitro.

Conclusion

Down‐regulation of Egr1 partially reduced the injurious effects of hyperglycaemia on retinal vascular function via inhibiting p53 expression.

Transcriptional Landscape of PARs in Epithelial Malignancies

G protein-coupled receptors (GPCRs), the largest family of cell receptors, act as important regulators of diverse signaling pathways. Our understanding of the impact of GPCRs in tumors is emerging, yet there is no therapeutic platform based on GPCR driver genes. As cancer progresses, it disrupts normal epithelial organization and maintains the cells outside their normal niche. The dynamic and flexible microenvironment of a tumor contains both soluble and matrix-immobilized proteases that contribute to the process of cancer advancement. An example is the activation of cell surface protease-activated receptors (PARs). Mammalian PARs are a subgroup of GPCRs that form a family of four members, PAR_1–4, which are uniquely activated by proteases found in the microenvironment. PAR₁ and PAR₂ play central roles in tumor biology, and PAR₃ acts as a coreceptor. The significance of PAR₄ in neoplasia is just beginning to emerge. PAR₁ has been shown to be overexpressed in malignant epithelia, in direct correlation with tumor aggressiveness, but there is no expression in normal epithelium. In this review, the involvement of key transcription factors such as Egr1, p53, Twist, AP2, and Sp1 that control PAR₁ expression levels specifically, as well as hormone transcriptional regulation by both estrogen receptors (ER) and androgen receptors (AR) are discussed. The cloning of the human protease-activated receptor 2; Par2 (hPar2) promoter region and transcriptional regulation of estrogen (E₂) via binding of the E₂–ER complex to estrogen response elements (ERE) are shown. In addition, evidence that TEA domain 4 (TEAD₄) motifs are present within the hPar2 promoter is presented since the YAP oncogene, which plays a central part in tumor etiology, acts via the TEAD₄ transcription factor. As of now, no information is available on regulation of the hPar3 promoter. With regard to hPar4, only data showing CpG methylation promoter regulation is available. Characterization of the PAR transcriptional landscape may identify powerful targets for cancer therapies.

DNA binding partners of YAP/TAZ

Hippo signaling plays critical roles in regulation of tissue homeostasis, organ size, and tumorigenesis by inhibiting YES-associated protein (YAP) and PDZ-binding protein TAZ through MST1/2 and LATS1/2 pathway. It is also engaged in cross-talk with various other signaling pathways, including WNT, BMPs, Notch, GPCRs, and Hedgehog to further modulate activities of YAP/TAZ. Because YAP and TAZ are transcriptional coactivators that lack DNA-binding activity, both proteins must interact with DNA-binding transcription factors to regulate target gene’s expression. To activate target genes involved in cell proliferation, TEAD family members are major DNA-binding partners of YAP/TAZ. Accordingly, YAP/TAZ were originally classified as oncogenes. However, YAP might also play tumor-suppressing role. For example, YAP can bind to DNA-binding tumor suppressors including RUNXs and p73. Thus, YAP might act either as an oncogene or tumor suppressor depending on its binding partners. Here, we summarize roles of YAP depending on its DNA-binding partners and discuss context-dependent functions of YAP/TAZ.

Expansion of adipose tissue-derived stromal cells at "physiologic" hypoxia attenuates replicative senescence

Multipotent mesenchymal stromal cells are considered as a perspective tool in cell therapy and regenerative medicine. Unfortunately, autologous cell therapy does not always provide positive outcomes in elder donors, perhaps as a result of the alterations of stem cell compartments. The mechanisms of stem and progenitor cell senescence and the factors engaged are investigated intensively. In present paper, we elucidated the effects of tissue-related O₂ on morphology, functions, and transcriptomic profile of adipose tissue-derived stromal cells (ASCs) in replicative senescence in vitro model. Replicatively senescent ASCs at ambient (20%) O₂ (12-21 passages) demonstrated an increased average cell size, granularity, reactive oxygen species level, including anion superoxide, lysosomal compartment activity, and IL-6 production. Decreased ASC viability and proliferation, as well as the change of more than 10 senescence-associated gene expression were detected (IGF1, CDKN1C, ID1, CCND1, etc). Long-term ASC expansion at low O₂ (5%) revoked in part the replicative senescence-associated alterations.

Radiation Induced Apoptosis of Murine Bone Marrow Cells Is Independent of Early Growth Response 1 (EGR1)

An understanding of how each individual 5q chromosome critical deleted region (CDR) gene contributes to malignant transformation would foster the development of much needed targeted therapies for the treatment of therapy related myeloid neoplasms (t-MNs). Early Growth Response 1 (EGR1) is a key transcriptional regulator of myeloid differentiation located within the 5q chromosome CDR that has been shown to regulate HSC (hematopoietic stem cell) quiescence as well as the master regulator of apoptosis—p53. Since resistance to apoptosis is a hallmark of malignant transformation, we investigated the role of EGR1 in apoptosis of bone marrow cells; a cell population from which myeloid malignancies arise. We evaluated radiation induced apoptosis of Egr1^+/+ and Egr1^-/- bone marrow cells in vitro and in vivo. EGR1 is not required for radiation induced apoptosis of murine bone marrow cells. Neither p53 mRNA (messenger RNA) nor protein expression is regulated by EGR1 in these cells. Radiation induced apoptosis of bone marrow cells by double strand DNA breaks induced p53 activation. These results suggest EGR1 dependent signaling mechanisms do not contribute to aberrant apoptosis of malignant cells in myeloid malignancies.

Demonstration of Tightly Radiation-Controlled Molecular Switch Based on CArG Repeats by In Vivo Molecular Imaging

PURPOSE

Promoters developed for radiogene therapy always show non-negligible transcriptional activities, even when cells are not irradiated. This study developed a tightly radiation-controlled molecular switch based on radiation responsive element (CArG) repeats for in vivo molecular imaging using the Cre/loxP system.

PROCEDURES

Different numbers of CArG repeats were cloned as a basal promoter directly, and its pre- and postirradiation transcriptional activities were analyzed by luciferase assay. Nine CArG repeats (E9) were chosen for use as a radiation-controlled molecular switch for the Cre/loxP system, and the feasibility of the switch in vitro and in vivo was demonstrated by luciferase assay and bioluminescence imaging, respectively.

RESULTS

The E9 promoter, which exhibits extremely low transcriptional activity, showed a 1.8-fold enhancement after irradiation with a clinical dose of 2 Gy. Both in vitro and in vivo results indicated that E9 is relatively inert but sufficient to trigger the Cre/loxP system. The luciferase activity of stable H1299/pSTOP-FLuc cells transfected with pE9-NLSCre and exposed to 2-Gy radiation can reach 44 % of that of the same cells transfected with pCMV-NLSCre and not subjected to irradiation. By contrast, no appreciable difference was observed in reporter gene expression in both H1299/pSTOPFluc cells and tumors transfected with pE4Pcmv-NLSCre before and after irradiation, because the strong basal transcriptional activity of the CMV promoter, which acts as a copartner of E4, masked the response of E4 to radiation.

CONCLUSIONS

Our results provide detailed insight into CArG elements as a radiation-controlled molecular switch that can facilitate the development of radiogene therapy.

Downregulation of ATG14 by EGR1-MIR152 sensitizes ovarian cancer cells to cisplatin-induced apoptosis by inhibiting cyto-protective autophagy

Cisplatin is commonly used in ovarian cancer treatment by inducing apoptosis in cancer cells as a result of lethal DNA damage. However, the intrinsic and acquired resistance to cisplatin in cancer cells remains a big challenge for improving overall survival. The cyto-protective functions of autophagy in cancer cells have been suggested as a potential mechanism for chemoresistance. Here, we reported MIR152 as a new autophagy-regulating miRNA that plays a role in cisplatin-resistance. We showed that MIR152 expression was dramatically downregulated in the cisplatin-resistant cell lines A2780/CP70, SKOV3/DDP compared with their respective parental cells, and in ovarian cancer tissues associated with cisplatin-resistance. Overexpression of MIR152 sensitized cisplatin-resistant ovarian cancer cells by reducing cisplatin-induced autophagy, enhancing cisplatin-induced apoptosis and inhibition of cell proliferation. A mouse subcutaneous xenograft tumor model using A2780/CP70 cells with overexpressing MIR152 was established and displayed decreased tumor growth in response to cisplatin. We also identified that ATG14 is a functional target of MIR152 in regulating autophagy inhibition. Furthermore, we found that EGR1 (early growth response 1) regulated the MIR152 gene at the transcriptional level. Ectopic expression of EGR1 enhanced efficacy of chemotherapy in A2780/CP70 cells. More importantly, these findings were relevant to clinical cases. Both EGR1 and MIR152 expression levels were significantly lower in ovarian cancer tissues with high levels of ERCC1 (excision repair cross-complementation group 1), a marker for cisplatin-resistance. Collectively, these data provide insights into novel mechanisms for acquired cisplatin-resistance. Activation of EGR1 and MIR152 may be a useful therapeutic strategy to overcome cisplatin-resistance by preventing cyto-protective autophagy in ovarian cancer.

Silencing Egr1 Attenuates Radiation-Induced Apoptosis in Normal Tissues while Killing Cancer Cells and Delaying Tumor Growth

Normal tissue toxicity reduces the therapeutic index of radiotherapy and decreases the quality of life for cancer survivors. Apoptosis is a key element of the radiation response in normal tissues like the hippocampus and small intestine, resulting in neurocognitive disorders and intestinal malabsorption. The Early Growth Response 1 (Egr1) transcription factor mediates radiation-induced apoptosis by activating the transcription of proapoptosis genes in response to ionizing radiation (IR). Therefore, we hypothesized that the genetic abrogation of Egr1 and the pharmacologic inhibition of its transcriptional activity could attenuate radiation-induced apoptosis in normal tissues. We demonstrated that Egr1-null mice had less apoptosis in the hippocampus and intestine following irradiation as compared with their wild-type littermates. A similar result was achieved using Mithramycin A (MMA) to prevent binding of Egr1 to target promoters in the mouse intestine. Abolishing Egr1 expression using shRNA dampened apoptosis and enhanced the clonogenic survival of irradiated HT22 hippocampal neuronal cells and IEC6 intestinal epithelial cells. Mechanistically, these events involved an abrogation of p53 induction by IR and an increase in the ratio of Bcl-2/Bax expression. In contrast, targeted silencing of Egr1 in two cancer cell lines (GL261 glioma cells and HCT116 colorectal cancer cells) was not radioprotective, since it reduced their growth while also sensitizing them to radiation-induced death. Further, Egr1 depletion delayed the growth of heterotopically implanted GL261 and HCT116 tumors. These results support the potential of silencing Egr1 in order to minimize the normal tissue complications associated with radiotherapy while enhancing tumor control.

p53 Contributes to Differentiating Gene Expression Following Exposure to Acetaminophen and Its Less Hepatotoxic Regioisomer Both In Vitro and In Vivo

The goal of the present study was to compare hepatic toxicogenomic signatures across in vitro and in vivo mouse models following exposure to acetaminophen (APAP) or its relatively nontoxic regioisomer 3′-hydroxyacetanilide (AMAP). Two different Affymetrix microarray platforms and one Agilent Oligonucleotide microarray were utilized. APAP and AMAP treatments resulted in significant and large changes in gene expression that were quite disparate, and likely related to their different toxicologic profiles. Ten transcripts, all of which have been implicated in p53 signaling, were identified as differentially regulated at all time-points following APAP and AMAP treatments across multiple microarray platforms. Protein-level quantification of p53 activity aligned with results from the transcriptomic analysis, thus supporting the implicated mechanism of APAP-induced toxicity. Therefore, the results of this study provide good evidence that APAP-induced p53 phosphorylation and an altered p53-driven transcriptional response are fundamental steps in APAP-induced toxicity.

EGR1 regulates radiation-induced apoptosis in head and neck squamous cell carcinoma

The transcription factor, early growth response 1 (EGR1) belongs to the early growth response family. EGR1 regulates the transactivation of genes involved in growth inhibition and apoptosis by ionizing radiation. The aims of the present study were to evaluate the expression of EGR1, and its relationship to prognosis, in patients with advanced laryngeal and hypopharyngeal squamous cell carcinoma (LHSCC) receiving chemoradiation therapy, and to observe the effect of EGR1 on the apoptosis of head and neck squamous cell carcinoma (HNSCC) cells treated with ionizing radiation. Expression of the EGR1 protein in tissue samples from patients with LHSCC was detected by immunohistochemistry. A high expression of the EGR1 protein was observed in 37 (67.3%) of the 55 LHSCC tissue samples examined. A high EGR1 protein expression in patients with LHSCC who were treated with chemoradiation was significantly associated with improved larynx-preservation survival (p=0.04). The 5-year disease-specific survival rate with larynx preservation was 59% in patients with a high EGR1 protein expression vs. 30% in those with a low EGR1 protein expression. In the human HNSCC cell line, PCI50, EGR1 mRNA expression was induced at 30-60 min, and EGR1 protein expression was induced at 60-120 min, after exposure to a 5 Gy dose of ionizing radiation. To evaluate the impact of EGR1 on radiation-induced apoptosis, we used small‑interfering RNA to knock down endogenous EGR1 gene expression. Cleaved caspase 3, cleaved caspase 7, and cleaved PARP were decreased, while XIAP was increased, in EGR1-knockdown PCI50 cells compared to negative control PCI50 cells, at all observed post-irradiation time points. These findings suggested that EGR1 knockdown inhibits radiation-induced apoptosis. In conclusion, EGR1 may be associated with larynx-preservation survival, through the regulation of radiation-induced apoptosis in patients with LHSCC treated with chemoradiation. Although further investigations are required to support the present study, EGR1 serves as a favorable biomarker of radiosensitivity in the treatment of LHSCC.

Inference of causal networks from time-varying transcriptome data via sparse coding

Temporal analysis of genome-wide data can provide insights into the underlying mechanism of the biological processes in two ways. First, grouping the temporal data provides a richer, more robust representation of the underlying processes that are co-regulated. The net result is a significant dimensional reduction of the genome-wide array data into a smaller set of vocabularies for bioinformatics analysis. Second, the computed set of time-course vocabularies can be interrogated for a potential causal network that can shed light on the underlying interactions. The method is coupled with an experiment for investigating responses to high doses of ionizing radiation with and without a small priming dose. From a computational perspective, inference of a causal network can rapidly become computationally intractable with the increasing number of variables. Additionally, from a bioinformatics perspective, larger networks always hinder interpretation. Therefore, our method focuses on inferring the simplest network that is computationally tractable and interpretable. The method first reduces the number of temporal variables through consensus clustering to reveal a small set of temporal templates. It then enforces simplicity in the network configuration through the sparsity constraint, which is further regularized by requiring continuity between consecutive time points. We present intermediate results for each computational step, and apply our method to a time-course transcriptome dataset for a cell line receiving a challenge dose of ionizing radiation with and without a prior priming dose. Our analyses indicate that (i) the priming dose increases the diversity of the computed templates (e.g., diversity of transcriptome signatures); thus, increasing the network complexity; (ii) as a result of the priming dose, there are a number of unique templates with delayed and oscillatory profiles; and (iii) radiation-induced stress responses are enriched through pathway and subnetwork studies.

Egr1 mediates p53-independent c-Myc-induced apoptosis via a noncanonical ARF-dependent transcriptional mechanism

c-Myc is frequently deregulated in human cancers. Although deregulated c-Myc leads to tumor growth, it also triggers apoptosis in partnership with tumor suppressors such as ARF and p53. Apoptosis induced by c-Myc is a critical fail-safe mechanism for the cell to protect against unrestrained proliferation. Despite the plethora of information on c-Myc, the molecular mechanism of how c-Myc induces both transformation and apoptosis is unclear. Oncogenic c-Myc can indirectly induce the expression of the tumor suppressor ARF, which leads to apoptosis through the stabilization of p53, but both c-Myc and ARF have apoptotic activities that are independent of p53. In cells without p53, ARF directly binds to c-Myc protein and inhibits c-Myc-induced hyperproliferation and transformation with a concomitant inhibition of canonical c-Myc target gene induction. However, ARF is an essential cofactor for p53-independent c-Myc-induced apoptosis. Here we show that ARF is necessary for c-Myc to drive transcription of a unique noncanonical target gene, Egr1. In contrast, c-Myc induces another family member, Egr2, through a canonical mechanism that is inhibited by ARF. We further demonstrate that Egr1 is essential for p53-independent c-Myc-induced apoptosis, but not ARF-independent c-Myc-induced apoptosis. Therefore, ARF binding switches the inherent activity of c-Myc from a proliferative to apoptotic protein without p53 through a unique noncanonical transcriptional mechanism. These findings also provide evidence that cofactors can differentially regulate specific transcriptional programs of c-Myc leading to different biological outcomes.

MicroRNA miR-183 functions as an oncogene by targeting the transcription factor EGR1 and promoting tumor cell migration

The transcription factor EGR1 is a tumor suppressor gene that is downregulated in many cancer types. Clinically, loss of EGR1 translates to increased tumor transformation and subsequent patient morbidity and mortality. In synovial sarcoma, the SS18-SSX fusion protein represses EGR1 expression through a direct association with the EGR1 promoter. However, the mechanism through which EGR1 becomes downregulated in other tumor types is unclear. Here, we report that EGR1 is regulated by microRNA (miR)-183 in multiple tumor types including synovial sarcoma, rhabdomyosarcoma (RMS), and colon cancer. Using an integrative network analysis, we identified that miR-183 is significantly overexpressed in these tumor types as well as in corresponding tumor cell lines. Bioinformatic analyses suggested that miR-183 could target EGR1 mRNA and this specific interaction was validated in vitro. miR-183 knockdown in synovial sarcoma, RMS, and colon cancer cell lines revealed deregulation of a miRNA network composed of miR-183-EGR1-PTEN in these tumors. Integrated miRNA- and mRNA-based genomic analyses indicated that miR-183 is an important contributor to cell migration in these tumor types and this result was functionally validated to be occurring via an EGR1-based mechanism. In conclusion, our findings have significant implications in the mechanisms underlying EGR1 regulation in cancers. miR-183 has a potential oncogenic role through the regulation of 2 tumor suppressor genes, EGR1 and PTEN, and the deregulation of this fundamental miRNA regulatory network may be central to many tumor types.

EGR-1 activation by EGF inhibits MMP-9 expression and lymphoma growth

Progression of hematologic malignancies is strongly dependent on bidirectional interactions between tumor cells and stromal cells. Expression of members of the matrix metalloproteinase (MMP) family by stromal cells is a central event during these interactions. However, although several studies have focused on the mechanisms responsible for induction of MMP in stromal cells, the signals that negatively regulate their secretion of in these cells remain largely unknown. Here, we provide evidence that MMP-9 production by stromal cells is suppressed through activation of early growth response protein 1 (EGR-1), thereby inhibiting the growth of thymic lymphoma. We found that EGR-1 expression is induced in stromal cells after contact with lymphoma cells via epidermal growth factor (EGF). Moreover, development of thymic lymphoma was inhibited when induced by lymphoma cells overexpressing EGF compared with control lymphoma cells. Using transgenic mice containing MMP-9 promoter-driven luciferase transgene in its genome, we further demonstrated that EGF/EGR-1 repressed transcriptional activation of the MMP-9 gene by stromal cells. De novo expression of EGR-1 alone by gene transfer or exposure to recombinant human EGF also inhibited MMP-9 expression. Taken together, these results indicate that EGR-1 could be a source of novel targets for therapeutic intervention in lymphoid tumors in which MMP-9 plays a critical role.

Is EGR1 a potential target for prostate cancer therapy?

Prostate cancer is a major cause of cancer-related death in American men, for which finding new therapeutic strategies remains a challenge. Early growth response-1 (EGR1) is a transcription factor involved in cell proliferation and in the regulation of apoptosis. Although it has long been considered a tumor suppressor, a wealth of new evidence shows that EGR1 promotes the progression of prostate cancer. This review addresses the paradoxes of EGR1 function. While EGR1 mediates apoptosis in response to stress and DNA damage by regulating a tumor suppressor network, it also promotes the proliferation of prostate cancer cells by a mechanism that is not fully understood. Thus, EGR1 might be targeted for prostate cancer therapy either by ectopic expression in combination with radiotherapy or chemotherapy, or by direct inhibition for systemic treatment. Possible strategies to antagonize EGR1 function in a therapeutic setting are discussed.

Preclinical biomarkers for a cyclin-dependent kinase inhibitor translate to candidate pharmacodynamic biomarkers in phase I patients

A genomics-based approach to identify pharmacodynamic biomarkers was used for a cyclin-dependent kinase inhibitory drug. R547 is a potent cyclin-dependent kinase inhibitor with a potent antiproliferative effect at pharmacologically relevant doses and is currently in phase I clinical trials. Using preclinical data derived from microarray experiments, we identified pharmacodynamic biomarkers to test in blood samples from patients in clinical trials. These candidate biomarkers were chosen based on several criteria: relevance to the mechanism of action of R547, dose responsiveness in preclinical models, and measurable expression in blood samples. We identified 26 potential biomarkers of R547 action and tested their clinical validity in patient blood samples by quantitative real-time PCR analysis. Based on the results, eight genes (FLJ44342, CD86, EGR1, MKI67, CCNB1, JUN, HEXIM1, and PFAAP5) were selected as dose-responsive pharmacodynamic biomarkers for phase II clinical trials.

Chemoprevention of pancreatic cancer: characterization of Par-4 and its modulation by 3,3' diindolylmethane (DIM)

PURPOSE

Cancer chemoprevention is defined as the use of natural, synthetic, or biological agents to suppress, reverse or prevent the carcinogenic process from turning into aggressive cancer. Prostate apoptosis response-4 (Par-4) is a unique pro-apoptotic protein that selectively induces apoptosis in prostate cancer cells. However, its role in other malignancies has not been fully explored. This study tries to identify the functional significance of Par-4 in pancreatic cancer.

METHODS

Multiple molecular techniques such as Western blot analysis, trypan blue assay for cell viability, MTT assay for cell growth inhibition and Histone/DNA ELISA for apoptosis were used.

RESULTS

Western blot analysis revealed that 3,3'-diindolylmethane (DIM) a chemopreventive agent, specifically its more bioavailable formulation, B-DIM, at low doses (20 micromol/L) induces Par-4, in L3.6pl and Colo-357 pancreatic cancer cells. At similar doses, DIM reduced cell viability and caused cell growth inhibition and apoptosis. Moreover, DIM pre-treatment sensitized the cells to cytotoxic action of chemotherapeutic drug gemcitabine through up-regulation of Par-4.

CONCLUSION

The induction of Par-4 is indirectly related to increased sensitivity and cell death through apoptosis. To our knowledge the results reported here showed, for the first time, the induction of Par-4 by chemopreventive agents, in general, and DIM, in particular, in pancreatic cancer cells in vitro.

Egr1 and Gas6 facilitate the adaptation of HEK-293 cells to serum-free media by conferring enhanced viability and higher growth rates

Animal-derived serum is an essential media supplement for mammalian cells in cell culture. For a number of reasons including cost, regulatory concerns, lot inconsistency, potential contamination with adventitious agents, and down-stream processing it is desirable to eliminate the use of serum. Existing protocols designed to adapt cells to serum-free media (SFM) are time-consuming and provide little insight into how the cells adapt. To better understand the physiological responses associated with serum withdrawal and to expedite the adaptation process, a Human Embryonic Kidney-293 (HEK-293) cell line was propagated in 10% fetal bovine serum (FBS) and was progressively adapted to SFM and analyzed at specific serum levels by oligonucleotide microarrays. Of the differentially expressed genes two, early growth response 1 (egr1) and growth arrest specific 6 (gas6), were selected for further analysis based on their level of differential expression, overall expression patterns, and proposed functionalities. HEK-293 cells, propagated in 10% FBS were transfected with egr1 or gas6 and then adapted to SFM. Results indicated that higher expression of either gene moderately enhanced the ability of both cell lines to adapt to SFM. Egr1 appeared to have a greater impact on adaptability than gas6. Results also indicated that specific protein production was unaltered when the expression of egr1 was increased. Flow cytometric analysis revealed increased expression of egr1 was associated with an increase in the percentage of cells in the G2/M phases. These results indicate that enhanced expression of egr1 or gas6 facilitate adaptation to SFM by improving growth and viability.

Role of tumor necrosis factor-alpha and TRAIL in high-dose radiation-induced bystander signaling in lung adenocarcinoma

In the present study, ionizing radiation (IR)-induced bystander effects were investigated in two lung cancer cell lines. A549 cells were found to be more resistant to radiation-conditioned medium (RCM) obtained from A549 cells when compared with the H460 exposed to RCM procured from H460 cells. Significant release of tumor necrosis factor-alpha (TNF-alpha) was observed in A549 cells after IR/RCM exposure, and the survival was reversed with neutralizing antibody against TNF-alpha. In H460 cells, significant release of TNF-related apoptosis-inducing ligand (TRAIL), but not TNF-alpha, was observed in response to IR, RCM exposure, or RCM + 2Gy, and neutralizing antibody against TRAIL diminished clonogenic inhibition. Mechanistically, TNF-alpha present in RCM of A549 was found to mediate nuclear factor-kappaB (NF-kappaB) translocation to nucleus, whereas the soluble TRAIL present in RCM of H460 cells mobilized the nuclear translocation of PAR-4 (a proapoptotic protein). Analysis of IR-inducible early growth response-1 (EGR-1) function showed that EGR-1 was functional in A549 cells but not in H460 cells. A significant decrease in RCM-mediated apoptosis was observed in both A549 cells stably expressing small interfering RNA EGR-1 and EGR-1(-/-) mouse embryonic fibroblast cells. Thus, the high-dose IR-induced bystander responses in A549 may be dependent on the EGR-1 function and its target gene TNF-alpha. These findings show that the reduced bystander response in A549 cells is due to activation of NF-kappaB signaling by TNF-alpha, whereas enhanced response to IR-induced bystander signaling in H460 cells was due to release of TRAIL associated with nuclear translocation of PAR-4.

Transcriptional regulation of human protease-activated receptor 1: a role for the early growth response-1 protein in prostate cancer

Transcriptional regulation plays a central role in the molecular pathways underlying preferential cancer growth and metastasis. In the present study, we investigated the regulation of human protease-activated receptor 1 (hPar1) gene overexpression in the malignant androgen hormone-resistant phase. We found increased hPar1 RNA chain elongation and no change in message stability in cells with high levels of PAR1 expression, indicating that increased transcription is largely responsible for the overexpression of hPar1 in prostate tumor progression. Enforced expression of early growth response-1 (Egr-1) plasmid markedly enhanced luciferase activity driven by the hPar1 promoter. The neuroendocrine peptide bombesin significantly induced hPar1 expression and increased the ability of the cells to invade Matrigel, an effect abolished by expression of hPar1 small interfering RNA, showing the importance of hPAR1 in invasion. Bombesin also markedly enhanced Egr-1 binding to the hPar1 promoter in vivo and in vitro. These data suggest that bombesin enhances Egr-1 expression leading to increased hPar1 transcription, thereby increasing PAR1 expression and function. Immunohistostaining of prostate tissue biopsy specimens revealed a direct correlation between the degree of prostate cancer malignancy, PAR1 expression, and EGR-1 expression. Altogether, we show that transcriptional regulation of hPar1 in the aggressive hormone-resistant prostate cancer stage is controlled in part by the transcription factor Egr-1 and may play a central role in invasiveness, an important indicator of malignancy.

EPO modulation of cell-cycle regulatory genes, and cell division, in primary bone marrow erythroblasts

Erythropoietin (EPO's) actions on erythroblasts are ascribed largely to survival effects. Certain studies, however, point to EPO-regulated proliferation. To investigate this problem in a primary system, Kit(pos)CD71(high) erythroblasts were prepared from murine bone marrow, and were first used in the array-based discovery of EPO-modulated cell-cycle regulators. Five cell-cycle progression factors were rapidly up-modulated: nuclear protein 1 (Nupr1), G1 to S phase transition 1 (Gspt1), early growth response 1 (Egr1), Ngfi-A binding protein 2 (Nab2), and cyclin D2. In contrast, inhibitory cyclin G2, p27/Cdkn1b, and B-cell leukemia/lymphoma 6 (Bcl6) were sharply down-modulated. For CYCLIN G2, ectopic expression also proved to selectively attenuate EPO-dependent UT7epo cell-cycle progression at S-phase. As analyzed in primary erythroblasts expressing minimal EPO receptor alleles, EPO repression of cyclin G2 and Bcl6, and induction of cyclin D2, were determined to depend on PY343 (and Stat5) signals. Furthermore, erythroblasts expressing a on PY-null EPOR-HM allele were abnormally distributed in G0/G1. During differentiation divisions, EPOR-HM Ter119(pos) erythroblasts conversely accumulated in S-phase and faltered in an apparent EPO-directed transition to G0/G1. EPO/EPOR signals therefore control the expression of select cell-cycle regulatory genes that are proposed to modulate stage-specific decisions for erythroblast cell-cycle progression.

Downregulation of PAR-4, a pro-apoptotic gene, in pancreatic tumors harboring K-ras mutation

Oncogenic ras is known to inhibit cell death and growth inhibitory genes and activate prosurvival genes. Proapoptotic gene PAR-4, has been found to be downregulated by oncogenic ras. Since pancreatic tumors harbor a high incidence of K-ras point mutations, we hypothesized that oncogenic K-ras might influence the function and expression of PAR-4. PAR-4 expression levels were analyzed in 4 established pancreatic tumor cell lines, 10 normal pancreatic tissues, 44 frozen tumor tissues and 25 paraffin-embedded pancreatic adenocarcinoma samples by Real Time RT-PCR, Western blot analysis and immunohistochemistry. K-ras mutational status was analyzed by allele-specific oligonucleotide-hybridization. Expression levels of PAR-4 were correlated with the K-ras mutational status and clinical characteristics. Further, modulation of endogenous PAR-4 was tested by transiently expressing oncogenic ras in a wild-type K-ras pancreatic cancer cell line, BxPC-3. Three cell lines with K-ras mutations showed low levels of PAR-4 when compared to a normal pancreatic tissue. Of 44 frozen tumors, 16 showed appreciable upregulation of Par mRNA and 27 showed significant downregulation of PAR-4 mRNA when compared to normal pancreatic tissue and 1 had levels equivalent to normal pancreatic tissue. Of 25 paraffin-embedded tumors, 9 showed downregulation of PAR-4 protein and this downregulation of PAR-4 correlated significantly with K-ras mutational status (p < 0.00002). In addition, the presence of PAR-4 mRNA or protein expression in pancreatic tumors correlated with prolonged survival. Transient overexpression of oncogenic ras in wild-type K-ras BxPC-3 cells significantly downregulated the endogenous PAR-4 protein levels and conferred accelerated growth. Thus, downregulation or loss of PAR-4 expression by oncogenic ras may provide a selective survival advantage for pancreatic tumors, through inhibition of proapoptotic pathway mediated by PAR-4.

Role of early growth response-1 (Egr-1) in interleukin-13-induced inflammation and remodeling

IL-13 is an important stimulator of inflammation and tissue remodeling at sites of Th2 inflammation, which plays a key role in the pathogenesis of a variety of human disorders. We hypothesized that the ubiquitous transcription factor, early growth response-1 (Egr-1), plays a key role in IL-13-induced tissue responses. To test this hypothesis we compared the expression of Egr-1 and related moieties in lungs from wild type mice and transgenic mice in which IL-13 was overexpressed in a lung-specific fashion. We simultaneously characterized the effects of a null mutation of Egr-1 on the tissue effects of transgenic IL-13. These studies demonstrate that IL-13 stimulates Egr-1 via an Erk1/2-independent Stat6-dependent pathway(s). They also demonstrate that IL-13 is a potent stimulator of eosinophil- and mononuclear cell-rich inflammation, alveolar remodeling, and tissue fibrosis in mice with wild type Egr-1 loci and that these alterations are ameliorated in the absence of Egr-1. Lastly, they provide insights into the mechanisms of these processes by demonstrating that IL-13 stimulates select CC and CXC chemokines (MIP-1alpha/CCL-3, MIP-1beta/CCL-4, MIP-2/CXCL2/3, MCP-1/CCL-2, MCP-2/CCL-8, MCP-3/CCL-7, MCP-5/CCL-12, KC/CXCL-1, and Lix/CXCL-5), matrix metalloproteinase-9, tissue inhibitor of metalloproteinase-1, and apoptosis regulators (caspase-3, -6, -8, and -9 and Bax) and activates transforming growth factor-beta1 and pulmonary caspases via Egr-1-dependent pathways. These studies demonstrate that Egr-1 plays a key role in the pathogenesis of IL-13-induced inflammatory and remodeling responses.

Expression of Egr-1 gene and its correlation with the oncogene proteins in non-irradiated and irradiated esophageal squamous cell carcinoma

We study the expression of early growth response gene-1 (Egr-1 gene) in non-irradiated and irradiated human esophageal cancer tissues, and its relationship with the expression of C-fos, C-jun onco-proteins as well as Egr-1 target gene proteins P53, Rb and Bax expression. In situ hybridization (ISH) and immunohistochemistry (IHC) were used respectively to detect Egr-1 mRNA, Egr-1, C-fos, C-jun, P53, Rb and Bax proteins in 80 surgically resected non-irradiated and irradiated tumor specimens of esophageal squamous cell carcinoma. Egr-1 gene mRNA and Bax protein were located in the cytoplasm, whereas Egr-1, C-fos, C-jun, P53, Rb proteins were located in the nuclei. Egr-1 was expressed in nine out of 40 cases (22.5%) of non-irradiated and 23 of 40 cases (57.5%) of irradiated tumor specimens. No correlation was found between Egr-1 gene expression and C-fos, C-jun onco-proteins expression, neither was any correlation disclosed between Egr-1 gene expression with its target gene protein expression. Patients who underwent radiotherapy with Egr-1 overexpressed in their cancer tissue had better prognosis. Radiotherapy up-regulates Egr-1 expression in esophageal carcinoma. Egr-1 overexpression may be a potential radiation response gene marker and may play an important role in prognosis of esophageal squamous cell carcinoma.

Early growth response 1 acts as a tumor suppressor in vivo and in vitro via regulation of p53

The early growth response 1 (Egr1) gene is a transcription factor that acts as both a tumor suppressor and a tumor promoter. Egr1-null mouse embryo fibroblasts bypass replicative senescence and exhibit a loss of DNA damage response and an apparent immortal growth, suggesting loss of p53 functions. Stringent expression analysis revealed 266 transcripts with >2-fold differential expression in Egr1-null mouse embryo fibroblasts, including 143 known genes. Of the 143 genes, program-assisted searching revealed 66 informative genes linked to Egr1. All 66 genes could be placed on a single regulatory network consisting of three branch points of known Egr1 target genes: TGFbeta1, IL6, and IGFI. Moreover, 19 additional genes that are known targets of p53 were identified, indicating that p53 is a fourth branch point. Electrophoretic mobility shift assay as well as chromatin immunoprecipitation confirmed that p53 is a direct target of Egr1. Because deficient p53 expression causes tumors in mice, we tested the role of Egr1 in a two-step skin carcinogenesis study (144 mice) that revealed a uniformly accelerated development of skin tumors in Egr1-null mice (P < 0.005). These studies reveal a new role for Egr1 as an in vivo tumor suppressor.

Phosphodiesterase-5 inhibitor sildenafil preconditions adult cardiac myocytes against necrosis and apoptosis. Essential role of nitric oxide signaling

We investigated the effect of sildenafil in protection against necrosis or apoptosis in cardiomyocytes. Adult mouse ventricular myocytes were treated with sildenafil (1 or 10 microM) for 1 h before 40 min of simulated ischemia (SI). Necrosis was determined by trypan blue exclusion and lactate dehydrogenase release following SI alone or plus 1 or 18 h of reoxygenation (RO). Apoptosis was assessed by terminal deoxynucleotidyl transferase-mediated nick end labeling assay and mitochondrial membrane potential measured using a fluorescent probe 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolyl-carbocyanine iodide (JC-1). Sildenafil reduced necrosis as indicated by decrease in trypan blue-positive myocytes and leakage of lactate dehydrogenase compared with untreated cells after either SI or SI-RO. The number of terminal deoxynucleotidyl transferase-mediated nick end labeling-positive myocytes or loss of JC-1 fluorescence following SI and 18 h of RO was attenuated in the sildenafil-treated group with concomitant inhibition of caspase 3 activity. An early increase in Bcl-2 to Bax ratio with sildenafil treatment was also observed in myocytes after SI-RO. The increase of Bcl-2 expression by sildenafil was inhibited by nitric-oxide synthase (NOS) inhibitor, L-nitro-amino-methyl-ester. The drug also enhanced mRNA and protein content of inducible NOS (iNOS) and endothelial NOS (eNOS) in the myocytes. Sildenafil-induced protection against necrosis and apoptosis was absent in the myocytes derived from iNOS knock-out mice and was attenuated in eNOS knock-out myocytes. The up-regulation of Bcl-2 expression by sildenafil was also absent in iNOS-deficient myocytes. Reverse transcription-PCR, Western blots, and immunohistochemical assay confirmed the expression of phosphodiesterase-5 in mouse cardiomyocytes. These data provide strong evidence for a direct protective effect of sildenafil against necrosis and apoptosis through NO signaling pathway. The results may have possible therapeutic potential in preventing myocyte cell death following ischemia/reperfusion.

Decreased expression of early growth response-1 and its role in uterine leiomyoma growth

Expression of early growth response (Egr)-1, a transcriptional factor implicated in growth regulation, is suppressed in several malignant tumors. The present study investigated the expression of Egr-1 and related genes in uterine leiomyoma and normal myometrium to determine possible contributions of Egr-1 to neoplastic growth in leiomyoma cells. Levels of Egr-1 transcripts were decreased in all leiomyomas (n = 20) to approximately 10% of levels in corresponding myometrium, where basal expression was high. Preoperative leuprorelin acetate therapy increased levels of Egr-1 mRNA in normal myometrium only. Northern blot analysis using additional sample sets (n = 5) revealed the full-length Egr-1 transcript. Western blot analysis (n = 5) confirmed decreased expression of Egr-1 protein. Southern blot analysis of the Egr-1 gene and microsatellite analysis of the chromosomal location at 5q31 (D5S414, D5S500, and D5S476) revealed neither DNA recombination nor loss of heterozygosity in leiomyomas. Moreover, Egr-1 retained identical responsiveness to phorbol 12-myristate 13-acetate in primary cultures derived from both leiomyoma and normal tissues. Electrophoretic mobility shift analysis revealed that phorbol 12-myristate 13-acetate-induced Egr-1 in leiomyoma cells retained DNA binding ability. Egr-1 thus appears functionally intact in leiomyoma cells. Finally, consistent with the role of Egr-1 in growth inhibition, transfection of Egr-1 expression vector into a myometrial cell line (KW) that expresses low levels of Egr-1 and displays rapid growth inhibited thymidine uptake in these cells. Egr-1 may display tumor-suppressing activity and offers a potential target for leiomyoma management.

Early growth response gene 1-mediated apoptosis is essential for transforming growth factor beta1-induced pulmonary fibrosis

Fibrosis and apoptosis are juxtaposed in pulmonary disorders such as asthma and the interstitial diseases, and transforming growth factor (TGF)-β₁ has been implicated in the pathogenesis of these responses. However, the in vivo effector functions of TGF-β₁ in the lung and its roles in the pathogenesis of these responses are not completely understood. In addition, the relationships between apoptosis and other TGF-β₁–induced responses have not been defined. To address these issues, we targeted bioactive TGF-β₁ to the murine lung using a novel externally regulatable, triple transgenic system. TGF-β₁ produced a transient wave of epithelial apoptosis that was followed by mononuclear-rich inflammation, tissue fibrosis, myofibroblast and myocyte hyperplasia, and septal rupture with honeycombing. Studies of these mice highlighted the reversibility of this fibrotic response. They also demonstrated that a null mutation of early growth response gene (Egr)-1 or caspase inhibition blocked TGF-β₁–induced apoptosis. Interestingly, both interventions markedly ameliorated TGF-β₁–induced fibrosis and alveolar remodeling. These studies illustrate the complex effects of TGF-β₁ in vivo and define the critical role of Egr-1 in the TGF-β₁ phenotype. They also demonstrate that Egr-1–mediated apoptosis is a prerequisite for TGF-β₁–induced fibrosis and remodeling.

Developmental regulation of galactokinase in suckling mouse liver by the Egr-1 transcription factor

The numerous changes in metabolic pathways that accompany liver development entail associated changes in gene expression. Egr-1 is a zinc-finger transcription factor that regulates genes involved in cellular growth, differentiation, stress response, and apoptosis in many cell types. Egr-1 is induced in liver regeneration in rodents, but its role in normal hepatocyte function has not been characterized. We examined the developmental expression of Egr-1 in mouse liver and found that its expression increased during the suckling period. In screening the sequences of the genes involved in lactose assimilation, we found that the galactokinase gene Glk contains four potential Egr-1 binding sites in its proximal promoter. A minimal promoter of 155 nucleotides encompassing the four Egr-1 sites exhibited activity in hepatoma cell lines by transient transfection assays. Moreover, co-transfection of an Egr-1 expression plasmid increased promoter activity. Finally, mutations introduced into three of the four Egr-1 binding sites decreased activity, whereas mutation of the remaining site increased promoter activity. These data tie Egr-1 and galactokinase together in a developmentally regulated chain to prepare the neonate for suckling.

Antisense to the early growth response-1 gene (Egr-1) inhibits prostate tumor development in TRAMP mice

Egr-1 is a transcription factor induced by stress or injury, mitogens, and differentiation factors. Egr-1 regulates the expression of genes involved in growth control or survival. Expression of Egr-1 results in either promotion or regression of cell proliferation, depending on cell type and environment. Egr-1 acts as a tumor suppressor in many cell types and loss of Egr-1 has been proposed to contribute to cancer progression. There is strong new evidence however suggesting that Egr-1 overexpression is involved in prostate cancer progression. For example, Egr-1 expression levels are elevated in human prostate carcinomas in proportion to grade and stage. Furthermore, prostate cancer progression was significantly delayed in two models of prostate cancer mice lacking Egr-1. Our objective in the present study is to test whether inhibition of Egr-1 function would block cell proliferation and inhibit the transformed phenotype of prostate cancer cells in vitro and in vivo. We describe the development of high affinity and high specificity antisense oligonucleotides that efficiently inhibit Egr-1 expression. We show that inhibition of Egr-1 expression in mouse or human prostate cancer cells decreased proliferation and reduced the capacity of these cells to form colonies and to grow in soft agar. Conversely, stable expression of Egr-1 in normal human prostate epithelial 267B1 cells promoted transformation. In TRAMP mice, treatment with Egr-1 antisense oligonucleotides delayed the occurrence of prostate tumors. Importantly, Egr-1 antisense showed little or no toxicity when injected into animals. Finally, we identified a few genes such as cyclin D2, p19ink4d, and Fas that are directly regulated by Egr-1 in prostate cancer cells and that control cell cycle and survival.

Antiestrogen resistance in breast cancer and the role of estrogen receptor signaling

Antiestrogens include agents such as tamoxifen, toremifene, raloxifene, and fulvestrant. Currently, tamoxifen is the only drug approved for use in breast cancer chemoprevention, and it remains the treatment of choice for most women with hormone receptor positive, invasive breast carcinoma. While antiestrogens have been available since the early 1970s, we still do not fully understand their mechanisms of action and resistance. Essentially, two forms of antiestrogen resistance occur: de novo resistance and acquired resistance. Absence of estrogen receptor (ER) expression is the most common de novo resistance mechanism, whereas a complete loss of ER expression is not common in acquired resistance. Antiestrogen unresponsiveness appears to be the major acquired resistance phenotype, with a switch to an antiestrogen-stimulated growth being a minor phenotype. Since antiestrogens compete with estrogens for binding to ER, clinical response to antiestrogens may be affected by exogenous estrogenic exposures. Such exposures include estrogenic hormone replacement therapies and dietary and environmental exposures that directly or indirectly increase a tumor's estrogenic environment. Whether antiestrogen resistance can be conferred by a switch from predominantly ERalpha to ERbeta expression remains unanswered, but predicting response to antiestrogen therapy requires only measurement of ERalpha expression. The role of altered receptor coactivator or corepressor expression in antiestrogen resistance also is unclear, and understanding their roles may be confounded by their ubiquitous expression and functional redundancy. We have proposed a gene network approach to exploring the mechanistic aspects of antiestrogen resistance. Using transcriptome and proteome analyses, we have begun to identify candidate genes that comprise one component of a larger, putative gene network. These candidate genes include NFkappaB, interferon regulatory factor-1, nucleophosmin, and the X-box binding protein-1. The network also may involve signaling through ras and MAPK, implicating crosstalk with growth factors and cytokines. Ultimately, signaling affects the expression/function of the proliferation and/or apoptotic machineries.

MAPK pathways in radiation responses

Within the last 15 years, multiple new signal transduction pathways within cells have been discovered. Many of these pathways belong to what is now termed 'the mitogen-activated protein kinase (MAPK) superfamily.' These pathways have been linked to the growth factor-mediated regulation of diverse cellular events such as proliferation, senescence, differentiation and apoptosis. Based on currently available data, exposure of cells to ionizing radiation and a variety of other toxic stresses induces simultaneous compensatory activation of multiple MAPK pathways. These signals play critical roles in controlling cell survival and repopulation effects following irradiation, in a cell-type-dependent manner. Some of the signaling pathways activated following radiation exposure are those normally activated by mitogens, such as the 'classical' MAPK (also known as the ERK) pathway. Other MAPK pathways activated by radiation include those downstream of death receptors and procaspases, and DNA-damage signals, including the JNK and P38 MAPK pathways. The expression and release of autocrine growth factor ligands, such as (transforming growth factor alpha) and TNF-alpha, following irradiation can also enhance the responses of MAPK pathways in cells and, consequently, of bystander cells. Thus, the ability of radiation to activate MAPK signaling pathways may depend on the expression of multiple growth factor receptors, autocrine factors and Ras mutation. Enhanced basal signaling by proto-oncogenes such as K-/H-/N-RAS may provide a radioprotective and growth-promoting signal. In many cell types, this may be via the PI3K pathway; in others, this may occur through nuclear factor-kappa B or multiple MAPK pathways. This review will describe the enzymes within the known MAPK signaling pathways and discuss their activation and roles in cellular radiation responses.

Altered expression of immune modulator and structural genes in neonatal unilateral ureteral obstruction

BACKGROUND

Congenital obstructive nephropathy is a condition characterized by hydronephrosis, tubular dilatation, apoptosis, and atrophy, as well as interstitial cellular infiltration and progressive interstitial fibrosis. The renal consequences of chronic unilateral ureteral obstruction (UUO) in the neonatal rat are similar to those of clinical congenital obstructive nephropathy.

METHODS

To define alterations in renal gene expression induced by chronic neonatal UUO, Sprague-Dawley rats were subjected to UUO or sham operation within the first 2 days of life, and kidneys were harvested after 12 days.

RESULTS

Microarray analysis revealed that the mRNA expression of multiple immune modulators, including krox24, interferon-gamma regulating factor-1 (IRF-1), monocyte chemoattractant protein-1 (MCP-1), interleukin-1beta (IL-1beta), CCAAT/enhancer binding protein (C/EBP), p21, c-fos, c-jun, and pJunB, was significantly increased in obstructed compared to sham-operated kidneys (all P < 0.05). Western blot analysis revealed significant changes in immune modulator protein abundance in the obstructed versus sham-operated kidney for krox24 (P = 0.0004), IRF-1 (P = 0.005), MCP-1 (P = 0.01), and JunD (P = 0.0008). Alternatively, the abundance of all of the immune modulator proteins was similar in sham-operated and obstructed kidneys in rats subjected to acute (4 days) neonatal UUO. Microarray analysis studies also reveal that structural genes that comprise the cytoskeleton and cell matrix are significantly up-regulated by chronic neonatal UUO, including calponin, desmin, dynamin, and lumican (all P < 0.05).

CONCLUSION

Multiple genes are aberrantly expressed in the kidney of rats subjected to chronic neonatal UUO. Elucidation of these genes involved in neonatal UUO may lead to new insight about congenital obstructive nephropathy.

Early growth response 1 protein, an upstream gatekeeper of the p53 tumor suppressor, controls replicative senescence

The proliferation of most primary cells in culture is limited by replicative senescence and crisis, p53-dependent events. However, the regulation of p53 itself has not been defined. We find that deletion of the early growth response 1 (EGR1) transcription factor leads to a striking phenotype, including complete bypass of senescence and apparent immortal growth consistent with loss of a suppressor gene. EGR1-null mouse embryo fibroblasts (MEFs) exhibit decreased expression of p53, p21(Cip1/Waf1), and other p53 "marker" proteins. Precrisis WT but not EGR1-null cells exhibit irradiation-induced arrest. WT MEFs that emerge from crisis exhibit a mutated p53 (sequence confirmed), colony formation, and tumorigenicity. In contrast, high-passage EGR1-null MEFs retain the WT p53 sequence but with much reduced expression, remain untransformed, and grow continuously. An EGR1-expressing retrovirus restores p53 expression and sencescence to EGR1-null but not p53-null MEFs or postcrisis WT cells. Taken together, the results establish EGR1 as a major regulator of cell senescence and previously undescribed upstream "gatekeeper" of the p53 tumor suppressor pathway.

Myeloid differentiation (MyD)/growth arrest DNA damage (GADD) genes in tumor suppression, immunity and inflammation

Myeloid differentiation (MyD) primary response and growth arrest DNA damage (Gadd) genes comprise a set of overlapping genes, including known (IRF-1, EGR-1, Jun) and novel (MyD88, Gadd45alpha, MyD118/Gadd45beta, GADD45gamma, MyD116/ Gadd34) genes, that have been cloned by virtue of being co-ordinately induced upon the onset of terminal myeloid differentiation and following exposure of cells to stress stimuli. In recent years it has become evident that MyD/Gadd play a role in blood cell development, where they function as positive regulators of terminal differentiation, lineage-specific blood cell development and control of blood cell homeostasis, including growth inhibition and apoptosis. MyD/Gadd are also involved in inflammatory responses to invading micro-organisms, and response to environmental stress and physiological stress, such as hypoxia, which results in ischemic tissue damage. An intricate network of interactions among MyD/GADD genes and gene products appears to control their diverse functions. Deregulated growth, increased cell survival, compromised differentiation and deficiencies in DNA repair are hallmarks of malignancy and its progression. Thus, the role MyD/Gadd play in negative growth control, including cell cycle arrest and apoptosis, and in DNA repair, make them attractive molecular targets for tumor suppression. The role MyD/Gadd play in innate immunity and host response to hypoxia also make these genes and gene products attractive molecular targets to treat immunity and inflammation disorders, such as septic shock and ischemic tissue damage.

Differential gene expression in the lens epithelial cells from selenite injected rats

The mechanism causing loss of integrity of lens epithelial cells induced by an overdose of sodium selenite remains to be elucidated. The aim of the present experiment was to search for changes in gene expression in epithelial cells of lenses from rats developing selenite cataract. One day after injection of selenite into 12 day old rats, gene expression in lens epithelial cells was analysed using a commercial DNA array (Atlas Rat 1.2 Array). Changes were confirmed by RT-PCR. Of 1176 genes assayed by hybridization, 91 genes showed differences in expression between normal and selenite lenses. The three genes showing the greatest changes were: cytochrome c oxidase subunit I (COX-I, decrease), gastric inhibitory polypeptide (GIP, decrease), and early growth response protein-1 (EGR-1, increase). Both COX-I and EGR-1 have been reported to be involved with apoptosis. These results suggest that changes in COX-I and EGR-1 expression in lens epithelial cells might play important roles in apoptosis and altered metabolism leading to selenite cataract.

Restoration of transforming growth factor-beta signaling enhances radiosensitivity by altering the Bcl-2/Bax ratio in the p53 mutant pancreatic cancer cell line MIA PaCa-2

In this study, we investigated whether lack of transforming growth factor beta (TGF-beta) type II receptor (RII) expression and loss of TGF-beta signaling played a role in radiation resistance of pancreatic cancer cells MIA PaCa-2 that possess a mutated p53 gene. Transfection of this cell line with a RII cDNA led to a stimulation of the transcriptional activity of p3TP-Lux, a TGF-beta-responsive reporter construct. The RII transfectants (MIA PaCa-2/RII) showed a significant increase in sensitivity to radiation when compared with MIA PaCa-2/vector cells. The increase in sensitivity to radiation was reversed by neutralizing antibodies to TGF-beta, indicating that these changes were dependent on TGF-beta signaling. Compared with MIA PaCa-2/vector cells, MIA PaCa-2/RII cells showed a greater than 3-fold increase in apoptosis after radiation. Enhanced radiation sensitivity of MIA PaCa-2/RII cells was associated with an induction of Bax mRNA and protein that was followed by a release of cytochrome c and activation of caspase-3 and poly(ADP-ribose) polymerase cleavage after radiation exposure. Overexpression of Bcl-x(L) or treatment with antisense oligodeoxynucleotides targeted against Bax significantly inhibited radiation-induced apoptosis in MIA PaCa-2/RII but not in MIA PaCa-2/Vector cells, suggesting that Bax induction is necessary for radiation-induced TGF-beta signaling-mediated apoptosis. Thus, restoration of TGF-beta signaling sensitized these cells to ionizing radiation, although these cells possess a mutated p53 gene. In addition, disruption of RII function by dominant negative mutant of RII inhibited the radiation-induced TGF-beta signaling and apoptosis in primary cultures of mouse embryonic fibroblasts. Together, these observations imply that RII is an important component of radiation-induced TGF-beta signaling, and loss of function of RII may enhance resistance to radiation-induced apoptosis.

A dominant negative inhibitor of the Egr family of transcription regulatory factors suppresses cerebellar granule cell apoptosis by blocking c-Jun activation

To investigate the role of the Egr family of transcription regulatory factors in neuronal apoptosis, we examined the effect of a dominant negative Egr inhibitor construct in a well characterized in vitro paradigm, cerebellar granule cell death induced by withdrawal of depolarizing concentrations of extracellular potassium. We found that this apoptotic stimulus increases the activity of a reporter gene driven by the Egr response element and that a dominant negative inhibitor of Egr-mediated transcription blocks granule cell apoptosis. In contrast, apoptosis of immature granule cells induced by cytosine arabinoside is not inhibited by the Egr inhibitor construct. Because activation of c-Jun is an essential step in granule cell death induced by potassium deprivation, but not cytosine arabinoside, we asked whether the Egr inhibitor acts by influencing c-Jun activation or its ability to induce apoptosis. We found that the Egr inhibitor does not block the ability of a constitutively active c-Jun construct to induce apoptosis in these cells but does suppress activation of c-Jun-mediated transcription induced by lowering extracellular potassium concentration. Furthermore, the Egr inhibitor blocks the ability of MEKK1 [mitogen-activated protein kinase (MAPK) kinase kinase 1], an upstream kinase capable of stimulating the JNK (c-Jun N-terminal protein kinase)-c-Jun pathway, to induce apoptosis and activate c-Jun. Together, these studies indicate that the Egr family of transcription factors plays a critical role in neuronal apoptosis and identify c-Jun activation as an important downstream target of the Egr family in this process.