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

Role of early growth response-1 as a tumor suppressor in oral squamous cell carcinoma

BACKGROUND

Oral squamous cell carcinoma (OSCC) exhibits pronounced local invasiveness and a propensity for lymph node metastasis. Given its frequent detection at advanced stages and the consequential postoperative functional impairments, the identification of effective molecular markers for early detection and treatment is imperative. Early growth response-1 (EGR-1) serves as a versatile transcription factor expressed across various cell types. Its role in cancer is contentious, acting as either an oncogene or a tumor suppressor gene.

METHODS

This study undertook comprehensive analyses, including big data scrutiny, expression profiling using 50 OSCC samples, and in vitro functional assessments, to elucidate EGR-1's involvement in OSCC.

RESULTS

Comparative analysis revealed significantly reduced EGR-1 expression in oral cancer tissues compared to healthy controls or normal oral mucosa. In vitro experimentation with multiple OSCC cell lines demonstrated that EGR-1 curbed cell proliferation, migration, and invasion capabilities. Additionally, it was observed that EGR-1 prompted G0/G1 arrest in OSCC cells by modulating the activity of cell cycle regulators.

CONCLUSIONS

These findings strongly support EGR-1's tumor-suppressive role in OSCC and hint at the potential for novel OSCC therapies aimed at restoring aberrant EGR-1 function.

The EGR1/miR-139/NRF2 axis orchestrates radiosensitivity of non-small-cell lung cancer via ferroptosis

Radiotherapy is one of the predominant treatment modalities for almost all kinds of malignant cancers, including non-small cell lung cancer (NSCLC). Increasing evidence shows that ionizing radiation (IR) induces reactive oxygen species (ROS) leading to lipid peroxidation and subsequently ferroptosis of cancer cells. However, cancer cells evolve multiple mechanisms against ROS biology resulting in resistance to ferroptosis and radiotherapy, of which NRF2 signaling is one of the most studied. In the current research, we identified that microRNA-139 (miR-139) could be a novel radiosensitizer for NSCLC by inhibiting NRF2 signaling. We found that miR-139 possessed great potential as a diagnostic biomarker for NSCLC and multiple other types of cancer. Overexpression of miR-139 increased radiosensitivity of NSCLC cells in vitro and in vivo. MiR-139 directly targeted cJUN and KPNA2 to impair NRF2 signaling resulting in enhanced IR-induced lipid peroxidation and cellular ferroptosis. We proved KPNA2 to be a binding partner of NRF2 that involved in nuclear translocation of NRF2. Moreover, we found that IR induced miR-139 expression through transcriptional factor EGR1. EGR1 bound to the promoter region and transactivated miR-139. Overall, our findings elucidated the effect of EGR1/miR-139/NRF2 in IR-induced ferroptosis of NSCLC cells and provided theoretical support for the potential diagnostic biomarkers and therapeutic targets for the disease.

Transcriptome Profiling of Cardiac Glycoside Treatment Reveals EGR1 and Downstream Proteins of MAPK/ERK Signaling Pathway in Human Breast Cancer Cells

Cardiac glycosides (CGs) constitute a group of steroid-like compounds renowned for their effectiveness in treating cardiovascular ailments. In recent times, there has been growing recognition of their potential use as drug leads in cancer treatment. In our prior research, we identified three highly promising CG compounds, namely lanatoside C (LC), peruvoside (PS), and strophanthidin (STR), which exhibited significant antitumor effects in lung, liver, and breast cancer cell lines. In this study, we investigated the therapeutic response of these CGs, with a particular focus on the MCF-7 breast cancer cell line. We conducted transcriptomic profiling and further validated the gene and protein expression changes induced by treatment through qRT-PCR, immunoblotting, and immunocytochemical analysis. Additionally, we demonstrated the interactions between the ligands and target proteins using the molecular docking approach. The transcriptome analysis revealed a cluster of genes with potential therapeutic targets involved in cytotoxicity, immunomodulation, and tumor-suppressor pathways. Subsequently, we focused on cross-validating the ten most significantly expressed genes, EGR1, MAPK1, p53, CCNK, CASP9, BCL2L1, CDK7, CDK2, CDK2AP1, and CDKN1A, through qRT-PCR, and their by confirming the consistent expression pattern with RNA-Seq data. Notably, among the most variable genes, we identified EGR1, the downstream effector of the MAPK signaling pathway, which performs the regulatory function in cell proliferation, tumor invasion, and immune regulation. Furthermore, we substantiated the influence of CG compounds on translational processes, resulting in an alteration in protein expression upon treatment. An additional analysis of ligand-protein interactions provided further evidence of the robust binding affinity between LC, PS, and STR and their respective protein targets. These findings underscore the intense anticancer activity of the investigated CGs, shedding light on potential target genes and elucidating the probable mechanism of action of CGs in breast cancer.

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.

MicroRNA-150 (miR-150) and Diabetic Retinopathy: Is miR-150 Only a Biomarker or Does It Contribute to Disease Progression?

Diabetic retinopathy (DR) is a chronic disease associated with diabetes mellitus and is a leading cause of visual impairment among the working population in the US. Clinically, DR has been diagnosed and treated as a vascular complication, but it adversely impacts both neural retina and retinal vasculature. Degeneration of retinal neurons and microvasculature manifests in the diabetic retina and early stages of DR. Retinal photoreceptors undergo apoptosis shortly after the onset of diabetes, which contributes to the retinal dysfunction and microvascular complications leading to vision impairment. Chronic inflammation is a hallmark of diabetes and a contributor to cell apoptosis, and retinal photoreceptors are a major source of intraocular inflammation that contributes to vascular abnormalities in diabetes. As the levels of microRNAs (miRs) are changed in the plasma and vitreous of diabetic patients, miRs have been suggested as biomarkers to determine the progression of diabetic ocular diseases, including DR. However, few miRs have been thoroughly investigated as contributors to the pathogenesis of DR. Among these miRs, miR-150 is downregulated in diabetic patients and is an endogenous suppressor of inflammation, apoptosis, and pathological angiogenesis. In this review, how miR-150 and its downstream targets contribute to diabetes-associated retinal degeneration and pathological angiogenesis in DR are discussed. Currently, there is no effective treatment to stop or reverse diabetes-caused neural and vascular degeneration in the retina. Understanding the molecular mechanism of the pathogenesis of DR may shed light for the future development of more effective treatments for DR and other diabetes-associated ocular diseases.

Transcriptional Regulation of GDF15 by EGR1 Promotes Head and Neck Cancer Progression through a Positive Feedback Loop

Growth and differentiation factor 15 (GDF15), a divergent member of the transforming growth factor-β (TGF-β) superfamily, has been reported to be overexpressed in different kinds of cancer types. However, the function and mechanism of GDF15 in head and neck cancer (HNC) remains unclear. The Cancer Genome Atlas (TCGA) data show that the expression of GDF15 is significantly associated with tumor AJCC stage, lymph vascular invasion and tumor grade in HNC. In this study, we confirmed that knockdown of GDF15 attenuated: cell proliferation, migration and invasion via regulation of EMT through a canonical pathway; SMAD2/3 and noncanonical pathways; PI3K/AKT and MEK/ERK in HNC cell lines. Furthermore, we found that early growth response 1 (EGR1) was a transcription factor of GDF15. Interestingly, we also demonstrated that GDF15 could regulate the expression of EGR1, which meant a positive feedback loop occurred between these two factors. Moreover, combined inhibition of both GDF15 and EGR1 in a HNC mouse xenograft model showed significantly decreased tumor volume compared to inhibition of EGR1 or GDF15 alone. Our study showed that the GDF15–EGR1 signaling axis may be a good target in HNC patients.

EGR1 Addiction in Diffuse Large B-cell Lymphoma

Early growth response gene (EGR1) is a transcription factor known to be a downstream effector of B-cell receptor signaling and Janus kinase 1 (JAK1) signaling in diffuse large B-cell lymphoma (DLBCL). While EGR1 is characterized as a tumor suppressor in leukemia and multiple myeloma, the role of EGR1 in lymphoma is unknown. Here we demonstrate that EGR1 is a potential oncogene that promotes cell proliferation in DLBCL. IHC analysis revealed that EGR1 expression is elevated in DLBCL compared with normal lymphoid tissues and the level of EGR1 expression is higher in activated B cell-like subtype (ABC) than germinal center B cell-like subtype (GCB). EGR1 expression is required for the survival and proliferation of DLBCL cells. Genomic analyses demonstrated that EGR1 upregulates expression of MYC and E2F pathway genes through the CBP/p300/H3K27ac/BRD4 axis while repressing expression of the type I IFN pathway genes by interaction with the corepressor NAB2. Genetic and pharmacologic inhibition of EGR1 synergizes with the BRD4 inhibitor JQ1 or the type I IFN inducer lenalidomide in growth inhibition of ABC DLBCL both in cell cultures and xenograft mouse models. Therefore, targeting oncogenic EGR1 signaling represents a potential new targeted therapeutic strategy in DLBCL, especially for the more aggressive ABC DLBCL. IMPLICATIONS: The study characterizes EGR1 as a potential oncogene that promotes cell proliferation and defines EGR1 as a new molecular target in DLBCL, the most common non-Hodgkin lymphoma.

Pathways involved in pony body size development

BACKGROUND

The mechanism of body growth in mammals is poorly understood. Here, we investigated the regulatory networks involved in body growth through transcriptomic analysis of pituitary and epiphyseal tissues of smaller sized Debao ponies and Mongolian horses at the juvenile and adult stages.

RESULTS

We found that growth hormone receptor (GHR) was expressed at low levels in long bones, although growth hormone (GH) was highly expressed in Debao ponies compared with Mongolian horses. Moreover, significant downregulated of the GHR pathway components m-RAS and ATF3 was found in juvenile ponies, which slowed the proliferation of bone osteocytes. However, WNT2 and PLCβ2 were obviously upregulated in juvenile Debao ponies, which led to premature mineralization of the bone extracellular matrix. Furthermore, we found that the WNT/Ca²⁺ pathway may be responsible for regulating body growth. GHR was demonstrated by q-PCR and Western blot analyses to be expressed at low levels in long bones of Debao ponies. Treatment with WNT antagonistI decreased the expression of WNT pathway components (P < 0.05) in vitro. Transduction of ATDC5 cells with a GHR-RNAi lentiviral vector decreased the expression of the GHR pathway components (P < 0.05). Additionally, the expression of the IGF-1 gene in the liver was lower in Debao ponies than in Mongolian horses at the juvenile and adult stages. Detection of plasma hormone concentrations showed that Debao ponies expressed higher levels of IGF-1 as juveniles and higher levels of GH as adults than Mongolian horses, indicating that the hormone regulation in Debao ponies differs from that in Mongolian horses.

CONCLUSION

Our work provides insights into the genetic regulation of short stature growth in mammals and can provide useful information for the development of therapeutic strategies for small size.

Hyperoxia sensitizes hypoxic HeLa cells to ionizing radiation by downregulating HIF‑1α and VEGF expression

The current study investigated whether hyperoxia may reverse hypoxia‑induced radioresistance (RR) in cervical cancer. Human HeLa cells exposed to hypoxic, normoxic or hyperoxic conditions were irradiated using X‑rays. Cell proliferation and apoptosis were analyzed using MTT assays and flow cytometry. The expression levels of hypoxia‑inducible factor‑1α (HIF‑1α), VEGF165, VEGFRs, Akt and ERK were measured via western blotting and/or ELISA. The results demonstrated that hypoxia stimulated HIF‑1α and VEGF expression, and induced RR in HeLa cells. The administration of recombinant VEGF or the forced expression of VEGF promoted RR, whereas inactivating HIF‑1α or blocking the VEGF‑VEGFR interaction abrogated hypoxia‑induced RR. Notably, hyperoxia decreased the level of hypoxia‑stimulated HIF‑1α and VEGF, and enhanced radiosensitivity in hypoxic HeLa cells. The results demonstrated that hyperoxia suppressed the hypoxia‑activated Akt and ERK signaling pathways in HeLa cells. Therefore, a high O2 concentration may be considered as a radiotherapeutic sensitizer for hypoxic HeLa cells.

Cigarette smoke, but not novel tobacco vapor products, causes epigenetic disruption and cell apoptosis

Heat-Not-Burn (HNB) products, generating vapor without combusting tobacco leaves, have been developed with the expectation that the number and quantity of chemicals in the vapor of these products would be reduced compared with the smoke from conventional combustible cigarettes. However, whether the lower chemical levels correlate with lower toxicity remains to be determined. Here we examined differences in the biological effects of conventional cigarette smoke (CS) and two HNB products, Ploom TECH and Ploom TECH+, using the cultured cancer cell line A549 and the normal bronchial epithelium cell line BEAS-2B. The conventional CS 3R4F extract (0.5%) markedly decreased cell proliferation of both A549 and BEAS-2B cells; however, 0.5% extracts of these commercially available HNB products did not affect cell growth. To determine the cause of decreased cell proliferation, a TUNEL assay was performed, and the results indicated that apoptosis had occurred in both A549 and BEAS-2B cells at 24 h after exposure to 3R4F. To further explore the effect of CS on epigenetics, we performed western blotting to detect histone H2A phosphorylation, which is known to affect transcriptional regulation. Only the 3R4F extract decreased histone H2A phosphorylation in both A549 and BEAS-2B cells. Next, we examined alterations in gene expression after treatment of A549 cells with Ploom TECH, Ploom TECH+, or 3R4F extracts. It was found that 339, 107, and 103 genes were upregulated more than 2 fold in A549 cells treated with 3R4F, Ploom TECH, or Ploom TECH + extracts, respectively. Among the 339 genes that were upregulated in response to 3R4F, we focused on EGR1, FOS, and FOSB, since they were upregulated more than 100 fold, which was confirmed using RT-qPCR. These results suggest that CS, but not HNB products, cause epigenetic disruption and cell apoptosis, possibly by elevating transcription of genes such as EGR1.

Immunotherapy orchestrates radiotherapy in composing abscopal effects: A strategic review in metastatic head and neck cancer

The treatment of metastatic head and neck squamous cell carcinoma (HNSCC) with a combination of radiotherapy (RT) and immunotherapy can augment treatment response and symptomatic relief. Combination therapy can also trigger a non-targeted tumor control event called the abscopal effect. This effect can be demonstrated by treatment with anti-programmed death 1/programmed death ligand 1 (PD-L1) and anti-cytotoxic T-lymphocyte-associated antigen 4 antibodies in combination with hypofractionated RT. Individual studies and clinical trials have revealed that combination radio-immunotherapy improves overall treatment response by successful initiation of the abscopal effect, which extends the treatment effects to non-targeted lesions. Growing attention to the abscopal effect may inspire innovations in current RT toward more effective and less toxic radiobiological treatment modalities for advanced HNSCC. We review the latest findings on the abscopal effect with emphases on therapeutic modalities and potential applications for treating metastatic HNSCC.

Transcription factor early growth response-1 plays an oncogenic role in salivary gland pleomorphic adenoma

OBJECTIVES

Although abnormal expression of early growth response-1 (Egr1) has been revealed in various human solid tumors, the functions and potential mechanisms of Egr1 in the progression of salivary gland pleomorphic adenoma (SGPA) are not entirely understood.

RESULTS

An elevated expression of Egr1 was observed both in the human salivary gland pleomorphic adenoma tissues and tumor-initiating cell (TIC) cells, when compared with control group. By loss-of-function assay, the proliferation and invasion capacities of TICs were inhibited, while the cell apoptosis was promoted, which were further evidenced by the protein expression analysis of several key apoptosis-related regulators. Furthermore, TICs with Mithramycin A (an Egr1 inhibitor) treatment achieved the same effects of endogenous Egr1 knockdown.

CONCLUSIONS

All these data collectively suggest that Egr1 act as an oncogenic factor in salivary gland pleomorphic adenoma, which may be a potential target for the treatment of SGPA.

Homologous recombination enhances radioresistance in hypopharyngeal cancer cell line by targeting DNA damage response

BACKGROUND

Radiotherapy is a central treatment option for hypopharyngeal squamous cell carcinoma, but the prognoses of patients treated with radiotherapy only are not satisfactory due to radioresistance. The underlying molecular mechanisms remain largely elusive, and mechanism-derived predictive markers of radioresistance are currently unavailable.

METHODS

In this study, we first established a specifically radioresistant FaDu cell line by repeated exposure to ionizing radiation with a total dose of 60 Gy (FaDu-RR). The validation of FaDu-RR cells was performed by clonogenic cell survival assay and cell proliferation assay. Microarrays and bioinformatics were analyzed to determine the differentially expressed mRNAs and their functions. DNA-repair capabilities were tested by cell cycle analysis and comet assay. The expressions of four key proteins in homologous recombination pathways, including BRCA1, BRCA2, RPA1, and Rad51, were detected both in FaDu-RR cells and radioresistant xenograft.

RESULTS

We established the specifically radioresistant FaDu cell line. Through microarrays and bioinformatics, homologous recombination pathways were suggested to play important roles in radioresistant mechanisms. High expression levels of key proteins in homologous recombination pathways were then detected both in FaDu-RR cells and radioresistant xenograft. Silencing RPA1 could reduce the radioresistance of FaDu-RR cells.

CONCLUSION

Our results provided strong evidence that homologous recombination enhances the radioresistance in hypopharyngeal carcinoma. Proteins in homologous recombination pathways may be potential biomarkers to predict hypopharyngeal carcinoma response to radiotherapy, establishing a basis for their utility in clinical practice.

Herbal formula Yangyinjiedu induces lung cancer cell apoptosis via activation of early growth response 1

Traditional Chinese Medicine (TCM) has been extensively used in clinical practices and proven to be effective against cancer. However, the underlying mechanisms remain to be investigated. In this study, we examined the anticancer activities of Chinese herbal formula Yangyinjiedu (YYJD) and found that YYJD exhibits cytotoxicity against lung cancer cells. Transcriptome analysis indicated that 2178 genes were differentially expressed (P < 0.05) upon YYJD treatment, with 1464 being (67.2%) up‐regulated. Among these, we found that the tumour suppressor early growth response 1 (EGR1) is the most activated. We demonstrated that EGR1 contributes to YYJD‐induced apoptosis in A549. Through dissecting EGR1‐associated transcriptional network, we identified 275 genes as EGR1 direct targets, some targets are involved in apoptosis. Lastly, we observed that YYJD enhances EGR1 expression and induces cell death in tumour xenografts. Collectively, these findings suggest that YYJD exerts its anticancer activities through EGR1 activation, thus providing the evidence for its potential clinical application for lung cancer patients.

Hepatic miR-181b-5p Contributes to Glycogen Synthesis Through Targeting EGR1

BACKGROUND/AIM

The miR-181 family plays an important role in the regulation of various cellular functions. However, whether miR-181b-5p mediates hepatic insulin resistance remains unknown. In this study, we investigated the effect of miR-181b-5p on the regulation of hepatic glycogen synthesis.

METHODS

The miR-181b-5p levels in the livers of diabetic mice were detected by real-time PCR. The glycogen levels and AKT/GSK pathway activation were examined in human hepatic L02 cells and HepG2 cells transfected with miR-181b-5p mimic or inhibitor. The potential target genes of miR-181b-5p were evaluated using a luciferase reporter assay and Western blot analysis. EGR1-specific siRNA and pCMV-EGR1 were used to further determine the role of miR-181b-5p in hepatic glycogen synthesis in vitro. Hepatic inhibition of miR-181b-5p in mice was performed using adeno-associated virus 8 (AAV8) vectors by tail intravenous injection.

RESULTS

The miR-181b-5p levels were significantly decreased in the serum and livers of diabetic mice as well as the serum of type 2 diabetes patients. Importantly, inhibition of miR-181b-5p expression impaired the AKT/GSK pathway and reduced glycogenesis in hepatocytes. Moreover, upregulation of miR-181b-5p reversed high-glucose-induced suppression of glycogenesis. Further analysis revealed that early growth response 1 (EGR1) was a downstream target of miR-181b-5p. Silencing of EGR1 expression rescued miR-181b-5p inhibition-reduced AKT/GSK pathway activation and glycogenesis in hepatocytes. Hepatic inhibition of miR-181b-5p led to insulin resistance in C57BL/6 J mice.

CONCLUSION

We demonstrated that miR-181b-5p contributes to glycogen synthesis by targeting EGR1, thereby regulating PTEN expression to mediate hepatic insulin resistance.

EGR1 interacts with TBX2 and functions as a tumor suppressor in rhabdomyosarcoma

EGR1, one of the immediate-early response genes, can function as a tumor suppressor gene or as an oncogene in cancer. The function of EGR1 has not been fully characterized in rhabdomyosarcoma (RMS), a pediatric cancer derived from the muscle linage. We found that EGR1 is downregulated in the alveolar RMS (ARMS) subtype but expressed at levels comparable to normal skeletal muscle in embryonal RMS (ERMS). We found that overexpression of EGR1 in ARMS significantly decreased cell proliferation, mobility, and anchorage-independent growth while also promoting differentiation. We found that EGR1 interacts with TBX2, which we have shown functions as an oncogene in RMS. The interaction inhibits EGR1 dependent gene expression, which includes the cell cycle regulators p21 and PTEN as well as other important cell growth drivers such as NDRG1 and CST6. We also found that EGR1 induced apoptosis by triggering the intrinsic apoptosis pathway. EGR1 also activated two pro-apoptotic factors, BAX and dephosphorylated BAD, which are both located upstream of the caspase cascades in the intrinsic pathway. EGR1 also sensitized RMS cells to chemotherapeutic agents, suggesting that activating EGR1 may improve therapeutic targeting by inducing apoptosis. Our results establish the important role of EGR1 in understanding RMS pathology.

ATF3-Dependent Regulation of EGR1 in vitro and in vivo

BACKGROUND/AIMS

Activating transcription factor 3 (ATF3) and early growth response protein 1 (EGR1) are reported to interact, but their use as prognostic factors in cancer is discussed controversially.

METHODS

We measured ATF3 and EGR1 gene expression changes in human mini-organ cultures (MOCs) of healthy nasal epithelia, UM-SCC-22B, and FADUDD cells after acid reflux exposure. Next, ATF3 and EGR1 gene expression was analysed in tumour tissues and related to the median expression of autologous reference tissue samples.

RESULTS

ATF3 and EGR1 mRNA expression was significantly reduced after consecutive exposure of MOCs at pH <7.0 to artificial gastric juice (refluxate). In contrast, ATF3 mRNA was upregulated significantly within the first hour of incubation. EGR1 mRNA exhibited no significant changes. The analysed cell lines exhibited a cell line-specific alteration. In FADUDD cells, the upregulation of EGR1 was significant after refluxate exposure, but in HN-SCC 22B, no significant changes were detected. The analysis of the HNSCC samples confirmed the heterogeneous data of the literature.

CONCLUSION

The data maintain the hypothesis that ATF3 and EGR1 are involved in the beginning of inflammatory processes. Whether these two transcription factors act as tumour suppressors or promoters is context dependent and warrants analysis in further studies.

Egr-1 regulates irradiation-induced autophagy through Atg4B to promote radioresistance in hepatocellular carcinoma cells

Although hepatocellular carcinoma (HCC) is usually response to radiation therapy, radioresistance is still the major obstacle that limits the efficacy of radiotherapy for HCC patients. Therefore, further investigation of underlying mechanisms in radioresistant HCC cells is warranted. In this study, we determined the effect of early growth response factor (Egr-1) on irradiation-induced autophagy and radioresistance in HCC cell lines SMMC-7721 and HepG2. We showed that autophagy-related gene 4B (Atg4B) is induced by Egr-1 upon ionizing radiation (IR) in HCC cells. Luciferase reporter assays and chromatin immunoprecipitation (ChIP) revealed that Egr-1 binds to the Atg4B promoter to upregulate its expression in HCC cells. Suppression of Egr-1 function by dominant-negative Egr-1 dampens IR-induced autophagy, cell migration, and increases cell sensitivity to radiotherapy. Together, these results suggest that Egr-1 contributes to HCC radioresistance through directly upregulating target gene Atg4B, which may serve as a protective mechanism by preferential activation of the autophagy.

Clair DK, Rangnekar VM, Bondada S. 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.

The progress of early growth response factor 1 and leukemia

Early growth response gene-1 (EGR1) widely exists in the cell nucleus of such as, zebrafish, mice, chimpanzees and humans, an it also can be observed in the cytoplasm of some tumors. EGR1 was named just after its brief and rapid expression of different stimuli. Accumulating studies have extensively demonstrated that the widespread dysregulation of EGR1 is involved in hematological malignancies such as human acute myeloid leukemia (AML), chronic myelogenous leukemia, chronic lymphocytic leukemia, multiple myeloma, and B cell lymphoma. With the deep research on EGR1, its expression, function and regulatory mechanism has been gradually elucidated, and provides more possibilities for treatment strategies of patients with leukemia. Herein, we summarize the roles of EGR1 in its biological function and relationship with leukemia.