Leptin is a direct transcriptional target of EGR1 in human breast cancer cells

EGR1 mediates MDR1 transcriptional activity regulating gemcitabine resistance in pancreatic cancer

BACKGROUND

Gemcitabine is a cornerstone drug for the treatment of all stages of pancreatic cancer and can prolong the survival of patients with pancreatic cancer, but resistance to gemcitabine in pancreatic cancer patients hinders its efficacy. The overexpression of Early growth response 1(EGR1) in pancreatic ductal adenocarcinoma as a mechanism of gemcitabine chemoresistance in pancreatic cancer has not been explored. The major mechanisms of gemcitabine chemoresistance are related to drug uptake, metabolism, and action. One of the common causes of tumor multidrug resistance (MDR) to chemotherapy in cancer cells is that transporter proteins increase intracellular drug efflux and decrease drug concentrations by inducing anti-apoptotic mechanisms. It has been reported that gemcitabine binds to MDR1 with high affinity. The purpose of this research was to investigate the potential mechanisms by which EGR1 associates with MDR1 to regulate gemcitabine resistance in pancreatic cancer cells.

METHODS

The following in vitro and in vivo techniques were used in this research to explore the potential mechanisms by which EGR1 binds to MDR1 to regulate gemcitabine resistance in pancreatic cancer cells. Cell culture; in vitro and in vivo study of EGR1 function by loss of function analysis. Binding of EGR1 to the MDR1 promoter was detected using the ChIP assay. qRT-PCR, Western blot assays to detect protein and mRNA expression; use of Annexin V apoptosis detection assay to test apoptosis; CCK8, Edu assay to test cell proliferation viability. The animal model of pancreatic cancer subcutaneous allograft was constructed and the tumours were stained with hematoxylin eosin and Ki-67 expression was detected using immunohistochemistry.

FINDINGS

We revealed that EGR1 expression was increased in different pancreatic cancer cell lines compared to normal pancreatic ductal epithelial cells. Moreover, gemcitabine treatment induced upregulation of EGR1 expression in a dose- and time-dependent manner. EGR1 is significantly enriched in the MDR1 promoter sequence.Upon knockdown of EGR1, cell proliferation was impaired in CFPAC-1 and PANC-1 cell lines, apoptosis was enhanced and MDR1 expression was decreased, thereby partially reversing gemcitabine chemoresistance. In animal experiments, knockdown of EGR1 enhanced the inhibitory effect of gemcitabine on tumor growth compared with the sh-NC group.

CONCLUSIONS

Our study suggests that EGR1 may be involved in the regulation of MDR1 to enhance gemcitabine resistance in pancreatic cancer cells. EGR1 could be a novel therapeutic target to overcome gemcitabine resistance in pancreatic cancer.

The JNK-EGR1 signaling axis promotes TNF-α-induced endothelial differentiation of human mesenchymal stem cells via VEGFR2 expression

Mesenchymal stem cells (MSCs) can differentiate into endothelial cells; however, the mechanisms underlying this process in the tumor microenvironment (TME) remain elusive. This study shows that tumor necrosis factor alpha (TNF-α), a key cytokine present in the TME, promotes the endothelial differentiation of MSCs by inducing vascular endothelial growth factor receptor 2 (VEGFR2) gene expression. EGR1 is a member of the zinc-finger transcription factor family induced by TNF-α. Our findings indicate that EGR1 directly binds to the VEGFR2 promoter and transactivates VEGFR2 expression. We also demonstrate that EGR1 forms a complex with c-JUN activated by c-JUN N-terminal kinase (JNK) to promote VEGFR2 transcription and endothelial differentiation in MSCs in response to TNF-α stimulation. The shRNA-mediated silencing of EGR1 or c-JUN abrogates TNF-α-induced VEGFR2 transcription and the endothelial differentiation of MSCs. To further evaluated the role of EGR1 in the endothelial differentiation of BM-MSCs, we used a syngenic tumor implantation model. 4T1 mouse mammary tumor cells were injected subcutaneously into BALB/c mice with primary mBM-MSCs isolated from wild-type (Egr1+/+) or Egr1-null (Egr1-/-) mice. CD31-positive cells were predominantly observed at the border of the tumor in the 4T1 plus wild-type MSC group, while staining less in the 4T1 alone or 4T1 plus Egr1-null MSC group. Collectively, these findings demonstrate that the JNK-EGR1 signaling axis plays a crucial role in the TNF-α-induced endothelial differentiation of MSCs in the TME, which could be a potential therapeutic target for solid tumors vasculatures.

Early growth response-1 is a new substrate of the GSK3β-FBXW7 axis

EGR1, a short-lived transcription factor, regulates several biological processes, including cell proliferation and tumor progression. Whether and how EGR1 is regulated by Cullin-RING ligases (CRLs) remains elusive. Here, we report that MLN4924, a small molecule inhibitor of neddylation, causes EGR1 accumulation by inactivating SCFFBXW7 (CRL1), which is a new E3 ligase for EGR1. Specifically, FBXW7 binds to EGR1 via its consensus binding motif/degron, whereas cancer-derived FBXW7 mutants showed a much reduced EGR1 binding. SiRNA-mediated FBXW7 knockdown caused EGR1 accumulation, whereas FBXW7 overexpression reduced EGR1 levels. Likewise, FBXW7 knockdown significantly extended EGR1 protein half-life, while FBXW7 overexpression promotes polyubiquitylation of wild-type EGR1, but not EGR1-S2A mutant with the binding site abrogated. GSK3β kinase is required for the FBXW7-EGR1 binding, and for enhanced EGR1 degradation by wild type FBXW7, but not by FBXW7 mutants. Likewise, GSK3β knockdown or treatment with GSK3β inhibitor significantly increased the EGR1 levels and extended EGR1 protein half-life, while reducing EGR1 polyubiquitylation. Hypoxia exposure reduces the EGR1 levels via enhancing the FBXW7-EGR1 binding, and FBXW7-induced EGR1 polyubiquitylation. Biologically, EGR1 knockdown suppressed cancer cell growth, whereas growth stimulation by FBXW7 knockdown is partially rescued by EGR1 knockdown. Thus, EGR1 is a new substrate of the GSK3β-FBXW7 axis, and the FBXW7-EGR1 axis coordinately regulates growth of cancer cells.

Celastrol inhibits the proliferation and migration of MCF-7 cells through the leptin-triggered PI3K/AKT pathway

Leptin is the pivotal modulator in the onset and progression of breast cancer and obesity. Celastrol, which is extracted from the roots of Tripterygium wilfordi plants, exerts various anticancer bioactivities and has recently emerged as a candidate to treat obesity by improving leptin sensitivity. However, the relationship between leptin and celastrol in the treatment of breast cancer is unknown. Here, the growth and migration of MCF-7 cells induced by leptin were tested to demonstrate the antineoplastic activity of celastrol. Transcriptomic analysis and western blotting were conducted to explore the biological roles of leptin in treating breast cancer with celastrol. The present findings showed that celastrol remarkably reversed leptin-triggered cell proliferation and migration in MCF-7 cells. Fifty-two mRNAs with fivefold higher counts and 149 mRNAs with fivefold lower counts were identified in the celastrol-treated MCF-7 cells. According to the GO and KEGG analyses, the effects of celastrol on MCF-7 cells forced lipid metabolism and the endocrine system. Moreover, leptin treatment induced phosphorylation of leptin receptor and PI3K/AKT in MCF-7 cells, whereas pretreatment with celastrol partly abrogated leptin activation. The binding of celastrol to the leptin receptor was also confirmed by molecular docking. The antitumor effect of celastrol is proposed to be mediated by its binding to the leptin receptor and controlled downregulation of the PI3K/AKT pathway.

WNT11 is a direct target of early growth response protein 1

WNT11 is a member of the non-canonical Wnt family and plays a crucial role in tumor progression. However, the regulatory mechanisms underlying WNT11 expression are unclear. Tumor necrosis factor-alpha (TNFα) is a major inflammatory cytokine produced in the tumor microenvironment and contributes to processes associated with tumor progression, such as tumor invasion and metastasis. By using site-directed mutagenesis and introducing a serial deletion in the 5'-regulatory region of WNT11, we observed that TNFα activates the early growth response 1 (EGR1)-binding sequence (EBS) in the proximal region of WNT11 and that the transcription factor EGR1 is necessary for the TNFα-induced transcription of WNT11. EGR1 bound directly to the EBSs within the proximal 5'-regulatory region of WNT11 and ectopic expression of EGR1 stimulated WNT11 promoter activity, whereas the knockdown of EGR1 expression by RNA interference reduced TNFα-induced WNT11 expression in T47D breast cancer cells. We also observed that mitogen-activated protein kinases (MAPK), extracellular signalregulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 kinase mediated TNFα-induced transcription of WNT11 via EGR1. Our results suggest that EGR1 directly targets WNT11 in response to TNFα stimulation in breast cancer cells. [BMB Reports 2020; 53(12): 628-633].

Oncogenic role of early growth response-1 in liver cancer through the regulation of the microRNA-675/sestrin 3 and the Wnt/β-catenin signaling pathway

Early growth response-1 (EGR1) is a multi-domain protein and an immediate early transcription factor that is induced during liver injury and controls the expression of a variety of genes implicated in metabolism, cell proliferation, and tumorigenesis. Liver cancer (LC) is a highly malignant disease with high mortality worldwide. This study focused on the function of EGR1 in LC development and the mechanism of action. Two LC-related datasets GSE101728 and GSE138178 downloaded from the Gene Expression Omnibus (GEO) database were used for identification of key genes involved in cancer progression. A microarray analysis was conducted to identify differentially expressed microRNAs (miRNAs) after EGR1 knockdown. The target gene of miR-675 was identified by integrated analysis. EGR1 and miR-675 were highly expressed, whereas sestrin 3 (SESN3) was poorly expressed in LC tissues and cells. High EGR1 expression was associated with poor liver function and disease severity in patients with LC. Knockdown of EGR1 weakened proliferation and invasiveness of LC cells. EGR1 bound to the miR-675 promoter and increased its transcription, and miR-675 bound to SESN3 mRNA to induce its downregulation. miR-675 upregulation promoted the malignance of LC cells, but further upregulation of SESN3 reduced invasiveness of cells. SESN3 was enriched in the Wnt/β-catenin signaling. EGR1 and miR-675 activated the Wnt/β-catenin through downregulating SESN3. This study demonstrated that EGR1 promotes the malignant behaviors of LC cells through mediating the miRNA-675/SESN3/Wnt/β-catenin axis.

ADAMTS-1: a novel target gene of an estrogen-induced transcription factor, EGR1, critical for embryo implantation in the mouse uterus

BACKGROUND

Recently, we demonstrated that estrogen (E₂) induces early growth response 1 (Egr1) to mediate its actions on the uterine epithelium by controlling progesterone receptor signaling for successful embryo implantation. EGR1 is a transcription factor that regulates the spectrum of target genes in many different tissues, including the uterus. E₂-induced EGR1 regulates a set of genes involved in epithelial cell remodeling during embryo implantation in the uterus. However, only few target genes of EGR1 in the uterus have been identified.

RESULT

The expression of ADAM metallopeptidase with thrombospondin type 1 motif 1 (Adamts-1) was significantly downregulated in the uteri of E₂-treated ovariectomized (OVX) Egr1(-/-) mice. Immunostaining of ADAMTS-1 revealed its exclusive expression in the uterine epithelium of OVX wild-type but not Egr1(-/-) mice treated with E₂. The expression profiles of Adamts-1 and Egr1 were similar in the uteri of E₂-treated OVX mice at various time points tested. Pre-treatment with ICI 182, 780, a nuclear estrogen receptor (ER) antagonist, effectively inhibited the E₂-dependent induction of Egr1 and Adamts-1. Pharmacologic inhibition of E₂-induced ERK1/2 or p38 phosphorylation interfered with the induction of EGR1 and ADAMTS-1. Furthermore, ADAMTS-1, as well as EGR1, was induced in stroma cells surrounding the implanting blastocyst during embryo implantation. Transient transfection with EGR1 expression vectors significantly induced the expression of ADAMTS-1. Luciferase activity of the Adamts-1 promoter containing EGR1 binding sites (EBSs) was increased by EGR1 in a dose-dependent manner, suggesting functional regulation of Adamts-1 transcription by EGR1. Site-directed mutagenesis of EBS on the Adamts-1 promoter demonstrated that EGR1 directly binds to the EBS at -1151/-1134 among four putative EBSs.

CONCLUSIONS

Collectively, we have demonstrated that Adamts-1 is a novel target gene of E₂-ER-MAPK-EGR1, which is critical for embryo implantation in the mouse uterus during early pregnancy.

Transcriptional study reveals a potential leptin-dependent gene regulatory network in zebrafish brain

The signal mediated by leptin hormone and its receptor is a major regulator of body weight, food intake and metabolism. In mammals and many teleost fish species, leptin has an anorexigenic role and inhibits food intake by influencing the appetite centres in the hypothalamus. However, the regulatory connections between leptin and downstream genes mediating its appetite-regulating effects are still not fully explored in teleost fish. In this study, we used a loss of function leptin receptor zebrafish mutant and real-time quantitative PCR to assess brain expression patterns of several previously identified anorexigenic genes downstream of leptin signal under different feeding conditions (normal feeding, 7-day fasting, 2 and 6-h refeeding). These downstream factors include members of cart genes, crhb and gnrh2, as well as selected genes co-expressed with them based on a zebrafish co-expression database. Here, we found a potential gene expression network (GRN) comprising the abovementioned genes by a stepwise approach of identifying co-expression modules and predicting their upstream regulators. Among the transcription factors (TFs) predicted as potential upstream regulators of this GRN, we found expression pattern of sp3a to be correlated with transcriptional changes of the downstream gene network. Interestingly, the expression and transcriptional activity of Sp3 orthologous gene in mammals have already been implicated to be under the influence of leptin signal. These findings suggest a potentially conserved regulatory connection between leptin and sp3a, which is predicted to act as a transcriptional driver of a downstream gene network in the zebrafish brain.

Transcription factor EGR-1 transactivates the MMP1 gene promoter in response to TNFα in HaCaT keratinocytes

Matrix metalloproteinase 1 (MMP-1), a calcium-dependent zinc- containing collagenase, is involved in the initial degradation of native fibrillar collagen. Tissue necrosis factor-alpha (TNFα) is a pro-inflammatory cytokine that is rapidly produced by dermal fibroblasts, monocytes/macrophages, and keratinocytes and regulates inflammation and damaged-tissue remodeling. MMP-1 is induced by TNFα and plays a critical role in tissue remodeling and skin aging processes. However, the regulation of the MMP1 gene by TNFα is not fully understood. We aimed to find additional cis-acting elements involved in the regulation of TNFα-induced MMP1 gene transcription in addition to the nuclear factor-kappa B (NF-kB) and activator protein 1 (AP1) sites. Assessments of the 5’-regulatory region of the MMP1 gene, using a series of deletion constructs, revealed the requirement of the early growth response protein 1 (EGR-1)-binding sequence (EBS) in the proximal region for proper transcription by TNFα. Ectopic expression of EGR-1, a zinc-finger transcription factor that binds to G-C rich sequences, stimulated MMP1 promoter activity. The silencing of EGR-1 by RNA interference reduced TNFα-induced MMP-1 expression. EGR-1 directly binds to the proximal region and transactivates the MMP1 gene promoter. Mutation of the EBS within the MMP1 promoter abolished EGR-1-mediated MMP-1 promoter activation. These data suggest that EGR-1 is required for TNFα-induced MMP1 transcriptional activation. In addition, we found that all three MAPKs, ERK1/2, JNK, and p38 kinase, mediate TNFα-induced MMP-1 expression via EGR-1 upregulation. These results suggest that EGR-1 may represent a good target for the development of pharmaceutical agents to reduce inflammation-induced MMP-1 expression.

Intermedin facilitates hepatocellular carcinoma cell survival and invasion via ERK1/2-EGR1/DDIT3 signaling cascade

As one of the most malignant cancer types, hepatocellular carcinoma (HCC) is highly invasive and capable of metastasizing to distant organs. Intermedin (IMD), an endogenous peptide belonging to the calcitonin family, has been suggested playing important roles in cancer cell survival and invasion, including in HCC. However, how IMD affects the behavior of HCC cells and the underlying mechanisms have not been fully elucidated. Here, we show that IMD maintains an important homeostatic state by activating the ERK1/2-EGR1 (early growth response 1) signaling cascade, through which HCC cells acquire a highly invasive ability via significantly enhanced filopodia formation. The inhibition of IMD blocks the phosphorylation of ERK1/2, resulting in EGR1 downregulation and endoplasmic reticulum stress (ER) stress, which is evidenced by the upregulation of ER stress marker DDIT3 (DNA damage-inducible transcript 3). The high level of DDIT3 induces HCC cells into an ER-stress related apoptotic pathway. Along with our previous finding that IMD plays critical roles in the vascular remodeling process that improves tumor blood perfusion, IMD may facilitate the acquisition of increased invasive abilities and a survival benefit by HCC cells, and it is easier for HCC cells to obtain blood supply via the vascular remodeling activities of IMD. According to these results, blockade of IMD activity may have therapeutic potential in the treatment of HCC.

Chrysoeriol Prevents TNFα-Induced CYP19 Gene Expression via EGR-1 Downregulation in MCF7 Breast Cancer Cells

Estrogen overproduction is closely associated with the development of estrogen receptor-positive breast cancer. Aromatase, encoded by the cytochrome P450 19 (CYP19) gene, regulates estrogen biosynthesis. This study aimed to identify active flavones that inhibit CYP19 expression and to explore the underlying mechanisms. CYP19 expression was evaluated using reverse transcription PCR, quantitative real-time PCR, and immunoblot analysis. The role of transcription factor early growth response gene 1 (EGR-1) in CYP19 expression was assessed using the short-hairpin RNA (shRNA)-mediated knockdown of EGR-1 expression in estrogen receptor-positive MCF-7 breast cancer cells. We screened 39 flavonoids containing 26 flavones and 13 flavanones using the EGR1 promoter reporter activity assay and observed that chrysoeriol exerted the highest inhibitory activity on tumor necrosis factor alpha (TNFα)-induced EGR-1 expression. We further characterized and demonstrated that chrysoeriol inhibits TNFα-induced CYP19 expression through inhibition of extracellular signal-regulated kinase 1/2 (ERK1/2)-mediated EGR-1 expression. Chrysoeriol may be beneficial as a dietary supplement for the prevention of estrogen receptor-positive breast cancer, or as a chemotherapeutic adjuvant in the treatment of this condition.

Reciprocal fine-tuning of progesterone and prolactin-regulated gene expression in breast cancer cells

Progesterone and prolactin are two key hormones involved in development and remodeling of the mammary gland. As such, both hormones have been linked to breast cancer. Despite the overlap between biological processes ascribed to these two hormones, little is known about how co-expression of both hormones affects their individual actions. Progesterone and prolactin exert many of their effects on the mammary gland through activation of gene expression, either directly (progesterone, binding to the progesterone receptor [PR]) or indirectly (multiple transcription factors being activated downstream of prolactin, most notably STAT5). Using RNA-seq in T47D breast cancer cells, we characterized the gene expression programs regulated by progestin and prolactin, either alone or in combination. We found significant crosstalk and fine-tuning between the transcriptional programs executed by each hormone independently and in combination. We divided and characterized the transcriptional programs into four broad categories. All crosstalk/fine-tuning shown to be modulated by progesterone was dependent upon the expression of PR. Moreover, PR was recruited to enhancer regions of all regulated genes. Interestingly, despite the canonical role for STAT5 in transducing prolactin-signaling in the normal and lactating mammary gland, very few of the prolactin-regulated transcriptional programs fine-tuned by progesterone in this breast cancer cell line model system were in fact dependent upon STAT5. Cumulatively, these data suggest that the interplay of progesterone and prolactin in breast cancer impacts gene expression in a more complex and nuanced manner than previously thought, and likely through different transcriptional regulators than those observed in the normal mammary gland. Studying gene regulation when both hormones are present is most clinically relevant, particularly in the context of breast cancer.

Leptin promotes fatty acid oxidation and OXPHOS via the c-Myc/PGC-1 pathway in cancer cells

Alteration in cellular energy metabolism plays a critical role in the development and progression of cancer. Leptin is a hormone secreted by adipose tissue. Recent reports have shown that leptin can induce cancer cell proliferation and regulate cell energy metabolism, but the regulatory mechanism is still unclear. Here, we showed that leptin could promote cell proliferation and maintain high adenosine triphosphate levels in HCT116 and MCF-7 cells. The expression levels of carnitine palmitoyl transferase 1A (CPT1A), pyruvate dehydrogenase, succinate dehydrogenase subunit A and mitochondrial respiratory chain-associated proteins NADH dehydrogenase 1 (ND1), NADH:ubiquinone oxidoreductase subunit B8, and mitochondrial transcription factor A (TFAM) were distinctly increased in leptin-treated HCT116 and MCF-7 cells, while fatty acid synthase and lactate dehydrogenase expression were downregulated. Simultaneously, we found that c-Myc and peroxisome proliferator-activated receptor gamma co-activator 1 (PGC-1) protein expression levels were significantly increased. These results indicated that leptin boosted fatty acid β-oxidation and the tricarboxylic acid cycle, enhanced oxidative phosphorylation (OXPHOS) activity, and inhibited fatty acid synthesis and glycolysis in tumor cells. Gene transfection experiments revealed that leptin could induce the expression of c-Myc. Moreover, the expressions of PGC-1, CPT1A, and TFAM proteins were downregulated in HCT116 cells with low expression of c-Myc, and the expression levels of these proteins were increased in HCT116 cells overexpressing c-Myc. These findings suggest that leptin plays an important role in the regulation of energy metabolism in tumor cells. It may regulate fatty acid oxidation and OXPHOS of tumor cells by regulating the c-Myc/PGC-1 pathway. Targeting metabolic pathways for cancer treatment has been investigated as potential preventive or therapeutic methods. This study has important implications for the clinical therapy of tumor cell metabolism through hormone regulation.

Egr1 mediates the effect of insulin on leptin transcription in adipocytes

In mammals, leptin production in adipocytes is up-regulated by feeding and insulin. Although this regulatory connection is central to all physiological effects of leptin, its molecular mechanism remains unknown. Here, we show that the transcription factor early growth response 1, Egr1, is rapidly but transiently induced by insulin in adipose cells both in vitro and in vivo, and its induction is followed by an increase in leptin transcription. ChIP and luciferase assays demonstrate that Egr1 directly binds to and activates the leptin promoter. Interestingly, the lipid droplet protein FSP27 may work as a co-factor for Egr1 in regulating leptin expression. By using siRNA-mediated knockout of Egr1 along with its overexpression in adipocytes, we demonstrate that Egr1 is both necessary and sufficient for the stimulatory effect of insulin on leptin transcription.