Phorbol myristate acetate-induced Egr-1 expression is suppressed by phospholipase D isozymes in human glioma cells

Pathogenetic implications of early growth response 1 in Ewing sarcoma

Ewing sarcoma (ES) is the second most common primary malignant bone tumour, mainly occurs in children and adolescents, and has an overwhelming mortality. Despite extensive studies, few effective oncogenic signals have been described. Therefore, it is crucial to exploit novel pathognomonic factors and targetable biomarkers for ES patients. Based on previous studies, we speculate that insulin-like growth factor 1 receptor (IGF1R), which is upregulated by early growth response 1 (EGR1), may play a pivotal role in strengthening the downward transmission of IGF1 cascades. Therefore, in this study, we concentrated on determining the pathogenetic contribution of EGR1 in diverse ES cells. This report is the first to study the pathogenic role of EGR1 in ES. ES cells were cultured and transfected with Stealth RNAi human EGR1 small interfering RNA (siRNA) or negative control. Cell proliferation and invasion potential were measured. mRNA and protein expression of EGR1, IGF1R, and EWS-FLI1 also were assessed. In all EGR1 siRNA-transfected cells (SK-ES-1, RD-ES, and HS863.T), cell proliferation and invasive potential decreased significantly in EGR1 siRNA-transfected ES cells. mRNA and protein expression for EGR1, IGF1R, and EWS-FLI1 were also significantly reduced. In conclusion, EGR1 upregulated IGF1R expression and enhanced the expression of the oncogenic fusion protein EWS-FLI1. The EWS-FLI1/EGR1/IGF1R cascade combined with the previously confirmed pathways can form a speculative circuit, implicating positive feedback for tumourigenesis in ES. Therefore, EGR1 inhibitors are expected to be useful for the treatment of ES by preventing oncogenic IGF1/IGF1R expression.

Antitumor effects of α-bisabolol against pancreatic cancer

In the present study, we investigated whether α-bisabolol, a sesquiterpene alcohol present in essential oils derived from a variety of plants, has antitumor effects against pancreatic cancer. α-Bisabolol induced a decrease in cell proliferation and viability in pancreatic cancer cell lines (KLM1, KP4, Panc1, MIA Paca2), but not in pancreatic epithelial cells (ACBRI515). α-Bisabolol treatment induced apoptosis and suppressed Akt activation in pancreatic cancer cell lines. Furthermore, α-bisabolol treatment induced the overexpression of early growth response-1 (EGR1), whereas EGR1 siRNA decreased the α-bisabolol-induced cell death of KLM1 cells. Tumor growth in both subcutaneous and peritoneal xenograft nude mouse models was significantly inhibited by intragastric administration of 1000 mg/kg of α-bisabolol, once a week for three weeks. The results indicate that α-bisabolol could be a novel therapeutic option for the treatment of pancreatic cancer.

Wilms tumor suppressor 1 (WT1) and early growth response 1 (EGR1) are regulators of STIM1 expression

Store-operated calcium entry (SOCE) is a key evolutionarily conserved process whereby decreases in endoplasmic reticulum Ca(2+) content lead to the influx of Ca(2+) across the plasma membrane. How this process is regulated in specific tumor cell types is poorly understood. In an effort to address this concern, we obtained and tested primary Wilms tumor cells, finding no detectable SOCE in this cell type. Analysis of the expression levels of STIM1 and ORAI1 (the molecular mediators of SOC) revealed poor STIM1 expression. Analysis of the STIM1 promoter using the TESS search system (University of Pennsylvania) revealed four putative response elements to the zinc-finger proteins WT1 (Wilms tumor suppressor 1) and EGR1 (early growth response 1). Either overexpression of WT1 or knockdown of EGR1 resulted in loss of STIM1 expression and a resultant decrease in SOCE. Furthermore, examination of Egr1 knock-out animals revealed loss of STIM1 expression in multiple tissues. Finally, using chromatin immunoprecipitation, we reveal direct binding of both WT1 and EGR1 to putative response elements located within 500 bp of the transcriptional start site of STIM1. Considering that WT1 and EGR1 are well described oncogenes and tumor suppressors, these observations may reveal new mechanisms responsible for distinct Ca(2+) signals in cancer cells.

Snail associates with EGR-1 and SP-1 to upregulate transcriptional activation of p15INK4b

Snail is a multifunctional transcriptional factor that has been described as a repressor in many different contexts. It is also proposed as an activator in a few cases relevant to tumor progression and cell-cycle arrest. This study investigated the detailed mechanisms by which Snail upregulates gene expression of the CDK inhibitor p15(INK4b) in HepG2 induced by the tumor promoter tetradecanoyl phorbol acetate (TPA). Using deletion mapping, the TPA-responsive element on the p15(INK4b) promoter was located between 77 and 228 bp upstream of the transcriptional initiation site, within which the putative binding regions of early growth response gene 1 (EGR-1) and stimulatory protein 1 (SP-1) were found. Gene expression of EGR-1, Snail and SP-1 can be induced by TPA within 0.5-6 h. In addition, basal levels of SP-1, but not of the other two transcriptional factors, were observed. Blockade of TPA-induced gene expression of Snail, EGR-1 or SP-1 suppressed activation of the p15-pro228 reporter plasmid harboring the TPA-responsive element. More detailed deletion mapping and site-directed mutagenesis further concluded that the overlapping EGR-1/SP-1-binding site was required for TPA-induced p15-pro228 activation. In an EMSA, a DNA-protein complex was elevated by TPA, which can be blocked by antibodies against EGR-1, SP-1 or Snail at 6 h. Immunoprecipitation/western blotting demonstrated that TPA could trigger the association of EGR-1 with Snail or SP-1. Furthermore, a double chromatin immunoprecipitation assay verified that EGR-1 could form a complex with Snail or SP-1 on the TPA-responsive element after treatment with TPA for 2-6 h. Finally, we demonstrated a novel Snail-target region which could be bound by Snail and was also required for TPA-induced p15-pro228 activation. In conclusion, Snail associates with EGR-1 and SP-1 to mediate TPA-induced transcriptional upregulation of p15(INK4b) in HepG2.