Egr-1 is activated by 17beta-estradiol in MCF-7 cells by mitogen-activated protein kinase-dependent phosphorylation of ELK-1

Early growth response-1 (Egr-1) is an immediate-early gene induced by E2 in the rodent uterus and breast cancer cells. E2 induces Egr-1 mRNA and protein levels in MCF-7 human breast cancer cells and reporter gene activity in cells transfected with pEgr-1A, a construct containing the -600 to +12 region of the Egr-1 promoter linked to the firefly luciferase gene. Deletion analysis of the Egr-1 promoter identified a minimal E2-responsive region of the promoter that contained serum response element (SRE)3 (-376 to -350) which bound Elk-1 and serum response factor (SRF) in gel mobility shift assays. Hormone-responsiveness of Egr-1 in MCF-7 cells was specifically inhibited by PD98059, a mitogen-activated protein kinase kinase inhibitor, but not by LY294002, an inhibitor of phosphatidylinositol-3-kinase (PI3-K). These results contrasted with hormone-dependent activation of the SRE in the c-fos promoter, which was inhibited by both PD98059 and LY294002. Differences in activation of the SREs in Egr-1 and c-fos were related to promoter sequence, which defines the affinities of Elk-1 and SRF to their respective binding sites. Thus, Egr-1, like c-fos, is activated through non-genomic (extranuclear) pathways of estrogen action in breast cancer cells.     

Placenta Growth Factor-induced Early Growth Response 1 (Egr-1) Regulates Hypoxia-inducible Factor-1α (HIF-1α) in Endothelial Cells

Leukotrienes, the lipid inflammatory products derived from arachidonic acid, are involved in the pathogenesis of respiratory and cardiovascular diseases and reactive airway disease in sickle cell disease. Placenta growth factor (PlGF), elaborated from erythroid cells, increased the mRNA expression of 5-lipoxygenase and 5-lipoxygenase-activating protein (FLAP) in human pulmonary microvascular endothelial cells. PlGF-induced both promoter activity and mRNA expression of hypoxia-inducible factor-1α (HIF-1α), which was abrogated by early growth response-1 (EGR-1) small interfering RNA. PlGF showed a temporal reciprocal relationship in the mRNA levels of EGR-1 and NAB2, the latter a repressor of Egr-1. Moreover, Nab2, but not mutant Nab2, significantly reduced promoter activity and mRNA expression of HIF-1α and also reduced expression of the HIF-1α target gene FLAP. Furthermore, overexpression of Egr-1 led to increased promoter activities for both HIF-1α and FLAP in the absence of PlGF. Additionally, the Egr-1-mediated induction of HIF-1α and FLAP promoters was reduced to basal levels by EGR-1 small interfering RNA. The binding of Egr-1 to HIF-1α promoter was corroborated by electrophoretic mobility shift assay and chromatin immunoprecipitation assay, which showed increased Egr-1 binding to the HIF-1α promoter in response to PlGF stimulation. These studies provide a novel mechanism for PlGF-mediated regulation of HIF-1α via Egr-1, which results in increased FLAP expression. This study provides a new therapeutic target, namely Egr-1, for attenuation of elevated leukotriene levels in patients with sickle cell disease and other inflammatory diseases.     

Ascochlorin inhibits growth factor-induced HIF-1α activation and tumor-angiogenesis through the suppression of EGFR/ERK/p70S6K signaling pathway in human cervical carcinoma cells

Ascochlorin, a non-toxic prenylphenol compound derived from the fungus Ascochyta viciae, has been shown recently to have anti-cancer effects on various human cancer cells. However, the precise molecular mechanism of this anti-cancer activity remains to be elucidated. Here, we investigated the effects of ascochlorin on hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) expression in human epidermoid cervical carcinoma CaSki cells. Ascochlorin inhibited epidermal growth factor (EGF)-induced HIF-1α and VEGF expression through multiple potential mechanisms. First, ascochlorin selectively inhibited HIF-1α expression in response to EGF stimulation, but not in response to hypoxia (1% O(2)) or treatment with a transition metal (CoCl(2)). Second, ascochlorin inhibited EGF-induced ERK-1/2 activation but not AKT activation, both of which play essential roles in EGF-induced HIF-1α protein synthesis. Targeted inhibition of epidermal growth factor receptor (EGFR) expression using an EGFR-specific small interfering RNA (siRNA) diminished HIF-1α expression, which suggested that ascochlorin inhibits HIF-1α expression through suppression of EGFR activation. Finally, we showed that ascochlorin functionally abrogates in vivo tumor angiogenesis induced by EGF in a Matrigel plug assay. Our data suggest that ascochlorin inhibits EGF-mediated induction of HIF-1α expression in CaSki cells, providing a potentially new avenue of development of anti-cancer drugs that target tumor angiogenesis.     

IGF-1通过SRF结合位点调节SMYD1在C2C12细胞中的表达

SMYD1是组蛋白甲基转移酶,在骨骼肌和心肌中特异表达,是调节心肌和骨骼肌发育的关键因子.虽然SMYD1的生物学功能比较清楚,但细胞外因子调节SMYD1基因表达的机制还没有报导.IGF-1能促进心肌和骨骼肌的发育、加速肌肉的损伤修复过程.通过Western印迹发现,在用IGF-1处理的C2C12细胞中,SMYD1的表达水平随处理时间逐步升高,SRF蛋白和Myogenin的表达也呈现类似的趋势.通过构建不同长度的SMYD1基因启动子荧光素酶报告基因载体,发现SMYD1基因启动子上IGF-1的应答区域位于-620～-110 bp;EMSA实验表明,SRF结合在SMYD1启动子的CArG位点,而IGF-1则能促进SRF与SMYD1启动子的结合;若将启动子上的CArG元件突变,IGF-1对SMYD1启动子的激活效应被削弱.可见IGF-1能够上调SMYD1在C2C12细胞中的表达,并且这种调控作用是部分通过调节SRF与SMYD1启动子上CArG位点的结合而实现的.此外,通过荧光素酶报告基因分析,发现SMYD1能够激活肌肉标志因子肌肉肌酸激酶(MCK)基因活性,而且与MyoD基因存在协同激活效应.因此,SMYD1可能是IGF-1的下游靶基因,SMYD1可能通过与MyoD协同作用,促进肌肉的分化。     

Hypoxic induction of human visfatin gene is directly mediated by hypoxia-inducible factor-1

Visfatin has been originally identified as a growth factor for early stage B cells and recently known as an adipokine. Here, we report that hypoxia induces the visfatin mRNA and protein levels in MCF7 breast cancer cells. We also demonstrate that induction of visfatin gene is regulated by hypoxia-inducible factor-1alpha (HIF-1alpha). Moreover, 5'-flanking promoter region of human visfatin gene contains two functional HIF responsive elements (HREs), activating the expression of visfatin. Mutation of these HREs in the visfatin promoter abrogates activation of a luciferase reporter gene driven by visfatin promoter under hypoxia. Taken together, our results demonstrate that visfatin is a new hypoxia-inducible gene of which expression is stimulated through the interaction of HIF-1 with HRE sites in its promoter region.