Constitutive overexpression of Nrf2-dependent heme oxygenase-1 in A549 cells contributes to resistance to apoptosis induced by epigallocatechin 3-gallate
Constitutive overexpression of Nrf2-dependent heme oxygenase-1 in A549 cells contributes to resistance to apoptosis induced by epigallocatechin 3-gallate
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DOI：
10.1074/jbc.m604748200
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发表时间：
2006-11-03
影响因子：
4.8
通讯作者：
Mukhtar, Hasan
中科院分区：
文献类型：
--
作者：
Kweon, Mee-Hyang;Adhami, Vaqar Mustafa;Mukhtar, Hasan
表没食子儿茶素没食子酸酯(EGCG)是绿茶中发现的主要多酚，在许多癌细胞中具有抗增殖和促凋亡作用。然而，我们发现，在许多癌细胞中，人肺腺癌A549细胞对EGCG诱导的凋亡具有明显的抵抗力(即使在100mM×72h)。应激刺激诱导的血红素氧合酶-1(HO-1)是一种主要的细胞防御机制，但它可能与促进某些癌细胞的增殖和化疗耐药有关。由于我们发现A549细胞结构性地过表达HO-1及其相关的转录因子Nrf2，所以我们检验了一种假设，即这些细胞中的EGCG抵抗可能与Nrf2介导的HO-1过表达有关。用锡原卟啉IX抑制HO-1和用RNA干扰沉默使细胞对EGCG和经典的氧化剂诱导的细胞凋亡更加敏感。有趣的是，高浓度的EGCG通过抑制HO-1蛋白和mRNA的表达来诱导细胞凋亡，这种作用与Nrf2-Are结合和HO-1-Are-荧光素酶活性的降低有关，提示Nrf2驱动HO-1的转录激活。由于我们观察到显著高水平的磷酸化蛋白激酶Cα，以及EGCG和去铁胺(一种铁螯合剂)对其抑制，因此进一步研究了涉及磷酸化蛋白激酶Cα和铁在Nrf2-HO-1激活中的可能机制。总之，我们的研究结果表明，Nrf2介导的HO-1过表达对EGCG诱导的细胞凋亡具有抵抗力；因此，其失活可能是克服化学预防和化疗抵抗力的一个靶点。
Epigallocatechin 3-gallate (EGCG), the major polyphenol found in green tea, exerts antiproliferative and proapoptotic effects in many cancer cells. However, we found that among many cancer cells human lung adenocarcinoma A549 cells are markedly resistant to apoptosis induction by EGCG ( even at 100 mu M for 72 h). Heme oxygenase-1 (HO-1) induced by stress stimuli represents a prime cellular defense mechanism, but it may be associated with enhanced cell proliferation and chemoresistance in some cancer cells. Because we found that A549 cells constitutively overexpress HO-1 and its associated transcription factor Nrf2, we tested an hypothesis that EGCG resistance in these cells may be linked with Nrf2-mediated HO-1 overexpression. HO-1 inhibition with tin-protoporphyrin IX and silencing with RNA interference rendered cells more sensitive to apoptosis induction by EGCG and classical prooxidants. Interestingly, EGCG at high concentration (> 200 mu M) induced apoptosis by suppressing expression of HO-1 protein and mRNA, and this effect correlated with a decrease in both Nrf2-ARE binding and HO-1-ARE- luciferase activity, suggesting Nrf2-driven transcriptional activation of ho-1. Because we observed notably high levels of phosphorylated protein kinase C alpha and its suppression by EGCG and deferoxamine (an iron chelator), a possible mechanism involving phosphorylated protein kinase C alpha and iron in Nrf2-HO-1 activation was further investigated. Collectively, our findings suggest that Nrf2-mediated HO- 1 overexpression confers resistance to apoptosis induction by EGCG; therefore, its inactivation may be a target for overcoming the resistance to chemoprevention and chemotherapy.