Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) 參與結直腸癌腫瘤惡化之角色

Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) 在腫瘤細胞內的表現位置與腫瘤患者臨床預後有關，例如膽囊癌、肺癌和乳癌。但Nrf2腫瘤細胞之表現位置與結直腸癌腫瘤化角色以及患者之臨床預後至今仍不清楚。本研究假設Nrf2 表現於細胞質 (cytoplasmic Nrf2, cNrf2) 可能會促進腫瘤之生長與侵襲能力。因此本研究收集160位結直腸癌患者之腫瘤組織，以免疫染色分析Nrf2與其下游基因NQO1、HO-1蛋白之表現。NAD(P)H-quinone oxidoreductase 1 (NQO1)與Heme oxygenase-1 (HO-1) 表現顯示大多Nrf2會進入細胞核轉錄活化以上兩種基因，因此稱此Nrf2為nuclear Nrf2 (nNrf2)，反之則稱為cNrf2。Kaplan-Meier與Cox regression分析顯示，表現cNrf2之患者較表現nNrf2之患者有較短的存活期。在結腸癌細胞中，cNrf2 經由活化NF-κB/AKT/β-catenin路徑促進腫瘤細胞侵襲 (invasion) 與軟瓊酯聚落 (soft agar) 形成之能力。又發現cNrf2經由HIF1α/β-catenin促進PSMD4表現和降解p53蛋白，並增強CRM1轉錄表現，使得Nrf2送出細胞核，增加cNrf2之表現。此相互正調控機制會促進NF-κB/AKT/β-catenin路徑持續活化，造成腫瘤更加惡化。在動物模式中，proteasomal 抑制劑carfilzomib以及β-catenin 抑制劑XAV939能有效抑制cNrf2高表現細胞所誘發的轉移肺腫瘤之形成。本研究發現cNrf2會促進結直腸癌之腫瘤惡化與患者有較差之臨床預後，並提出cNrf2與PSMD4之相互調控機制是造成腫瘤惡化的主要分子機制。因此cNrf2可做為結直腸癌之腫瘤惡化與預後之生物標記。建議使用PSMD4 inhibitor 前臨床用藥carfilzomib或許能抑制cNrf2高表現之結直腸癌之腫瘤惡化以及改善患者之臨床預後和生命品質。

Differences in subcellular localization of Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) have been associated with poor outcomes in human cancers. However, the prognostic value of subcellular localization of Nrf2 in colorectal cancer and the underlying mechanism in tumor invasion remain unknown. We enrolled tumors from colorectal patients to evaluate Nrf2, NQO1, and HO-1 expression by immunohistochemistry. NQO1 and HO-1 positive tumors showed nearly complete expression of Nrf2 in the nucleus and/or showed partial expression in the nucleus/cytoplasm (nNrf2); however, tumors negative for NAD(P)H-quinone oxidoreductase 1 (NQO1) and Heme oxygenase-1 (HO-1) showed almost complete expression of Nrf2 in the cytoplasm and/or partial expression in the nucleus/cytoplasm (cNrf2). Kaplan-Meier and Cox regression analysis indicated poorer overall survival in patients with cNrf2 tumors than with nNrf2 tumors. Cell models provided evidence that cNrf2, rather than nNrf2, was responsible for cell invasion and soft agar growth triggered by activation of the NF-κB/AKT/β-catenin cascade. Mechanistically, cNrf2 persistently increased PSMD4 expression by the HIF1α/β-catenin axis, whereas PSMD4 reciprocally enhanced Nrf2 nuclear export by increasing CRM1 expression through p53 degradation. The mechanistic action of the cell model was further confirmed with a nude mouse animal model in which xenograft tumors induced by cNrf2 were nearly completely suppressed by the proteasomal inhibitor carfilzomib or the β-catenin inhibitor XAV939. We therefore suggest that PSMD4 or β-catenin might be potential targets for suppressing tumor aggressiveness, and consequently, improving outcomes in patients whose tumors express cNrf2.