NF-κB在结肠癌细胞适应酸性微环境中的作用及调控机制

Because of increased glycolysis that produces lactic acids and poorly functional vasculature in solid tumors, cancer cells are usually immersed in an acidic microenvironment. Acidic extracellular pH is also known to promote tumor progression. We previously found that colorectal cancer cells that have become acclimated to acidic microenvironment (CRC-AA) exhibit increased autophagy, reduced level of reactive oxygen species (ROS) and rely more on high level of reduced glutathione (GSH). Autophagy and NRF2, however, do not contribute to the reduction in ROS. We found that NF-kB, a master regulator of stress response, is upregulated in CRC-AA and is essential for the survival of CRC-AA under acidic pH. This study will further confirm the critical role of NF-kB in the acclimation to chronic acidosis and determine whether NF-kB mediates the antioxidant defense in CRC-AA. We will test whether the reduction in p62, an adaptor for specific autophagy of GATA4, leads to the upregulation of GATA4-NF-kB pathway. Research findings will help understand how cells become adapted to stressful environment and how extracellular acidosis drives tumor malignance. Such knowledge is also critical for more effective cancer therapy.

肿瘤细胞的糖代谢偏向糖酵解，产生大量乳酸，同时由于实体瘤血流不畅，使乳酸在局部积累，造成局部酸性微环境。酸性微环境促进肿瘤恶性程度。目前对癌细胞如何适应酸性微环境所知甚少。我们前期发现长期适应酸性微环境的结肠癌细胞（CRC-AA）自噬水平升高，活性氧（ROS)水平下降，且细胞的生存更加依赖还原型谷胱甘肽（GSH）。但该体系中ROS降低不依赖自噬和NRF2。我们还发现在CRC-AA细胞中应激转录因子NF-kB功能上调且为酸性条件下CRC-AA细胞的生存所必须。本课题拟通过体内外实验进一步明确NF-kB在结肠癌细胞适应酸性微环境过程中的作用，尤其是明确NF-kB在抵抗ROS水平升高中的作用。我们将验证细胞自噬是否通过降解p62促进GATA4-NF-kB通路上调。研究结果将推进我们对细胞适应逆境机制的理解，并对酸性微环境如何促进癌细胞恶性进程提供更深度的认识。相关知识对肿瘤治疗有一定指导意义。

细胞如何适应逆境是重要的生物学问题，细胞适应逆境的机制也是理解癌细胞如何耐受营养缺乏以及抵抗放化疗的生物学基础。我们发现在适应慢性酸性微环境的结肠癌（CRC-AA）细胞中应激转录因子NF-kB功能显著上调且为酸性条件下CRC-AA细胞的生存所必须。我们通过体内外实验明确了NF-kB在结肠癌细胞适应酸性微环境过程中的作用及其功能上调的机制。我们发现在CRC-AA细胞中，自噬高度活跃，由此使SQSTM1/p62快速耗尽。GATA4的选择性自噬降解依赖p62，其缺乏导致GATA4的累积，从而驱动GATA4-NF-kB通路。NF-kB转录激活了众多抗氧化基因的表达，代替NRF2发挥抗氧化作用帮助细胞适应酸性微环境。我们还揭示了CRC-AA细胞的若干代谢特征，包括对糖酵解途径依赖性的降低、对氨基需求的升高以及线粒体功能的增强等。与CRC-AA细胞线粒体功能的增强相反，停滞于有丝分裂期的细胞所聚集的大量线粒体却处于功能紊乱状态。研究结果拓展了我们对NF-kB功能的认识，推进了我们对细胞适应逆境机制的理解，并对酸性微环境如何促进癌细胞恶性进程提供了更深度的信息。相关知识对肿瘤的治疗有重要指导意义。