结直肠癌分化细胞传输乳酸增强癌干细胞自我更新及其分子机制

Tumor cell population is heterogeneous, containing differentiated cells and cancer stem cells (CSCs). CSCs possess self-renewal capacity, which is relating to tumor initiation, progression and recurrence in colorectal cancer (CRC). Recent studies have shown that intratumor subpopulations can positively interact to promote the tumor progression. It is still unclear whether differentiated cells promote self-renewal of CSCs. Although lactate is generally considered a waste product, our preliminary data has demonstrated that differentiated cells primarily use glucose for glycolytic energy production and generate abundant lactate，while CSCs have been thought to primarily use glucose for oxidative energy production with a low level of lactate production and high level of reactive oxygen species (ROS). In addition, increased level of ROS in CSCs promotes self-renewal capacity. After exported by differentiated cells, lactate is able to be taken by CSCs and then promotes self-renewal capacity and ROS production in CRCs. Moreover, inhibition of lactate production of differentiated cells converts this effect. Further investigations have shown that differentiated cells-released lactate is able to enhance the Wnt activity in CSCs. Based on our preliminary data, we hypothesize that lactate transferred from differentiated cells to CSCs mediates Wnt signaling and thus enhances self-renewal capacity. We proposed the following main aims: 1) To find out whether enhancement or inhibition of lactate shuttle between differentiated cells and CSCs promotes or decreases the self-renewal of CSCs; 2) To investigate the role of ROS in regulating self-renewal capacity and Wnt activity; 3) To explore whether Wnt signaling pathway involves in promoting self-renewal of CSCs upon lactate transfer from differentiated cells to CSCs, and to further investigate the underlying mechanisms. If the proposed aims are well accomplished, the findings will provide great benefit for patients suffering cancer, especially CRC.

肿瘤包含不同细胞亚群，包括癌分化细胞和癌干细胞；癌干细胞具有自我更新的特性，是结直肠癌复发和转移的重要原因。别人和我们前期研究均表明癌分化细胞和癌干细胞糖代谢方式不同，前者依赖糖酵解产生乳酸，后者进行有氧呼吸生成活性氧（ROS），且ROS可促进癌干细胞自我更新。肿瘤不同亚群可相互协作促进肿瘤进展，但癌分化细胞能否促进癌干细胞自我更新尚无报道。我们进一步研究表明癌分化细胞可将乳酸传输至癌干细胞，增强其氧化磷酸化提高ROS，促进其自我更新；而抑制癌分化细胞和癌干细胞之间乳酸穿梭可削弱这一效应。本课题拟在前期研究基础上，探讨增加或抑制结直肠癌分化细胞和癌干细胞之间的乳酸穿梭能否增强或削弱癌干细胞的自我更新；此外，探讨癌干细胞摄取乳酸后是如何调控Wnt信号通路，揭示结直肠癌分化细胞通过传输乳酸并被癌干细胞摄取从而增强其自我更新，并初步阐明其分子机制，为治疗提供新思路。

肿瘤包含不同的细胞亚群，包括癌分化细胞和癌干细胞。癌干细胞具有自我更新的特性，是结直肠癌复发和转移的重要原因。别人和我们的前期研究均表明癌分化细胞和癌干细胞糖代谢的方式不同，前者依赖糖酵解产生乳酸，后者进行有氧呼吸生成活性氧（ROS），且ROS可促进癌干细胞自我更新。肿瘤不同亚群可相互协作促进肿瘤进展，但癌分化细胞能否促进癌干细胞自我更新尚无报道。本项目组通过体外和体内实验探讨增强/抑制乳酸穿梭后，结直肠癌分化细胞对癌干细胞自我更新的影响，揭示ROS对结直肠癌干细胞自我更新的影响，阐明结直肠癌分化细胞传输乳酸通过ROS促进癌干细胞自我更新的机制。我们的研究结果显示结直肠癌分化细胞能增强癌干细胞的线粒体氧化磷酸化和细胞内ROS水平，并促进其自我更新；而抑制结直肠癌分化细胞和癌干细胞之间乳酸穿梭可削弱这一效应。进一步研究发现，乳酸通过促进结直肠癌干细胞的线粒体氧化磷酸化，升高其细胞内ROS水平从而增强细胞Wnt信号通路活性，促进其自我更新；抑制结直肠癌分化细胞的乳酸分泌可以显著削弱其增强癌干细胞Wnt信号通路活性的效应。进一步的机制研究表明，结直肠癌分化细胞传输乳酸增强结直肠癌干细胞线粒体有氧代谢，升高其ROS水平，促进PTEN降解，从而促进AKT及其下游β-catenin的磷酸化，增加β-catenin稳定性和核内移，从而增强癌干细胞的Wnt活性和自我更新能力。本项目揭示了结直肠癌分化细胞传输乳酸增强结直肠癌干细胞的自我更新，并初步阐明了其分子机制。在上述基础上，探讨靶向结直肠癌分化细胞与癌干细胞间的乳酸穿梭或针对结直肠癌干细胞的线粒体氧化磷酸化的代谢特点，为结直肠癌的治疗提供新的线索和思路。