Sirt3调控SFXN1去乙酰化促进一碳代谢重编程逆转胰腺癌恶性生物学行为的机制研究

Pancreatic cancer has a very high degree of malignancy, lack of early diagnosis and effective post-treatment, resulting in a very poor prognosis of patients. Metabolic reprogramming is a crucial hallmark in pancreatic cancer carcinogenesis. Previous work demonstrated serine metabolism is abnormally activated in pancreatic cancer, but molecular mechanism is unclear. Recent study has revealed SFXN1 is a novel serine transporter and indispensable for serine metabolism. In this study, we found Sirt3 could deacetylate SFXN1 and possibly promote SFXN1 degradation which subsequently inhibiting serine metabolism and reversing the malignant phenotype of pancreatic cancer. To realize this hypothesis, this project will focus on elucidating the deacetylation modification of SFXN1 by Sirt3 from the cell, animal model and clinical samples. Protein modification mass spectrometry, seahorse XFe96 bioenergetic analyzer and RTCA will be performed to clarify the regulation of SFXN1 deacetylation modification and the key mechanism of SFXN1 protein quality control, and systematically reveal the molecular mechanism of Sirt3-mediated SFXN1 deacetylation modification in promoting serine metabolic reprogramming to reverse the malignant biological behavior of pancreatic cancer, which finally provide a new basis for the early diagnosis and therapy of pancreatic cancer.

胰腺癌具有极高恶性度，缺乏早期诊断及有效的后期治疗，导致患者非常差的预后。代谢重编程是胰腺癌发生发展的一个重要过程，研究发现丝氨酸一碳代谢途径在胰腺癌中异常活跃，但具体的调控机制尚不明确。最新的研究揭示了线粒体跨膜蛋白SFXN1是调控丝氨酸进入线粒体的关键转运体。本项目前期研究发现去乙酰化酶Sirt3可对SFXN1进行去乙酰化修饰并可能调控其蛋白质降解，进而抑制细胞丝氨酸代谢过程逆转胰腺癌的恶性表型。为证实这一假说，本项目拟通过从细胞，动物及临床水平，应用蛋白质修饰质谱、seahorse XFe96生物能量分析仪及RTCA等技术深入探究Sirt3对SFXN1的去乙酰化修饰作用，阐明乙酰化修饰调控SFXN1蛋白质稳定性的关键机理，进而系统地揭示由Sirt3介导SFXN1去乙酰化修饰促进丝氨酸代谢重编程逆转胰腺癌恶性生物学行为的分子机制，为胰腺癌的早期诊断及治疗提供新的依据。

丝氨酸与叶酸代谢重编程被证实在肿瘤发生及进展中具有重要的作用，其所介导的一碳单位的转移被认为是调节甲基化等表观遗传修饰的关键因素。SFXN1作为线粒体丝氨酸转运体在调控肿瘤发生及进展中的作用尚不明确。本项目通过前期研究发现SFXN1可能是Sirt3调控细胞代谢的一个重要靶点，而其具体分子机理尚待进一步研究。通过本项目的支持，我们发现敲低SFXN1可显著抑制胰腺癌细胞生长及迁移。同时，研究证实SFXN1可维护线粒体呼吸链及氧化还原的稳态。进一步地，敲低SFXN1可显著降低叶酸代谢相关酶MTHFD1、MTHFD2及MTHFD1L的表达，通过过表达SFXN1可回补MTHFD2和MTHFD1L的表达。同时，通过相关性分析证实SFXN1与MTHFD1和MTHFD2在胰腺癌中的表达呈正相关，且MTHFD1和MTHFD2高表达与胰腺癌患者的预后呈显著负相关。研究发现，MTHFD2敲低或酶活性抑制可显著降低细胞增殖和迁移能力。重要的是，研究证实MTHFD2可调控ACLY调节组蛋白H3乙酰化修饰水平，这一发现为理解线粒体逆行信号提供了重要的支持。此外，基于SFXN1对MTHFD1的调节作用，本项目通过研究分析了FDA批准药物富马酸二甲酯(DMF)可抑制MTHFD1的表达，诱导代谢危机并最终抑制胰腺癌进展的关键作用。总的来说，本项目研究了丝氨酸转运体SFXN1调控胰腺癌生长和迁移的关键作用，并揭示了SFXN1介导丝氨酸转运与叶酸代谢的紧密联系。研究结果将加深SFXN1介导丝氨酸转运并协同叶酸代谢促进胰腺癌进展的认识，也将为基于SFXN1-MTHFD1-MTHFD2进行胰腺癌早期诊断以及靶向一碳代谢稳态治疗胰腺癌提供一定的实验依据。