6-丙酮酰四氢生物蝶呤合成酶调控TGF-β信号通路的分子机制及其在结直肠癌发展中的作用

6-pyruvoyltetrahydropterin synthase (PTS), a key enzyme for the production of tetrahydrobiopterin (BH4), is closely related to the physiological roles, such as cellular proliferation, vascular and neurological function. However, the relationship between the function of PTS and tumor has rarely been investigated. The preliminary study demonstrated that the expression of PTS was inversely associated with the progression of colorectal cancer (CRC) and the invasion of tumor cells. Moreover, PTS depletion led to the impaired latent TGF-β binding protein 1 (LTBP1)-mediated TGF-β secretion under hypoxia, and biochemical analysis indicated that the interaction between LTBP1 and PTS is dependent on the AMPK-mediated protein phosphorylation. We hypothesize that AMPK-PTS signaling affects the invasion of tumor cells through regulating TGF-β secretion. In the present project, we will further explore the concrete mechanism and site of AMPK mediated PTS phosphorylation under hypoxia and the molecular mechanisms underlying the effects of PTS and BH4 on TGF-β secretion. Moreover, the effects of AMPK-PTS-TGF-β pathway on the development of CRC will be clarified by using relevant cell lines, mice models and clinical samples. Above all, this study aims to reveal the mechanism underlying the effect of PTS on TGF-β signaling pathway and its implication in the development and metastasis of CRC. The results of this study will contribute to the theoretical basis of the clinical diagnosis and treatment.

6-丙酮酰四氢生物蝶呤合成酶（PTS）作为催化代谢产物四氢生物蝶呤（BH4）生成的关键酶，与细胞增殖、血管和神经系统功能相关；然而，目前对于PTS的功能与肿瘤之间的关系了解尚少。前期研究发现PTS的表达水平与结直肠癌进展程度以及肿瘤细胞侵袭能力呈负相关；还发现在氧化应激条件下，PTS抑制了肿瘤细胞中TGF-β的分泌；并且，在此条件下激活的AMPK磷酸化PTS，促进了PTS与LTBP1的相互作用。提示AMPK-PTS通过调控TGF-β分泌影响肿瘤细胞侵袭能力。本项目拟研究：在氧化应激条件下，AMPK作用于PTS的磷酸化位点及确切机制；PTS及其代谢产物BH4调控TGF-β分泌的分子机制；在细胞、动物模型、临床中明确AMPK-PTS-TGF-β信号通路对结直肠癌发展的影响。本项目将阐明PTS调控TGF-β信号通路的分子机制及其在结直肠癌发展中的作用，为临床诊治提供理论依据。

6-丙酮酰四氢生物蝶呤合成酶（PTS）是催化四氢生物蝶呤（BH4）的必需酶。我们前期研究发现在结直肠癌组织中PTPS的表达水平较癌旁组织显著升高, 并且，在早期结直肠癌亚组中，肿瘤大小与PTS表达显著相关，这揭示了在肿瘤发生早期对高水平PTS的特殊要求。机制研究表明PTS是稳定iNOS-LTBP1相互作用所必需的，低氧可以诱导PTS与LTBP1结合，并且这一结合依赖于AMPK介导的PTS-Thr58磷酸化。低氧刺激的PTS-Thr58磷酸化及PTS的催化活性是iNOS与LTBP1形成复合物的必需条件；这反过来促进了NO介导的LTBP1 S-亚硝基化和相关蛋白酶体导致的LTBP1蛋白降解。最终，PTS/iNOS介导的LTBP1下调可抑制低氧条件下TGF-β的分泌以及TGF-β诱导的细胞生长，从而可以解释在低氧条件下如何维持肿瘤细胞的生长这一科学问题。以上研究结果经整理后，已经发表于Molecular Cell杂志。此外，项目负责人专注于代谢与肿瘤转移（特别是早期转移）这一科学问题和临床难点，在该项国家自然科学基金的资助下，开展了相关基础和临床研究。探索了缺糖条件下增强表达的精氨酸合成酶ASNS促进癌转移机制，发表于International Journal of Medical Sciences；并评估了软镜微创治疗消化道肿瘤的效果，发表于the Journal of American College of Surgeons和Gut杂志。