State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, West China Medical School, and Collaborative Innovation Center for Biotherapy, Sichuan University, Chengdu 610041, China.
National Chengdu Center for Safety Evaluation of Drugs, State Key Laboratory of Biotherapy, West China Hospital, West China Medical School, and Collaborative Innovation Center for Biotherapy, Sichuan University, Chengdu 610041, China.
Theranostics. 2021 Jan 1;11(6):2966-2986. doi: 10.7150/thno.48699. eCollection 2021.
Serine hydroxymethyltransferase 2 (SHMT2) plays a critical role in serine-glycine metabolism to drive cancer cell proliferation. However, the nonmetabolic function of SHMT2 in tumorigenesis, especially in human colorectal cancer (CRC) progression, remains largely unclear. SHMT2 expression in human CRC cells was identified by western blot and immunofluorescence assay. The CRC cell proliferation, migration, and invasion after SHMT2 knockdown or overexpression were explored through and assays. Immunofluorescence, mRNA-seq, co-immunoprecipitation, chromatin immunoprecipitation-qPCR and immunohistochemistry assays were used to investigate the underlying mechanisms behind the SHMT2 nonmetabolic function. We demonstrated that SHMT2 was distributed in the cytoplasm and nucleus of human CRC cells. SHMT2 knockdown resulted in the significant inhibition of CRC cell proliferation, which was not restored by serine, glycine, or formate supplementation. The invasion and migration of CRC cells were suppressed after SHMT2 knockdown. Mechanistically, SHMT2 interacted with β-catenin in the cytoplasm. This interaction inhibited the ubiquitylation-mediated degradation of β-catenin and subsequently modulated the expression of its target genes, leading to the promotion of CRC cell proliferation and metastasis. Notably, the lysine 64 residue on SHMT2 (SHMT2) mediated its interaction with β-catenin. Moreover, transcription factor TCF4 interacted with β-catenin, which in turn increased expression, forming an SHMT2/β-catenin positive feedback loop. xenograft experiments confirmed that SHMT2 promoted the growth and metastasis of CRC cells. Finally, the level of SHMT2 was found to be significantly increased in human CRC tissues. The SHMT2 level was correlated with an increased level of β-catenin, associated with CRC progression and predicted poor patient survival. Taken together, our findings reveal a novel nonmetabolic function of SHMT2 in which it stabilizes β-catenin to prevent its ubiquitylation-mediated degradation and provide a potential therapeutic strategy for CRC therapy.
丝氨酸羟甲基转移酶 2（SHMT2）在丝氨酸-甘氨酸代谢中发挥关键作用，促进癌细胞增殖。然而，SHMT2 在肿瘤发生中的非代谢功能，特别是在人类结直肠癌（CRC）进展中的作用，仍很大程度上不清楚。通过 Western blot 和免疫荧光检测鉴定人 CRC 细胞中的 SHMT2 表达。通过 CCK-8 和划痕实验探讨 SHMT2 敲低或过表达后 CRC 细胞增殖、迁移和侵袭的变化。免疫荧光、mRNA-seq、免疫共沉淀、染色质免疫沉淀-qPCR 和免疫组化实验用于研究 SHMT2 非代谢功能的潜在机制。我们发现 SHMT2 分布在人 CRC 细胞的细胞质和细胞核中。SHMT2 敲低显著抑制 CRC 细胞增殖，而丝氨酸、甘氨酸或甲酸盐补充并不能恢复这一抑制作用。SHMT2 敲低抑制 CRC 细胞的侵袭和迁移。机制上，SHMT2 与细胞质中的β-catenin 相互作用。这种相互作用抑制了 β-catenin 的泛素化介导降解，进而调节其靶基因的表达，促进 CRC 细胞增殖和转移。值得注意的是，SHMT2 上的赖氨酸 64 残基（SHMT2）介导其与β-catenin 的相互作用。此外，转录因子 TCF4 与β-catenin 相互作用，进而增加了下游基因的表达，形成了 SHMT2/β-catenin 的正反馈回路。异种移植实验证实 SHMT2 促进了 CRC 细胞的生长和转移。最后，发现 SHMT2 在人 CRC 组织中的水平显著升高。SHMT2 水平与β-catenin 水平升高相关，与 CRC 进展相关，并预测患者预后不良。综上所述，我们的研究结果揭示了 SHMT2 的一个新的非代谢功能，即稳定β-catenin，防止其泛素化介导的降解，并为 CRC 治疗提供了一种潜在的治疗策略。
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