Proteomic and metabolic changes in cancer cells after alternation of SHMT2 expressions

In order to understand the underline mechanism of SHMT2 (serine hydroxymethyltransferase 2) effect on tumor growth, proteome and metabolome analysis were carried on an engineered HeLa cell line (HeLa-SHMT2-shSHMT2, short as HeLa-Ss), which has inducible SHMT2 over-expression or suppression by treating cell with tetracycline or IPTG, respectively. SHMT2 over-expression in HeLa-ss cell increased cell proliferation in vitro and in vivo, deceased expression of several mitochondrial complex I and III proteins, and increased glycine and glutathione levels in cells. BioID method identified more than 20 SHMT2 associated proteins that are involved in oxidation-reduction process. These results indicate SHMT2 involves in the regulation of cellular redox balance. SHMT2 suppression only reduced growth of cells under glycine depletion condition in cell culture. It increased expression of several proteins involved in glutaminolysis and amino acid transporters, and elevated metabolites related to glutamine metabolism. These results indicate tumor cells have a compensatory reaction after SHMT2 suppression. Further reducing glycine levels in cells by sodium benzoate caused cell death in cultured cell and slightly reduced tumor growth in vivo. Benzoate treatment induces more changes in protein expressions and metabolite levels, and it may provide a new addition for tumor treatment.

为阐明丝氨酸羟甲基转移酶2（SHMT2，serine hydroxymethyltransferase 2）影响肿瘤生长的潜在机制，本研究对工程化HeLa细胞系（HeLa-SHMT2-shSHMT2，简称HeLa-Ss）开展蛋白质组学与代谢组学分析。该细胞系可通过分别添加四环素或异丙基β-D-硫代半乳糖苷（IPTG），实现SHMT2的诱导过表达或敲低。在HeLa-Ss细胞中过表达SHMT2，可在体外及体内促进细胞增殖，下调线粒体复合物I与III的多种蛋白表达，并提升细胞内甘氨酸与谷胱甘肽水平。采用BioID技术鉴定出20余种与SHMT2存在相互作用的蛋白，这些蛋白参与氧化还原过程。上述结果表明，SHMT2参与调控细胞氧化还原稳态。仅在细胞培养时的甘氨酸缺失条件下，敲低SHMT2可抑制细胞增殖。此时细胞内参与谷氨酰胺分解及氨基酸转运的多种蛋白表达上调，谷氨酰胺代谢相关代谢物水平升高。上述结果提示，肿瘤细胞在SHMT2被敲低后会产生代偿性应答。进一步通过苯甲酸钠降低细胞内甘氨酸水平，可诱导培养细胞死亡，并在体内轻度抑制肿瘤生长。苯甲酸钠处理会引发更多的蛋白表达与代谢物水平变化，或可为肿瘤治疗提供新的思路。