Downregulation of Cdc6 and pre-replication complexes in response to methionine stress in breast cancer cells
Downregulation of Cdc6 and pre-replication complexes in response to methionine stress in breast cancer cells
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DOI：
10.4161/cc.22767
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发表时间：
2012-12-01
期刊：
影响因子：
4.3
通讯作者：
Kaiser, Peter
中科院分区：
文献类型：
--
作者：
Booher, Keith;Lin, Da-Wei;Kaiser, Peter
甲硫氨酸和同型半胱氨酸是导致甲基供体S-腺苷蛋氨酸合成的转甲基化途径的代谢物。大多数癌细胞在蛋氨酸应激条件下停止增殖，此时生长介质中的蛋氨酸被其直接代谢前体同型半胱氨酸(Met-Hcy+)取代。未转化的细胞在Met-Hcy+介质中增殖，使癌细胞的蛋氨酸代谢需求成为一个有吸引力的治疗靶点，但目前对癌细胞中蛋氨酸应激反应的分子机制知之甚少。为了研究乳腺癌细胞中的这种现象，我们选择了来自MDAMB468乳腺癌细胞的蛋氨酸独立耐药细胞系。耐药细胞在Met-Hcy+培养液中生长正常，而其亲本MDAMB468细胞迅速停滞于G1期。添加S-腺苷蛋氨酸的蛋氨酸抑制了细胞的增殖缺陷，表明蛋氨酸胁迫是腺苷限制的结果，而不是低氨基酸浓度的结果。因此，对氨基酸限制作出反应的主要效应者mTORC1活性保持较高水平。然而，我们发现，在蛋氨酸应激的MDAMB468细胞中，复制因子CDC6的水平降低，复制前复合体不稳定，但不是耐药细胞。我们的研究描述了乳腺癌细胞在蛋氨酸应激过程中的代谢物需求和细胞周期反应，并有助于解释癌细胞的代谢独特性。
Methionine and homocysteine are metabolites in the transmethylation pathway leading to synthesis of the methyl-donor S-adenosylmethionine (SAM). Most cancer cells stop proliferating during methionine stress conditions, when methionine is replaced in the growth media by its immediate metabolic precursor homocysteine (Met-Hcy+). Non-transformed cells proliferate in Met-Hcy+ media, making the methionine metabolic requirement of cancer cells an attractive target for therapy, yet there is relatively little known about the molecular mechanisms governing the methionine stress response in cancer cells. To study this phenomenon in breast cancer cells, we selected methionine-independent-resistant cell lines derived from MDAMB468 breast cancer cells. Resistant cells grew normally in Met-Hcy+ media, whereas their parental MDAMB468 cells rapidly arrest in the G 1 phase. Remarkably, supplementing Met-Hcy+ growth media with S-adenosylmethionine suppressed the cell proliferation defects, indicating that methionine stress is a consequence of SAM limitation rather than low amino acid concentrations. Accordingly, mTORC1 activity, the primary effector responding to amino acid limitation, remained high. However, we found that levels of the replication factor Cdc6 decreased and pre-replication complexes were destabilized in methionine-stressed MDAMB468 but not resistant cells. Our study characterizes metabolite requirements and cell cycle responses that occur during methionine stress in breast cancer cells and helps explain the metabolic uniqueness of cancer cells.