PDF(Pubmed)
Abstract：
Methionine dependence is a characteristic of most cancer cells where they are unable to proliferate when the essential amino acid methionine is replaced with its precursor homocysteine in the growing media. Normal cells, on the other hand, thrive under these conditions and are referred to as methionine-independent. The reaction that adds a methyl group from 5-methyltetrahydrofolate to homocysteine to regenerate methionine is catalyzed by the enzyme methionine synthase with the cofactor cobalamin (vitamin B12). However, decades of research have shown that methionine dependence in cancer is not due to a defect in the activity of methionine synthase. Cobalamin metabolism has been tied to the dependent phenotype in rare cell lines. We have identified a human colorectal cancer cell line in which the cells regain the ability to proliferation in methionine-free, L-homocystine-supplemented media when cyanocobalamin is supplemented at a level of 1 µg/mL. In human SW48 cells, methionine replacement with L-homocystine does not induce any measurable increase in apoptosis or reactive oxygen species production in this cell line. Rather, proliferation is halted, then restored in the presence of cyanocobalamin. Our data show that supplementation with cyanocobalamin prevents the activation of the integrated stress response (ISR) in methionine-deprived media in this cell line. The ISR-associated cell cycle arrest, characteristic of methionine-dependence in cancer, is also prevented, leading to the continuation of proliferation in methionine-deprived SW48 cells with cobalamin. Our results highlight differences between cancer cell lines in the response to cobalamin supplementation in the context of methionine dependence.
摘要：
蛋氨酸依赖性是大多数癌细胞的特征，当必需氨基酸蛋氨酸在生长培养基中被其前体高半胱氨酸取代时，它们无法增殖。正常细胞,另一方面,在这些条件下茁壮成长，被称为不依赖蛋氨酸的。将甲基从5-甲基四氢叶酸添加到高半胱氨酸以再生甲硫氨酸的反应由甲硫氨酸合酶与辅因子钴胺素（维生素B12）催化。然而,几十年的研究表明，癌症中的蛋氨酸依赖性并不是由于蛋氨酸合酶活性的缺陷。在稀有细胞系中，钴胺的代谢与依赖性表型有关。我们已经确定了一种人类结直肠癌细胞系，其中细胞重新获得无蛋氨酸的增殖能力，当氰钴胺以1µg/mL的水平补充时，L-高半胱氨酸补充的培养基。在人类SW48细胞中，用L-高半胱氨酸替代蛋氨酸不会诱导该细胞系中细胞凋亡或活性氧产生的任何可测量的增加。相反，扩散停止了，然后在氰钴胺存在下恢复。我们的数据表明，补充氰钴胺可防止该细胞系中甲硫氨酸剥夺培养基中整合应激反应（ISR）的激活。ISR相关的细胞周期停滞，癌症中蛋氨酸依赖的特征，也被阻止了，导致蛋氨酸剥夺的SW48细胞继续增殖与钴胺素。我们的结果强调了在蛋氨酸依赖的情况下，癌细胞系对钴胺素补充的反应之间的差异。
