Dolnick B J, Black A R, Winkler P M, Schindler K, Hsueh C T
Department of Experimental Therapeutics, Roswell Park Cancer Institute, Buffalo, NY 14263, USA.
Adv Enzyme Regul. 1996;36:165-80. doi: 10.1016/0065-2571(95)00009-7.
rTS is a recently discovered gene, phylogenetically conserved and found to be expressed in a wide variety of cell lines. rTS has also been found to be overexpressed in two cell lines resistant to FU and to MTX. The MTX-resistant cell line was found to have a high degree of cross resistance to several TS inhibitors. An apparent paradox to this correlation of rTS overexpression and resistance to TS inhibitors is the observation that expression of transfected rTS alpha results in enhanced sensitivity of cells to the TS inhibitor prodrug TFT and a modest increase in resistance to FUdR. Since immunoprecipitation of TS leads to the co-immunoprecipitation of two proteins within the expected molecular weight range of the two rTS proteins, it may be that both proteins bind to TS in vivo and modify its activity. Preliminary data substantiate this conclusion. It is conceivable that the ratio of the two rTS proteins associated with TS in vivo may differentially alter TS activity depending upon their stoichiometry or possibly posttranslational modification. Thus it may be possible for rTS to confer greater sensitivity to one pyrimidine analog (e.g., TFT) which is a product analog but to increase resistance or have a minor effect on a substrate analog (e.g., FdUMP) by stabilizing different conformations of TS. The structure of the rTS proteins suggests they are expected to have catalytic activity which involves proton abstraction from an alpha-carbon of a carboxyl group. Whether this enzyme activity is functional and related to pyrimidine metabolism awaits further study.
rTS是一个最近发现的基因，在系统发育上保守，且在多种细胞系中都有表达。rTS在两种对氟尿嘧啶（FU）和甲氨蝶呤（MTX）耐药的细胞系中也被发现过表达。发现MTX耐药细胞系对几种胸苷酸合成酶（TS）抑制剂有高度交叉耐药性。与rTS过表达和对TS抑制剂耐药性这种相关性明显矛盾的是，观察到转染的rTSα的表达导致细胞对TS抑制剂前药替加氟（TFT）的敏感性增强，以及对氟尿苷（FUdR）的耐药性适度增加。由于TS的免疫沉淀导致在两种rTS蛋白预期分子量范围内的两种蛋白质共免疫沉淀，可能这两种蛋白质在体内都与TS结合并改变其活性。初步数据证实了这一结论。可以想象，体内与TS相关的两种rTS蛋白的比例可能会根据它们的化学计量比或可能的翻译后修饰而不同地改变TS活性。因此，rTS有可能对一种作为产物类似物的嘧啶类似物（例如TFT）赋予更高的敏感性，但通过稳定TS的不同构象来增加对底物类似物（例如氟脱氧尿苷一磷酸（FdUMP））的耐药性或产生较小影响。rTS蛋白的结构表明它们预期具有催化活性，这涉及从羧基的α-碳上夺取质子。这种酶活性是否具有功能以及与嘧啶代谢是否相关有待进一步研究。
