Sun X L, Jayaram H N, Gharehbaghi K, Li Q J, Xiao X, Antony A C
Department of Medicine, Indiana University School of Medicine, Indianapolis 46202, USA.
Cancer Res. 1999 Feb 15;59(4):940-6.
Cervical carcinoma is an AIDS-defining illness. The expression of folate receptors (FRs) in cervical carcinoma (HeLa-IU1) cells was modulated by stable transduction of FR cDNA encapsidated in recombinant adeno-associated virus-2 in the sense and antisense orientation (sense and antisense cells, respectively). Although sense cells proliferated slower than antisense or untransduced cells in vivo and in vitro in 2% (but not 10%) FCS, [methyl-3H]thymidine incorporation into DNA was significantly increased in sense cells in 10% serum; therefore, the basis for this discrepancy was investigated. The activity of thymidine kinase (TK) was subsequently directly correlated with the extent of FR expression in single cell-derived clones of transduced cells. This elevated TK activity was not a result of recruitment of the salvage pathway based on the presence of adequate dTTP pools, normal thymidylate synthase (TS) activity, persistence of increased thymidine incorporation despite the exogenous provision of excess 5,10-methylene-tetrahydrofolate, and documentation of adequate folates in sense cells. The increase in TK activity conferred significant biological properties to sense cells (but not antisense or untransduced cells) as demonstrated by augmented phosphorylation of 3'-azido-3'-deoxythymidine (AZT) and concomitantly greater sensitivity to the cytotoxic effects of AZT. Conversely, sense cells were highly resistant to methotrexate, but this was reversed by the addition of AZT. The direct correlation of FR expression and TK activity indicates a previously unrecognized consequence of FR overexpression.
宫颈癌是一种艾滋病界定疾病。通过重组腺相关病毒2包装的叶酸受体（FRs）cDNA以正义和反义方向稳定转导（分别为正义细胞和反义细胞）来调节宫颈癌（HeLa-IU1）细胞中FRs的表达。尽管在2%（而非10%）胎牛血清中，正义细胞在体内和体外的增殖速度均慢于反义细胞或未转导细胞，但在10%血清中，[甲基-³H]胸苷掺入DNA的量在正义细胞中显著增加；因此，对这种差异的原因进行了研究。随后，胸苷激酶（TK）的活性与转导细胞单细胞衍生克隆中FR表达的程度直接相关。基于充足的脱氧胸苷三磷酸（dTTP）池的存在、正常的胸苷酸合成酶（TS）活性、尽管外源提供过量的5,10-亚甲基四氢叶酸但胸苷掺入量仍持续增加以及正义细胞中叶酸充足的记录，这种升高的TK活性并非补救途径募集的结果。TK活性的增加赋予了正义细胞（而非反义细胞或未转导细胞）显著的生物学特性，这表现为3'-叠氮-3'-脱氧胸苷（AZT）磷酸化增强以及对AZT细胞毒性作用的敏感性相应增加。相反，正义细胞对甲氨蝶呤高度耐药，但添加AZT后这种情况得到逆转。FR表达与TK活性的直接相关性表明了FR过表达一个此前未被认识到的后果。
