Chresta C M, Masters J R, Hickman J A
Cancer Research Campaign Molecular and Cellular Pharmacology Research Group, School of Biological Sciences, The University of Manchester, United Kingdom.
Cancer Res. 1996 Apr 15;56(8):1834-41.
Metastatic testicular cancers are curable, whereas bladder cancers and most other solid tumors are not. Cell lines derived from human testicular (GH, GCT27, and 833K) and bladder (RT4, RT112, and HT1376) tumors retain this differential chemosensitivity in vitro. We have investigated the hypothesis that differential sensitivity to chemotherapy is related to differences in the threshold of susceptibility to undergoing apoptosis. Sensitivity to etoposide was not directly related to the frequency of DNA strand breaks. DNA damage was on average 2-fold greater in the testicular than the bladder tumor cell lines; in contrast, the testicular tumor lines were 15-fold more sensitive to etoposide cytotoxicity than the bladder tumor lines (IC90 values of 19 +/- 6 versus 293 +/- 180 microM, respectively). Using equidamaging (550 rad equivalents) etoposide treatments, the percentage of cells that underwent drug-induced apoptosis was on average higher in the testicular tumor cell lines than the bladder tumor cell lines. The testicular tumor lines have two characteristics that could confer sensitivity to drug-induced apoptosis. First, they have functional p53: the product of the p53-dependent gene waf-1 was increased after etoposide treatment. Second, the testicular tumor lines expressed relatively high levels of the apoptosis-promoting protein Bax, but there was no expression of the suppressor of apoptosis Bcl-2. In contrast, only one of the three bladder cell lines (RT4) had functional p53, and all of the bladder lines had readily detectable levels of Bcl-2 and low levels of Bax. In the testicular cell lines, increases in p53 and p53-transactivated genes were associated with apoptosis but not arrest in G1. In contrast, in the bladder cell line (RT4), increases in p53 and Waf-1 were associated with both arrest in G1 and apoptosis. The differences in the ratio of Bax:Bcl-2 could contribute to the differential sensitivity of the two tumor types. However, in contrast to earlier reports, the ratio of Bax and Bel-2 was not perturbed by DNA damage.
转移性睾丸癌是可治愈的，而膀胱癌和大多数其他实体瘤则不然。源自人类睾丸（GH、GCT27和833K）和膀胱（RT4、RT112和HT1376）肿瘤的细胞系在体外保留了这种不同的化学敏感性。我们研究了以下假设：对化疗的不同敏感性与对凋亡易感性阈值的差异有关。对依托泊苷的敏感性与DNA链断裂的频率没有直接关系。睾丸肿瘤细胞系中的DNA损伤平均比膀胱肿瘤细胞系大2倍；相比之下，睾丸肿瘤细胞系对依托泊苷细胞毒性的敏感性比膀胱肿瘤细胞系高15倍（IC90值分别为19±6和293±180 microM）。使用等效损伤（550拉德当量）的依托泊苷处理，睾丸肿瘤细胞系中发生药物诱导凋亡的细胞百分比平均高于膀胱肿瘤细胞系。睾丸肿瘤细胞系有两个可能赋予对药物诱导凋亡敏感性的特征。首先，它们具有功能性p53：依托泊苷处理后，p53依赖性基因waf-1的产物增加。其次，睾丸肿瘤细胞系表达相对高水平的促凋亡蛋白Bax，但凋亡抑制蛋白Bcl-2没有表达。相比之下，三个膀胱细胞系中只有一个（RT4）具有功能性p53，并且所有膀胱细胞系都有易于检测到的Bcl-2水平和低水平的Bax。在睾丸细胞系中，p53和p53反式激活基因的增加与凋亡相关，但与G1期停滞无关。相比之下，在膀胱细胞系（RT4）中，p53和Waf-1的增加与G1期停滞和凋亡都相关。Bax:Bcl-2比例的差异可能导致两种肿瘤类型的不同敏感性。然而，与早期报告相反，Bax和Bel-2的比例不受DNA损伤的干扰。
