Hsueh C T, Kelsen D, Schwartz G K
Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
Clin Cancer Res. 1998 Sep;4(9):2201-6.
UCN-01, a protein kinase C/cyclin-dependent kinase inhibitor, suppressed thymidylate synthase (TS) protein expression in a dose-dependent manner with near complete suppression at 1 microM after a 24-h exposure in human gastric cancer cell line SK-GT5. Other protein kinase C/cyclin-dependent kinase inhibitors, including flavopiridol and safingol, had a similar effect on TS protein expression, but to a lesser degree. Moreover, UCN-01 repressed the induction of TS after 5-fluorouracil (FU) exposure by 90-95% and significantly enhanced the induction of apoptosis by FU from 4-8% with either FU or UCN-01 alone to 46+/-1% (P < 0.005 versus either single drug, reverse sequence, or the combination) when UCN-01 was given after FU. The effect of UCN-01 on TS was associated with a dose-dependent suppression of the E2F-1 protein, a transcriptional activator of TS. Northern blot analysis revealed that TS mRNA levels decreased gradually as the concentration of UCN-01 increased, but that E2F-1 mRNA levels remained relatively unchanged. UCN-01 may provide a novel way to enhance cellular sensitivity toward FU by means of suppressing TS expression mediated mainly by down-regulation of E2F-1.
UCN - 01是一种蛋白激酶C/细胞周期蛋白依赖性激酶抑制剂，在人胃癌细胞系SK - GT5中，经24小时暴露后，它以剂量依赖性方式抑制胸苷酸合成酶（TS）蛋白表达，在1微摩尔浓度时接近完全抑制。其他蛋白激酶C/细胞周期蛋白依赖性激酶抑制剂，包括黄酮哌啶醇和沙芬戈，对TS蛋白表达有类似作用，但程度较小。此外，UCN - 01可将5 - 氟尿嘧啶（FU）暴露后TS的诱导抑制90 - 95%，并显著增强FU诱导的凋亡，单独使用FU或UCN - 01时凋亡诱导率为4 - 8%，当在FU后给予UCN - 01时，凋亡诱导率提高到46±1%（与单一药物、相反顺序或联合用药相比，P < 0.005）。UCN - 01对TS的作用与E2F - 1蛋白（TS的转录激活因子）的剂量依赖性抑制有关。Northern印迹分析显示，随着UCN - 01浓度增加，TS mRNA水平逐渐降低，但E2F - 1 mRNA水平相对保持不变。UCN - 01可能通过主要下调E2F - 1介导的TS表达，为增强细胞对FU的敏感性提供一种新方法。
