Torrey Pines Institute for Molecular Studies, 3550 General Atomics Court, San Diego, California 92121, United States.
Biochemistry. 2011 Feb 8;50(5):704-14. doi: 10.1021/bi101110e. Epub 2011 Jan 12.
Topoisomerase I (topo I) is required to unwind DNA during synthesis and provides the unique target for camptothecin-derived chemotherapeutic agents, including Irinotecan and Topotecan. While these agents are highly effective anticancer agents, some tumors do not respond due to intrinsic or acquired resistance, a process that remains poorly understood. Because of treatment toxicity, there is interest in identifying cellular factors that regulate tumor sensitivity and might serve as predictive biomarkers of therapy sensitivity. Here we identify the serine kinase, protein kinase CK2, as a central regulator of topo I hyperphosphorylation and activity and cellular sensitivity to camptothecin. In nine cancer cell lines and three normal tissue-derived cell lines we observe a consistent correlation between CK2 levels and camptothecin responsiveness. Two other topo I-targeted serine kinases, protein kinase C and cyclin-dependent kinase 1, do not show this correlation. Camptothecin-sensitive cancer cell lines display high CK2 activity, hyperphosphorylation of topo I, elevated topo I activity, and elevated phosphorylation-dependent complex formation between topo I and p14ARF, a topo I activator. Camptothecin-resistant cancer cell lines and normal cell lines display lower CK2 activity, lower topo I phosphorylation, lower topo I activity, and undetectable topo I/p14ARF complex formation. Experimental inhibition or activation of CK2 demonstrates that CK2 is necessary and sufficient for regulating these topo I properties and altering cellular responses to camptothecin. The results establish a cause and effect relationship between CK2 activity and camptothecin sensitivity and suggest that CK2, topo I phosphorylation, or topo I/p14ARF complex formation could provide biomarkers of therapy-responsive tumors.
拓扑异构酶 I（topo I）在合成过程中需要解开 DNA，并为喜树碱衍生的化疗药物提供独特的靶标，包括伊立替康和拓扑替康。虽然这些药物是高效的抗癌药物，但由于内在或获得性耐药，一些肿瘤没有反应，这个过程仍然知之甚少。由于治疗毒性，人们有兴趣确定调节肿瘤敏感性的细胞因子，并将其作为治疗敏感性的预测生物标志物。在这里，我们确定丝氨酸激酶蛋白激酶 CK2 是拓扑异构酶 I 过度磷酸化和活性以及细胞对喜树碱敏感性的核心调节因子。在 9 种癌细胞系和 3 种正常组织衍生的细胞系中，我们观察到 CK2 水平与喜树碱反应性之间存在一致的相关性。另外两种靶向拓扑异构酶 I 的丝氨酸激酶蛋白激酶 C 和细胞周期蛋白依赖性激酶 1 则没有显示出这种相关性。喜树碱敏感的癌细胞系显示出高 CK2 活性、拓扑异构酶 I 的过度磷酸化、升高的拓扑异构酶 I 活性以及升高的拓扑异构酶 I 和 p14ARF 之间磷酸化依赖性复合物形成，p14ARF 是拓扑异构酶 I 的激活剂。喜树碱耐药的癌细胞系和正常细胞系显示出较低的 CK2 活性、较低的拓扑异构酶 I 磷酸化、较低的拓扑异构酶 I 活性和无法检测到的拓扑异构酶 I/p14ARF 复合物形成。CK2 的实验抑制或激活表明，CK2 是调节这些拓扑异构酶 I 特性和改变细胞对喜树碱反应的必要和充分条件。结果确立了 CK2 活性与喜树碱敏感性之间的因果关系，并表明 CK2、拓扑异构酶 I 磷酸化或拓扑异构酶 I/p14ARF 复合物形成可以提供治疗反应性肿瘤的生物标志物。
