Kurland John F, Voehringer David W, Meyn Raymond E
Department of Experimental Radiation Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
J Biol Chem. 2003 Aug 22;278(34):32465-70. doi: 10.1074/jbc.M212919200. Epub 2003 Jun 11.
In a previously published report (Kurland, J. F., Kodym, R., Story, M. D., Spurgers, K. B., McDonnell, T. J., and Meyn, R. E. (2001) J. Biol. Chem. 276, 45380-45386), we described the NF kappa B status for two murine B-cell lymphoma cell lines, LY-as (apoptosis-sensitive) and LY-ar (apoptosis-refractory) and provided evidence that NF kappa B1 (p50) homodimers contribute to the expression of Bcl-2 in the LY-ar line. In the present study, we investigated the upstream signals leading to p50 homodimer activation and Bcl-2 expression. We found that in LY-ar cells, ERK1 and ERK2 were constitutively phosphorylated, whereas LY-as cells had no detectable ERK1 or ERK2 phosphorylation. Treatment of LY-ar cells with the MEK inhibitors PD 98059, U0126, and PD 184352 led to a loss of phosphorylated ERK1 and ERK2, a reversal of nuclear p50 homodimer DNA binding, and a decrease in Bcl-2 protein expression. Similarly, activation of the MEK/ERK pathway in LY-as cells by phorbol ester led to Bcl-2 expression that could be blocked by PD 98059. Furthermore, treatment of LY-ar cells with tumor necrosis factor-alpha, an I kappa B kinase activator, did not alter the suppressive effect of PD 98059 on p50 homodimer activity, suggesting an I kappa B kinase-independent pathway for p50 homodimer activation. Lastly, all three MEK inhibitors sensitized LY-ar cells to radiation-induced apoptosis. We conclude that the MEK/ERK pathway acts upstream of p50 homodimer activity and Bcl-2 expression in this B-cell lymphoma cell system and suggest that the use of MEK inhibitors could be useful clinically in combination with ionizing radiation to treat lymphoid malignancies.
在之前发表的一篇报告中（Kurland, J. F., Kodym, R., Story, M. D., Spurgers, K. B., McDonnell, T. J., and Meyn, R. E. (2001) J. Biol. Chem. 276, 45380 - 45386），我们描述了两种小鼠B细胞淋巴瘤细胞系LY-as（凋亡敏感型）和LY-ar（凋亡耐受型）的核因子κB（NFκB）状态，并提供证据表明NFκB1（p50）同二聚体有助于LY-ar细胞系中Bcl-2的表达。在本研究中，我们调查了导致p50同二聚体激活和Bcl-2表达的上游信号。我们发现，在LY-ar细胞中，ERK1和ERK2持续磷酸化，而LY-as细胞中未检测到ERK1或ERK2磷酸化。用MEK抑制剂PD 98059、U0126和PD 184352处理LY-ar细胞，导致磷酸化的ERK1和ERK2丧失、核p50同二聚体DNA结合逆转以及Bcl-2蛋白表达降低。同样，佛波酯激活LY-as细胞中的MEK/ERK途径导致Bcl-2表达，而这可被PD 98059阻断。此外，用肿瘤坏死因子-α（一种IκB激酶激活剂）处理LY-ar细胞并未改变PD 98059对p50同二聚体活性的抑制作用，表明存在一条不依赖IκB激酶的p50同二聚体激活途径。最后，所有三种MEK抑制剂均使LY-ar细胞对辐射诱导的凋亡敏感。我们得出结论，在这个B细胞淋巴瘤细胞系统中，MEK/ERK途径在p50同二聚体活性和Bcl-2表达的上游起作用，并表明MEK抑制剂与电离辐射联合使用在临床上可能对治疗淋巴恶性肿瘤有用。
