Department of Pathophysiology, Guangdong Medical College, Dongguan, Guangdong, 523808, China.
Key Laboratory for Medical Diagnostics of Guangdong Province, Sino-American Cancer Research Institute, Guangdong Medical College, Dongguan, Guangdong, 523808, China.
BMC Cancer. 2015 May 10;15:390. doi: 10.1186/s12885-015-1398-3.
Mitogen- and Stress-Activated Kinase 1 (MSK1) is a nuclear kinase that serves as active link between extracellular signals and the primary response of gene expression. However, the involvement of MSK1 in malignant transformation and cancer development is not well understood. In this study, we aimed to explore the role of MSK1 in Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1)-promoted carcinogenesis of nasopharyngeal carcinoma (NPC).
The level of MSK1 phosphorylation at Thr581 was detected by the immunohistochemical analysis in NPC tissues and normal nasopharynx tissues, and its correlation with LMP1 was analyzed in NPC tissues and cell lines. Using MSK1 inhibitor H89 or small interfering RNA (siRNA)-MSK1, the effects of MSK1 on LMP1-promoted CNE1 cell proliferation and transformation were evaluated by CCK-8 assay, flow cytometry and focus-forming assay respectively. Furthermore, the regulatory role of MSK1-mediated histone H3 phosphorylation at Ser10 on the promoter activity and expression of Fra-1 or c-Jun was determined by reporter gene assay and western blotting analysis.
Immunohistochemical analysis revealed that the level of MSK1 phosphorylation at Thr581 was significantly higher in the poorly differentiated NPC tissues than that in normal nasopharynx tissues (P < 0.001). Moreover, high level of phosphorylated MSK1 was positively correlated with the expression of LMP1 in NPC tissues (r = 0.393, P = 0.002) and cell lines. MSK1 inhibitor H89 or knockdown of MSK1 by siRNA dramatically suppressed LMP1-promoted CNE1 cell proliferation, which was associated with the induction of cell cycle arrest at G0/G1 phase. In addition, the anchorage-independent growth promoted by LMP1 was blocked in MSK1 knockdown cells. When the activity or expression of MSK1 was inhibited, LMP1-induced promoter activities of Fra-1 and c-Jun as well as their protein levels were greatly reduced. It was found that only H3 WT, but not mutant H3 S10A, dramatically increased LMP1 induction of Fra-1 and c-Jun genes compared with mock cells.
Increased MSK1 activity is critically important for LMP1-promoted cell proliferation and transformation in NPC, which may be correlated with its induction of Fra-1 and c-Jun through phosphorylation of histone H3 at Ser10.
有丝分裂原和应激激活激酶 1（MSK1）是一种核激酶，作为细胞外信号与基因表达的主要反应之间的活性连接。然而，MSK1 参与恶性转化和癌症发展的机制尚不清楚。在这项研究中，我们旨在探讨 MSK1 在 Epstein-Barr 病毒（EBV）潜伏膜蛋白 1（LMP1）促进鼻咽癌（NPC）发生中的作用。
通过免疫组织化学分析检测 NPC 组织和正常鼻咽组织中 MSK1 磷酸化 Thr581 的水平，并分析 NPC 组织和细胞系中 MSK1 与 LMP1 的相关性。使用 MSK1 抑制剂 H89 或小干扰 RNA（siRNA）-MSK1，通过 CCK-8 测定、流式细胞术和焦点形成测定分别评估 MSK1 对 LMP1 促进的 CNE1 细胞增殖和转化的影响。此外，通过报告基因测定和 Western blot 分析确定 MSK1 介导的组蛋白 H3 磷酸化 Ser10 对 Fra-1 或 c-Jun 启动子活性和表达的调节作用。
免疫组织化学分析显示，低分化 NPC 组织中 MSK1 磷酸化 Thr581 的水平明显高于正常鼻咽组织（P<0.001）。此外，高磷酸化 MSK1 水平与 NPC 组织（r=0.393，P=0.002）和细胞系中 LMP1 的表达呈正相关。MSK1 抑制剂 H89 或 siRNA 敲低 MSK1 显著抑制 LMP1 促进的 CNE1 细胞增殖，这与细胞周期阻滞在 G0/G1 期有关。此外，LMP1 诱导的锚定非依赖性生长在 MSK1 敲低细胞中被阻断。当抑制 MSK1 的活性或表达时，LMP1 诱导的 Fra-1 和 c-Jun 启动子活性及其蛋白水平大大降低。结果发现，只有野生型 H3（WT），而不是突变型 H3 S10A，与 mock 细胞相比，明显增加了 LMP1 诱导的 Fra-1 和 c-Jun 基因的表达。
MSK1 活性的增加对于 LMP1 促进 NPC 中的细胞增殖和转化至关重要，这可能与其通过磷酸化组蛋白 H3 Ser10 诱导 Fra-1 和 c-Jun 有关。
