Faculty of Medicine and Health Sciences, Universiti Malaysia Sarawak, Lot 77, Seksyen 22 KTLD, Jalan Tun Ahmad Zaidi Adruce, 93150 Kuching, Sarawak, Malaysia.
J Biomed Sci. 2010 Sep 22;17(1):77. doi: 10.1186/1423-0127-17-77.
Nasopharyngeal carcinoma (NPC) is commonly found in Southern China and South East Asia. Epstein-Barr virus (EBV) infection is well associated with NPC and has been implicated in its pathogenesis. Moreover, various chromosome rearrangements were reported in NPC. However, the underlying mechanism of chromosome rearrangement remains unclear. Furthermore, the relationship between EBV and chromosome rearrangement with respect to the pathogenesis of NPC has not been established. We hypothesize that during virus- or stress-induced apoptosis, chromosomes are initially cleaved at the base of the chromatin loop domain structure. Upon DNA repair, cell may survive with rearranged chromosomes.
In this study, cells were seeded at various densities to induce apoptosis. Genomic DNA extracted was processed for Southern hybridization. In order to investigate the role of EBV, especially the latent membrane protein 1 (LMP1), LMP1 gene was overexpressed in NPC cells and chromosome breaks were analyzed by inverse polymerase chain (IPCR) reaction.
Southern analysis revealed that high cell density resulted in cleavage of the mixed lineage leukemia (MLL) gene within the breakpoint cluster region (bcr). This high cell density-induced cleavage was significantly reduced by caspase inhibitor, Z-DEVD-FMK. Similarly, IPCR analysis showed that LMP1 expression enhanced cleavage of the MLL bcr. Breakpoint analysis revealed that these breaks occurred within the matrix attachment region/scaffold attachment region (MAR/SAR).
Since MLL locates at 11q23, a common deletion site in NPC, our results suggest a possibility of stress- or virus-induced apoptosis in the initiation of chromosome rearrangements at 11q23. The breakpoint analysis results also support the role of chromatin structure in defining the site of chromosome rearrangement.
鼻咽癌（NPC）在中国南方和东南亚地区较为常见。EB 病毒（EBV）感染与 NPC 密切相关，其在发病机制中起作用。此外，在 NPC 中还报道了各种染色体重排。然而，染色体重排的潜在机制尚不清楚。此外，尚未确定 EBV 与染色体重排与 NPC 发病机制之间的关系。我们假设，在病毒或应激诱导的细胞凋亡过程中，染色体最初在染色质环域结构的底部被切割。在 DNA 修复过程中，细胞可能会带有重排的染色体而存活。
在这项研究中，将细胞接种在不同的密度以诱导凋亡。提取基因组 DNA 进行 Southern 杂交。为了研究 EBV 的作用，特别是潜伏膜蛋白 1（LMP1）的作用，在 NPC 细胞中过表达 LMP1 基因，并通过反向聚合酶链（IPCR）反应分析染色体断裂。
Southern 分析显示，高细胞密度导致混合谱系白血病（MLL）基因在断裂点簇区（bcr）内发生切割。这种高细胞密度诱导的切割被半胱天冬酶抑制剂 Z-DEVD-FMK 显著减少。同样，IPCR 分析表明 LMP1 表达增强了 MLL bcr 的切割。断裂点分析显示，这些断裂发生在基质附着区/支架附着区（MAR/SAR）内。
由于 MLL 位于 NPC 中常见缺失的 11q23 上，我们的结果提示应激或病毒诱导的细胞凋亡可能在 11q23 染色体重排的起始中起作用。断裂点分析结果也支持染色质结构在确定染色体重排部位中的作用。
