探討細胞激素IL-6 誘導抗細胞凋亡基因表現之機轉(3/3)

細胞凋亡在維持族群中個體之基因穩定及完整性上扮演著非常重要的角色。當母群體中 存在有嚴重傷害之細胞個體，便活化細胞凋亡程式將之移除。自由基及一些實驗反應的細胞 激素在致癌突變過程中多常可偵測到明顯的增加，然而，這些自由基及細胞實驗反應激素中 間的交互作用，其生物意義仍不甚明瞭。本篇研究發現細胞介蛋白質-6(IL-6)能有效保護胃 癌細胞株免於因過氧化氫（H2O2）處理所引致的細胞凋亡。而過氧化氫活化的細胞死亡訊息傳 導路徑JNK 也受IL-6 所抑制。進一步我們發現，IL-6 會活化Bcl-2 實驗中之Mcl-1，此為細 胞存活之訊息路徑。我們將Mcl-1 之表現質體轉殖入AGS 細胞株中，並使用穩定表現株進行 實驗。流式細胞儀分析使用過氧化氫誘導AGS 轉殖株進行細胞凋亡，Mcl-1 轉殖株明顯較對 照組有較大之抗性。同樣的，過氧化氫誘導之JNK 死亡訊息在Mcl-1 殖株上則不明確。此實 驗結果顯示IL-6 之抗細胞凋亡效應，一部分是藉由增加Mcl-1 表現量而達成。令人意外的是， 以過氧化氫處理AGS 細胞所造成的細胞內peroxides 的量並無法以暴露IL-6 或過度表現 Mcl-1 而抑制。本篇亦證明處理IL-6 會延後AGS 細胞清除DNA 氧化傷害之指示型蛋白 8-OH-dGua 的速度達50%以上；於Mcl-1 基因轉殖株中的60-70%之8-OH-dGua 不會進行修補 而遺留在基因庫中。本篇研究提供了一個新的模式以解釋IL-6 能提高Mcl-1 表現量，促使過 氧化氫誘發的DNA 氧化傷害修補力降低，而使抵抗細胞凋亡。Apoptosis plays a critical role in maintaining genomic integrity by selectively removing the most heavily damaged cells from the population. Reactive oxygen species (ROS) and certain inflammatory cytokines are always elevated during the human carcinogenic process. However, the biological significance of the interplay between ROS and inflammatory cytokine remains elusive. This study demonstrates that interleukin-6 (IL-6) effectively protects gastric cancer cells from the apoptosis induced by hydrogen peroxide (H2O2). The cell death signaling JNK pathway elicited by H2O2 is also inhibited by IL-6. We further found that Mcl-1, but not other Bcl-2 family members, was up-regulated by IL-6, by a substantial level over 24 h. We further transfected a mcl-1 expression vector, pCMV-mcl-1, into the AGS cells, and successfully obtained several mcl-1-overexpressing clones. Flow cytometric analysis shows that these mcl-1-overexpressing AGS cells are more resistant to the apoptosis induced by H2O2 when compared with the neo control AGS cells. Consistently, the activation of the JNK pathway induced by H2O2 is also blocked in mcl-1-overexpressed cells. These results indicate that the anti-apoptotic effect of IL-6 is, at least in part, due to the up-regulation of mcl-1. To our surprise, either IL-6 exposure or mcl-1 overexpression fails to reduce the level of intracellular peroxides in theAGS cells triggered by H2O2. This study also determined the level of 8-hydroxydeoxyguanosine (8-OH-dGua), an indicator for oxidative DNA lesions in IL-6-treated or mcl-1-overexpressedAGS cells after treatment with H2O2. Notably, our results indicate that a majority of the 8-OH-dGua is efficiently removed in the AGS cells without IL-6 treatment, whereas only ~50% of the 8-OH-dGuawas repaired in the IL-6-treated AGS cells after 24 h. Similarly, ~60–70% of the 8-OH-dGua also failed to repair and was retained in the genomic DNA of the mcl-1 transfectants. Results in this study provide a novel mechanism by which up-regulation of the Mcl-1 protein by IL-6 may enhance the susceptibility to H2O2-induced oxidative DNA lesions by overriding apoptosis