薯蕷皂苷透過PI3K/Akt和ERK及JNK信號途徑誘導肺癌細胞自噬作用及凋亡

尋找新抗癌藥物來治療目前危害人類的癌症是當前癌症治療研究的重大課題之一，然而要開發一種新抗癌藥物，能有效治療癌症卻不會傷害到人體的正常細胞，實為一項艱鉅又困難的工作。雖然直到目前為止，在癌症的治療上已有顯著突破的進展，許多新而有效的抗癌藥物已被開發應用於臨床的治療，部份延續患者的生命，改善病人的生活品質，但仍未能達到根治病源的理想目標。追究其原因不外乎是生化學、分子生物學家或細胞學家仍然無法分辨正常細胞與癌細胞在生化學或分子生物學上的特異性，以致無法尋找具特異選擇性的藥物來抑制癌細胞。從以前我們的研究顯示，薯蕷皂苷(Dioscin)為具有抗炎、降脂、抗癌和保肝作用的化合物，其可誘發肝癌細胞自噬(Autophagy)。自噬是一種溶酶體降解途徑，是對細胞的存活及組織的動態平衡至關重要。在這項研究中，利用人肺癌細胞在薯蕷皂苷誘導的細胞凋亡中的作用，所產生之自噬及相關細胞信號途徑進行了研究。結果從4′-6-Diamidino-2-Phenylindole 和Annexin-V/PI Double-Staining檢測顯示在以薯蕷皂苷處理24小時後，進行檢測Caspase-3、 Caspase-8和劑量依賴性和Apoptoses是有相關性。同時，在以暴露於低劑量薯蕷皂苷12小時後，即可檢測到自噬的現象，是通過LC3-II的上調表達，並如所示的Beclin-1蛋白。自噬與bafilomycin A1或 3-methyladenine sensitized的A549和H1299細胞凋亡。A549和H1299細胞與薯蕷皂苷的一起處理所引起的劑量依賴性，使ERK1 / 2和JNK1 / 2活性增加，伴隨有降低PI3K的表現，及降低Akt和mTOR的磷酸化。綜合以上，這項研究首次證明了薯蕷皂苷誘導的人肺癌細胞自噬發生比細胞凋亡更早發生。薯蕷皂苷誘導自噬是透過ERK1 / 2和JNK1 / 2通路，此作用未來可以針對薯蕷皂甙誘導的細胞自噬作用，提供為減少抗藥性之研究及應用。

Our previous study has revealed that Dioscin, a compound with anti-inflammatory, lipid-lowering, anticancer and hepatoprotective effects, may induce Autophagy in hepatoma cells. Autophagy is a lysosomal degradation pathway that is essential for cell survival and tissue homeostasis. In this study, the role of Autophagy and related signaling pathways during Dioscin-induced Apoptosis in human lung cancer cells was investigated. Results from 4’-6-diamidino-2-phenylindole and annexin-V/PI double-staining assay showed that caspase-3- and caspase-8-dependent, and dose-dependent apoptoses were detected after a 24-h Dioscin treatment. Meanwhile, Autophagy was detected as early as 12 h after an exposure to low-dose Dioscin, as indicated by an up-regulated expression of LC3-II and beclin-1 proteins. Blockade of Autophagy with bafilomycin A1 or 3-methyladenine sensitized the A549 and H1299 cells to Apoptosis. Treatment of A549 and H1299 cells with Dioscin caused a dose-dependent increase in ERK1/2 and JNK1/2 activity, accompanied with a decreased PI3K expression and decreased phosphorylation of Akt and mTOR. Taken together, this study demonstrated for the first time that Autophagy occurred earlier than Apoptosis during Dioscin-induced human lung cancer cell line Apoptosis.Dioscin-induced Autophagy via ERK1/2 and JNK1/2 pathways may provide a protective mechanism for cell survival against Dioscin-induced Apoptosis to act as a cytoprotective reaction.