酸性與低氧環境對肺癌細胞幹性之影響

Abstract

肺癌在世界各地皆占癌症死亡的首位。即使許多新的治療方法與藥物出現能增加肺癌病人的存活率，然後病人的癒後仍然不佳。近年來的研究指出，癌症細胞中存在一群癌症幹細胞(Cancer stem cell)，與抗藥性、腫瘤生成和遠端轉移有關；癌症幹細胞被視為類似幹細胞且具有幹性(Stemness)，意指其具備維持自我更新與分化成其他種類細胞之能力。癌症幹細胞周圍的微環境也同時參與了癌症幹性的調控，而在此微環境中除了癌細胞與各種不同的基質細胞外，還包含了因為腫瘤快速生長所產生的環境壓力，像是低氧以及酸。然而這些微環境壓力對於癌症幹性的調控仍然不清楚；因此，我們想要找出酸性與低氧環境對於肺癌幹細胞的影響為何以及這兩者之間是否具有協同加成的效果。首先，我們利用定量即時聚合酶連鎖反應來檢測肺癌細胞給予酸以及低氧的刺激後，幹細胞標誌 Nanog、Oct3/4、Sox2 mRNA的表現量上升；接著，在球體形成的實驗中，我們發現這兩種環境壓力皆能增加細胞形成球體的能力。最後透過全基因組關聯的分析，其結果顯示這些與癌症幹性正相關的實驗結果可能是透過CD44這個被廣泛研究的幹細胞標誌所調控BMP2-SMAD4 及 STAT1/3等下游訊息路徑。綜合上述，不論是酸或是低氧的微環境壓力皆能增加肺癌細胞的幹性，且在大多數的情形下兩者對於增強癌症幹性具有協同加成的效果。我們的研究顯示，在惡劣壓力環境下(例如：缺氧、酸化)，癌細胞可能會透過獲得幹性進行腫瘤惡性演化以求生存繁延。

Lung cancer is the leading cause of cancer-related death around the world. After lots of excursions for advancing the survival, the prognosis of lung cancer remained poor. Recently, cancer stem cells (CSCs) have been identified to be responsible for drug resistance, tumor initiation and metastasis. CSCs can be considered to have the“stemness”property as stem cells with multipotency which maintain self-renewal and differentiate to other cell types. The surrounding microenvironment of CSCs participates in maintaining the stemness of CSCs, and actually the driving forces of tumor microenvironmental evolution are not only the communication between malignant cancer cells and assistant stromal cells but also stimulations of tumor-growth-induced stress, such as hypoxia and acid conditions. However, the regulation and mechanisms of these microenvironment stresses on cancer stemness remains unknown. Therefore, we want to find out the influence of an acidic stress on lung cancer stemness and whether it will be a synergistic effect with hypoxia. First, we found that the expression level of stemness markers, Nanog, Oct3/4 and Sox2 could be significantly up-regulated under the acidic and hypoxic conditions; as well as, enhancement of tumor initiating abilities and self-renew capacities represented by the ability to grow as tumors spheres. Furthermore, genome-wide transcriptomic analysis indicated that this phenomenon could be associated with the induction of CD44, and it would further regulate other downstream signaling on cancer stemness through BMP2-SMAD4 and STAT1& 3. To sum up, we demonstrated that both of acidic and hypoxic stresses could enhance lung cancer stemness, and in most instances there was a synergistic effect among them. Our results suggest that the tumor cells could survive and go malignant evolution via gain of the stemness characteristics under the stressful condition, such as hypoxia and acidic microenvironments.