探討第二型間質蛋白酶在人類攝護腺癌細胞轉移中所扮演的角色

Abstract

攝護腺癌(Prostate cancer, PCa)為已開發國家男性好發癌症之一，且癌症轉移與否與病人預後不佳及死亡上升呈正相關。蛋白酶活性失調已被報導高度與癌症轉移相關，高度轉移是癌症惡化原因之一，進而導致死亡。細胞周圍蛋白酶活性失調被指出和癌症細胞轉移能力有正相關，且會影響其周圍微環境。第二型細胞間質蛋白酶(Matriptase-2, MT-2)，為近期發現之絲胺酸蛋白酶，主要在肝臟表達且調控鐵的代謝。然而在癌症中，研究顯示MT-2可能為抑制者且其機制仍尚未明瞭。實驗結果顯示MT-2表現量和攝護腺癌進程成負相關，且MT-2表達能抑制具轉移特性PCa細胞株(PC3與DU-145)侵襲能力，證實其抑制者角色。乙型轉化生長因子(Transforming growth factor-beta1, TGF-beta1)為一多功能的生長因子，且已被報導在癌症進程具有雙面影響，在初期抑制生長為抑制者，但隨疾病演進累積且轉為腫瘤促進者。我們發現MT-2會藉由調控癌細胞鐵代謝來促進NR4A3 (Nuclear Receptor Subfamily 4 Group A Member 3)表現量上升，讓PCa細胞對於TGF-beta1刺激反應從腫瘤促進者趨向抑制作用。NR4A3降底由TGF-β引起細胞間質轉型[Epithelial-mesenchymal transition (EMT)]程度，且促進由TGF-beta引起細胞周期抑制蛋白p21與PAI-1[第一型胞漿素原活化抑制蛋白(Plasminogen Activator Inhibitor-1)]的表現，此外上升之PAI-1可抑制尿激酶型胞漿素原活化劑uPA (Urokinase Plasminogen Activator)活性，進而抑制細胞增生與侵襲移動能力。透過共免疫沉澱法進一步發現NR4A3藉由和TGF-beta下游Smad2蛋白結合，進而促進p21與PAI-1表達。此外上升之PAI-1導致PAI-1與uPA下降。最後在臨床資料庫TCGA中也顯示MT-2與NR4A3表現量與病人復發率為負相關。本篇研究指出MT-2和NR4A3兩者在攝護腺癌中均為抑癌因子，且讓PAI-1/uPA比例上升，顯示三者可能為未來用來檢視病症是否惡化的指標因子。由於NR4A3參與癌細胞如何反應TGF-beta刺激，顯示其表達量的高低可做且具潛能做為篩選病人是否適合使用TGF-beta抑制劑的生物標記。

Dysregulation of pericellular proteolysis is strongly implicated in cancer metastasis through alteration of cell invasion and the microenvironment. Matriptase-2 (MT-2) is a membrane-anchored serine protease which can suppress prostate cancer (PCa) cell invasion. In this study, we showed that MT-2 was down-regulated in PCa and could suppress PCa cell motility, tumor growth, and metastasis. Using microarray and biochemical analysis, we found that MT-2 shifted TGF-β action towards its tumor suppressor function by repressing epithelial-to-mesenchymal transition (EMT) and promoting Smad2 phosphorylation and nuclear accumulation to up-regulate two TGF-β1 downstream effectors (p21 and PAI-1), culminating in hindrance of PCa cell motility and malignant growth. Mechanistically, MT-2 could dramatically up-regulate the expression of nuclear receptor NR4A3 via iron metabolism in PCa cells. MT-2-induced NR4A3 further coactivated Smad2 to activate p21 and PAI-1 expression. In addition, NR4A3 functioned as a suppressor of PCa and mediated MT-2 signaling to inhibit PCa tumorigenesis and metastasis. These results together indicate that NR4A3 sustains MT-2 signaling to suppress PCa cell invasion, tumor growth, and metastasis, and serves as a contextual factor for the TGF-β/Smad2 signaling pathway in favor of tumor suppression via promoting p21 and PAI-1 expression.