Protease-activated receptors (PARs) 調控癌症進程之機轉探討

Abstract

癌症已連續十年蟬聯十大死因之首，而因癌症所引起之併發症亦可能是導致癌症致死之因素，其中以靜脈血栓炎最為常見。自1865年，法國醫生Armand Trousseau發現反覆性產生靜脈血栓栓塞的病人，其後不久會被診斷出罹患惡性腫瘤，因此將癌症所引起之血栓症命名為Trousseau syndrome，自此開啟了血栓與癌症關聯性的研究。 本論文第一部分的研究中，我們探討凝血酶Thrombin 透過活化蛋白酶激活接受器Protease-activated receptors (PARs) 造成癌症轉移的機轉。在大腸直腸癌細胞實驗中，Thrombin 以及專一性PAR-1之activating peptides (APs) 可以引起缺氧誘導因子hypoxia-inducible factor-1α (HIF-1α) 蛋白之累積、增加HIF-1α轉錄能力、下游蛋白Twist表現以及細胞移行能力；然而，PAR-4 AP則無此作用。給予PAR-1抑制劑SCH79797或轉譯路徑相關抑制劑：如ERK、PI3K/Akt或mTOR抑制劑，則可以阻斷Thrombin以及PAR-1 AP之作用。此外，我們還進一步證實Thrombin藉由Twist增加N-cadherin調控epithelial-mesenchymal transition (EMT)，進而調控癌細胞移行能力。 第二部分的研究則是證實在過度表現組織凝血因子tissue factor (TF)之胰臟癌細胞中，活化PAR-2會造成癌細胞增加HIFs蛋白，transforming growth factor-α (TGF-α) 表現，以及促進血管新生。不論是給予FVIIa或是PAR-2 AP，活化PAR-2之後HIF-1α以及HIF-2α蛋白皆會累積，TGF-α以及vascular endothelial growth factor-A (VEGF-A) 之轉錄和轉譯作用皆有增加。藉由small interfering RNA (siRNA) 減少integrin-linked kinase (ILK)、HIF-1α或HIF-2α皆可以抑制PAR-2誘導之TGF-α蛋白增加，然而卻無法減少PAR-2誘導之VEGF-A蛋白。於是藉由microarray分析PAR-2所影響之訊息路徑，我們發現PAR-2會活化MEK-ERK路徑、轉錄因子EST-1以及VEGF-A蛋白。給予MEK抑制劑之後，可以大幅降低PAR-2增加之VEGF-A蛋白以及抑制VEGF誘導之血管內皮細胞增生和移行，阻斷了血管新生之形成。 經由以上結果得知不正常表現凝血因子如Thrombin或是TF，會活化癌細胞表面上之PARs以及增加轉錄因子HIFs之活性，最終促使癌症之進程、血管新生以及轉移，而PARs則扮演一個連結癌症與血栓交互作用的角色。

Cancer is the top one leading cause of death over ten years and cancer-related complications are also the reasons of death. Venous thromboembolism (VTE) is a common complication in cancer patients. Since 1865, Armand Trousseau has discovered the clinical phenomena in patients with recurrent VTE. These patients were subsequently diagnosed with advanced cancer. Therefore, deep vein thrombosis associated with advanced cancer is known as Trousseau’s syndrome. Until now, many researchers have been interested in exploring the association between cancer and thrombosis. In the first part of study, we hypothesized that thrombin has an effect on tumor metastasis through activation of PARs. We demonstrated that thrombin and the PAR-1 activating peptide (AP) SFLLRN, but not the PAR-4 AP GYPGKF, induced HIF-1α activities, protein expression, upregulation of Twist and cell motility in colorectal cancer cells, and these actions were significantly inhibited by the PAR-1 antagonist SCH79797, translation pathway inhibitors, including the ERK, PI3K, and mTOR inhibitors. Moreover, thrombin-mediated Twist regulated epithelial–mesenchymal transition (EMT) by increase of N-cadherin to promote cell motility. The aim of the second study was to investigate the activation of PAR-2-increased HIFs-α, transforming growth factor-α (TGF-α) and angiogenesis in pancreatic cancer with overexpression of tissue factor (TF). PAR-2 signaling activated by FVIIa or PAR-2 AP induced accumulation of HIF-1α as well as HIF-2α. Furthermore, PAR-2 signaling increased transcription and translation of TGF-α as well as VEGF. Using small interfering RNA (siRNA) assay, depletion of integrin-linked kinase (ILK), HIF-1α or HIF-2α abolished the activated PAR-2-mediated TGF-α but not VEGF-A. According to microarray analysis, PAR-2 signaling enhanced MEK-ERK pathway, transcriptional factor ETS-1 and VEGF-A. Therefore, PAR-2-induced VEGF-A enhanced endothelial cell proliferation and tube formation, which were blocked by the MEK inhibitor. In summary, our thesis demonstrates that aberrant coagulant factors, such as thrombin or TF, may promote cancer progression, angiogenesis and metastasis through a PARs signaling-mediated HIFs activity. PARs play an important role in the crosstalk with cancer-related thrombosis and cancer progression.