BRAF(V600E)突變在造釉細胞瘤中所扮演的致病機轉

Abstract

造釉細胞瘤是一種常見的齒源性上皮腫瘤，主要好發在顎骨，此腫瘤雖然在定義上為良性，但卻相當具有侵襲性，並且容易復發，而目前標準治療造釉細胞瘤的方法是廣泛性大範圍切除且合併顎骨切除，而造成臉部顏面功能的損傷且影響美觀甚劇，然而在近年來對於造釉細胞瘤之致病機轉有了突破性的發現，有超過八成的造釉細胞瘤的病人都有MAPK (FGFR-RAS-RAF) pathway上的突變，而其中的BRAF(V600E)的突變占了其中的六成，顯示BRAF(V600E)可能是造成造釉細胞瘤的關鍵基因，此外在Sonic hedgehog pathway (SHH) 裡的SMO基因則是被發現有近四成的基因突變，在不同突變上的造釉細胞瘤也會造就不同病理形態上的差別。而在黑色素細胞瘤和大腸直腸癌中都有利用MAPK pathway和Sonic hedgehog pathway相關的標靶藥物的治療案例，而在先前的文獻中也有提到三位造釉細胞瘤患者，使用了MAPK pathway的小分子標靶藥物治療而讓腫瘤縮小的案例，這顯示了標靶藥物可能在未來是可以成為取代手術性切除的治療方式。 我們的研究致力於找出MAPK pathway中的BRAF(V600E)突變在造釉細胞瘤中所扮演著角色，分別在齒源性上皮細胞中送入了GFP和BRAF(V600E)的基因，模擬正常齒源性細胞在受到致癌基因的調控下所產生的變化，並針對其致癌基因所調控的基因去做一系列研究，結果發現在具有BRAF(V600E)表現的齒源性上皮細胞呈現老化的細胞型態，並且在會跨越老化型態走向進入細胞週期中，且與幹細胞基因SOX2有非常巨大的相關；而在我們自己建立的老鼠模型中也發現了在具有BRAF(V600E)大量表現的齒源性上皮細胞能使老鼠產生腫瘤，這也顯示了BRAF(V600E)的確在造釉細胞瘤中的致病機轉中扮演著莫大的角色，若能清楚的了解BRAF(V600E)的致病機轉，相信以後在治療造釉細胞瘤中是一個莫大的突破。

Ameloblastoma is a benign and rare neoplasm and the most prevalent amongst epithelial odontogenic neoplasm. Because of its locally aggressive property and high recurrence rate, surgical resection is often required to treat the condition, which could lead to facial dysfunction and significant morbidity. Recent studies have reported frequent mutations in MAPK (FGFR-RAS-RAF) pathway and SMO in ameloblastoma, among which BRAF(V600E) mutations is most commonly found. Since MAPK pathway and SMO mutations have also been identified in other cancers such as malignant melanoma and colorectal cancer, targeted therapy for treating those cancers by targeting these mutations. In addition, there have been three case reports suggesting the success of BRAF and MEK inhibitors in treating BRAF mediated ameloblastoma patients. In order to establish targeted therapy in the future, the aim of our study is to investigate the role of BRAF(V600E) mutations in the pathogenesis of ameloblastoma. We transfected GFP and BRAF(V600E) individually into odential epithelial cells- HERS (Hertwig's epithelial cells) to mimic series of situations for the normal odential epithelial cells effected by the oncogene BRAF(V600E). We discovered that the BRAF(V600E) infected HERS takes on a cellular senescence look in the cellular morphology and overcomes the senescence status in cellular cycle at the late stage. The phenomenon of senescence is thought to have direct relation with stemness gene, SOX2. We established the ameloblastoma mouse model and showed that BRAF(V600E) harboring but not GFP only HERS could initiate tumorigenesis on the back of nude mice. This result showed that BRAF(V600E) has a great impact on the pathogenesis of ameloblastoma. Better understanding of the pathogenesis cascade of BRAF(V600) could have significant impact on developing the treatment for ameloblastoma.