探討蛋白質N端乙醯基轉移酶在食道癌中的表現調控及其在食道癌細胞侵襲能力所扮演的角色

Abstract

目前食道癌治療方式主要是手術切除、放射線及化療，但病人預後不佳且復發機率高。而食道癌尚無有效的標靶藥物。一旦癌細胞遠端轉移，病人的五年存活率僅5%，故尋找能夠調控食道癌進程的專一性分子對於發展標靶治療藥物相當重要。蛋白質N端乙醯基轉移酶(Protein N-terminal Acetyltransferases, NATs)會針對蛋白質進行乙醯化，藉此調控蛋白質功能，其中N-α-acetyltransferase 10 protein (Naa10p)為NatA乙醯基轉移酶複合體中具有催化活性的次單元。在過去的文獻中曾報導Naa10p在不同癌症中，可能透過不同的機制扮演致癌基因或抑癌基因，本研究中我們試圖探討Naa10p在食道癌中的角色，評估其做為新穎食道癌藥物標靶的可能性。首先經由分析The Cancer Genome Atlas 資料庫，我們發現在食道癌病人中Naa10p表現量高的病人存活率較差，可做為預後指標分子。在細胞實驗中進一步抑制Naa10p在食道癌細胞株中的Naa10p表現量，觀察到細胞migration能力不變，但invasion能力及分解Gelatin的能力下降，推測Naa10p可能會對蛋白酶(protease)的表現及活性或胞外分泌量進行調控。而Protease inhibitor array的結果指出在抑制Naa10p表現後，Cystatin E/M, Serpin E1, Lipocalin-1的胞外分泌量增加。故推測Naa10p可能會對這些Protease inhibitor的胞外分泌量進行調控。而我們也同時對Naa10p在食道癌中被過度表現的原因進行探討，針對NAA10的轉錄層級去進行資料庫分析，目前已知NAA10基因啟動子(promoter)序列甲基化程度與NAA10 RNA表現量呈負相關，並發現miR-361可能調控Naa10p的表現。綜合以上，DNA的甲基化與miR-361可能對Naa10p在食道癌中的表現調控，而Naa10p 可能透過調控protease inhibitors的分泌進一步影響食道癌轉移。

The main treatment options for esophageal cancer patients are usually surgery, radiation therapy, and chemotherapy. There is no effective target therapy for esophageal cancer patients with poor prognosis and high recurrence. Once the cancer cell metastasis, the 5-year survival rate of esophageal cancer patients only 5%. It is urgent to find out a molecule that is specific to esophageal cancer progression as a therapeutic target. N-α-acetyltransferase 10 protein (Naa10p) is a catalytic subunit of NatA and acetylates the N-terminal amino group of protein to regulate protein function. In previous studies, Naa10p plays multiple roles in regulating cancer progression. Here, we investigate the role of Naa10p in esophageal cancer to assess its potential to be a novel therapeutic target. We analyzed The Cancer Genome Atlas (TCGA) and discovered that patients with the high expression of Naa10p had poor prognosis. We then assumed that Naa10p as an oncogene in esophageal cancer. We knocked down Naa10p expression in Esophagus Squamous Cell Carcinoma (ESCC) cell lines, there was no significant altered in cell migration ability, but cell invasion ability and cell gelatinolytic activity were down regulated. Data of Protease inhibitor array indicated that secretion of Cystatin E/M, Serpin E1, and Lipocalin-1 were up regulated after Naa10p knocked down. We suggested that Naa10p would regulate the secretion of these protease inhibitor. Otherwise, we also inspected the dysregulation of Naa10p in esophageal cancer. We discovered that DNA methylation level at NAA10 promoter had negative correlation with patients’ survival and miR-361 probably could repress NAA10 expression. As mention above, the DNA methylation of NAA10 promoter and miR-361 might regulate the expression of Naa10p in esophageal cancer. Naa10p would affect esophageal cancer metastasis by regulating the secretion of protease inhibitors.