B7-H3在口腔癌的表現、醣化修飾及免疫反應

Abstract

口腔癌居全球癌症發病率的第十一名，而在台灣，口腔癌的發生率佔十大癌症的第五名。即使發生率已經下降，但口腔癌的預後仍然不佳，整體存活率在過去二十年只改善了百分之五。口腔癌的五年存活率大約是50%，而當復發時，能治癒的機會是微乎其微。口腔癌治療的困境與缺乏有效的早期診斷方式和暴露於環境致癌因子的機會增加有關。因此，研究口腔癌的機制是非常重要的。近年來已經證實醣化現象與癌症有關，本實驗先利用醣探針標定細胞中的醣蛋白，比較口腔癌細胞株及正常口腔上皮細胞的差異，得到B7-H3在口腔癌細胞株中會有過量表現。B7-H3是一種位於細胞膜上的醣蛋白，一開始在免疫細胞中發現，與T細胞的生長及細胞激素INF-gamma的產生有關。許多癌症組織也會表現B7-H3蛋白，且與癌化程度、癌症轉移及低存活率有關。根據這些證據，探討B7-H3在口腔癌中所扮演的角色。 從大量口腔麟狀細胞癌的組織檢體中，發現B7-H3的表現有顯著的增加，且與較大的腫瘤(p=0.0001)及臨床分期(p=0.004)相關。並且B7-H3標記分數高於55%者，口腔麟狀細胞癌病人有較差的全存活率。細胞及動物實驗證明，減弱醣蛋白B7-H3會抑制口腔癌細胞的生長及種植在小鼠口腔及背部之腫瘤大小，反之亦然。進一步以質譜儀分析口腔癌細胞B7-H3的醣化現象及醣分子結構，比起正常細胞，癌細胞之B7-H3有顯著的fucosylation，醣分子結構的支鏈較多，且表現正常細胞所沒有的terminal alpha-galactose，而癌細胞B7-H3的這些特殊醣分子結構會與凝集素如DC-SIGN及Langerin結合，說明B7-H3與免疫反應的關係。研究結果顯示，醣蛋白B7-H3在口腔癌細胞中的過度表現及異常的醣化修飾會與腫瘤的生長和免疫反應有關。

Oral cancer is the eleventh most-common cancer worldwide and the fifth most prevalent cancer in Taiwan. Although the incidence has decreased over the last decade, outcomes of oral cancer remain difficult with only 5% improvement in overall survival in the last 20 years. The five-year survival rate of oral cancer is about 50% and complete recovery is almost not possible as recurrence is occurred. It is partly due to the lack of effective early diagnosis and increasing environmental exposure to cancer-causing agents. It has been proved that aberrant glycosylation is involved in cellular transformation. To identify new markers for oral cancer, we employed a glycosylation probe to investigate the function of sialylated glycoproteins differentially expressed on oral cancer cells and B7-H3 was found to be significant. B7-H3 is a membrane protein originally identified from immune cells. It is a costimulatory molecule related with the proliferation and IFN-gamma production in T cells. B7-H3 is also found in a variety of cancers and correlated with tumor progression. The purpose of this study is to explore the role of B7-H3 involved in oral cancer. B7-H3 was found to be overexpressed in oral squamous cell carcinoma (OSCC) specimens and correlated with larger tumor size (p=0.0001), advanced clinical stage (p=0.004) and low survival rate in OSCC patients (B7-H3 labeling score >= 55%). In addition, knockdown of B7-H3 suppressed tumor cell proliferation, and restoration of B7-H3 expression enhanced tumor growth. We also observed differences in the glycoforms of B7-H3 between cancer and normal cells; higher fucosylation, higher branching and terminal alpha-galacosylation of N-linked glycans were observed in the cancer cells but not in the normal cells. Moreover, B7-H3 derived from Ca9-22 oral cancer cells had better interaction with the lectin receptors DC-SIGN and Langerin than B7-H3 derived from normal cells. Overall, this study demonstrates that B7-H3 overexpression with characteristic aberrant glycosylation correlates with tumor growth and immune response.