探討己酮糖磷酸激酶在子宮內膜腺癌惡性進程之角色

Abstract

己酮糖磷酸酶（Ketohexokinase, KHK）在過去的研究中被發現具有果糖代謝的功能，能將果糖磷酸化使其進入三羧酸循環代謝。過去研究發現KHK-A能藉由刺激核苷酸合成促進癌細胞生長引起我們的興趣。分析KHK在各種不同的癌症中臨床上的重要性後，選擇子宮內膜癌做為我們的癌症模式。子宮內膜癌逐年升高的發生率近年來已成為不可忽視的問題，其中超過八成的個案為子宮內膜腺癌，因此我們希望探討KHK在子宮內膜腺癌的角色，並進一步評估未來是否可能作為子宮內膜腺癌的生物標記。首先我們分析了The Cancer Genome Atlas (TCGA) 資料庫，發現KHK表現量高的病人預後較差，並與其他預後因子包括了臨床階段與組織分級顯著相關，且這樣的現象只出現在子宮內膜腺癌的病人中，因此KHK更能作為獨立的預後因子。接著我們分析臨床病人檢體後發現KHK只在癌細胞中高度表現，且進一步將正常子宮內膜的表皮細胞與癌細胞做比較後印證了此項結果，還發現癌細胞中高度表現的KHK以KHK-A的形式佔多數。細胞實驗中，我們透過抑制KHK以及過度表現KHK-A或KHK-C的方式觀察其對於癌細胞各種功能的影響，發現KHK能促進癌細胞的生長，且對於癌細胞長期的生長較為明顯，也能驅使與腫瘤新生相關的非貼附性生長，甚至能更進一步促使癌幹細胞生成。動物實驗中，同樣可以發現高度表現KHK的組別，腫瘤也長得越大。最後，我們針對三個先前已知與癌幹細胞以及腫瘤新生相關的重要轉錄因子分別為Hedgehog路徑中的GLI1、Wnt路徑中的β-catenin和NF-κB路徑中的NF-κB/p65做分析，發現KHK-A以及KHK-C皆會入核，且會促使GLI1、β-catenin和NF-κB/p65細胞核表現量以及活性微幅增加。總結來說，KHK可能會透過調控GLI1、β-catenin和NF-κB/p65促進子宮內膜腺癌生長，腫瘤新生以及癌幹細胞生成。

Ketohexokinase (KHK) is a rate-limiting enzyme of fructose metabolism. It can phosphorylate the fructose to generate fructose-1-phosphate which is the precursor of tricarboxylic acid cycle. However, it interested us that KHK-A isoform was discovered to induce cancer cell proliferation through nucleotide synthesis. As a result, we analyzed the correlation between KHK expression and patient survival in sixteen kinds of cancer type in clinical database and chose the endometrial cancer (EC) as our cancer model. The rising incidence of EC is too serious to ignore this problem. Further, endometrioid adenocarcinoma (EAC) accounts for over 80% of new cases of EC. Hence, we wanted to investigate the roles of KHK in EAC. Furthermore, we evaluated whether KHK could become a novel biomarker of EAC in the future. First, we found overexpression of KHK was correlated to poor survival, late clinical stage, and high histologic grade of EC patients in The Cancer Genome Atlas (TCGA) database. In addition, KHK can be regarded as the independent unfavorable-prognostic factor of EAC. After that, we collected the normal, hyperplastic, cancerous endometrial tissues from patients and found KHK overexpressed in cancerous tissue. These results were supported by the comparison of endometrial epithelial cells (eECs) and EAC cells. Besides that, there are almost all of increment of KHK was KHK-A isoform. We observed KHK affected the functions of cancer cells through knockdown of KHK and overexpression of KHK-A or KHK-C. In vitro, we found KHK induced the proliferation of EAC, especially long term proliferation. On the other hand, KHK promoted anchorage-independent growth and cancer stemness. In vivo, the average tumor size was bigger in the KHK-overexpressed groups compared with the control. Finally, we chose the cancer-stemness-related transcription factors GLI1, β-catenin, and NF-κB/p65 as potential target genes of KHK. We found the KHK can boost the GLI1, β-catenin, and NF-κB/p65 expression and activity slightly. In conclusion, KHK can induce the proliferation, tumorigenesis, and cancer stemness of EAC through GLI1, β-catenin, and NF-κB/p65 activation.