鐵調控基因在肝癌的表現及其病理、臨床與流行病學意義

Abstract

近年來在鐵相關基因發現的快速進展，已確立了肝在調控鐵代謝的重要地位，最主要是因肝分泌鐵荷爾蒙hepcidin。本研究目的在以新知探討肝癌細胞鐵缺少的原因，以及未曾被探討過的肝癌病人鐵營養的可能變化。 本實驗以普魯士藍染色半定量鐵濃度，以即時聚合酶連鎖反應定量16 個鐵相關基因之訊息核醣核酸，比較從50位肝癌病人切除的肝癌及鄰近非腫瘤組織之間的差別。結果顯示相對於非腫瘤組織，癌細胞鐵量明顯減少，五個鐵調控基因—hepcidin, ceruloplasmin, transferrin, transferrin receptor 1 and 2—表現異常，其中hepcidin的缺失最為顯著；hepcidin表現量與鐵濃度最為相關。基因表現與慢性肝病無統計上關聯。進一步以免疫組織化學染色顯示CEBPA在肝癌有減少情形，即時聚合酶連鎖反應顯示HNF4A3在肝癌有增加現象。HNF4A3表現與癌分化程度呈負相關。Kaplan–Meier活存分析及Cox比例風險分析顯示CEBPA缺失的病人活存期較短。 綜合分析看來，CEBPA與hepcidin的缺失可能導致肝癌細胞無法積存鐵；而隨著肝癌進展，鐵調控基因的異常表現將使身體往組織鐵過度負荷及貧血的方向進行。建議以CEBPA缺失做為肝癌治療可能標的，期能抑制腫瘤生長並改善鐵代謝及其它肝功能，以延長病人生命且改善生活品質。HNF4A 亞型或可作肝癌分化程度的標記。另外，本研究提出一新假說：肝非腫瘤部份可能有增加 hepcidin的免疫反應，以對抗肝癌生長。

Recent advance in the discovery of iron-regulatory genes (IRGs) has identified the liver as the principal organ controlling iron metabolism, particularly for its secretion of the iron hormone hepcidin. This study aimed to answer the long-term pathologic curiosity as to why hepatoma cells do not accumulate iron, and the almost never explored question about the disturbance of iron nutrition in patients with hepatocellular carcinoma (HCC). The study used Perls’ Prussian blue stain to assess iron stores, and real-time polymerase chain reaction (PCR) to measure 16 IRGs’ mRNA, in resected HCCs and adjacent nontumor specimens of 50 HCC patients. The results showed iron was depleted, and expression of five IRGs—hepcidin, ceruloplasmin, transferrin, transferrin receptor 1 and 2—was altered in HCC, as compared with those in nontumor specimens. Hepcidin particularly showed a dramatic reduction in HCC and a strong correlation with iron stores. The IRGs’ expression was not altered in chronic liver diseases preceding HCC. Immunohistochemistry showed CCAAT/enhancer binding protein alpha (CEBPA) was reduced, while real-time PCR showed hepatocyte nuclear factor 4 alpha 3 (HNF4A3) was increased in HCC. Increased HNF4A3 correlated with less differentiated HCC. Kaplan–Meier survival analysis and Cox proportional hazards analysis indicated that reduced CEBPA was associated with shortened patient survival. Several implications can be drawn from this study. Loss of CEBPA and hepcidin may significantly contribute to iron-negative phenomenon in hepatoma cells. The altered expression of IRGs in HCC may result in paradoxical iron imbalance towards tissue iron overload and anemia. Targeting CEBPA downregulation for HCC treatment may not only inhibit tumor progression but also improve patient iron metabolism and other liver functions, thus raising patient survival and quality of life. HNF4A isoforms might be used as biomarkers for status of HCC differentiation. The liver might overexpress hepcidin in response to HCC formation.