miR-122(英語:miR-122 microRNA)是一個miRNA,在脊椎動物保守,但不存在無脊椎動物基因組中,且無旁系同源[1]。miR-122在肝臟中高表達[2],可調節脂肪酸代謝,也與肝細胞癌丙型肝炎病毒複製有關[3]

pri-miR-122
mir-122的二級結構保守序列
識別符
代號 mir-122
Rfam RF00684
miRBase MI0000442
miRBase MIPF0000095
其他數據
RNA類型 Gene; miRNA
Eukaryota

表現與調控

miR-122於2002年克隆小鼠組織特異性miRNA的研究中發現,僅在肝臟細胞中表現[2],後續實驗在斑馬魚中也發現此miRNA於肝臟細胞中特異性地表現[4]。miR-122的表現在胚胎發育的過程中逐漸增加,成年人肝臟中有高達72%的miRNA為miR-122,為人體所有組織中表現量最大的miRNA[5]。人類的miR-122由18號染色體上的單一基因座編碼,該基因座可轉錄產生miR-122的前驅物pri-miR-122(如右圖所示),過程受HNF4A英語HNF4A蛋白調控[6];pri-miR-122可再被若干RNA酶切割產生長22nt的成熟miR-122[2][7]。成熟的miR-122之3′端會由GLD-2英語GLD-2聚合酶加上一個A,可提升此miRNA的穩定度[8]

有研究顯示miR-122的表現也受晝夜節律蛋白Rev-ErbA alpha英語Rev-ErbA alpha調控,因此其表現可能隨生理時鐘變化,且此miRNA也可調控PPARβ/δ英語Peroxisome proliferator-activated receptor delta等數個晝夜節律蛋白之mRNA的基因表現[9]

標的

miR-122可與許多mRNA結合以調控其基因表現,例如它可與CAT-1英語High affinity cationic amino acid transporter 1mRNA的3'UTR結合以抑制其轉譯,並使該mRNA被送入處理小體中;而當細胞面臨特定逆境時,有另一蛋白HuR英語HuR會從細胞核移至細胞質中,此蛋白也可與CAT-1之mRNA的3'UTR結合,可將該mRNA自處理小體中釋出,並恢復其轉譯,解除miR-122的抑制效果[10]

miR-122的標的mRNA還有CD320英語CD320ALDOABCKDK英語BCKDK等(給小鼠施予miR-122的抑制劑後,以mRNA微陣列英語Microarray的實驗分析發現),此miRNA控制許多和脂肪酸代謝相關的基因表現,受抑制劑抑制後會降低小鼠的血脂含量、促進肝臟代謝脂肪酸、並抑制肝臟合成脂肪酸和膽固醇,但具體機制尚未被完整闡明[11][12][13]。此外miR-122的標的mRNA還有HJV英語HemojuvelinHFE英語HFE (gene)等與鐵代謝相關的基因[14],以及SIRT6英語SIRT6等與心血管疾病相關的基因[15]

許多研究亦指出miR-122可調控許多參與干擾素(IFN)反應途徑的基因,活化干擾素反應,增強抗病毒基因的表現[16][17][17][18][19][20]。有細胞實驗結果顯示miR-122過表達的細胞抗RNA病毒的干擾素等先天免疫反應較強[18]

肝細胞癌患者肝細胞中的miR-122表現量經常較未患病者低,且低miR-122表現與較差的預後呈正相關[21][22]。細胞實驗顯示miR-122屬於腫瘤抑制基因,其表現可抑制癌變,並增強索拉非尼阿黴素化療藥物的療效[23][24]。已知ADAM10英語ADAM10IGF-1RCCNG1英語CCNG1ADAM17英語ADAM17等miR-122的標的基因都與肝細胞的癌變有關[23][24][25]

調控C型肝炎病毒

C型肝炎病毒在肝細胞中的複製英語Viral replication仰賴miR-122[26],miR-122可與C型肝炎病毒RNA5′端兩個相鄰的位點結合[27],這兩個位點在不同基因型的C型肝炎病毒中均高度保守[28]。miRNA的功能一般為抑制基因表現,miR-122促進C型肝炎病毒基因表現的機制尚不完全明朗,它可促進C型肝炎病毒RNA的轉譯,例如近期研究發現miR-122結合C型肝炎病毒RNA後可能改變其二級結構,生成內部核糖體進入位點(IRES)而提升轉譯[29],此外可能還有其他機制參與促進病毒的複製[30][31]。miR-122促進C型肝炎病毒RNA表現的機制應需AGO蛋白英語Argonaute的參與[32](但miR-122表現量夠高時可能不需[33]),DDX6英語DDX6等其他miRISC複合體的組成蛋白則非必須[34]

Peginterferon alfa-2a英語Peginterferon alfa-2a利巴韋林等現有治療C型肝炎病毒的藥物療效有限且副作用強[35],miR-122抑制劑為一種具潛力的藥物,即以與miR-122互補的核酸和其結合以抑制其功能,但因低miR-122與肝細胞癌正相關,此類藥物需經謹慎測試,且不應長期施用[18]。丹麥製藥公司Santaris Pharma英語Santaris Pharma開發中的抗C型肝炎病毒藥物Miravirsen英語Miravirsen即為與miR-122互補的鎖核酸[36]

生物標記

miR-122被用作許多肝病的生物標記,血液中miR-122的含量可作為病毒、酒精或藥物性的肝臟損傷[37][38][39]以及肝臟移植英語Liver transplantation後發生排斥的指標[40][41],其含量改變可能比轉氨酶含量的改變更早發生,因此可用作肝臟損傷的早期指標[40][42]。此外miR-122還可用作纖維化高血壓動脈粥狀硬化等心血管疾病的早期指標[15]

參考文獻

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外部連結