HBx經由IKKα/microRNA路徑抑制maspin表現促進肝癌惡化

Abstract

Maspin 透過促進細胞貼附和細胞凋亡，以及抑制細胞移動能力而抑制腫瘤進展。然而maspin在肝癌(hepatocellular carcinoma, HCC)中的角色尚未釐清。因此，本篇研究主要探討maspin蛋白在肝癌中的調控機制，以及其表現與HCC病人的預後之間的關聯性。本研究發現，Hepatitis B virus (HBV)感染誘發的肝癌中maspin蛋白之表現量降低，並與肝癌病人的預後較差有高度相關性。我們進一步發現，HBV主要透過X蛋白(HBx)增加microRNA-7/107/21的表現，直接結合maspin mRNA而抑制maspin蛋白表現，進而促進肝癌細胞的移動能力以及增加細胞對anoikis和化療的抗性。在臨床檢體中也發現，高度表現這些microRNA的HCC病人其maspin表現量較低並有較差的存活率。此外，在HBV感染的HCC病人檢體中nuclear inhibitor-kB kinase-α (IKKα)的表現量和maspin表現量呈高度負相關。我們也發現maspin mRNA 和蛋白的表現量會受到nuclear IKKα抑制，但卻不受IKKβ影響。抑制IKKα 可以有效回復HBx造成的maspin表現抑制和化療抗性。更進一步證實，HBx過度表現會促使nuclear IKKα直接結合到microRNA-7、microRNA -103、microRNA -107和microRNA-21的promoter上，誘發這些microRNA的轉錄，進而抑制maspin的表現。 此研究不僅證實了HBV感染降低maspin表現的分子機制，更指出nuclear IKKα是造成HBx誘發HCC腫瘤侵略性和化療抗性的主要調控因子。因此，IKKα可望成為治療標靶以提升臨床上HCC病人的療效。

Maspin suppresses tumor progression by promoting cell adhesion and apoptosis and by inhibiting cell motility. However, its role in tumorigenesis of hepatocellular carcinoma (HCC) remains unclear. The gene regulation of maspin and its relationship with HCC patient prognosis were investigated in this study. Maspin expression was specifically reduced in HBV-associated patients and correlated with their poor prognosis. Maspin downregulation in HCC cells was induced by HBV X protein (HBx) to promote their motility and resistance to anoikis and chemotherapy. HBx-dependent induction of microRNA-7, -107, and -21 was further demonstrated to directly target maspin mRNA, leading to its protein downregulation. Higher expressions of these microRNAs were also correlated with maspin downregulation in HBV-associated HCC patients, and were associated with their poor overall survival. Our data further revealed that nuclear inhibitor-kB kinase-α (IKKα) expression was inversely correlated with maspin expression in HBV-associated patients. Nuclear IKKα but not IKKβ reduced maspin protein and mRNA expression, and inhibition of IKKα reverses HBx-mediated maspin downregulation and chemoresistance. In response to HBx overexpression, nuclear IKKα was further demonstrated to induce the gene expressions of microRNA-7, -103, -107, and -21 by directly targeting their promoters, thereby leading to maspin downregulation. These data not only provided new insights into the molecular mechanisms of maspin deficiency by HBx, but also indicated nuclear IKKα as a critical regulator for HBx-mediated aggressiveness and chemoresistance in HCC, and suggested IKKα as a promising target to improve the therapeutic outcome of HCC patients.