Hepatitis B virus X protein induces expression of alpha-fetoprotein and activates PI3K/mTOR signaling pathway in liver cells

Abstract

// Mingyue Zhu 1, 2, * , Junli Guo 1, 3, * , Wei Li 1, 2 , Yan Lu 1, 2 , Shigan Fu 1 , Xieju Xie 4 , Hua Xia 1, 2 , Xu Dong 1, 2 , Yi Chen 1, 2 , Ming Quan 3 , Shaojiang Zheng 1, 5 , Keping Xie 3 , Mengsen Li 1, 2 1 Hainan Provincial Key Laboratory of Carcinogenesis and Intervention, Hainan Medical College, Haikou, Hainan 571199, P. R. China 2 Key Laboratory of Molecular Biology, Hainan Medical College, Haikou, Hainan 571199, P. R. China 3 Department of Gastroenterology, Hepatology & Nutrition, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA 4 Department of Physiology and Pathophysiology, Hainan Medical College, Haikou, Hainan 571199, P. R. China 5 Tumor Institute, Affiliated Hospital of Hainan Medical College, Haikou, Hainan 570102, P. R. China * These authors have contributed equally to this work Correspondence to: Mengsen Li, e-mail: mengsenli@163.com Keping Xie, e-mail: kepxie@mdanderson.org Keywords: AFP, HBx, PI3K/mTOR signaling, Liver cells, Hepatocarcinogenesis Received: October 10, 2014      Accepted: December 11, 2014      Published: January 21, 2015 ABSTRACT The hepatitis B virus (HBV)-X protein (HBx) induces malignant transformation of liver cells, and elevated expression of alpha-fetoprotein (AFP) is a significant biomarker of hepatocarcinogenesis. However, the role of AFP in HBV-related hepatocarcinogenesis is unclear. In this study, we investigated the regulatory impact of AFP expression on HBx-mediated malignant transformation of human hepatocytes. We found that HBV induced the expression of AFP before that of oncogenes, e.g ., Src, Ras and chemokine (C-X-C motif) receptor 4 (CXCR4), and AFP activated protein kinase B (AKT) and mammalian target of rapamycin (mTOR) in HBV-related HCC tissues and in human liver cells transfected with HBx. Cytoplasmic AFP interacted with and inhibited phosphatase and tensin homolog deleted on chromosome 10 (PTEN), activating the phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway and promoting mTOR-mediated stimulation of the transcription factor hypoxia inducible factor-1α (HIF-1α), and therefore led to the activation of the promoters of Src, CXCR4, and Ras genes. On the contrary, reduced expression of AFP by siRNA resulted in the repression of p-mTOR, pAKT, Src, CXCR4, and Ras in human malignant liver cells. Taken together, for the first time our study indicates that HBx-induced AFP expression critically promote malignant transformation in liver cells through the activation of PI3K/mTOR signaling.