Signal Pathway of Cell Migration Mediated by HBx Figure 6. NF-kB is responsible for the Capn4-mediated upregulation of OPN. (A, B and C) Capn4-overexpressed HepG2 (or H7402) cells were treated with the indicated doses of siRNA targeting NF-kB mRNA (Si-NF-kB) for 48 h. (A) The promoter activity of OPN was examined by luciferase reporter gene assay (**P,0.01 Student’s t test). (B) The mRNA levels of OPN, Capn4 and NF-kB/p65 were detected by RT-PCR. (C) The protein levels of OPN, Capn4 and NF-kB/p65 were measured by western blot analysis. doi:10.1371/journal.pone.0031458.g006 Discussion Recent studies have shown that HBx is associated with cell migration. Moreover, our previous studies demonstrated that HBx is able to promote cell migration through the regulation Capn4 or mir-29a [19,37]. However, the mechanisms of promotion of cell migration mediated by HBx are not fully understood. In the present study, we investigated the signaling pathways of hepatoma cell migration mediated by HBx. Studies demonstrate that OPN is closely related to tumor metastasis and is often overexpressed in multiple tumor tissues and correlated with metastatic tissues [22,23]. Thus, we first tested whether HBx was able to upregulate OPN. The data demonstrated that HBx significantly upregulated OPN in HepG2-X (or H7402-X) cells. Our laboratory previously found that 5-LOX and COX-2 were involved in cell proliferation and migration [10,11]. Accordingly, 5-LOX is often overexpressed PLoS ONE | www.plosone.org 8 February 2012 | Volume 7 | Issue 2 | e31458