P- 26 EFFECT OF PROTEIN X OF THE HEPATITIS B VIRUS AND HEXACHLOROBENZENE ON LIVER CELL GROWTH DYSREGULATION

Introduction and Objectives

Chronic hepatitis B and exposure to persistent organic pollutants (COPs) can lead to cellular hepatocarcinoma (HCC), the most common liver tumor. HBV DNA encodes transactivator x, HBx protein. The HBx is required to initiate and maintain HBV replication. Hexachlorobenzene (HCB), COPs´member, is a promoter of hepatic preneoplastic foci. We have shown that HCB increases in rat liver PCNA, TGF-β1, VEGF and neo-angiogenesis in vivo models. This study aimed to analyze in vitro two models of HCC generation -associated with HCB or with the expression of HBx-.

Materials and Methods

The HCB effect on cell number (BrdU incorporation by Immunohistochemistry), PCNA (Western blot), TGF-β1 (RT-PCR) was studied in vitro in: 1.1) Huh-7; 1.2) Huh-7 transfected with HBx; 2) HepG2.2.15 (stable expression HBV) and 3) EA-hy926 (endothelial cell). In these last, an inhibitor of TGF-β1-RII (SB431542) was used. In 1.2, 2 and 3 used, 5µM HCB, 24h; in 1, we performed time (30, 60, 90 and 120) and dose (0,005; 0,05; 0,5 and 5µM) curves. Evaluated: a) PCNA protein levels, b) TGF-β1 levels and positive cell number/total cell.

Results

In Huh-7, TGF-β1 increased (20%, 69% and 78%, with 0.05, 0.5 and 5µM HCB, respectively) and PCNA (45% and 60%, with 0.5 and 5 µM HCB, respectively). In Huh-7/HBx, PCNA and TGF-β1 increased by 86% and 71%, respectively. In Huh-7/HBx and 5µM HCB, PCNA increased by 120% and TGF-β1 by 91%. In HepG2.2.15 PCNA was overexpressed by 76%. In EA-hy926, PCNA 29% and TGF-β1 by 43% increased. Both effects were prevented by pre-incubating endothelial cells with the specific inhibitor of TGF-B1 RII after HCB 5µM.

Conclusions

HCB and HBx induce cell proliferation in vitro. This effect is equivalent for both agents (HCB and HBx) and is enhanced by combining them. The proliferative effect is associated with TGF-β1 increase, which mediates the proliferation generated on both HCC and endothelial cell lines. These findings could partially explain the molecular mechanism involved in human HCC cell proliferation, disease progression and neo-angiogenesis.