THE ROLE OF TETRASPANIN-8 IN ASTROCYTE ELEVATED GENE-1 MEDIATED PROGRESSION OF HEPATOCELLULAR CARCINOMA

Hepatocellular carcinoma (HCC) is a devastating form of liver cancer that accounts for 80% of liver cancers. HCC has a poor prognosis with five-year survival of less than 12% in the United States. We in previous studies have identified Astrocyte Elevated Gene-1 (AEG-1) as an aberrantly overexpressed gene in many cancers including HCC, regulating tumor progression. Microarray studies identified the small transmembrane protein, tetraspanin8 (TSPAN8) as a downstream of AEG-1. TSPAN8 belongs to the family of TETRASPANINS with the characteristic of crossing the membrane four times, and regulating a wide range of cellular phenomena. TSPAN8 is implicated in metastasis and is classified as a metastasis promoting tetraspanin. To understand the role of TSPAN8 in the context of AEG-1 regulated tumor progression of HCC, we generated knockdown clones of TSPAN8 in AEG-1-8 cell lines (HepG3 cell lines with stable overexpression of AEG-1), and analyzed cellular events that mediate metastasis such as migration, invasion and in-vivo tumorogenesis. Our in-vitro studies show that knockdown of TSPAN8 in AEG-1 overexpressing cells significantly abrogated migration, matrigel invasion, proliferation and endothelial cell activation. Moreover, we show that knockdown of TSPAN8 significantly inhibited intrahepatic metastasis of orthotopic xenografts in the livers of athymic nude mice. TSPAN8 might be a useful diagnostic marker and potential therapeutic target for HCC. These findings indicate that upregulation of TSPAN8 might be an important event in mediating the oncogenic function of AEG-1