Hepatitis B virus X antigen promotes transforming growth factor-b1 (TGF-b1) activity by up-regulation of TGF-b1 and down-regulation of a2-macroglobulin

Received 12 September 2003 Accepted 10 October 2003 Hepatitis B virus (HBV) X antigen (HBxAg) may contribute to the development of hepatocellular carcinoma (HCC) by activation of signalling pathways such as NF-kB. To identify NF-kB target genes differentially expressed in HBxAg-positive compared to -negative cells, HepG2 cells consistently expressing HBxAg (HepG2X cells) were stably transfected with pZeoSV2 or pZeoSV2-IkBa. mRNA from each culture was isolated and compared by PCR select cDNA subtraction. The results showed lower levels of a2-macroglobulin (a2-M) in HepG2X-pZeoSV2 compared to HepG2X-pZeoSV2-IkBa cells. This was confirmed by Northern and Western blotting, and by measurement of extracellular a2-M levels. Elevated transforming growth factor-b1 (TGF-b1) levels were also seen in HepG2X compared to control cells. Serum-free conditioned medium (SFCM) from HepG2X cells suppressed DNA synthesis in a TGF-b-sensitive cell line, Mv1Lu. The latter was reversed when the SFCM was pretreated with exogenous, activated a2-M or with anti-TGF-b. Since elevated TGF-b1 promotes the development of many tumour types, these observations suggest that the HBxAg-mediated alteration in TGF-b1 and a2-M production may contribute importantly to the pathogenesis of HCC.