Proteomic analysis of hepatitis B surface antigen positive transgenic mouse liver and decrease of cyclophilin A.

The small, 22-nm spherical particles associated with hepatitis B infection are composed of hepatitis B surface antigen (HBsAg) and usually outnumber the virions by a ratio of 10(2) or 10(3). To study the interactions and pathogenesis between liver cells and the expression of HBsAg, global protein profiles were compared by two dimensional gel-based differential proteomics between the livers of a lineage of HBsAg positive transgenic mice and their HBsAg negative control siblings. A total of 93 proteins were identified in the HBV transgenic mice. Around 45% of these differentially expressed proteins were enzymes associated with metabolism, suggesting that the processing of lipids, carbohydrates and certain amino acids were up- or down-regulated. Among these proteins, cyclophilin A (CypA), the major target for the potent immunosuppressive drug cyclosporin A, was found decreased in HBsAg positive transgenic mouse liver and in a stable cell line expressing HBsAg when compared to their controls. The decrease of intracellular CypA was accompanied by an increased secretion of this protein into the supernatant of HBsAg positive cells. Possible implications of HBsAg expression and the intracellular decrease of CypA are discussed.