Enhanced production of hepatitis B virus surface antigen in mouse C127 cell on a bovine papillomavirus-metallothionein vector.

We have constructed a recombinant plasmid pCPS12 containing the hepatitis B viral surface antigen (HBsAg) gene linked to the mouse metallothionein promoter on a BPV-pML2 vector. Two stable clones S12-8 and S12-2, obtained by transfection of the mouse C127 cells with pCPS12 propagated in dam+ dcm+ and dam- dcm- Escherichia coli respectively, exhibited different types of response to 5-azacytidine (5-aza-CR) and cadmium (Cd) induction. In S12-8, the productivity of HBsAg was enhanced by 5-aza-CR or 5-aza-CR plus Cd, but not by Cd alone. In S12-2, the expression of HBsAg was not affected by 5-aza-CR but was induced by Cd in the presence or absence of 5-aza-CR. This suggests that methylation may be important in controlling the HBsAg expression and the inducibility of Cd in the transfectants.