RESUMEN
Mutant clones of human hepatocarcinoma PLC-PRF-5 cells carrying a hepatitis B virus (HBV) genome have been obtained using selection for resistance to the toxic action of a variety of preparations to induce cell differentiation. The clones differed in various features such as expression of alpha-fetoprotein (AFP) and albumin as well as in growth rates, ability to grow in semisolid media and to be cloned in agar. Expression of the surface antigen (HBsAg) was significantly increased in mutant cells exhibiting differentiation features in contrast to the parental cells. In addition, the core antigen (HBcAg), which was silent in the original cells, was detected in some clones. There was no temporal correlation between the peak of enhanced expression of HBsAg and activation of HBcAg observed at different life periods of each clone. Evidence of cell fusion in cell culture such as premature chromatin condensation and increased numbers of binucleate cells was detected in clones with differentiation features and an increased level of viral gene expression. The approach used in this study can be used to develop cell lines of the same origin with different degrees of differentiation whilst maintaining HBV expression. This model system may be useful in the study of HBV.