PROLIFERATION AND TUMORIGENICITY INDUCED BY CCAAT ENHANCER-BINDING PROTEIN/

A plasmid containing the CCAAT/enhancer-binding protein (C/EBP alpha) gene transcriptionally controlled by the metallothionein promoter was constructed, The gene was transfected into the human hepatocellular ca rcinoma cell lines Hep3B and HepG2. When cultured in vitro in the pres ence of 100 mu M ZnSO4, C/EBP alpha expression caused reversible growt h arrest, In soft agar clonogenic assays, C/EBP alpha expression decre ased both the colony size and the total number of colonies compared wi th zinc-free controls, C/EBP alpha expressing cells s.c. implanted in CD-1 nu/nu mice were essentially nontumorigenic, whereas C/EBP alpha t umor cells implanted into immunodeficicnt SCID mice demonstrated a sig nificantly delayed time of tumor appearance compared with cells transf ected with a vector control plasmid. These studies suggest that the ex pression of endogenous genes normally associated with a quiescent, dif ferentiated state, such as C/EBP alpha, can result in impaired prolife rative activity and suppressed tumorigenicity of hepatoma cell lines.