Polychlorinated biphenyls modulate protooncogene expression in Chang liver cells.

In Chang liver cells we studied the influence of polychlorinated biphenyls (PCB) on the expression of different protooncogenes. In cells incubated with medium supplemented with PCB we observed an early effect after 3 h on c-erbA and c-erbH RNA level. This reduction of RNA was due to a delayed transcriptional activation of the genes. The PCB congener 3,3',4,4',5-pentachlorobiphenyl (5-CB) in a 1,000-fold lower concentration influenced protooncogene expression in the same manner. In contrast c-raf RNA level increased transiently after 24 h. The fact that persistent chemicals like PCB interfere with protooncogene expression is particularly interesting in view of their tumor promoting activity