A possible mechanism of inverse developmental regulation of alpha-fetoprotein and albumin genes. Studies with epidermal growth factor and phorbol ester

Abstract

Epidermal growth factor (EGF) and 12-O-tetradecanoylphorbol-13-acetate (TPA) synergistically suppress activities of the promoter and enhancer of the human alpha-fetoprotein (AFP) gene in HuH-7 human hepatoma cells as analyzed by transient transfection assays using the chloramphenicol acetyltransferase gene as a reporter. In contrast to the AFP gene, albumin promoter and enhancer activities were not affected by EGF and TPA. Unexpectedly, however, Northern blot analysis revealed that the albumin mRNA level as well as the AFP mRNA level were reduced by treatment with EGF and TPA. We propose that in HuH-7 cells, the AFP enhancer stimulates the albumin promoter as well as the AFP promoter; and consequently, inhibition of the AFP enhancer by EGF and TPA results in reduction of both AFP and albumin mRNA levels. The significance of the involvement of the AFP enhancer in albumin transcription is discussed in relation to the inverse pattern of expression of the AFP and albumin genes in neonatal growth.