[Cell-specific expression of AFP gene is dependent on some nuclear proteins]

AFP is an oncodevelopmental protein. Its level decreases abruptly after birth and reaches almost undetectable level during normal adult life. However, reexpression of the gene can be observed during hepatocarcinogenesis. To further understand mechanism of regulating AFP expression, we checked several restriction enzyme map of 5' terminal and flanking sequences of AFP gene. There are no differences among adult rat liver, fetal liver and hepatoma cells. Using +2(-)-255 bp sequence probe of AFP gene to do southwestern blotting assay, the result showed that the gene-active cells, such as hepatoma cells, contained binding-proteins which were apparently lacking in adult rat liver, lung, spleen, heart and kidney cells. While the fractions of nuclear proteins from adult rat liver cells were devoid of any stimulatory effect on transcription, those of binding-proteins from hepatoma stimulated the transcription of AFP gene in vitro. The hepatoma binding-proteins can rescue transcription activity of fraction of nuclear proteins from adult rat liver cells. These results indicate that cell-specific expression of AFP gene is regulated by protein-factors.