Abstract
Previously an Mr 46, 000 protein (named p46) was shown to be induced in the culture medium of human hepatoblastoma cells, Huh-6 C1-5, treated with 12-0-tetradecanoyl phorbol-13-acetate (TPA). For further characterization of p46, Huh-7 C1-4, another line of well differentiated liver cells, was incubated in the presence and absence of TPA, and proteins were labeled with [35S]methionine, and the proteins secreted into the medium were analyzed by one-and two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis. A protein of Mr 46, 000 was observed in the culture medium of Huh-7 C1-4 cells treated by TPA or plated at low density, but only slightly in the culture medium of Huh-7 Cl-4 cells plated at high density. As these results suggested that the expression of p46 was regulated by a factor that was ac-tivated in the growth state and by TPA treatment, the effect of introduction of the competence gene c-myc into Huh-7 C1-4 cells was examined. All 37 indepen-dent transfected colonies obtained showed enhanced expression of p46. As a control, the c-Ha-ras gene was introduced into Huh-7 C1-4 cells and shown not to enhance expression of p46. These results strongly suggested that the expres-sion of p46 was regulated by the competence gene c-myc.
