Quantitative Analysis of Protein Synthesis Altered by Estrogen in Cultured Xenopus Liver Parenchymal Cell

Abstract

Using the primary culture system of male X. laevis hepatocytes consisting of > 95% parenchymal cells, the effect of estradiol-17.beta. (10-6 M) on protein synthesis was quantitatively analyzed by 3H-leucine incorporation kinetics and the estimation of specific radioactivity of newly synthesized secretory protein. Cells in a well defined culture revealed high plating efficiency and very low DNA synthetic activity. Cultured cells could synthesize several secretory proteins containing serum albumin. Pattern of secreted proteins in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) did not alter with culture time but secretion rate of protein increased for 7 days, starting on the 3rd day following inoculation. Estradiol added to the cluture media extensively induced the synthesis of yolk precursor protein vitellogenin which accounted for 40-50% of the overall secretory protein synthesis and 20-30% of the total protein synthesis on day 7 of estradiol treatment. Ultimately, the total protein synthesis and secretory protein synthesis were stimulated 1.2- to 1.3- and 2.0- to 2.2-fold, respectively, over those of the control cells cultured in the absence of estradiol. Stimulation of protein synthesis was largely due to vitellogenin production. Such an estradiol-dependent stimulation of protein synthesis was also detected in the low MW protein(s). Albumin synthesis was evidently reduced by estradiol. Estradiol had 2 different effects on protein synthesis. These results are discussed in relation to the findings of in vivo experiments.