Selective block of albumin gene expression in chick embryo hepatocytes cultured without hormones and its partial reversal by insulin.

Abstract

Listen

Translate article

Rates of synthesis of albumin and transferrin were compared with the levels of their cognate mRNAs in primary monolayer cultures of chick embryo hepatocytes over a period of 72 h. These liver cells were exposed, from the onset of culture, only to a chemically defined medium devoid of hormonal or macromolecular supplement. Synthesis of transferrin was constant whereas synthesis of albumin diminished to near 0 in 3 days. RNA prepared from hepatocyte monolayers, maintained for various lengths of time in culture, was translated in wheat germ extracts and Xenopus oocytes. Translation products were immunoprecipitated and analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. In addition, total RNA from the cultured cells was hybridized to labeled cDNA probes to determine the number of sequences specific for each protein. Albumin mRNA was found to decrease with time in culture in all three assay systems, while transferrin mRNA remained constant. Analysis of the kinetics suggests a selective decay, with a half-life of 7 h, of the amount of albumin-specific RNA present at the beginning of culture. Apparently, in the hormone-deprived hepatocytes, there is little or no further transcription of the albumin gene. After addition of insulin to the cultures, albumin mRNA levels increased, suggesting an effect of this hormone on albumin gene utilization.