Hormonal regulation of protein degradation in hepatoma cells in tissue culture.

Abstract

The effects of dexamethasone and insulin on the degradation of total cellular protein have been investigated in an established line of rat hepatoma cells (HTC) in suspension culture by measuring the release of acid-soluble radioactivity from previously labeled protein. When incubated in a chemically-defined, serum-free medium, HTC cells lose approximately 2 to 3% of their labeled protein per hour. Dexamethasone (0.1 μM) causes a 20% increase in the apparent rate of protein degradation. The addition of insulin (0.1 U/ml) to dexamethasone-treated cells causes a 26% decrease in the rate of protein degradation by a mechanism which does not require concomitant RNA synthesis. Since actinomycin D blocks the modest enhancement of amino acid incorporation into protein stimulated by insulin, but does not affect the inhibition of protein breakdown by insulin, it appears that the effect of insulin on protein degradation is independent of its effects on protein synthesis. Bovine serum (5%), which mimics the insulin st...