The acute effects of N-hydroxy-acetylaminofluorene on rat liver protein synthesis

A single intraperitoneal injection of N-hydroxy-acetylaminofluorene (N-hydroxy-AAF) at a dosage of 30 mg/kg significantly inhibited rat liver protein synthesis within 15 min. Marked alterations in the subcellular distribution of hepatic RNA accompanied the decline in protein synthesis in treated rats. These changes included decreases in nuclear and bound polysomal RNA and increases in free polysomal and non-sedimentable RNA. Heavy polysomal aggregates, both free and bound, were almost completely degraded to monomers and dimers during this period. Sedimentation profiles of total cytoplasmic RNA revealed no evidence of gross RNA breakdown in N-hydroxy-AAF-treated animals. To determine the mechanisms responsible for the inhibition of protein synthesis by N-hydroxy-AAF, cellular components involved in protein synthesis were purified from control and treated animals and examined in two cell-free systems. In a system which measures polypeptide chain elongation and release, the incorporation of amino acids into protein was reduced by 35% using polysomes from N-hydroxy-AAF treated animals compared with controls. By contrast, the function of the pH 5 fraction (containing aminoacylating enzymes and tRNA) from the carcinogen-treated animals was unimpaired. A wheat germ lysate system was used to determine the ability of mRNA to program polypeptide chain initiation and elongation. Cytoplasmic poly(A)⁺ RNA from N-hydroxy-AAF treated rats showed reduced capacity to stimulate protein synthesis in wheat germ lysates compared with similar preparations from DMSO-injected control rats. The rapid inhibition of protein synthesis by N-hydroxy-AAF may be an important contributing factor to other toxic effects of the carcinogen, including the inhibition of rRNA synthesis.