Effects of hydrocortisone and aspirin on protein synthesis and post-translational protein modification in cultured...

Arginyl-tRNA transferase is suggested to function as a post-translational modifier of proteins through the addition of arginine to the NH2-terminus of specific acceptor proteins. Both hydrocortisone and aspirin produced an age-dependent stimulation of protein synthesis in normal human fibroblasts (IMR90), while producing an inhibition of protein synthesis in SV40 virus-transformed IMR90 cells. The effect of aspirin was confined primarily to the cytoplasmic compartment, whereas hydrocortisone produced its effect at both cytoplasmic and nuclear levels. Neither hydrocortisone nor aspirin had a direct effect on arginyl-tRNA transferase activity in vitro; however, hydrocortisone resulted in a marked increase in the availability of chromosomal proteins subject to modification by arginyl-tRNA transferase. This stimulatory effect was attenuated by increasing culture age. The modified chromosomal proteins were found to be dissociated from native chromatin, suggesting that arginylation either triggered their release or prevented reassociation with chromatin thereafter. Hydrocortisone produced a moderate decrease in the availability of chromosomal proteins for arginylation in SV40 virus-transformed cells, and this effect was not modulated by aging phenomena.