Retinoylation of HL-60 proteins. Comparison to labeling by palmitic and myristic acids

Recent studies suggest that a retinoic acid (RA) nuclear receptor or a retinoylated nuclear protein may be involved in the action of RA. We showed previously (Takahashi, N., and Breitman, T. R. (1989) J. Biol. Chem. 264, 5159-5163) that retinoylation involves the formation of a thioester bond and occurs on protein in newly formed cells and in pre-existing cells. In this study, we saw at least 14 retinoylated proteins in HL-60 cells. Greater than 90% of the retinoylation was associated with the nuclear protein described previously. This protein, partially purified from isolated nuclei, bound to DNA-cellulose and was eluted with NaCl. Retinoylation occurred in HL-60 cells exposed to cycloheximide. Thus, retinoylation resembled palmitoylation, both in the covalent bond and the exchangeable reaction involving preformed protein. These similarities prompted us to compare retinoylation with two other fatty acylations in growing HL-60 cells. We found that the major retinoylated protein was labeled by either radioactive palmitic acid or myristic acid. The extent of [3H]palmitic acid labeling of this protein was not reduced by growth in the presence of RA. The extent of retinoylation of this protein was not reduced by growth in the presence of increasing concentrations of palmitic acid. These results raise the possibility that the same protein is a substrate for retinoylation, palmitoylation, and myristoylation.