Retinoylation of proteins in a macrophage tumor cell line J774, following uptake of chylomicron remnant retinyl ester

Following uptake of chylomicron remnant retinyl esters by the macrophage ce ll line J774, the retinyl esters are hydrolyzed to retinol before retinol i s further metabolized to retinal and the various retinoic acid isoforms. On e hour after the addition of chylomicron remnant [H-3]retinyl esters to the cells, the percentage of cell-associated radioactivity in the retinyl este r fraction had decreased from approximately 90% to approximately 40%, where as the radioactivity in the retinol fraction increased correspondingly. Aft er 4 hours of incubation, more than 79% of the radioactive retinyl esters h ad been hydrolyzed to retinol. When we measured incorporation of radioactiv ity in the protein fraction, we observed that the level of [H-3]retinoylate d proteins increased rapidly the first 4 hours, and then continued to incre ase at a lo,ver rate up to 24 hours, when approximately 0.6% of the cell-as sociated radioactivity was covalently bound to protein. These data suggest that approximately 0.18% of all the cellular proteins might be retinoylated under such conditions. In summary, in the present study we have demonstrat ed that retinoids taken lip by a macrophage cell line as chylomicron remnan t retinyl esters, a physiologic plasma transport molecule for vitamin A, mi ght be covalently linked to proteins. Such retinoylation might be relevant both for normal function, as well as for the toxic and teratogenic effects of vitamin A. (J. Nutr. Biochem. 9:705-711, 1998) (C) Elsevier Science Inc. 1998.