Covalent binding of 17 beta-estradiol and retinoic acid to proteins in the human breast cancer cell line MCF-7.

Both retinoic acid and 17 beta-estradiol formed covalent bonds with proteins of the human breast cancer cell line MCF-7. Two-dimensional gel patterns of the labeled proteins were unique for each ligand. There were four major retinoylated proteins in MCF-7 consisting of two doublets with molecular masses of 37 kDa and 20 kDa. These proteins were designated 37a, 37b, 20c, and 20d. The extent of retinoylation was very low in a 55 kDa protein that we previously identified in the human myeloid leukemia cell line HL60 [Takahashi, N. and Breitman, T. R. (1989) J. Biol. Chem. 264, 5159-5163]. These results indicated that the protein substrates for retinoylation may vary among cell-types. About 10 proteins were labeled from 17 beta-estradiol. Two of these proteins had mobilities that were identical to the retinoylated proteins 37a and 20c. These results indicate that in MCF-7 cells there are two proteins that can be retinoylated and labeled from estradiol. The demonstration that some ligands of the steroid/thyroid receptor family are covalently linked to cellular proteins suggests new mechanisms for the many effects of these agents on cells.