Estrogen receptor cofactors expression in breast and endometrial human cancer cells

In order to approach the molecular basis of the tissue-specific agonistic a ctivity of antioestrogens, we have compared, at the mRNA level, the express ion of various transcriptional cofactors (activators or repressors) of estr ogen receptors in different breast (MCF7, ZR75-1, T47D, MDA-MB231) and endo metrial (Ishikawa, RL-95-2 and HEC1A) human cancer cell lines. We showed th at for SRC-1, CBP, TIF1 alpha, RIP140, N-CoR, and SMRT, no:significant: dif ferences in the expression levels were observed between breast and endometr ial cells. For TIF1 alpha mRNA, both isoforms were also detected at similar levels in all the cells tested. By contrast, over-expression of AIB1 mRNA was observed in MCF7 cells, but not in other breast or endometrial cells, i rrespective: of their ER-status. We then used protein-protein interaction a ssay (far-Western blot) to confirm the increased expression of at least one of the p160 proteins in MCF7 cells. Finally, we demonstrated that RIP140 m RNA is directly induced by estrogens in ER-positive MCF7 breast cancer cell lines but not in Ishikawa endometrial cells. Together these results indica te that some differences exist between breast and endometrial cancer cell l ines at the level of estrogen receptor transcription cofactor expression. ( C) 1999 Elsevier Science Ireland Ltd. All rights reserved.