Phorbol diester 12-O-tetradecanoylphorbol 13-acetate (TPA) up-regulates the expression of estrogen receptors in human THP-1 leukemia cells

In the present work, we have inspected expression of estrogen receptors (ER ) and their regulation by the phorbol diester 12-O-tetradecanoylphorbol 13- acetate (TPA) in a leukemic cell line, the THP-1 cells, using multiple expe rimental approaches. Firstly, ligand binding assay (LBA) revealed that cont rol (unstimulated) THP-1 cells express type I (high affinity, limited capac ity) ER in the nuclear fraction only, whilst treatment of cells with TPA re sulted in the appearance of type I ER in the soluble fraction as well, with the 50 ng/ml dose and the 48 h incubation time being the most effective ex perimental condition. A concomitant increase of type II ER was also seen in both soluble and nuclear cell fractions. Unstimulated THP-1 cells were fou nd to be ER negative by immunocytochemistry; conversely, cells exposed to 5 0 ng/ml TPA for 48 h stained positively for ER, with the majority of cells having a strong nuclear staining. Scrutiny of ER mRNA expression using reve rse transcriptase-polymerase chain reaction showed the presence of a wild t ype ER transcript in both control and TPA-treated THP-1 cells, though level s of ER mRNA were found to be comparatively higher in the latter. This comb ined evidence would imply that the TPA-induced differentiation of THP-1 cel ls is accompanied by the rise of high affinity (type I) ER, suggesting that estrogens may play a role in the regulation of macrophage activity during the inflammatory and/or the immune response. J. Cell. Biochem. 83: 390-400, 2001. (C) 2001 Wiley-Liss, Inc.