Induction of p21 (CIP1/WAF1/SID1) by estradiol in a breast epithelial cell line transfected with the recombinant estrogen receptor gene: a possible mechanism for a negative regulatory role of estradiol.
Estrogens stimulate the growth of a majority of estrogen receptor (ER)-positive breast cancer cells. In contrast, estradiol exerted a 75% inhibition of DNA synthesis in the MCF-10AE(wt5) cell line, obtained by the transfection of the ER gene into a normal breast epithelial cell line, MCF-10A. The estradiol-mediated growth inhibitory effect was reversed by ICI 164384, a pure anti-estrogen. Analysis of cell cycle by flow cytometry showed a significant increase of G1 cells by estradiol treatment compared to controls. To understand the mechanism of action of estradiol on MCF-10AE(wt5) cells, we examined the level of a cyclin dependent kinase inhibitor (CKI), p21, by Western blot analysis. Our results showed a 5- to 10-fold increase in the level of p21 in estradiol-treated MCF-10AE(wt5) cells compared to controls. ICI 164384 reversed estradiol-mediated induction of p21. Northern blot analysis of p21 mRNA indicated that estradiol stimulated its message in MCF-10AE(wt5) cells. Analysis of a panel of 6 breast cancer cell lines showed the absence of p21 protein, whereas it was present at a very low level in MCF-10A cells. Comparison of p21 in MCF-10A and MCF-10AE(wt5) cells showed an abundance of p21 in the ER-transfected cells. However, this p21 appears to be inactive in the absence of estradiol. These results suggest a p21-mediated pathway as a possible mechanism for the growth inhibitory effects of estradiol on at least a subset of ER-transfected cell lines.
Thomas
T J
TJ
Department of Medicine, The Cancer Institute of New Jersey, New Brunswick, USA.
Faaland
C A
CA
Adhikarakunnathu
S
S
Watkins
L F
LF
Thomas
T
T
D001940:Breast / Q000187:drug effects* / Q000378:metabolism; D001943:Breast Neoplasms / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology*; D005260:Female; D006801:Humans; D053284:Polyunsaturated Alkamides; D012333:RNA, Messenger; D011960:Receptors, Estrogen / Q000378:metabolism; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D053284:Polyunsaturated Alkamides; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D016159:Tumor Suppressor Protein p53; D004958:Estradiol; C051781:ICI 164384