TY - JOUR
T1 - Tamoxifen induction of CCAAT enhancer-binding protein α is required for tamoxifen-induced apoptosis
AU - Cheng, Jingwei
AU - Yu, David V.
AU - Zhou, Jian Hua
AU - Shapiro, David J.
PY - 2007/10/19
Y1 - 2007/10/19
N2 - Low concentrations of tamoxifen or its active metabolite 4-hydroxytamoxifen (OHT) induce estrogen receptor α(ERα)-dependent apoptosis. To analyze the pathway of OHT-ERα-induced apoptosis, we developed stably transfected lines of HeLa cells expressing wild-type ER and an inactive mutant ERα unable to bind estrogen response elements. HeLa cells expressing the mutant ERα and HeLa cells expressing wild-type ERα in which the ER was knocked down with an ER-specific small interfering RNA were not killed by Tam or OHT, suggesting that estrogen response element-mediated transcription is required for Tam- and OHT-induced apoptosis. Microarray analysis to identify a gene(s) whose expression is important in OHT-ER-mediated apoptosis identified 19 mRNAs that OHT up-regulated by >1.6-fold and 15 down-regulated mRNAs. Gene function and the time course of induction by OHT-ERα led us to further investigate CCAAT enhancer-binding protein α (C/EBPα), which has roles in cell cycle progression and apoptosis, and p21. Quantitative reverse transcription-PCR, Western blot analysis, and RNA interference knockdown suggest that cell cycle arrest resulting from OHT-ERα induction of p21 may facilitate apoptosis. OHT-ERα, but not E2-ERα, induced C/EBPα mRNA and protein. RNA interference knockdown of C/EBPα nearly abolished OHT-ERα-induced apoptosis. We isolated stable cell lines that were resistant to OHT-induced apoptosis, contain full-length functional ERα, and undergo apoptosis in response to etoposide. In these OHT-resistant cell lines both before and after OHT treatment, C/EBPα levels are much lower than in OHT-sensitive cells. These studies establish a novel molecular site responsible for Tam- and OHT-ERα-induced apoptosis of cancer cells.
AB - Low concentrations of tamoxifen or its active metabolite 4-hydroxytamoxifen (OHT) induce estrogen receptor α(ERα)-dependent apoptosis. To analyze the pathway of OHT-ERα-induced apoptosis, we developed stably transfected lines of HeLa cells expressing wild-type ER and an inactive mutant ERα unable to bind estrogen response elements. HeLa cells expressing the mutant ERα and HeLa cells expressing wild-type ERα in which the ER was knocked down with an ER-specific small interfering RNA were not killed by Tam or OHT, suggesting that estrogen response element-mediated transcription is required for Tam- and OHT-induced apoptosis. Microarray analysis to identify a gene(s) whose expression is important in OHT-ER-mediated apoptosis identified 19 mRNAs that OHT up-regulated by >1.6-fold and 15 down-regulated mRNAs. Gene function and the time course of induction by OHT-ERα led us to further investigate CCAAT enhancer-binding protein α (C/EBPα), which has roles in cell cycle progression and apoptosis, and p21. Quantitative reverse transcription-PCR, Western blot analysis, and RNA interference knockdown suggest that cell cycle arrest resulting from OHT-ERα induction of p21 may facilitate apoptosis. OHT-ERα, but not E2-ERα, induced C/EBPα mRNA and protein. RNA interference knockdown of C/EBPα nearly abolished OHT-ERα-induced apoptosis. We isolated stable cell lines that were resistant to OHT-induced apoptosis, contain full-length functional ERα, and undergo apoptosis in response to etoposide. In these OHT-resistant cell lines both before and after OHT treatment, C/EBPα levels are much lower than in OHT-sensitive cells. These studies establish a novel molecular site responsible for Tam- and OHT-ERα-induced apoptosis of cancer cells.
UR - http://www.scopus.com/inward/record.url?scp=35649023187&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=35649023187&partnerID=8YFLogxK
U2 - 10.1074/jbc.M704829200
DO - 10.1074/jbc.M704829200
M3 - Article
C2 - 17716978
AN - SCOPUS:35649023187
VL - 282
SP - 30535
EP - 30543
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
SN - 0021-9258
IS - 42
ER -