Induction of p21WAF1 expression via Sp1-binding sites by tamoxifen in estrogen receptor-negative lung cancer cells.
Although originally synthesized as an anti-estrogen, tamoxifen (Tam) was found to be able to inhibit proliferation of estrogen receptor (ER)-negative cancer cells in vitro. However, the molecular basis of such ER-independent growth inhibition is largely unknown. We have previously demonstrated that Tam induces p21WAF1 and p27KIP1 expression in human lung cancer cells which lack ER-alpha and -beta. We found that Tam induced p21WAF1 expression via transcriptional activation. In order to determine the molecular mechanism responsible for p21WAF1 induction by Tam, we performed a deletion analysis on the p21WAF1 promoter. The minimal region in the p21WAF1 promoter required for Tam-activated induction was mapped to a contiguous stretch of 10 bp located 83 bases upstream of the transcription initiation site. Our results showed that transcription factor Sp1 and Sp3 bound to this GC-rich region and mutation of Sp1-binding sites dramatically attenuated Tam-induced p21WAF1 promoter activity. We also tried to elucidate the signaling pathway that mediated the activation of p21WAF1 by Tam. Inhibition of mitogen-activated protein kinase pathways did not block Tam-induced p21WAF1. Similarly, protein kinase C inhibitor calphostin C could not suppress Tam-induced p21WAF1. Conversely, pretreatment of a specific protein kinase A inhibitor H89 significantly attenuated the induction of p21WAF1 by Tam. Furthermore, PKA activators forskolin and dibutyryl-cAMP activated p21WAFI promoter activity and increased p21wAF1 protein level in lung cancer cells. Taken together, these results demonstrate that Tam activates the p21WAF1 promoter via Sp1-binding sites and suggest that PKA may be involved in the induction of p21wAF1 by Tam in ER-negative lung cancer cells.
Lee
T H
TH
Graduate Institute of Medicine, Kaohsiung Medical University, Taiwan.
Chuang
L Y
LY
Hung
W C
WC
D018931:Antineoplastic Agents, Hormonal / Q000378:metabolism / Q000494:pharmacology*; D001665:Binding Sites; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000378:metabolism; D004965:Estrogen Antagonists / Q000494:pharmacology*; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D008175:Lung Neoplasms; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D016296:Mutagenesis; D009687:Nuclear Proteins / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011960:Receptors, Estrogen / Q000378:metabolism*; D020218:Response Elements; D020845:Selective Estrogen Receptor Modulators / Q000378:metabolism / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D016329:Sp1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D051705:Sp3 Transcription Factor; D013629:Tamoxifen / Q000494:pharmacology*; D014157:Transcription Factors / Q000378:metabolism; D014407:Tumor Cells, Cultured
D018931:Antineoplastic Agents, Hormonal; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004268:DNA-Binding Proteins; D004965:Estrogen Antagonists; D009687:Nuclear Proteins; D011960:Receptors, Estrogen; C497121:SP3 protein, human; D020845:Selective Estrogen Receptor Modulators; D016329:Sp1 Transcription Factor; D014157:Transcription Factors; D013629:Tamoxifen; D051705:Sp3 Transcription Factor; D008156:Luciferases; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D020928:Mitogen-Activated Protein Kinases