Induction of p21WAF1 expression via Sp1-binding sites by tamoxifen in estrogen receptor-negative lung cancer cells.

Abstract

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.

• Authors: T H Lee, L Y Chuang, W C Hung
• Journal: Oncogene (Oncogene) Vol. 19 Issue 33 Pg. 3766-73 (Aug 03 2000) ISSN: 0950-9232 [Print] England
• PMID: 10949931 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Antineoplastic Agents, Hormonal
• CDKN1A protein, human
• Cyclin-Dependent Kinase Inhibitor p21
• Cyclins
• DNA-Binding Proteins
• Estrogen Antagonists
• Nuclear Proteins
• Receptors, Estrogen
• SP3 protein, human
• Selective Estrogen Receptor Modulators
• Sp1 Transcription Factor
• Transcription Factors
• Tamoxifen
• Sp3 Transcription Factor
• Luciferases
• Cyclic AMP-Dependent Protein Kinases
• Protein Kinase C
• Mitogen-Activated Protein Kinases

Topics

• Antineoplastic Agents, Hormonal (metabolism, pharmacology)
• Binding Sites
• Cyclic AMP-Dependent Protein Kinases (antagonists & inhibitors, metabolism)
• Cyclin-Dependent Kinase Inhibitor p21
• Cyclins (genetics)
• DNA-Binding Proteins (metabolism)
• Estrogen Antagonists (pharmacology)
• Gene Expression (drug effects)
• Humans
• Luciferases (genetics, metabolism)
• Lung Neoplasms
• Mitogen-Activated Protein Kinases (antagonists & inhibitors)
• Mutagenesis
• Nuclear Proteins (metabolism)
• Promoter Regions, Genetic
• Protein Kinase C (antagonists & inhibitors)
• Receptors, Estrogen (metabolism)
• Response Elements
• Selective Estrogen Receptor Modulators (metabolism, pharmacology)
• Signal Transduction (drug effects)
• Sp1 Transcription Factor (genetics, metabolism)
• Sp3 Transcription Factor
• Tamoxifen (pharmacology)
• Transcription Factors (metabolism)
• Tumor Cells, Cultured