Vitamin E δ-tocotrienol induces p27(Kip1)-dependent cell-cycle arrest in pancreatic cancer cells via an E2F-1-dependent mechanism.

Abstract

Vitamin E δ-tocotrienol has been shown to have antitumor activity, but the precise molecular mechanism by which it inhibits the proliferation of cancer cells remains unclear. Here, we demonstrated that δ-tocotrienol exerted significant cell growth inhibition pancreatic ductal cancer (PDCA) cells without affecting normal human pancreatic ductal epithelial cell growth. We also showed that δ-tocotrienol-induced growth inhibition occurred concomitantly with G(1) cell-cycle arrest and increased p27(Kip1) nuclear accumulation. This finding is significant considering that loss of nuclear p27(Kip1) expression is a well-established adverse prognostic factor in PDCA. Furthermore, δ-tocotrienol inactivated RAF-MEK-ERK signaling, a pathway known to suppress p27(Kip1) expression. To determine whether p27(Kip1) induction is required for δ-tocotrienol inhibition of PDCA cell proliferation, we stably silenced the CDKN1B gene, encoding p27(Kip1), in MIAPaCa-2 PDCA cells and demonstrated that p27(Kip1) silencing suppressed cell-cycle arrest induced by δ-tocotrienol. Furthermore, δ-tocotrienol induced p27(Kip1) mRNA expression but not its protein degradation. p27(Kip1) gene promoter activity was induced by δ-tocotrienol through the promoter's E2F-1 binding site, and this activity was attenuated by E2F-1 depletion using E2F-1 small interfering RNA. Finally, decreased proliferation, mediated by Ki67 and p27(Kip1) expression by δ-tocotrienol, was confirmed in vivo in a nude mouse xenograft pancreatic cancer model. Our findings reveal a new mechanism, dependent on p27(Kip1) induction, by which δ-tocotrienol can inhibit proliferation in PDCA cells, providing a new rationale for p27(Kip1) as a biomarker for δ-tocotrienol efficacy in pancreatic cancer prevention and therapy.

• Authors: Pamela J Hodul, Yanbin Dong, Kazim Husain, Jose M Pimiento, Jiandong Chen, Anying Zhang, Rony Francois, Warren J Pledger, Domenico Coppola, Said M Sebti, Dung-Tsa Chen, Mokenge P Malafa
• Journal: PloS one (PLoS One) Vol. 8 Issue 2 Pg. e52526 ( 2013) ISSN: 1932-6203 [Electronic] United States
• PMID: 23393547 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• E2F1 Transcription Factor
• E2F1 protein, human
• Vitamin E
• Cyclin-Dependent Kinase Inhibitor p27
• tocotrienol, delta

Topics

• Blotting, Western
• Cell Cycle Checkpoints (drug effects, genetics)
• Cell Line
• Cell Line, Tumor
• Cell Proliferation
• Cyclin-Dependent Kinase Inhibitor p27 (genetics, metabolism)
• E2F1 Transcription Factor (genetics, metabolism)
• Flow Cytometry
• Humans
• Immunohistochemistry
• Microscopy, Confocal
• Pancreatic Neoplasms (genetics, metabolism)
• Reverse Transcriptase Polymerase Chain Reaction
• Vitamin E (analogs & derivatives, pharmacokinetics)