NF-κB p65 repression by the sesquiterpene lactone, Helenalin, contributes to the induction of autophagy cell death

Chuan Bian Lim,Xiaoling Feng,Yan Zhao,Mohamed Sabry Hamza,Hong Shuang Zhu,Kandhadayar Gopalan Srinivasan,Nung Ky,Pan You Fu,Jinming Li

doi:10.1186/1472-6882-12-93

Abstract

BackgroundNumerous studies have demonstrated that autophagy plays a vital role in maintaining cellular homeostasis. Interestingly, several anticancer agents were found to exert their anticancer effects by triggering autophagy. Emerging data suggest that autophagy represents a novel mechanism that can be exploited for therapeutic benefit. Pharmacologically active natural compounds such as those from marine, terrestrial plants and animals represent a promising resource for novel anticancer drugs. There are several prominent examples from the past proving the success of natural products and derivatives exhibiting anticancer activity. Helenalin, a sesquiterpene lactone has been demonstrated to have potent anti-inflammatory and antitumor activity. Albeit previous studies demonstrating helenalin’s multi modal action on cellular proliferative and apoptosis, the mechanisms underlying its action are largely unexplained.MethodsTo deduce the mechanistic action of helenalin, cancer cells were treated with the drug at various concentrations and time intervals. Using western blot, FACS analysis, overexpression and knockdown studies, cellular signaling pathways were interrogated focusing on apoptosis and autophagy markers.ResultsWe show here that helenalin induces sub-G1 arrest, apoptosis, caspase cleavage and increases the levels of the autophagic markers. Suppression of caspase cleavage by the pan caspase inhibitor, Z-VAD-fmk, suppressed induction of LC3-B and Atg12 and reduced autophagic cell death, indicating caspase activity was essential for autophagic cell death induced by helenalin. Additionally, helenalin suppressed NF-κB p65 expression in a dose and time dependent manner. Exogenous overexpression of p65 was accompanied by reduced levels of cell death whereas siRNA mediated suppression led to augmented levels of caspase cleavage, autophagic cell death markers and increased cell death.ConclusionsTaken together, these results show that helenalin mediated autophagic cell death entails inhibition of NF-κB p65, thus providing a promising approach for the treatment of cancers with aberrant activation of the NF-κB pathway.

Highlights

Numerous studies have demonstrated that autophagy plays a vital role in maintaining cellular homeostasis
We provide a mechanism by which NF-κB p65 plays a significant role in modulating autophagy induced cell death by the sesquiterpene lactone, helenalin
Helenalin Inhibits Cell Proliferation and Clonogenic Survival in cancer cells To examine the effect of helenalin on cell proliferation and clonogenic survival, human ovarian cancer A2780 cells were treated with helenalin and effects on cell proliferation and survival was determined using phase contrast microscopy, crystal violet staining and MTT assays

Summary

Introduction

Numerous studies have demonstrated that autophagy plays a vital role in maintaining cellular homeostasis. The efforts of many researchers during the past dozen years to identify novel compounds with anticancer activity have pointed to plants and herbs used in herbal medicine. The rationale behind this approach is that herbal medicine looks back on a 5000-years tradition. The chances to find novel compounds with activity against tumor cells in natural product libraries are higher than in synthetic libraries. In this regard, helenalin, a naturally occurring sesquiterpene lactone has generally been considered as a distinctly promising and potent antitumor compound. Helenalin has been shown to be a potent inhibitor of hTERT (human Telomerase Reverse Transcriptase) and telomerase in hematopoietic cancer cell [5], induces apoptosis in activated CD4+ T cells through the mitochondrial apoptosis pathway [6] and have been shown to selectively alkylate the p65 subunit of NF-κB [7]

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