[Show abstract][Hide abstract] ABSTRACT: Numerous 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.
To 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.
We 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.
Taken 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.
Preview · Article · Jul 2012 · BMC Complementary and Alternative Medicine
[Show abstract][Hide abstract] ABSTRACT: Kruppel-like factor 4 (KLF4) belongs to a family of evolutionarily conserved zinc finger-containing transcription factors.
It has been shown to mediate self renewal and pluripotency, regulate adipogenesis and play a critical role in monocyte differentiation.
KLF4 is also highly expressed in squamous cell carcinomas and in 70% of all primary human breast cancers, suggesting a putative
role for KLF4 as being an oncogene and as an antiapoptotic factor. However, the mechanism of this regulation remains unclear.
Here, we show that KLF4 is induced during histone deacetylase inhibitor treatment, and regulates the extrinsic apoptosis pathway
by inhibiting caspase cleavage. In addition, KLF4 binds to the p57Kip2 promoter and transcriptionally upregulates its expression, which in turn inhibits the stress activated protein kinase cascade
and c-Jun phosphorylation. Our findings indicate that in cancer cells that express high levels of KLF4 may be refractory to
HDACi treatment. Results of our study demonstrate an unexpected antiapoptotic function of KLF4, and suggest an important cell fate
determinant following histone deacetylase inhibitor induced apoptosis.