Yan Zhao

Nanyang Technological University, Singapore, Singapore

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Publications (3)8.39 Total impact

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    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.
    BMC Complementary and Alternative Medicine 07/2012; 12:93. · 2.08 Impact Factor
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    ABSTRACT: An essential oil extract, derived from the rhizome of Curcuma wenyujin (CWE), possesses antioxidative, antimicrobial, and anti-inflammatory properties. However, it remains unknown how exactly CWE inhibits tumor growth. In this study, using human cervical cancer HeLa cells, the authors postulated that CWE has the ability to inhibit tumor growth. The study shows that CWE dose-dependently suppressed colony formation and inhibited the proliferation of HeLa cells through blockade of cell cycle progression at G1 phase and apoptosis. CWE-induced G1 arrest was associated with retinoblastoma protein dephosphorylation and reduced amounts of cyclins D1 and D3, and cyclin-dependent kinase 4 and 6 proteins. CWE treatment resulted in apoptosis in HeLa cells as evidenced by morphological changes, caspase activation and PARP cleavage, which can be reversed by a pan-caspase inhibitor. It was observed that CWE treatment activated the mitochondrial apoptotic pathway indicated by a decrease in Mcl-1 and Bcl-xL levels, resulting in mitochondrial membrane potential loss and caspases 9 activation. CWE-treated cells displayed reduced PTEN, AKT, and STAT3 phosphorylation and downregulation of NFkappaB signaling, providing a mechanism for the G1 arrest and apoptosis observed. Furthermore, CWE inhibited tumor growth of HeLa in a xenograft mouse tumor model, suggesting that CWE inhibited tumorigenesis by inhibiting cell proliferation and inducing apoptosis. These findings are the first to reveal the molecular basis for the anticervical cancer action of CWE. The results suggest that CWE could be developed as a drug for the management of cervical cancer.
    Integrative Cancer Therapies 02/2010; 9(1):36-49. · 2.35 Impact Factor
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    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.
    APOPTOSIS 14(9):1095-1107. · 3.95 Impact Factor