Abstract
Hypoxia stress plays a pivotal role in tumor formation, proliferation, and invasion. Conventional chemotherapy is less effective in the hypoxia microenvironment of solid tumor. Heat shock protein 90 (Hsp90) is an important molecular chaperone in cancer cells and has been a pharmaceutical target for decades. However, Hsp90 inhibitors demonstrate limited effect on solid tumor and the mechanism underlying is not clear. To determine whether hypoxia impairs the therapeutic effect of Hsp90 N-terminal inhibitor, 17-demethoxygeldanamycin hydrochloride (17-DMAG), in live cancer cells, we measured cell proliferation and cell cycle distribution. Cell proliferation assay indicates that hypoxia obviously promotes the proliferation of HepG2 and Huh7 cells after 24, 48, and 72 h and impairs 17-DMAG-induced G2/M arrest in liver cancer cells. As a client protein of Hsp90, cyclin B1 is critical for the transition from G2 to M phase and is related to the prognosis of the patients. We further checked the cyclin B1 messenger RNA (mRNA) level, protein level, ubiquitination of cyclin B1, nuclear translocation, and degradation of cyclin B1 affected by hypoxia after 17-DMAG treatment. The results demonstrate that hypoxia decreases the transcription of cyclin B1 and accelerates the ubiquitination, nuclear translocation, and degradation of cyclin B1. Taken together, our results suggest that hypoxia attenuates cyclin B1 accumulation induced by 17-DMAG and, hence, alleviates 17-DMAG-induced G2/M arrest.
Highlights
Hepatocellular carcinoma (HCC) is one of the most common malignancies and the second most frequent cause of cancer mortality worldwide (Lin et al 2012)
Cell proliferation assay indicated that hypoxia obviously promoted the proliferation of HepG2 and Huh7 cells after 24, 48, and 72 h (Fig. 1b)
Most cancer cells have deregulated G1 checkpoints making them dependent on their S and G2 checkpoints, so S and G2 checkpoints become an attractive target therapy of cancer (Chen et al 2012). 17-AAG abrogates hepatocellular cancer growth through G2/M cell cycle arrest (Watanabe et al 2009). 17-DMAG is a water-soluble analogue of 17-AAG (Kummar et al 2010), and our results show that hypoxia decreases the chemosensitivity to 17-DMAG and attenuates 17-DMAGinduced G2/M arrest, with lower cyclin B1 level
Summary
Hepatocellular carcinoma (HCC) is one of the most common malignancies and the second most frequent cause of cancer mortality worldwide (Lin et al 2012). According to 2014 Cancer Country Profiles from World Health Organization, 394,770 of new liver cancer cases and 380,772 cancer deaths occurred in China. Besides China, the number of cases diagnosed with HCC is expected to increase in western countries (Venook et al 2010). Identification of novel therapeutic agents via molecular targeting offers the promise of treatment for advanced liver cancer. The therapy targeted for one single molecular faces the potential peril of being subverted by the inherent genetic plasticity of cancer cells. Multiple molecular targets have been used in combination, which are involved in a multitude of signaling pathways leading to simultaneous adverse effects on oncogenic proteins, would prove promising, and would make therapy more complicated and prolong the trials (Patki and Pawar 2013; Isaacs et al 2003)
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