p53 Is Regulated in a Biphasic Manner in Hypoxic Human Papillomavirus Type 16 (HPV16)-Positive Cervical Cancer Cells.

Although the effect of hypoxia on p53 in human papillomavirus (HPV)-positive cancer cells has been studied for decades, the impact of p53 regulation on downstream targets and cellular adaptation processes during different periods under hypoxia remains elusive. Here, we show that, despite continuous repression of HPV16 E6/E7 oncogenes, p53 did not instantly recover but instead showed a biphasic regulation marked by further depletion within 24 h followed by an increase at 72 h. Of note, during E6/E7 oncogene suppression, lysosomal degradation antagonizes p53 reconstitution. Consequently, the transcription of p53 responsive genes associated with senescence (e.g., PML and YPEL3) cannot be upregulated. In contrast, downstream genes involved in autophagy (e.g., DRAM1 and BNIP3) were activated, allowing the evasion of senescence under hypoxic conditions. Hence, dynamic regulation of p53 along with its downstream network of responsive genes favors cellular adaptation and enhances cell survival, although the expression of the viral E6/E7-oncogenes as drivers for proliferation remained inhibited under hypoxia.

Simultaneous NF-κB inhibition and E-cadherin upregulation mediate mutually synergistic anticancer activity of celastrol and SAHA in vitro and in vivo.

Suberoylanilide hydroxamic acid (SAHA) is a promising histone deacetylase (HDAC) inhibitor approved by the US Food and Drug Administration (FDA) and whose clinical application for solid tumours is partially limited by decreased susceptibility in cancer cells due to nuclear factor (NF)-κB activation. As an NF-κB inhibitor, celastrol exhibits potent anticancer effects but has failed to enter clinical trials due to its toxicity. In this report, we demonstrated that the combination of celastrol and SAHA exerted substantial synergistic efficacy against human cancer cells in vitro and in vivo accompanied by enhanced caspase-mediated apoptosis. This drug combination inhibited the activation of NF-κB caused by SAHA monotherapy and consequently led to increased apoptosis in cancer cells. Interestingly, E-cadherin was dramatically downregulated in celastrol-resistant cancer cells, and E-cadherin expression was closely related to decreased sensitivity to celastrol. However, our combination treatment significantly augmented the expression of E-cadherin, suggesting that mutual mechanisms contributed to the synergistic anticancer activity. Furthermore, the enhanced anticancer efficacy of celastrol combined with SAHA was validated in a human lung cancer 95-D xenograft model without increased toxicity. Taken together, our data demonstrated the synergistic anticancer effects of celastrol and SAHA due to their reciprocal sensitisation, which was simultaneously regulated by NF-κB and E-cadherin; thus, the combination of celastrol and SAHA was superior to other combination regimens that rely on a single mechanism. Our findings not only open new opportunities for the clinical development of SAHA but should also motivate the clinical investigation of celastrol, which has been hampered by its toxicity.

Nuclear translocation and activation of YAP by hypoxia contributes to the chemoresistance of SN38 in hepatocellular carcinoma cells.

Although hypoxia is a prominent feature contributing to the therapeutic resistance of hepatocellular carcinoma cells (HCC) against chemotherapeutic agents, including the Topoisomerase I inhibitor SN38, the underlying mechanism is not fully understood and its understanding remains a major clinical challenge. In the present study, we found that hypoxia-induced nuclear translocation and accumulation of YAP acted as a survival input to promote resistance to SN38 in HCC. The induction of YAP by hypoxia was not mediated by HIF-1α because manipulating the abundance of HIF-1α with CoCl2, exogenous expression, and RNA interference had no effect on the phosphorylation or total levels of YAP. The mevalonate-HMG-CoA reductase (HMGCR) pathway may modulate the YAP activation under hypoxia. Combined YAP inhibition using either siRNA or the HMGCR inhibitor statins together with SN38 treatment produced improved anti-cancer effects in HCC cells. The increased anti-cancer effect of the combined treatment with statins and irinotecan (the prodrug of SN-38) was further validated in a human HepG2 xenograft model of HCC in nude mice. Taken together, our findings identify YAP as a novel mediator of hypoxic-resistance to SN38. These results suggest that the administration of SN28 together with the suppression of YAP using statins is a promising strategy for enhancing the treatment response in HCC patients, particularly in advanced stage HCC cases presenting hypoxic resistance.

Inactivation of hypoxia-induced YAP by statins overcomes hypoxic resistance tosorafenib in hepatocellular carcinoma cells.

Sorafenib is a multikinase inhibitor used as a first-line treatment for advanced hepatocellular carcinoma (HCC), but it has shown modest to low response rates. The characteristic tumour hypoxia of advanced HCC maybe a major factor underlying hypoxia-mediated treatment failure. Thus, it is urgent to elucidate the mechanisms of hypoxia-mediated sorafenib resistance in HCC. In this study, we found that hypoxia induced the nuclear translocation of Yes associate-Protein (YAP) and the subsequent transactivation of target genes that promote cell survival and escape apoptosis, thereby leading to sorafenib resistance. Statins, the inhibitors of hydroxymethylglutaryl-CoA reductase, could ameliorate hypoxia-induced nuclear translocation of YAP and suppress mRNA levels of YAP target genes both in vivo and in vitro. Combined treatment of statins with sorafenib greatly rescued the loss of anti-proliferative effects of sorafenib under hypoxia and improved the inhibitory effects on HepG2 xenograft tumour growth, accompanied by enhanced apoptosis as evidenced by the increased sub-G1 population and PARP cleavage. The expression levels of YAP and its target genes were highly correlated with poor prognosis and predicted a high risk of HCC patients. These findings collectively suggest that statins utilization maybe a promising new strategy to counteract hypoxia-mediated resistance to sorafenib in HCC patients.