Upregulating Noxa by ER Stress, Celastrol Exerts Synergistic Anti-Cancer Activity in Combination with ABT-737 in Human Hepatocellular Carcinoma Cells

Abstract

The human hepatocellular carcinoma (HCC) represents biologically aggressive and chemo-resistant cancers. Owing to the low affinity with the apoptotic factor Mcl-1, the BH3 mimetic drug ABT-737 failed to exert potent cancer-killing activities in variety of cancer models including HCC. The current study demonstrated that combining ABT-737 and Celastrol synergistically suppressed HCC cell proliferation, and induced apoptosis which was accompanied with the activation of caspase cascade and release of cytochrome c from mitochondria. Further study revealed that the enhanced Noxa caused by Celastrol was the key factor for the synergy, since small interfering RNA-mediated knockdown of Noxa expression in HCC cells resulted in decreased apoptosis and attenuated anti-proliferative effects of the combination. In addition, our study unraveled that, upon Celastrol exposure, the activation of endoplasmic reticulum (ER) stress, specifically, the eIF2α-ATF4 pathway played indispensable roles in the activation of Noxa, which was validated by the observation that depletion of ATF4 significantly abrogated the Noxa elevation by Celastrol. Our findings highlight a novel signaling pathway through which Celastrol increase Noxa expression, and suggest the potential use of ATF4-mediated regulation of Noxa as a promising strategy to improve the anti-cancer activities of ABT-737.

Celastrol induces unfolded protein response-dependent cell death in head and neck cancer

“…Immunoblot analysis of whole cell lysates further demonstrated celastrol treatment reduced the pro-form of caspase 9 and led to the accumulation of active caspase 3 (Fig. 3B), consistent with the observations of others [34–36]. Increased accumulation of pro-apoptotic BAK was also observed following celastrol treatment (Fig.…”

“…These data confirm a role for the intrinsic (mitochondrial) apoptotic pathway in celastrol-mediated cancer cell death and extend previous observations that it can induce apoptosis in cultured cells [29,34,37]. The ability of celastrol to induce ubiquitination (Ub) in whole cell lysates has been reported in different cancer subtypes [20,36,37]. Immunoblot analysis revealed that celastrol-resistant cell lines (CAL27 and FaDu) accumulated Ub proteins much more slowly than celastrol-sensitive UMSCC23 cells (Fig.…”

“…Recently, celastrol has been studied as an anticancer agent in a variety of in vitro and xenograft models, and has been reported to activate the heat shock response [40], the UPR [36,41], inhibit NK-κB [15,42,43] and interfere with angiogenesis via VEGF suppression [44]. The mechanisms by which these compounds mete out their cytotoxic effects have also been well studied.…”

miR-224 is Critical for Celastrol-Induced Inhibition of Migration and Invasion of Hepatocellular Carcinoma Cells

“…Although several reports mentioned about the involvement of celastrol in apoptosis of hepatoma cells, no study has been reported the anti-metastatic function of celastrol in HCC [25,26]. In this study, we investigated the effect of celastrol on migration and invasion ability of HCC cells.…”

Celastrol targets proteostasis and acts synergistically with a heat-shock protein 90 inhibitor to kill human glioblastoma cells

“…Most notably, Zhu et al 57 showed previously that celastrol activates the ER-stress response in human hepatocellular carcinoma cells via a mechanism that is dependent on preserved eIF2 α -ATF4-Noxa signaling. In line with these results, celastrol induces cytoplasmic vacuolation in several human cancer cell lines in conjunction with elevated membrane-bound LC3 (LC3-II).…”