CASK Silence Enhances Chemosensitivity of Hepatocellular Carcinoma Through Activating Apoptosis, Inducing JNK/c-Jun-Mediated Autophagic Cell Death and Decreasing ABCG2

Abstract Background: Advanced hepatocellular carcinoma (HCC) patients usually fail to be treated because of drug resistance, including sorafenib. Methods: The expression and prognostic role of calcium/calmodulin-dependent serine protein kinase (CASK) in HCC were assessed by combination of bioinformatic analysis and experimental validation. The effects of CASK in regulating proliferation, apoptosis and drug resistance of HCC cells in vitro and in vivo were investigated using gain- or loss-of-function strategies by performing lots of specific methods including Cell Counting kit-8 (CCK8), colony formation assay, flow cytometry, transmission electron microscopy, immunofluorescent confocal laser microscopy and tumor xenograft experiments, immunohistochemistry staining. Moreover, the underlying molecular mechanisms responsible for CASK’s functions in HCC were also explored. Results: Currently, we discovered that CASK was positively associated with sorafenib resistance of HCC in vitro and in vivo, and was significantly related with poor prognosis in HCC. Moreover, inhibition of CASK can increase the effect of sorafenib partially by promoting apoptosis and autophagy, while CASK overexpression presented the opposite results. Besides, all the pan-caspase inhibitor Z-VAD-FMK, autophagy inhibitor 3-Methyladenine (3-MA) and small interfering RNA (siRNA) of LC3B reversed CASK knockout-induced effects with sorafenib treatment, suggesting that both apoptosis and autophagy were involved in CASK-mediated above functions and autophagy played a pro-death role in this research. Intriguingly, similar results were observed in vivo. In molecular level, CASK knockout activated the c-Jun N-terminal kinase (JNK) pathway, and treatment with JNK inhibitor SP600125 or transiently transfected with si-JNK significantly attenuated CASK knockout-mediated autophagic cell death. Besides, knockout of CASK dramatically inhibited the expression of ATP binding cassette subfamily G member 2 (ABCG2) and reversed of multidrug-resistance (MDR) of HCC. Conclusions: Collectively, all these results together indicated that CASK might be a promising biomarker for HCC patients and a potential therapeutic target for relieving drug resistance of HCC.