Abstract 355: CIP2A mediates effects of bortezomib on phospho-Akt and apoptosis in hepatocellular carcinoma cells

Abstract

Abstract Previously, we reported that Akt inactivation determines the sensitivity of hepatocellular carcinoma (HCC) cells to bortezomib (Chen et al, Cancer Res 2008). Here, we report that cancerous inhibitor of protein phosphatase 2A (CIP2A), a cellular inhibitor of protein phosphatase 2A (PP2A), mediates the apoptotic effect of bortezomib in HCC. Silencing PP2A by small interference RNA (siRNA) abolishes bortezomib-induced down-regulation of phospho-Akt and apoptosis. Bortezomib increases PP2A activity in sensitive HCC cells, including Sk-Hep1, Hep3B and Huh-7 but not in resistant PLC5 cells. Bortezomib down-regulates CIP2A in a dose- and time-dependent manner in all sensitive HCC cells whereas no alterations in CIP2A were found in resistant PLC5 cells. Knockdown of CIP2A by siRNA restored bortezomib's effects on apoptosis and PP2A activity in PLC5 cells. Moreover, over-expression of CIP2A up-regulated phospho-Akt and protected Sk-Hep1 cells from bortezomib-induced apoptosis. Importantly, ectopic expression of CIP2A decreased Akt-related PP2A activity whereas silencing CIP2A increased this activity, indicating that CIP2A negatively regulates Akt-related PP2A activity in HCC cells, Furthermore, our in vivo data showed that bortezomib down-regulates CIP2A and up-regulates PP2A activity in Huh-7 tumors but not in PLC5 tumors. In conclusion, inhibition of CIP2A determines effects of bortezomib on apoptosis and PP2A-dependent Akt inactivation in HCC. CIP2A may be a biomarker for predicting clinical response of bortezomib in HCC treatment. Supported by NTUH98P03, NTUH98FTN21, NSC97-2314-B-002-182, NSC98-2314-B-002-067-MY3, and NSC98-3112-B-002-037. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 355.