Cancerous inhibitor of protein phosphatase 2A mediates bortezomib-induced autophagy in hepatocellular carcinoma independent of proteasome.

Abstract

Previously, we reported that cancerous inhibitor of protein phosphatase 2A (CIP2A) mediates the apoptotic effect of bortezomib in hepatocellular carcinoma (HCC). Here, we report a proteasome-independent mechanism by which bortezomib induces autophagy in HCC. Our data indicate that bortezomib activated autophagy in a dose- and time- dependent manner in HCC cell lines including Huh-7, Sk-Hep1, and Hep3B. Bortezomib downregulated CIP2A, phospho-Akt (P-Akt) and phospho-4EBP1 (P-4EBP1) in a dose- and time-dependent manner in all tested HCC cells. Ectopic expression of CIP2A abolished the effect of bortezomib on autophagy. Co-treatment of bortezomib and calyculin A, a PP2A inhibitor, reduced the effect of bortezomib on P-Akt, P-4EBP1, and autophagy. Increased phosphorylation of either Akt or 4EBP1 by ectopic overexpression protected cells from bortezomib-induced autophagy. Furthermore, we examined the effect of ΔBtz, a bortezomib derivative that closely resembles bortezomib structurally but has no proteasome activity, in HCC. Interestingly, ΔBtz demonstrated similar effects to bortezomib on autophagy, CIP2A, P-Akt and P-4EBP1, suggesting that the effect of bortezomib on autophagy is independent of proteasome inhibition. Moreover, our in vivo data showed that both bortezomib and ΔBtz inhibited tumor growth, downregulated CIP2A, P-Akt and induced autophagy in Huh-7 tumors. In conclusion, bortezomib induces autophagy in HCC through a CIP2A-PP2A-Akt-4EBP1 pathway.

• Authors: Hui-Chuan Yu, Duen-Ren Hou, Chun-Yu Liu, Chen-Si Lin, Chung-Wai Shiau, Ann-Lii Cheng, Kuen-Feng Chen
• Journal: PloS one (PLoS One) Vol. 8 Issue 2 Pg. e55705 ( 2013) ISSN: 1932-6203 [Electronic] United States
• PMID: 23383345 (Publication Type: Journal Article)

Chemical References

• Autoantigens
• Boronic Acids
• CIP2A protein, human
• Intracellular Signaling Peptides and Proteins
• Membrane Proteins
• Pyrazines
• Bortezomib
• Protein Phosphatase 2
• Proteasome Endopeptidase Complex
• Acridine Orange

Topics

• Acridine Orange
• Autoantigens (metabolism)
• Autophagy (drug effects)
• Blotting, Western
• Boronic Acids (metabolism, pharmacology)
• Bortezomib
• Carcinoma, Hepatocellular (metabolism)
• Cell Line, Tumor
• Dose-Response Relationship, Drug
• Flow Cytometry
• Fluorescent Antibody Technique
• Gene Expression Regulation (drug effects)
• Humans
• Intracellular Signaling Peptides and Proteins
• Liver Neoplasms (metabolism)
• Membrane Proteins (metabolism)
• Microscopy, Fluorescence
• Phosphorylation
• Proteasome Endopeptidase Complex (metabolism)
• Protein Phosphatase 2 (antagonists & inhibitors, metabolism)
• Pyrazines (metabolism, pharmacology)
• Time Factors