Whether currently known autophagy inhibitors such as bafilomycin A1, 3-MA or chloraquine can synergize with these CIP2Ainhibiting agents to kill cancer cells warrants future studies. In addition to the finding that oncogenic CIP2A mediates bortezomib induced autophagy, this study identified p-4EBP-1 as a participant in bortezomib induced autophagy downstream of p- Akt. The role of A 412997 dihydrochloride p-4EBP1 was validated by ectopic expression of 4EBP1, which resulted in an increase in p-4EBP1, and subsequently reduced the effect of bortezomib on autophagy. 4EBP-1 is known as downstream effector of PI3K/ Akt/mTOR signaling that in non-phosphorylated form binds tightly to eIF4E and inhibits a key step in translation initiation. EIF4E is a key factor in cap-dependent translation initiation that controls tumor cell growth and survival. Our data suggest that bortezomib downregulated CIP2A-PP2A-p-Akt associated p-4EBP1. It is possible that downregulation of p-4EBP1 suppressed eIF4Edependent translation thereby 2-TEDC promoting bortezomib-induced autophagy. This supposition is supported by a recent study showing that suppression of 4EBP1 expression resulted in resensitization of MYC-expressing prostate cancer cells to rapamycin- induced autophagy. Indeed, we also noticed that bortezomib also suppressed the expression of 4EBP-1 in Sk- Hep1, and Hep3B cells, which might also contribute to bortezomib-induced autophagy. Alternatively, PP2A may directly dephosphorylate eIF4E and contribute to bortezomib-induced autophagy. Nevertheless, the exact mechanism by which p- 4EBP1 participates in autophagy activation in HCC remains to be elucidated and further study is necessary. Despite the current results, the detailed mechanism by which bortezomib inhibits CIP2A remains unknown and further mechanistic studies are needed. The possible mechanisms through which bortezomib may affect the transcription of CIP2A include direct or indirect promoter regulation of CIP2A mRNA, epigenetic regulation of the CIP2A gene by DNA methylation or micro-RNA machinery, or affecting other as yet unknown molecules that may regulate CIP2A expression. In conclusion, bortezomib induces autophagy in HCC cells through a novel proteasome-independent mechanism: CIP2Adependent p-4EBP-1 downregulation. This study identifies the novel oncoprotein CIP2A as a major mediator of HCC cells to bortezomib-induced autophagy and suggests that CIP2A may be a potential new drug target in HCC. Furthermore, discovery of compounds/drugs acting as CIP2A inhibitors may have therapeutic potential in HCC therapy. Cyclic dipeptides, or 2,5-diketopiperazines, are found endogenously in many organisms and in large amounts in some foods and beverages, e.g., aged sake, beer, cocoa, roasted coffee, roasted malt, dried squid, and chicken essence.