Hibitors could inhibit many forms of HDAC enzymes and Allylestrenol Purity mediate potent anti-cancer effect within a wide range of malignancies [16]. We reported that FDAapproved HDAC inhibitors, which includes suberoylanilide hydroxamic acid (SAHA) and romidepsin, could induce development arrest and apoptosis of EBV-positive gastric carcinoma and nasopharyngeal carcinoma cells by disrupting EBV latency [179]. HDAC inhibitors could also induce expression of p21WAF1 which was downregulated by EBNA3C [13, 20]. Proteasome inhibitor, including bortezomib, belongs to an emerging class of anti-cancer drugs which induce endoplasmic reticulum (ER) stressrelated cell death by way of inhibition on the proteasomal degradation of unfolded proteins [21]. We and other individuals had reported that combination of HDAC and proteasome inhibitors could mediate sturdy synergistic killing of cancer cells by way of generation of reactive oxygen species (ROS), activation of ER pressure and induction of autophagy [215]. In addition, we found that combination of SAHA and bortezomib (SAHA/bortezomib) could preferentially induce killing of LCLs and BL cells of Wp-restricted latency, each of which express EBNA3A, -3B and -3C proteins [26]. These data suggested the involvement in the EBNA3 protein(s) within the cell death mechanism mediated by SAHA/bortezomib. Mixture of HDAC and proteasome inhibitors was identified to induce DNA damage response (DDR) in different tumor cells [27, 28]. In response to DDR, cells had been arrested at cell cycle checkpoints so as to present sufficient time for the cells to repair the broken DNA [29]. Ataxia telangiectasia mutated/Rad3-related (ATM/ATR) pathways have been known to mediate G1 arrest by means of p53/p21 pathway and G2/M arrest by means of inactivation of cdc25c [30, 31]. EBNA3C was shown to release the DDR-induced G2/M arrest via dysregulated cdc25c phosphorylation when cells have been exposed to nocodazole [11]. Yet, the effects of combination of HDAC and proteasome inhibitors on the cell cycle progression and survival of EBNA-3 expressing cells have not been investigated. We hypothesize that SAHA/bortezomib can induce synergistic killing of BL and LCLs by way of targeting the survival functions of EBNA3 proteins. To test this hypothesis, we examined the impact of SAHA/ bortezomib around the survival of BL cell lines which harbor EBNA3A or -3B or -3C knockout EBV with or with no the person revertant. We identified that EBNA3C played a more important role in the synergistic killing of BL cells and LCLs when compared with EBNA3A and EBNA3B. Our data recommended that SAHA/bortezomib targeted the survival functions of EBNA3C protein in BL and LCLs. This can be the very first study to show that mixture of HDAC/ proteasome inhibitors can indeed target latent viral protein function in EBV-associated LPDs.OncotargetRESULTSCombination of HDAC and proteasome inhibitors (i.e. SAHA /bortezomib) synergistically inhibited the proliferation of EBNA3C-expressing BL cellsWe had reported that combination of HDAC and proteasome inhibitors could induce precise synergistic killing of EBV-positive BL cells and LCLs which express EBNA3 proteins. To investigate the essential role of EBNA-3 proteins within the survival of cells, we tested that effects of mixture of HDAC and proteasome inhibitors on the proliferation of eight distinctive BL31 cell lines, which includes a EBV-negative BL31 cell line (EBV -ve) and BL31 cell lines infected with wild kind EBV (EBV +ve), EBNA-3A-knockout (3A-KO), EBNA-3Bknockout (3B-KO), EBNA-3C-knockout.
