However, the 2KR and 5KR mutants did not support an increase in doxorubicin induced cell death (Additional file 2: Figure S3D). Inactive SIRT7 enhances doxorubicin toxicity both in vitro and in vivo The above studies demonstrate that overexpression SIRT7 greatly decreased doxorubicin induced cell death. localization of p53 wild type (WT), K320,373R (2KR), K320,381,382R (3KR-A), K120,320,373R (3KR-B), K372,373,381,382R(4KR), K120,372,373,381,382R(5R). (D)p53 knockdown Huh7.5 cells Valdecoxib were transfected with WT, 2KR, 2KQ(K320,373Q) or 5KR for 24 hours and treated with doxorubicin. p53 levels were evaluated by western blot (upper) and cell death were evaluated by TUNEL assay (lower). **Depletion of SIRT7 from multiple liver malignancy cell lines significantly increased doxorubicin toxicity while overexpression of SIRT7 largely abolished doxorubicin induced apoptosis. At the molecular level, we observed that SIRT7 interacts with and induces deacetylation of p53 at lysines 320 and 373. Deacetylated p53 showed significantly less affinity for the NOXA promoter and its transcription. In mouse xenografts, SIRT7 suppression increased doxorubicin induced p53 activation, inhibited tumor growth and induced apoptosis. Conclusion The newly recognized SIRT7-p53-NOXA axis partially illustrates the molecular mechanism of HCC resistance to therapy and represents a novel potential therapeutic target for HCC treatment. Electronic supplementary material The online version of this article (10.1186/s13046-019-1246-4) contains supplementary material, which is available to authorized users. value low high

Sex1.000?Female624?Male1147Age(mean??SD)62.2??4.762.7??8.10.9598Tumor size0.6000?>?3?cm1138?CD350 overall HCC (Fig. ?(Fig.1h).1h). IHC staining indicated strong nuclear staining of SIRT7 compared with na?ve HCC (Fig. ?(Fig.1h).1h). These data suggest that SIRT7 may play a role in regulating HCC proliferation and chemosensitivity. SIRT7 regulates doxorubicin induced cell death in HCC cell lines To further explore the role of SIRT7 in therapy sensitivity of HCC, we treated Huh7.5 and HepG2 cells with doxorubicin (0.75?M) and examined changes of SIRT7 expression. Doxorubicin treatment resulted in significant downregulation of SIRT7 mRNA and protein levels as early as 12?h (Fig.?2a, b). Immunofluorescence indicated doxorubicin decreased global SIRT7 intensity from 24?h post-treatment (Additional file 2: Physique S2A). Downregulation of SIRT7 was associated with doxorubicin induced cell death as evidenced by PARP cleavage and caspase 3 activation (Fig. ?(Fig.2b).2b). We next measured SIRT7 protein stability in the presence of cycloheximide (CHX). As shown in Fig. ?Fig.2c2c and d, doxorubicin decreased the half-life of SIRT7 and the proteasome inhibitor MG-132 increased the Valdecoxib amount of SIRT7 after doxorubicin (Fig. ?(Fig.2e).2e). This suggests that an active process of SIRT7 proteolysis is usually induced by doxorubicin and the Valdecoxib decrease in protein level results both from changes in mRNA expression and protein stability. We also observed that doxorubicin induced a decrease of SIRT6 mRNA and protein levels, however, in contrast to SIRT7 this decrease was only observed 36?h after treatment (Fig. ?(Fig.2a,2a, b). Open in a separate windows Fig. 2 SIRT7 is critical in determining doxorubicin induced cell death. a Huh7.5 cells were untreated (Control) or treated with doxorubicin (DOX, 0.75?M) for 36?h. Cells were harvested at numerous time points as indicated. mRNA levels of SIRT1-7 were evaluated by RT-PCR. *P?P?P?P?P?