Fig. 6

SIRT7 promotes PD-L1 expression via IRE1α-XBP1 axis. a Relative mRNA and protein levels of PD-L1 in A2058 cells with indicated treatment. b Relative membrane expression of PD-L1 in A2058 cells with indicated treatment. c Immunohistochemical staining and correlation analysis of SIRT7 and PD-L1 in TMA. Scale bar, 100 μm. r value was calculated by Spearman correlation. d Co-culture of A2058 cells transfected with control or SIRT7 overexpression plasmid with TG treatment and activated T cells (1:3) for 24 h with or without the treatment with PD-L1 neutralizing antibody (Avelumab, 20 μg/mL) for 8 h. Cytotoxicity was then quantified by a spectrometer at OD (570 nm) followed by crystal violet staining. e FACS of CD69⁺in CD8⁺T cells and GZMB⁺CD8⁺ TILs from co-culture system with indicated treatment and corresponding quantification. f A schematic view of the treatment plan that C57BL/6 mice burdened with negative control (sh-NC) and sh-SIRT7-1-transfected B16F10 tumors with or without PD-1 mAb treatment as indicated. Tumor volumes and weights in each group were calculated and displayed in (g) and (h). The quantification of FACS of CD3⁺in CD45⁺cells (i), CD8⁺ in CD3⁺ TILs (j) and GZMB⁺CD8⁺ TILs (k) from B16F10 xenografts with indicated treatment. Symbols of one dot indicates one mouse, and the error bars are mean with ±S.D. l Chromatin immunoprecipitation analysis of the enrichment of XBP1 to the promoter of CD274 in A2058 cells. m Chromatin immunoprecipitation analysis of the enrichment of XBP1 to the promoter of CD274 in WM35 cells with or without SIRT7 overexpression under the treatment with TG (1 μM) for 24 h. n, o Relative mRNA and protein levels of PD-L1 in WM35 cells with indicated treatment. Data represent the mean ± SD of triplicates. p A schematic model summarizing how SIRT7 orchestrates melanoma progression by simultaneously promoting tumor cell survival and immune evasion via the activation of unfolded protein response. Under ER stress condition, NF-κB p65 contributes to SIRT7 up-regulation in melanoma. SIRT7 directly interacts with and de-acetylates SMAD4 to promote the transcription of IRE1α. Then, SIRT7 promotes melanoma cell survival by selective activation of IRE1α-XBP1 branch of UPR and downstream ERK pathway. Apart from the direct effect on tumor cell survival, SIRT7 up-regulation also eradicates anti-tumor immunity by promoting PD-L1 expression via IRE1α-XBP1 axis. Based on this, the knockdown of SIRT7 prominently increases the treatment efficacy of anti-PD-1 antibody by potentiating CD8⁺T cells-dependent anti-tumor immunity. Data represent the mean ± SD of triplicates. P value was calculated by two tailed Student’s t-test. *P < 0.05, **P < 0.01, ***P < 0.001. ns non-significant