Fig. 6
Spermine promotes PD-L1 protein N-glycosylation and stability through inducing STT3A expression in HCC. A Effects of PNGase F on the molecular weight of PD-L1 in the lysates of SNU-368 cells treated with or without spermine (200 µM) for 24 h. B, C Effects of spermine (200 µM) on the expression of STT3A mRNA (B) and protein (C) in SNU-368 cells. *p < 0.05, **p < 0.01, one-way ANOVA, n = 5 independent experiments per group. D, E Effects of spermine (200 µM) on the expression of STT3B mRNA (D) and protein (E) in SNU-368 cells. one-way ANOVA, n = 5 independent experiments per group. F, G Effects of STT3A (F) and STT3B (G) knockdown on spermine-induced PD-L1 protein expression in SNU-368 cells. 24 h after two specific siRNA transfection, cells were incubated in the presence or absence of spermine (200 µM) for 24 h. Scr: Scramble; 1#siA: 1# STT3A siRNA; 2#siA: 2# STT3A siRNA; 1#siB: 1# STT3B siRNA; 2#siB: 2# STT3B siRNA; *p < 0.05, ***p < 0.001, one-way ANOVA, n = 5 independent experiments per group. H, I The expression of CD274 mRNA (H) and PD-L1 protein (I) in SNU-368 cells expressing STT3A or STT3B for 24 h. ***p < 0.001 compared with Vector group, one-way ANOVA, n = 4 independent experiments per group. J IHC staining of STT3A and PD-L1 in 24 human HCC specimens. Scale bar, 50 μm. K Spearman correlation test between blood spermine concentration and tumor STT3A IHC scores. L Spearman correlation analysis of STT3A and PD-L1 IHC scores. Note that the scores of some samples overlap