Objective:To investigate the regulatory effects of ring finger protein 43 (RNF43) on CD8 + T cell-mediated anti-tumor immune reaction in melanoma. Methods:RNF43 gene was over-expressed and knockdown in mouse melanoma cells line B16-OVA by lentivirus infection; In vivo proliferation of mouse melanoma cells line B16-OVA in the Lv-Ctrl-OE, Lv-RNF43-OE, Lv-Ctrl-KD and Lv-RNF43-KD groups was detected by subcutaneous tumorigenesis assay in mice, and the expression levels of CD8 + T cells perforin and interferon γ (IFN-γ) in tumor immune microenvironment of melanoma were detected by flow cytometry; The expression levels of β-catenin and programmed death-ligand 1 (PD-L1) mRNA in cells were detected by quantitative real-time PCR assay; The effect of RNF43 on the transcriptional regulation of PD-L1 was detected by dual-luciferase reporter gene assay. Results:Stable RNF43 over-expressing and RNF43 knockdown mouse melanoma cells lines Lv-RNF43-OE and Lv-RNF43-KD were successfully constructed. The results of subcutaneous tumorigenesis experiment in mice showed that the tumor mass of the Lv-RNF43-OE group was (0.08±0.06) g, which was significantly smaller than that of the Lv-Ctrl-OE group [ (1.04±0.52) g], with a statistically significant difference ( t=3.71, P=0.032) ; The tumor mass of Lv-RNF43-KD group was (1.94±0.29) g, with no statistically significant difference ( t=-1.70, P=0.164) compared with that of the Lv-Ctrl-KD group (1.15±0.74) g. The flow cytometry results showed that the fluorescence intensity of CD8 + T cell perforin in the Lv-RNF43-OE group was 9 034 ± 2 628, which was significantly higher than that in the Lv-Ctrl-OE group (3 847 ±1 637), with a statistically significant difference ( t=-3.35, P=0.015) ; The fluorescence intensity of CD8 + T cell perforin in the Lv-RNF43-KD group was 966±247, which was significantly lower than that in the Lv-Ctrl-KD group (2 226±646), with a statistically significant difference ( t=3.16, P=0.034) ; The fluorescence intensity of IFN-γ of CD8 + T cell in the Lv-RNF43-OE group was 2 422±429, which was significantly higher than that of 1 688±324 in the Lv-Ctrl-OE group, with a statistically significant difference ( t=-2.73, P=0.034) ; The fluorescence intensity of IFN-γ of CD8 + T cell in the Lv-RNF43-KD group was 614 (454, 863), with a statistically significant difference ( Z=-1.96, P=0.050) compared with 1 159 (1 152, 2 068) in the Lv-Ctrl-KD group. The results of quantitative real-time PCR showed that the relative expression level of β-catenin mRNA in the Lv-RNF43-OE group was 0.67±0.16, which was significantly lower than that of 1.00±0.11 in the Lv-Ctrl-OE group, with a statistically significant difference ( t=2.98, P=0.041) ; The relative expression level of PD-L1 mRNA in the Lv-RNF43-OE group was 0.32±0.09, which was significantly lower than that of 1.00±0.09 in the Lv-Ctrl-OE group, with a statistically significant difference ( t=9.13, P=0.001). The results of the dual-luciferase reporter gene assay showed that the PD-L1 promoter luciferase activity in the pCMV6-NC, RNF43, RNF43+β-catenin and β-catenin groups were 1.00±0.00, 0.84±0.00, 1.49±0.00 and 1.57±0.03 ( F=2 218.33, P<0.001). Further pairwise comparison showed that compared with the pCMV6-NC group, PD-L1 promoter luciferase activity was significantly lower in the RNF43 group ( P<0.001) and significantly higher in the RNF43+β-catenin and β-catenin groups ( P<0.001; P=0.003) ; compared with the RNF43 group, PD-L1 promoter luciferase activity was significantly higher in the RNF43+β-catenin group ( P<0.001) . Conclusion:RNF43 may reduce the expression of PD-L1 mRNA in melanoma by inhibiting the expression of β-catenin and promote CD8 + T cell-mediated anti-tumor immune reaction.