[High RNF7 expression enhances PD-1 resistance of non-small cell lung cancer cells by promoting CXCL1 expression and myeloid-derived suppressor cell recruitment via activating NF-κB signaling].

Objective: To investigate the mechanism of RNF7 for regulating myeloid-derived suppressor cells (MDSCs) in nonsmall cell lung cancer (NSCLC).

Methods: TIMER2.0 database and immunohistochemistry were used to analyze RNF7 expression level and its correlation with immune cell infiltration in non-small cell lung cancer. The impact of RNF7 expression levels on prognosis of lung cancer patients was analyzed using Kaplan-Meier survival analysis. CMT-167 cells with RNF7 overexpression or knockdown were inoculated subcutaneously in C57BL/6 mice, and the mice in RNF7 knockdown group were treated with anti-PD-1 or IgG isotype control 7 days after the inoculation. The tumor tissues were harvested after 30 days for tumor volume measurement, detection of S100A8+A9 and Gr-1 expressions with immunohistochemistry, and analysis of MDSC infiltration. Gene set enrichment analysis (GSEA) was performed to identify the potential pathways regulated by RNF7 in NSCLC. Western blotting and luciferase assays were used to assess the impact of RNF7 on the NF-κB signaling pathway. ELISA and RT-qPCR were used to measure chemokine (C-X-C motif) ligand 1 (CXCL1) expression.

Results: RNF7 expression was significantly upregulated in NSCLC, and high RNF7 expression levels were associated with poor prognosis of the patients (P < 0.001). TIMER2.0 analysis revealed a positive correlation between RNF7 expression and MDSC infiltration (P < 0.001). GSEA suggested that RNF7 was enriched in the NF-κB signaling pathway. In NSCLC cells, RNF7 knockdown significantly inhibited NF-κB activation and reduced CXCL1 expression. In the tumor-bearing mice, RNF7 overexpression significantly increased MDSC infiltration in the tumor tissue, and RNF7 knockdown obviously reduced MDSC infiltration and enhanced the efficacy of anti-PD-1 therapy.

Conclusion: High expression of RNF7 in NSCLC cells promotes CXCL1 expression by activating the NF-κB signaling pathway, thus leading to the chemotactic recruitment of MDSCs, which contributes to tumor resistance to antiPD-1 therapy.