<i>PBRM1</i> Mutation Recruits More Mast Cells by Upregulating CCL5 in a Clear Cell Renal Cell Carcinoma Tumor Microenvironment

Abstract

Background: PBRM1 (Polybromo-1) is the second most frequently mutated gene in ccRCC (clear cell renal cell carcinoma), and loss of PBRM1 was correlated with advanced tumor and tyrosine kinase inhibitor or immune checkpoint inhibitor clinical therapy in previously reported studies. However, the mechanisms of PBRM1 mutation in tumor microenvironment characterization are poorly understood. Methods: We investigated the tumor microenvironment in ccRCC by estimating immune cells in malignant tumors using CIBERSORT and estimating stromal and immune cells in malignant tumors using an expression data (ESTIMATE) algorithm. Gene set enrichment analysis hierarchical clustering and weighted correlation network analysis were used to analyze the characteristics and clinicopathologic features of ccRCC. Mast cell recruitment assay, colony formation assay, cell cycle assay, ELISA, and tube formation assay were applied to test PBRM1 function in vitro. Findings: We discovered that ccRCC patients with PBRM1 mutations were associated with inhibited CD8 T-cell infiltration but more resting mast cells in the tumor microenvironment. Silenced PBRM1 improved mast cell recruitment, angiogenesis, and cell proliferation among ccRCC cells. The molecular mechanism involved the upregulation ofCCL5 levels through PBRM1 mutations. CCL5 evoked immune-related pathways [including interferon-inflammatory signaling, interferon-gamma signaling, and IL-6-JAK- STAT3 (interleukin-6-Janus kinase-signal transducers and activators of transcription 3)] and recruited more mast cells to the tumor microenvironment. Furthermore, we confirmed that vascular endothelial growth factor family genes are overexpressed and that hypoxia-inducible factor-related processes are activated. Interpretation: These results demonstrated that PBRM1 mutation-CCL5-mast cell infiltration plays a key role in ccRCC clinical therapy. Funding Statement: This study was supported by the National Natural Science Foundation of China (NSFC No. 81602244 to Shan Xu) and Natural Science Basic Research Plan in Shaanxi Province of China (Program No. 2017JM8018 to Shan Xu). Declaration of Interests: The authors stated: None. Ethics Approval Statement: Not required.