RBX1 regulates uveal melanoma immune-related genes via STAT1

Abstract

Objective·To investigate the role of RBX1 (ring-box protein 1) in the regulation of immune-related genes in uveal melanoma (UVM) tumor cells.Methods·The Cancer Genome Atlas (TCGA) was searched to analyze the expression levels of RBX1 in tumors and the correlation with clinical stages and survival prognosis. RBX1 was transiently knocked down in the UVM cell lines, i.e., 92.1, OMM2.3 and MEL290 by using small interfering RNAs (siRNAs) targeting RBX1. RNA sequencing was performed on the 92.1 cells with transient knockdown of RBX1, and the differentially expressed genes between the siRBX1-transfected cells and control cells were analyzed by gene set enrichment analysis (GSEA) to investigate the relationship between RBX1 and tumor immune-related genes. Based on the results of the analysis, signal transducer and activator of transcription 1 (STAT1) and its downstream CXC chemokine ligand 9 (CXCL9) and CXCL10 mRNA expression levels were detected by real-time fluorescence quantitative PCR (qPCR) in 92.1, OMM2.3 and MEL290 cells with transient knockdown of RBX1, respectively. The protein expression levels of STAT1 and p-STAT1 in 92.1 cells were detected by Western blotting. The cell lines OMM2.3 and MEL290, in which RBX1 was transiently knocked down, were treated with 5 nmol/L or 10 nmol/L STAT1 inhibitor fludarabine for 48 h, and the mRNA expression levels of CXCL9 and CXCL10 were detected by qPCR.Results·TCGA database analysis showed that RBX1 was highly expressed in a variety of tumors compared to the normal tissues, particularly in adrenocortical carcinoma and UVM. In addition, the patients with late stage of these two kinds of tumors had higher expression level of RBX1, and the patients with higher expression level of RBX1 had shorter overall survival time (P<0.05). RNA sequencing of 92.1 cells with transiently knocked down RBX1 and control cells revealed differential genes, and GSEA showed that RBX1 was involved in the regulation of tumor immune-related pathways. Heat map analysis showed an increase in STAT1 expression after RBX1 knockdown. In the 92.1, OMM2.3 and MEL290 cell lines, qPCR showed increases in STAT1, CXCL9 and CXCL10 mRNA expression after transient knockdown of RBX1, and Western blotting showed that STAT1 and p-STAT1 expression increased after knockdown of RBX1 in 92.1 cell lines. The increases of CXCL9 and CXCL10 mRNA in OMM2.3 and MEL290 cell lines were suppressed by STAT1 inhibitors.Conclusion·RBX1 may regulate CXCL9 and CXCL10 expression via STAT1 in UVM cells and is involved in tumor immune regulation.

Keywords

• uveal melanoma (uvm)
• ring-box protein 1 (rbx1)
• tumor immunity
• signal transducer and activator of transcription 1 (stat1)