Gao L, et al. DNA Cell Biol 2020.
The roof plate-specific spondin (RSPO) family of proteins has critical roles in the tumorigenesis and progression of several carcinomas; however, little is known about their functions in bladder cancer (BLCA). This study aimed to investigate RSPO in terms of their expression levels, prognostic value, and potential mechanisms of action in BLCA. mRNA expression profiles and clinical information of BLCA patients were collected from The Cancer Genome Atlas database. Genetic alteration and DNA methylation data were obtained from cBioPortal and MethHC databases, respectively, and SurvExpress was used to determine the prognostic risk score of each RSPO. R software was used to analyze the expression levels and prognostic roles of RSPOs in BLCA. The effects of RSPO2 overexpression in BLCA cells were detected using MTT, colony formation, and Transwell invasion assays. Gene set enrichment analysis (GSEA) was used to analyze the functions of RSPOs and associated signaling pathways in BLCA. All members of the RSPO family were differentially expressed in BLCA cells compared with normal control cells. Aberrant RSPO expression levels were associated with higher histological stages and worse prognosis. The frequency of genetic alterations in RSPO genes was very high, which was related to a less favorable prognosis. Moreover, the effects of mutations in the RSPO2 gene were reversed using a Wnt/β-catenin inhibitor, IWP-2. In addition, GSEA demonstrated that RSPOs were associated with focal adhesion and immune cell infiltration, which was then confirmed by tumor immune cell infiltration analysis. RSPOs are potential biomarkers for predicting the prognosis of patients with BLCA and may serve as novel therapeutic targets. Moreover, overexpressed RSPO2 promoted BLCA cell growth and invasion through the Wnt/β-catenin pathway. In addition, RSPOs may regulate the progression of BLCA through modulating cell adhesion, focal adhesion, and CD4+ T cell and macrophage infiltration.