The Role of CXCL12-Mediated Aberrant Methylation and Tumor Microenvironment Remodeling in Carcinogenesis and Prognosis of Bladder Cancer
Authors: Du Yiheng , Cao Jin , Jiang Xiang , Cai Xiaowei , Wang Bo , Wang Yi , Wang XiZhi , Xue Boxin 
Published: September 2021

Abstract
Background

Bladder cancer (BLCA) is the most common genitourinary tumor but lacks specific diagnostic biomarkers. Recent years have seen significant advances in the use and approval of immune checkpoint blockade (ICB) therapy to manage bladder cancer at advanced stages when platinum-based therapy has failed. The tumor microenvironment (TME) in bladder cancer is an essential player in patient's responsiveness to ICB therapy. Therefore, this manuscript explored the TME and identified CXCL12, a specific marker for inflammatory cancer associated fibroblasts(iCAFs), as potential molecular markers and therapeutic targets for bladder cancer.
Methods

We examined the gene expression profiles in the TCGA and GEO datasets to reveal the potential association of CXCL12 with the carcinogenesis and prognosis of bladder cancer. Methylation analysis of CXCL12 was performed using the UALCAN and MethSurv databases. The MCP-COUNTER, ESTIMATE, and TIDE algorithms were applied to estimate the TME components and predict immunotherapy responsiveness. An iCAFs signature was constructed using the ssGSEA algorithm. Bioinformatics analysis results were validated through immunohistochemistry of clinical samples. IMvigor210 cohort was used to validate bioinformatic predictions of therapeutic responsiveness to immune checkpoint inhibitors
Results

Our analysis revealed the potential association between aberrant promoter methylation of CXCL12 and bladder cancer carcinogenesis. CpG sites methylation of the CXCL12 gene body was associated with bladder cancer prognosis. Moreover, the expression level of CXCL12 exhibited a significant correlation with patients' pathological features and prognosis. Through gene enrichment analysis, CXCL12 was demonstrated to be associated with immune modulation and tumor microenvironment remodeling. The MCP-COUNTER and ESTIMATE algorithms verified significant correlations between CXCL12 and TME components, particularly CAFs, macrophages, and T cells. The TIDE algorithm provided evidence that T-cell clearance and dysfunction were more pronounced in bladder cancers characterized by high CXCL12 expression and high iCAFs scores, contributing to inferior responsiveness to ICB therapy. Patients who expressed high CXCL12 levels and had high iCAFs scores were likely to have less frequent FGFR3 mutation and a stromal-rich molecular subtype. Immunohistochemistry revealed that the close association of CXCL12 with iCAFs in bladder cancer potentially influenced the intratumoral infiltration of CD8 + T cells. CXCL12 expression in MIBC was increased significantly in NMIBC, which supports the bioinformatics analysis results. The IMvigor210 cohort confirmed the iCAFs score to be significantly associated with the responsiveness to immune checkpoint blockade therapy.
Conclusions

This work explores carcinogenesis and cancer-promoting roles of CXCL12 in bladder cancer. As a specific marker gene of iCAFs, CXCL12 potentially promotes bladder cancer progression by regulating the tumor microenvironment. Further exploration of the association between CXCL12 and iCAFs may unravel potential therapeutic targets for bladder precision medicine and improve the responsiveness of immune checkpoint blockade therapy.