Background: Muscle-invasive bladder cancer (MIBC) is characterized as bladder tumors that infiltrate into the muscle layer, along with multiple metastasis and poor prognosis. Numerous research studies have been performed to identify the underlying clinical and pathological alterations that occur. However, few studies have revealed the molecular mechanism of its progression based upon the immunotherapy response. Our present study was designed to identify biomarkers which may predict the immunotherapy response by investigating the tumor microenvironment (TME) in MIBC.
Methods: The transcriptome and clinical data of MIBC patients were obtained and analyzed with R version 4.0.3 (POSIT Software, Boston, MA, USA) ESTIMATE package. Differentially expressed immune-related genes (DEIRGs) were identified and further analyzed via the protein-protein interaction network (PPI). Meanwhile, univariate Cox analysis was utilized to screen out the prognostic DEIRGs (PDEIRGs). Then, the PPI core gene was matched with PDEIRGs to obtain the target gene-fibronectin-1 (FN1). Human MIBC and control tissues were collected and FN1 was measured with Quantitative Reverse Transcription PCR (qRT-PCR) and Western-Blot. Finally, the relationship between FN1 expression level and MIBC was validated through survival, univariate Cox, multivariate Cox, Gene Set Enrichment Analysis (GSEA) and correlation analysis of tumor infiltrating immune cells.
Results: TME DEIRGs were identified and the target gene FN1 was obtained. The higher expression of FN1 was confirmed in MIBC tissues via bioinformatics analysis, qRT-PCR and Western-Blot. Moreover, higher FN1 expression correlated with reduced survival time and FN1 expression was further favorably correlated with clinic-pathological features (grade, TNM stage, invasion, lymphatic and distant metastasis). Additionally, the genes in the high FN1 expression group were mainly enriched in immune-related activities and macrophage M2, T cell CD4, T cell CD8 and T cell follicular helper cells were correlated with FN1. Finally, it was observed that FN1 was closely related to key immune checkpoints.
Conclusions: FN1 was identified as a novel and independent prognostic factor for MIBC. Our data also suggests FN1 can predict MIBC patients' response to immune checkpoints inhibitors.
Keywords: fibronectin 1 (FN1); immune checkpoint inhibitors (ICIs); muscle-invasive bladder cancer (MIBC); tumor microenvironment (TME); tumor-infiltrating immune cells.