SLC4A4 Moulds the Inflammatory Tumor Microenvironment and Predicts Therapeutic Expectations in Colorectal Cancer

Colorectal cancer (CRC) cases with advanced or distal metastases experience a survival rate of less than 20%, with the lack of spectral therapeutic targets and prognostic markers posing a significant challenge for CRC treatment. SLC4A4 may be a CRC-targeted therapy for which there is currently inadequate evidence.

In this report, we performed a comprehensive analysis of data on colorectal cancer (CRC) to elucidate the association among Solute Carrier Family 4 Member 4 (SLC4A4) and the abundance of immunological features and immune cell infiltration in CRC and to explore the impact of SLC4A4 on the CRC tumor microenvironment.

The objective of this study was to systematically reveal the characteristics of the tumor microenvironment created by SLC4A4.

We downloaded RNA sequencing files from the Cancer Genome Atlas (TCGA- COADREAD). The correlations of SLC4A4 with immune-related characteristics were analyzed. A Limma package was applied for selecting SLC4A4/immunity-related differentially expressed genes (DEGs). An assessment system for predicting CRC prognosis was constructed based on univariate COX and multivariate COX analyses. A nomogram was also designed to assess the survival risk status of CRC. Besides, we evaluated the potential association of SLC4A4 to immunotherapy through TIDE analysis.

We found that SLC4A4 expression was positively correlated with immune checkpoint expression (PD-L1 ).SLC4A4 promoted the infiltration of CD8 T cells, dendritic cells, macrophages, NK cells, and Th1 cells in CRC, shaping the inflammatory tumor microenvironment. Up-regulated SLC4A4 might improve drug response to anti- FGFR3 therapy, anti-PPARG therapy, nivolumab, and ipilimumab in CRC patients, and down-regulated SLC4A4 might promote drug response to anti-EGFR therapy and Aflibercept drug response. The constructed RiskScore model showed excellent predictive effect and robustness. RiskScore presented a trend of negative correlation with SLC4A4, which was consistent with the trend of the effect of SLC4A4 on CRC survival. TIDE analysis further disclosed that high-risk groups with high levels of SLC4A4 were possible for immune escape. Finally, the constructed nomogram also showed potential clinical value.

Overall, upregulation of SLC4A4 expression promoted an inflammatory tumor microenvironment in CRC, and RiskScore predicted therapeutic expectancy. SLC4A4 could be a potentially clinically valuable target for CRC therapy.