SLC4A4 Moulds the Inflammatory Tumor Microenvironment and Predicts Therapeutic Expectations in Colorectal Cancer
Authors: Xiang Dan , Li Huiyu , Pan Jun , Chen Yitian 
Published: February 2024

Background:
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.

background:
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.

Aim:
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.

objective:
To deeply and systematically reveal the characteristics of the tumor microenvironment created by SLC4A4.

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

method:
We downloaded RNA sequencing files (TCGA-COADREAD), clinical data for Colon Cancer (COAD) and Rectal Cancer (READ) from the Cancer Genome Atlas. We evaluated the spearman correlation of SLC4A4 with immune features, Tracking Tumor Immunophenotype (TIP) score, and immune checkpoint gene expression. SLC4A4/immunity-related differentially expressed genes (DEGs) were identified in SLC4A4 expression groups and immune groups, and an assessment system for predicting CRC prognosis was constructed based on univariate COX and multivariate COX analyses. Based on the prognostic factors in CRC, we also constructed a nomogram to assess the survival risk status of CRC. Besides, we evaluated the potential association of SLC4A4 to immunotherapy.

Methods:
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.

result:
We found that SLC4A4 expression trended positively with immune checkpoint [removed]PD-L1, CTLA4) and promoted infiltration of 27 immune cells. SLC4A4 promoted the infiltration of CD8 T cells, Dendritic cells, Macrophage, NK cells, and Th1 cells in CRC, shaping the inflammatory tumor microenvironment. Up-regulation of SLC4A4 expression might promote drug response to Anti-FGFR3_therapy, Anti-PPARG_therapy, Nivolumab, Ipilimumab in CRC patients, and down-regulation of SLC4A4 expression might promote drug response to Anti-EGFR_therapy, Aflibercept drug response. Based on the SLC4A4/immunization-related DEGs, we constructed RiskScore to assess the prognosis of CRC, which showed excellent predictive effect and robustness. RiskScore showed a trend of negative correlation with SLC4A4, which was consistent with the trend of the effect of SLC4A4 on CRC survival. Besides, RiskScore could also be useful for predicting patient prognosis. Finally, we constructed a nomogram for predicting CRC survival based on metrics with independent prognostic value (Age, M stage, Stage, RiskScore), which showed potential clinical value.

Results:
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.

Conclusion:
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.