# Hsa-miR-99a deficiency contributes to MSI-H colorectal cancer progression by activating the mTOR pathway and inducing Th1/Th2 imbalance

## TL;DR

This study shows that low levels of hsa-miR-99a in a type of colorectal cancer called MSI-H lead to cancer progression by affecting the mTOR pathway and changing immune cell activity.

## Contribution

The study identifies hsa-miR-99a as a novel regulator of mTOR signaling and immune imbalance in MSI-H colorectal cancer.

## Key findings

- Hsa-miR-99a is significantly downregulated in MSI-H colorectal cancer compared to MSS tumors.
- Deficiency in hsa-miR-99a correlates with activation of mTOR pathway genes like ATP6V1G2 and WNT6.
- MSI-H tumors show reduced Th1 and increased Th2/Th17 immune infiltration linked to hsa-miR-99a deficiency.

## Abstract

Hsa-miR-99a has been linked to the advancement of several malignancies, including colorectal cancer (CRC). This investigation seeks to elucidate its function and regulatory network in CRC.

Differential expression of hsa-miR-99a was analyzed between microsatellite stable (MSS) and microsatellite instability-high (MSI-H) subgroups. Potential target mRNAs of hsa-miR-99a were retrieved from TargetScan and miRWalk databases. Overlapping mRNAs were subjected to correlation analysis, with candidate genes selected based on |correlation coefficient| > 0.3 and p < 0.05. Enrichment analyses were performed, highlighting key pathways, particularly mTOR signaling. Immune infiltration profiles were compared between MSS and MSI-H groups. Correlation between hsa-miR-99a and mTOR pathway-related genes was validated by RT-qPCR and Western blot. Additionally, multiplex immunohistochemistry (mIHC) with tyramine signal amplification (TSA) was used to characterize the immune microenvironment in MSI-H CRC samples.

Hsa-miR-99a expression was significantly higher in MSS compared to MSI-H groups. Twelve key target genes were identified, including ATP2B2, ATP2B4, SLC8A1, KCNJ5, NTRK3, TNFRSF19, GHR, CXCL12, NTNG1, SDC2, SFRP1, and PRICKLE2. Immune infiltration analysis revealed significant differences in 24 cell types between MSS and MSI-H groups, including Th1, Th2, Th17, and effector memory CD8+ T cells. Ten mTOR pathway-related genes (ATP6V1G2, WNT2, WNT6, WNT9A, WNT9B, FZD1, FZD4, FZD8, IGF1, AKT3) exhibited strong correlation with hsa-miR-99a. Among these, ATP6V1G2 and WNT6 were upregulated in the MSI-H group. mIHC analysis indicated reduced Th1 but increased Th2 and Th17 biomarkers in MSI-H CRC.

This study identified key genes and immune microenvironment alterations regulated by hsa-miR-99a in CRC, offering novel insights and potential therapeutic targets for CRC treatment.