Extracellular Vesicles-derived MicroRNA-222 Promotes Immune Escape Via Interacting with ATF3 to Regulate AKT1 Transcription in Colorectal Cancer

Background: Immunotherapy has been recently established as a new direction for the treatment of colorectal cancer (CRC), a gastrointestinal cancer. In this investigation, we aimed to expound how the posttranscriptional regulation modulated by microRNA-222 (miR-222) from mesenchymal stem cells-derived extracellular vesicles (MSC-EVs) affected the AKT pathway and the immune escape in CRC.

Methods: CRC cell malignant phenotype, including proliferation, migration, invasion, and apoptosis, was firstly detected after co-culture with MSC-EVs. miRNAs with differential changes in CRC cells before and after EVs treatment were filtered by microarray analysis. miR-222 was then downregulated to examine its role in CRC cells in response to EVs. Cells were implanted in mice to induce xenograft tumors, and infiltrating T cells was assessed by immunohistochemistry. The mRNA microarray was used to screen target genes, followed by rescue experiments. ChIP and western blot were conducted to validate the downstream biomolecule of ATF3.

Results: After treatment of CRC cells with MSC-EVs, the expression of miR-222 was upregulated, and cell activity was increased. Inhibition of miR-222 decreased CRC malignant aggressiveness in vitro and reduced tumorigenesis and immune escape in vivo. miR-222 targeted and bound to ATF3. Downregulation of ATF3 enhanced CRC cell malignant aggressiveness, tumorigenic capacity and immune escape. Mechanistically, ATF3 inhibited AKT1 transcription and mediated the AKT pathway.

Conclusion: MSC-EVs carry miR-222 to promote CRC cell malignant aggressiveness and immune escape. miR-222 targets and binds to ATF3, which inhibits AKT1 transcriptional activity and thereby mediates the AKT pathway.