Transcription factor RUNX3 promotes CD8+ T cell recruitment by CCL3 and CCL20 in lung adenocarcinoma immune microenvironment.

Considering the existence of immune-desert in tumor microenvironment, the clinical efficacy of immunotherapy for lung adenocarcinoma is limited. This study aims to investigate the ability of transcription factors in regulating tumor immune microenvironment in lung adenocarcinoma. RNA-seq data were collected from the The Cancer Genome Atlas database. The relationships between transcription factors and immune infiltrates were assessed. Runt-related transcription factor 3 (RUNX3)-associated immune pathways were investigated by the Kyoto Encyclopedia of Genes and Genomes, Gene Ontology, and Gene set enrichment analysis. Upregulated chemokines in the RUNX3-overexpressed cell line were determined by quantitative real-time polymerase chain reaction, western blot, and enzyme-linked immunosorbent assay. These chemokines were further confirmed in RUNX3-downregulated cell lines. Immunochemistry was conducted to determine the expression of RUNX3, CCL3, CCL20, and the numbers of CD8+ T lymphocytes in human lung cancer tissues. Chemokine receptors in CD8+ T cells were explored by flow cytometry and immunofluorescence. T cell recruitment was investigated by transwell assay. After screening 406 transcription factors, RUNX3 was found strongly correlated T cells, cytotoxic lymphocytes, and CD8+ T cells. RUNX3 was associated with a variety of immunomodulators, including LAG3, CTLA-4, PD-1, and TIGIT. More importantly, RUNX3 was involved in immune-related pathways, especially immune cell migration-related pathways. Further investigation exhibited RUNX3 could upregulate CCL3 and CCL20 whose receptors CCR5 and CCR6 were upregulated in CD8+ effector T cells, while downregulation of RUNX3 decreased the expression of CCL3 and CCL20 and the infiltration of CD8+ T cells in RUNX3-downregulated lung cancer cell lines. Immunochemistry exhibited positive correlations of RUNX3 with CCL3 and CD8+ T cells in clinical lung adenocarcinoma samples. The chemotaxis assay proved RUNX3 could promote CD8+ T cell recruitment by upregulating CCL3 and CCL20. This study unearths RUNX3 related molecular mechanisms of tumor immune microenvironment and may reverse the immune-desert condition in lung adenocarcinoma and be combined with immune checkpoint blockade and adoptive cell therapy.