Phenylalanyl-tRNA synthetase subunit beta downregulation by spi1 proto-oncogene modulates lung adenocarcinoma progression and immune microenvironment via mammalian target of rapamycin pathway.

[BACKGROUND] Phenylalanyl-tRNA synthetase subunit beta (FARSB) is implicated in the progression of multiple cancers and represents a potential therapeutic target. However, its role in lung adenocarcinoma (LUAD) progression and the immune microenvironment remains poorly understood, warranting further investigation into its regulatory mechanisms.

[METHODS] We conducted bioinformatics analyses to investigate the expression levels of FARSB in LUAD, identify enriched pathways, and assess its correlation with patient prognosis and CD8 + T cell infiltration. Bioinformatics analysis was also used to explore the transcriptional repression of FARSB by spi1 proto-oncogene (SPI1) and to validate the targeting relationship between SPI1 and FARSB. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was utilized to measure the mRNA expression of FARSB and SPI1, while western blot was used to detect the expression of FARSB, SPI1, programmed death-ligand 1 (PD-L1), and related signaling pathway proteins. Functional assays were performed, including CCK-8 assay for cell viability, EdU incorporation for cell proliferation, and flow cytometry for apoptosis analysis. Carboxyfluorescein succinimidyl ester (CFSE) staining was used to analyze CD8 + T cell proliferation, and flow cytometry was used to assess the expression of cytokines interferon-gamma (IFN-γ), Granzyme B (GZMB), and tumor necrosis factor-alpha (TNF-α).

[RESULTS] FARSB expression was significantly upregulated in LUAD tissues and cells, and it inhibited CD8 + T cell infiltration. Mechanistically, FARSB activated the mammalian target of rapamycin (mTOR) signaling pathway, enhancing LUAD cell viability, proliferation, and anti-apoptotic capabilities, consequently promoting CD8 + T cell exhaustion. The transcription factor SPI1 repressed FARSB expression, thus inhibiting LUAD progression and promoting CD8 + T cell anti-tumor immunity.

[CONCLUSION] SPI1 downregulated FARSB expression through transcriptional repression, thereby blocking the mTOR signaling pathway and suppressing LUAD progression and promoting CD8 + T cell anti-tumor immunity.