miR-873 and miR-105-2 May Affect the Tumour Microenvironment and are Potential Biomarkers for Lung Adenocarcinoma.

Background: Lung adenocarcinoma (LUAD) accounts for approximately 40% of all lung cancer cases. The tumour microenvironment (TME) and microRNAs affect the occurrence, metastasis, recurrence and treatment of tumours. However, the role of microRNAs in the TME and LUAD still needs to be further investigated. Methods: RNA-seq and microRNA-seq data of LUAD and NSCLC samples were downloaded from the TCGA and GEO database. The immune and stromal components in the TME and the abundance of tumour-infiltrating immune cells (TICs) were calculated by the ESTIMATE and CIBERSORT algorithms, respectively. The differentially expressed microRNAs (DEMs) between different StromalScore and ImmuneScore groups were screened out by the edgeR package. Bioinformatics analysis was performed to screen out important DEMs and explore their functional effect. Results: Our results revealed that a low StromalScore, ImmuneScore and ESTIMATEScore led to poor prognosis of LUAD. Then, 62 DEMs were screened out as downregulated in both the high StromalScore and ImmuneScore groups. Among these DEMs, elevated expression levels of miR-873, miR-105-2 and miR-516a-2 significantly shortened the survival time of LUAD patients. Subsequent analysis revealed that the expression levels of miR-873 and miR-105-2 were increased significantly in tumour tissues. The expression patterns of these 2 microRNAs were confirmed by GSE102286, implying the important roles of these 2 microRNAs in LUAD. Further analysis showed that miR-873 and miR-105-2 were mainly involved in immune-related pathways and that high expression levels of miR-873 and miR-105-2 decreased the abundance of monocytes and resting dendritic cells in the TME. Conclusion: Although further exploration is still needed, our results revealed that miR-873 and miR-105-2 were closely related to the TME and affected the prognosis of LUAD by altering the abundance of TICs.