Cancer-associated fibroblasts (CAFs) promote EMT (epithelial-mesenchymal transition), invasion, and metastasis of cancer cells in the tumor microenvironment. To identify microRNAs (miRNAs) associated with the reprogramming of normal lung fibroblasts (LFs) into CAFs, global miRNA expression was profiled in LFs and CAFs through Nanostring nCounter. miR-224 was one of the increased miRNAs in CAFs, and its expression was higher in tumors than in normal tissues in dbDEMC and TCGA_lung adenocarcinoma data. miR-224 levels were then checked by qRT-PCR in paraffine-embedded tumor samples from patients with lung adenocarcinoma. Kaplan-Meier survival analysis showed that high miR-224 expression was related to poor survival. These data show that lung cancer progression is promoted by miR-224. To discover the roles of increased miR-224 in CAFs, miR-224 was overexpressed by lentiviral infection in LFs. LF_miR-224 overexpression enhanced the expression of CAF activation markers including Fap, S100a4, and Vim. In spheroid invasion assay using co-culture of LFs and cancer cells, as an experimental model of the tumor microenvironment, LF_miR-224 promoted invasion of lung cancer cells compared with control LFs. In transwell migration assay, LF_miR-224 stimulated migration of lung cancer cells more than control LFs. Collectively, these results indicate that CAFs reprogrammed by miR-224 promote the migration and invasion of lung cancer cells. Citation Format: Seonyeong Oh, Inyoung Cheon, Young-Ho Ahn. miR-224 activates cancer-associated fibroblasts to promote cancer cell invasion in lung tumor microenvironment. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5843.