Cancer‐associated fibroblast‐derived circFARP1 modulates non–small cell lung cancer invasion and metastasis through the circFARP1/miR‐338‐3p/SOX4 axis

Abstract The pleiotropic effect of cancer‐associated fibroblasts (CAFs) on tumour progression depends on the environment. circFARP1 is critical for CAFs‐induced gemcitabine (GEM) resistance in pancreatic cancer. Its specific role and mechanism in non–small cell lung cancer (NSCLC) have not been reported yet. We prepared a cancer‐associated fibroblasts‐conditioned medium (CAF‐CM) to incubate the A549 cells. Quantitative real‐time polymerase chain reaction was used to detect RNA levels. We detected protein expression by immunohistochemistry, immunocytochemistry, western blot and immunofluorescence. We also detected the targeting impact between circFARP1, miR‐338‐3p and SRY‐box transcription factor 4 (SOX4) by using dual‐luciferase reporter and RNA pull‐down assays. We determined cell proliferation, migration and invasion capabilities through Cell Counting Kit‐8 and transwell assays. In addition, we measured tumour volume and weight in vivo by establishing a xenograft tumour model. CircFARP1 levels were remarkably high in the CAFs. The transfection experiments found that circFARP1 downregulation in CAFs caused migration, proliferation and invasion inhibition of CAFs and A549 cells, whereas inhibiting miR‐38‐3p or overexpressing SOX4 in CAFs could significantly reverse the inhibition. In vivo study in nude mice confirmed that CAFs could promote NSCLC tumour growth and knockdown of circFARP1 could inhibit tumour growth of NSCLC, whereas miR‐38‐3p downregulation or SOX4 overexpression could significantly reverse the inhibition. circFARP1 promotes NSCLC development by stimulating miR‐338‐3p/SOX4 signalling axis to regulate CAFs.