Dipeptidyl peptidase 4-positive cancer-associated fibroblasts enhance lung adenocarcinoma growth.

Cancer-associated fibroblasts (CAFs) are a heterogeneous population of fibroblasts with various features in the cancer stroma and have been reported to influence cancer progression through cell-cell interactions in various types of malignancies, including lung adenocarcinoma (LUAD). Dipeptidyl peptidase 4 (DPP4) is a transmembrane protein with serine protease activity and is involved in the progression of tumors, metabolic diseases, and autoimmune diseases. In the present study, we focused on the role of DPP4-positive CAFs in LUAD. Immunohistochemistry revealed that 38 of 89 LUAD patients showed DPP4 expression in the fibrous stroma, and patients harboring DPP4-positive CAFs were more often male, had a higher Brinkman index, and had a higher Ki-67 labeling index of tumor cells than those with DPP4-negative CAFs. DPP4-positivity was associated with the expression of other CAF markers, α-SMA, periostin, and podoplanin, as well as a cellular senescence marker, p16. In the in vitro study, conditioned media collected from pulmonary fibroblast (OUS-11, HPF, and HPF-C)-induced overexpression of DPP4 significantly promoted the proliferation of LUAD cells (A549 and PC-9) and increased the expression levels of MCP-1, IL-8, IL-6, and GCSF in the media compared to those in controls. In addition, OUS-11 overexpression in DPP4 overexpression increased periostin expression. In conclusion, DPP4-positive CAFs could promote lung adenocarcinoma cell growth by producing soluble factors, and DPP4 inhibition may inhibit cancer progression.