MHC class II+ macrophage differentiation is impaired in metastasized lungs via PGE2 receptor EP2.

Monocytes differentiate into macrophages (Mφs) to facilitate lung metastasis, but the monocyte-to-Mφ transition during this process is not well understood. To investigate, we performed bulk RNA sequencing on Mφs isolated from the lungs of mice bearing Lewis lung carcinoma tumors and from naive lungs. Our results showed impaired differentiation of monocytes into major histocompatibility complex (MHC) class II+ Mφs, with an upregulation of PGE2-inducible genes, including Arg1, in tumor-associated Mφs (TAMs). In vitro experiments confirmed that prostaglandin E2 (PGE2) inhibits the differentiation of MHC class II+ Mφs while promoting Arg1+ Mφs via the E prostanoid 2 (EP2) receptor, accompanied by DNA methylation. Whole-genome bisulfite sequencing revealed that PGE2-EP2 signaling drives the hypermethylation and downregulation of gene sets related to myeloid cells in non-neoplastic tissues. Our study highlights PGE2-EP2-driven DNA methylation in the monocyte-to-TAM transition, suggesting potential therapeutic avenues for lung metastasis.