COX-2 mediates tumor-stromal Prolactin signaling to initiate tumorigenesis [cell lines]

Tumor-stromal communication within the microenvironment contributes to initiation of metastasis and may present a therapeutic opportunity. Using serial single cell RNA-sequencing in an orthotopic mouse prostate cancer model, we find upregulation of Prolactin receptor as cancer cells that have disseminated to the lung expand into micrometastases. Secretion of the ligand Prolactin by adjacent lung stromal cells is induced by tumor cell production of the COX-2 synthetic product prostaglandin E-2 (PGE-2). PGE-2 treatment of fibroblasts activates the nuclear orphan receptor NR4A (Nur77), with Prolactin as a major transcriptional target for the NR4A-Retinoid X receptor (RXR) heterodimer. Ectopic expression of Prolactin receptor in mouse cancer cells enhances micrometastasis, while treatment with the COX-2 inhibitor Celecoxib abrogates Prolactin secretion by fibroblasts and reduces tumor initiation. Across multiple human cancers, COX-2, Prolactin, and Prolactin receptor show consistent differential expression in tumor and stromal compartments. Such paracrine crosstalk may thus contribute to the documented efficacy of COX-2 inhibitors in cancer suppression. Five subclonal cell lines were established from CE1-4 prostate cancer cells, derived from tissue-specific inactivation of PTEN [Pubmed ID: 20631921]. RNA-seq was performed on the five subclonal cell lines and the parental line.