GSE96674
COX-2 mediates tumor-stromal Prolactin signaling to initiate tumorigenesis [single cells]
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. Overall design: Primary tumors were established by direct prostate inoculation into immunosuppressed NSG mice of CE1-4 prostate cancer cells, derived from tissue-specific inactivation of PTEN [Pubmed ID: 20631921].  These cells, which were GFP-luciferase tagged, are noteworthy in that they have preserved expression of the androgen receptor and epithelial markers and recapitulate biological features of human prostate cancer. Six weeks following intra-prostate inoculation, multiple single DTCs were identified microscopically within the lungs (394 cells/hpf), with a smaller number in liver (54 cells/hpf), brain (9 cells/hpf) and bone marrow (1 cell/hpf). To undertake RNA sequencing of single cells during progression from quiescent DTCs to proliferative lesions, we identified GFP-tagged single tumor cells from lung harvested at various intervals, analyzing these separately from microdissected multicellular lesions. Individual DTCs collected at 6-7 weeks (DTC-I; N=20) and at 9-11 weeks (DTC-II; N=55) were compared with single cells derived from the primary tumor (N=29), lung micro-metastases (N=33), and CTCs isolated by microfluidic capture from blood specimens (N=12) [Pubmed ID: 28181495].