ABSTRACT
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 up-regulation of prolactin receptor as cancer cells that have disseminated to the lungs 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 E2 (PGE2). PGE2 treatment of fibroblasts activates the orphan nuclear 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 cross-talk may thus contribute to the documented efficacy of COX-2 inhibitors in cancer suppression.
Subject(s)
Carcinogenesis/metabolism , Prolactin/metabolism , Prostatic Neoplasms/metabolism , Prostatic Neoplasms/pathology , Signal Transduction/physiology , Stromal Cells/metabolism , Animals , Carcinogenesis/drug effects , Celecoxib/pharmacology , Cell Transformation, Neoplastic/drug effects , Cell Transformation, Neoplastic/metabolism , Cell Transformation, Neoplastic/pathology , Cyclooxygenase 2/metabolism , Cyclooxygenase 2 Inhibitors/pharmacology , Dinoprostone/metabolism , Disease Models, Animal , Fibroblasts/drug effects , Fibroblasts/metabolism , Humans , Male , Mice , Nuclear Receptor Subfamily 4, Group A, Member 1/metabolism , Prostatic Neoplasms/drug therapy , Retinoid X Receptors/metabolism , Signal Transduction/drug effects , Stromal Cells/drug effects , Stromal Cells/pathology , Up-Regulation/drug effects , Up-Regulation/physiologyABSTRACT
Prostate cancer is initially responsive to androgen deprivation, but the effectiveness of androgen receptor (AR) inhibitors in recurrent disease is variable. Biopsy of bone metastases is challenging; hence, sampling circulating tumor cells (CTCs) may reveal drug-resistance mechanisms. We established single-cell RNA-sequencing (RNA-Seq) profiles of 77 intact CTCs isolated from 13 patients (mean six CTCs per patient), by using microfluidic enrichment. Single CTCs from each individual display considerable heterogeneity, including expression of AR gene mutations and splicing variants. Retrospective analysis of CTCs from patients progressing under treatment with an AR inhibitor, compared with untreated cases, indicates activation of noncanonical Wnt signaling (P = 0.0064). Ectopic expression of Wnt5a in prostate cancer cells attenuates the antiproliferative effect of AR inhibition, whereas its suppression in drug-resistant cells restores partial sensitivity, a correlation also evident in an established mouse model. Thus, single-cell analysis of prostate CTCs reveals heterogeneity in signaling pathways that could contribute to treatment failure.
