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PURPOSE Prostate cancer (PCa) bone metastasis (BM) plays a crucial role in disease outcome and poses a significant clinical obstacle due to its heterogeneity. In this sense, Osteopontin (SPP1/OPN) is elevated in a subset of patients with advanced disease. However understanding its regulation is an unmet need. In this work we investigated the factors controlling SPP1/OPN expression in a subgroup of patients with BM. METHODS We performed a comprehensive transcriptomics analysis (DEG, Ingenuity Pathway Analysis (IPA)) of publicly available patients datasets (GSE74685, SU2C-PCF and Westbrooke et al), comparing PCa on different metastatic sites and/or treatment status. Using an indirect co-culture (24h) to mimic the dialogue between PCa cells (PC3/C42B) and osteoblast precursors (MC3T3) in vitro, we integrated transcriptomics (RT-qPCR and RNAseq) and secretomic (ESI-MS/MS of conditioned media (CM)) data to dissect key players involved in the bi-directional crosstalk between PCa and bone cells. Protein Kinase A (PKA) pathway implication was evaluated by its induction (forskolin 1uM) or suppression (H89 10uM). Clinically relevant patient derived xenograft (PDX) models growing intrafemorally (i.f.) were used for in vivo validation. RESULTS Across different datasets, we consistently found a sub-population of patients with BM characterized by high levels of SPP1 expression, associated with an active PKA pathway. By functionalizing this response experimentally, we demonstrated that specific bone secreted factors, particularly Col1a1 and Fn1, significantly induce SPP1 expression in PCa cells via PKA activation. Further, experimental and clinical settings suggest that the androgen receptor (AR) is implicated on this bone-induced PKA/SPP1 axis. Notably, longitudinal analysis of patients samples revealed an increased SPP1 expression alongside signs of PKA pathway activation, in a subpopulation of BM upon AR signaling inhibition with enzalutamide. CONCLUSION Herein, we uncovered PKA as a novel upstream regulator of SPP1/OPN expression in PCa triggered by the bone microenvironment that could possibly be implicated in treatment resistance. These results highlight the potential of SPP1/OPN as a marker of tumors with active PKA to improve disease management.
Sanchis et al. (Mon,) studied this question.