Single-Cell RNA Sequencing Identifies CCR6-Driven Immune Landscape Changes in RM1 Prostate Cancer Bone Metastasis

Prostate cancer commonly metastasizes to bone, creating an immunosuppressive microenvironment that supports tumor progression. The RM1 (Ras/Myc) mouse model is a valuable tool for studying interactions between prostate tumors and the bone marrow immune landscape.

Single-cell RNA sequencing was employed to investigate how CCR6 deficiency affects immune cell comsmunication in bone marrow from RM1 prostate cancer bone metastasis. Immune responses were compared between wild-type and CCR6 knockout (CCR6ko) C57BL/6-mice injected with RM1-BoM3 cells.

Distinct immune cell dynamics were observed between the two groups. CCR6ko bone marrow showed enhanced signaling from macrophages, regulatory T cells, and myeloid-derived suppressor cell-like cells, with altered receptor activity in naïve T cells, NK cells, and conventional dendritic cells. Differential gene expression highlighted immune regulation pathways and transcriptional networks centered on JUN, JUNB, and FOSB, linked to immune suppression and tumor progression. Cell-cell communication analysis revealed changes in CCL, TGFb, MIF, and CXCL pathways, aligning with observations in human castration-resistant prostate cancer (CRPC) bone-metastasis. Profiling of immune cell populations showed increased tumor-infiltrating monocytic cells, M2 macrophages, and NKT-like CD8 cells in RM1 tumors compared to CCR6ko bone marrow. Pathway enrichment analysis identified upregulated pathways, including IL-17 signaling and osteoclast differentiation, associated with immune-modulation and inflammation. Gene regulatory networks in the RM1 bone metastasis microenvironment involved NFKB1, STAT1, IRF8, and JUN family proteins, emphasizing their roles in immune suppression and tumor progression.

These results suggest that targeting CCR6 may enhance immunotherapy efficacy in prostate cancer bone metastasis by reshaping the immune microenvironment. Validation in human CRPC bone metastasis datasets revealed conserved immune interactions.