Deficiency of myeloid discoidin domain receptor 2 aggravates melanoma lung and bone metastasis.

Melanoma, one of the most prevalent cancers worldwide, frequently metastasizes to the lung and bones. Tumor-associated macrophages play essential roles in melanoma metastasis but the underlying mechanism remains obscure. We previously demonstrated that specific knockout of Ddr2, a receptor tyrosine kinase, exacerbates systemic inflammation via modulating macrophage repolarization. To investigate whether myeloid Ddr2 regulates melanoma growth and metastasis, we injected B16BL6 melanoma cells into Ddr2^LysM (cKO) mice via subcutaneous neck, tail vein, and left ventricle, respectively. We found that the growth of melanoma cells in cKO mice was significantly retarded, as demonstrated by the subcutaneous transplantation tumor model. Unexpectedly, the melanoma metastasis to the lung or bone was significantly stimulated in cKO mice, indicating the complicated role of Ddr2 in macrophages in melanoma development. Furthermore, Ddr2 in macrophages regulated the migration of B16BL6 cells in the co-culture system. Bioinformatics analysis showed that Ddr2 expression correlates with improved prognostic outcomes in melanoma, and high expression of Ddr2 is protective in melanoma metastasis. Our results enrich the current knowledge of Ddr2 in tumor biology and indicate that more consideration should be taken when applying Ddr2 inhibition as a melanoma treatment strategy.