Cancer Sci. 2020 Feb 03.
Bone marrow-derived mesenchymal stem or stromal cells (MSCs) have been shown to be recruited to various types of tumor tissues, where they interact with tumor cells to promote their proliferation, survival, invasion, and metastasis, depending on the type of the tumor. We have previously shown that Ror2 receptor tyrosine kinase and its ligand, Wnt5a, are expressed in MSCs, and Wnt5a-Ror2 signaling in MSCs induces expression of CXCL16, which in turn promotes proliferation of co-cultured MKN45 gastric cancer cells via CXCL16-CXCR6 axis. However, it remains unclear how CXCL16 regulates proliferation of MKN45 cells. Here, we show that knockdown of CXCL16 in MSCs by siRNA suppresses not only proliferation, but also migration of co-cultured MKN45 cells. We also show that MSC-derived CXCL16 or recombinant CXCL16 upregulates expression of Ror1 through activation of STAT3 in MKN45 cells, leading to promotion of proliferation and migration of MKN45 cells in vitro. Furthermore, co-injection of MSCs with MKN45 cells in nude mice promoted tumor formation in a manner dependent on expression of Ror1 in MKN45 cells, and anti-CXCL16 neutralizing antibody suppressed tumor formation of MKN45 cells co-injected with MSCs. These results suggest that CXCL16 produced through Ror2-mediated signaling in MSCs within the tumor microenvironment acts on MKN45 cells in a paracrine manner to activate CXCR6-STAT3 pathway, which in turn induces expression of Ror1 in MKN45 cells, thereby promoting tumor progression.
Keywords: Bone marrow-derived mesenchymal stem cells; CXCL16; Ror1; STAT3; gastric cancer