CXCL13 Activation of c-Myc Induce RANK Ligand Expression in Stromal/Preosteoblast Cells in the Oral Squamous Cell Carcinoma Tumor-Bone Microenvironment

CXC chemokine ligand-13 (CXCL13) has been implicated in oral squamous cell carcinoma (OSCC) tumor progression and osteolysis. Tumor necrosis factor family member, RANKL (receptor activator of NF-κB ligand), a critical bone resorbing osteoclastogenic factor plays an important role in cancer invasion of bone/osteolysis. Here, we show high level expression of CXCL13 in primary human OSCC tumor specimens; however human bone marrow derived stromal (SAKA-T) and murine preosteoblast (MC3T3-E1) cells produce at very low level. Recombinant CXCL13 (0–15 ng/ml) dose dependently induced CXCR5 expression in SAKA-T and MC3T3-E1 cells. Conditioned media obtained from OSCC cell lines increased the RANKL expression and an antibody against the CXCL13 specific receptor, CXCR5 markedly decreased RANKL expression in these cells. Furthermore, CXCL13 increased hRANKL-Luc promoter activity. Superarray screening identified c-Myc and NFATc3 transcription factors upregulated in CXCL13 stimulated SAKA-T cells. Immunohistochemical analysis of OSCC tumors developed in athymic mice demonstrated RANKL and NFATc3 expression in tumor and osteoblast cells, however p-c-Myc expression specific to osteoblastic cells at the tumor-bone interface. We further identified NFATc3 expression but not c-Myc activation in primary human OSCC tumor specimens compared to adjacent normal tissue. Also, CXCL13 significantly increased p-ERK1/2 in SAKA-T and MC3T3-E1 cells. siRNA suppression of c-Myc expression markedly decreased CXCL13 induced RANKL and NFATc3 expression in preosteoblast cells. Chromatin-immuno precipitation (ChIP) assay confirmed p-c-Myc binding to the hRANKL promoter region. In summary, c-Myc activation through CXCL13-CXCR5 signaling axis stimulates RANKL expression in stromal/preosteoblast cells. Thus, our results implicate CXCL13 as a potential therapeutic target to prevent OSCC invasion of bone/osteolysis.