Myeloid WNT7b Mediates the Angiogenic Switch and Metastasis in Breast Cancer

Oncogenic targets acting in both tumor cells and tumor stromal cells may offer special therapeutic appeal. Interrogation of the Oncomine database revealed that 52/53 human breast carcinomas showed substantial upregulation WNT family ligand WNT7B. Immunolabeling of human mammary carcinoma showed that WNT7B immunoreactivity was associated with both tumor cells and with tumor associated macrophages (TAMs). In the MMTV-PymT mouse model of mammary carcinoma, we found tumor progression relied upon Wnt7b produced by myeloid cells in the microenvironment. Wnt7b deletion in myeloid cells reduced the mass and volume of tumors due to a failure in the angiogenic switch. In the tumor overall, there was no change in expression of Wnt/β-catenin pathway target genes, but in vascular endothelial cells (VEC) expression of these genes was reduced suggesting that VEC respond to Wnt/β-catenin signaling. Mechanistic investigations revealed that failure of the angiogenic switch could be attributed to reduced Vegfa mRNA and protein expression in VECs, a source of Vegfa mRNA in the tumor which was limiting in the absence of myeloid Wnt7b. We also noted a dramatic reduction in lung metastasis associated with decreased macrophage-mediated tumor cell invasion. Together these results illustrated the critical role of myeloid Wnt7b in tumor progression, acting at the levels of angiogenesis, invasion and metastasis. We suggest that therapeutic suppression of Wnt7b signaling might be advantageous due to targeting multiple aspects of tumor progression.