Myeloid Cell-Derived TGFβ Signaling Regulates ECM Deposition in Mammary Carcinoma via Adenosine-Dependent Mechanisms

TGF beta plays a crucial role in the tumor microenvironment by regulating cell-cell and cell-stroma interactions. We previously demonstrated that TGF beta signaling on myeloid cells regulates expression of CD73, a key enzyme for production of adenosine, a protumorigenic metabolite implicated in regulation of tumor cell behaviors, immune response, and angiogenesis. Here, using an MMTV-PyMT mouse mammary tumor model, we discovered that deletion of TGF beta signaling on myeloid cells (PyMT/TGFbRII(LysM)) affects extracellular matrix (ECM) formation in tumor tissue, specifically increasing collagen and decreasing fibronectin deposition. These changes were associated with mitigated tumor growth and reduced metastases. Reduced TGFb signaling on fibroblasts was associated with their proximity to CD73(+) myeloid cells in tumor tissue. Consistent with these findings, adenosine significantly downregulated TGF beta signaling on fibroblasts, an effect regulated by A(2A) and A(2B) adenosine receptors. METABRIC dataset analysis revealed that patients with triple-negative breast cancer and basal type harbored a similar signature of adenosine and ECM profiles; high expression of A2B adenosine receptors correlated with decreased expression of Col1 and was associated with poor outcome. Taken together, our studies reveal a new role for TGF beta signaling on myeloid cells in tumorigenesis. This discovered crosstalk between TGF beta/CD73 on myeloid cells and TGF beta signaling on fibroblasts can contribute to ECM remodeling and protumorigenic actions of cancer-associated fibroblasts. Significance: TGF beta signaling on fibroblasts is decreased in breast cancer, correlates with poor prognosis, and appears to be driven by adenosine that accelerates tumor progression and metastasis via ECM remodeling.