Osteopontin at the Crossroads of Inflammation and Tumor Progression

Figure 5

Tumor-promoting functions of OPN. OPN (blue sphere) induces increased proliferation and survival of tumor cells; it is also associated with the recruitment of myeloid-derived suppressor cells (MDSC), from bone marrow stem cells. MDSC create an immunosuppressive niche both in the primary tumor and in the metastatic tissue, thereby creating a favorable place for tumor growth. OPN favors dissemination and angiogenesis to counteract hypoxia, and concomitantly reprograms tissue fibroblasts to cancer-associated fibroblasts (CAFs), which by secreting TGF-β1, promote epithelial to mesenchymal transition (EMT) allowing tumor cells to detach from the primary mass and disseminate to the premetastatic niche. Here, OPN promotes mesenchymal to epithelial transition (MET) favoring the metastatic processes.