TGF-β transactivates EGFR and facilitates breast cancer migration and invasion through canonical Smad3 and ERK/Sp1 signaling pathways

Transforming growth factor-beta (TGF-β) functions as a potent proliferation inhibitor and Apoptosis inducer in the early stages of breast Cancer, yet promotes Cancer aggressiveness in the advanced stages. The dual effect of TGF-β on Cancer development is known as TGF-β paradox, and the remarkable functional conversion of TGF-β is a pivotal and controversial phenomenon that has been widely investigated for decades. This phenomenon may be attributed to the cross talk between TGF-β signaling and other pathways, including EGF receptor (EGFR) signaling during Cancer progression. However, the underlying mechanism by which TGF-β shifts its role from a tumor suppressor to a Cancer promoter remains elusive. In this study, TGF-β is positively correlated with EGFR expression in breast Cancer tissues, and a functional linkage is observed between TGF-β signaling and EGFR transactivation in breast Cancer cell lines. TGF-β promotes the migration and invasion abilities of breast Cancer cells, along with the increase in EGFR expression. EGFR is also essential for TGF-β-induced enhancement of these abilities of breast Cancer cells. Canonical SMAD3 signaling and ERK/Sp1 signaling pathways mediate TGF-β-induced EGFR upregulation. Hence, our study provided insights into a novel mechanism by which TGF-β supports breast Cancer progression.