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

Transforming growth factor-beta (TGF-) 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- on cancer development is known as TGF- paradox, and the remarkable functional conversion of TGF- is a pivotal and controversial phenomenon that has been widely investigated for decades. This phenomenon may be attributed to the cross talk between TGF- signaling and other pathways, including EGF receptor (EGFR) signaling during cancer progression. However, the underlying mechanism by which TGF- shifts its role from a tumor suppressor to a cancer promoter remains elusive. In this study, TGF- is positively correlated with EGFR expression in breast cancer tissues, and a functional linkage is observed between TGF- signaling and EGFR transactivation in breast cancer cell lines. TGF- promotes the migration and invasion abilities of breast cancer cells, along with the increase in EGFR expression. EGFR is also essential for TGF--induced enhancement of these abilities of breast cancer cells. Canonical Smad3 signaling and ERK/Sp1 signaling pathways mediate TGF--induced EGFR upregulation. Hence, our study provided insights into a novel mechanism by which TGF- supports breast cancer progression.