Upon stimulation by various extracellular cues such as transforming
growth factor-β1 (TGF-β1), angiotensin II (Ang II), epidermal
growth factor (EGF), or extracellular matrix (ECM), intracellular Src kinase is
activated. Src activation leads to phosphorylation of the signaling proteins
STAT3, AKT, and plasma membrane epidermal growth factor receptor (EGFR).
Activation of Src also promotes TGF-β1–mediated Smad3 activation
by multiple mechanisms (dashed line).