The development of the mammary gland requires an integrated response to specific 
growth factors and steroid hormones. Hepatocyte growth factor (HGF) and its 
tyrosine kinase receptor, MET, are expressed and temporally regulated during 
mammary development and differentiation. Epidermal growth factor receptor (EGFR) 
and its ligands have also been implicated in mammary gland growth and 
morphogenesis. Since both cytokines seem to exert a morphogenic program in this 
tissue, we have investigated the possible concerted action of EGF and HGF on the 
HC11 cell line, a widely used model of nontumorigenic mammary cells. Western 
blot analysis indicated that HC11 expressed MET and EGFR, and showed ERK1/2 and 
AKT activation following HGF or EGF treatment. Analysis by real-time PCR and 
western blot showed that after an EGF but not HGF or insulin-like growth 
factor-I treatment, HC11 mammary cells exhibited an increase in MET expression 
at both the mRNA and protein levels, which was dependent on the AKT pathway. 
Simultaneous treatment with HGF and EGF increased proliferation, scatter, and 
invasion as assessed by cell count, cell cycle, scatter, and transwell assays. 
AKT inhibition did not influence the cooperation on proliferation or invasion 
after HGF+EGF treatment, while ERK1/2 inhibition abolished MET/EGFR cooperation 
on proliferation. HGF+EGF treatment increased the duration of ERK1/2 and AKT 
activation compared to HGF or EGF alone. All these data indicate that a 
crosstalk between the EGF and HGF pathways in mammary epithelial cells may 
modulate the development of the mammary gland.