The coordinated activity of
estrogens and
epidermal growth factor receptor (EGFR) family agonists represents the main determinant of
breast cancer cell proliferation. Stromal cell-derived factor-1 (SDF-1) enhances
extracellular signal-regulated kinases 1 and 2 (ERK1/2) activity via the transactivation of EGFR and 17beta-estradiol (E2) induces SDF-1 production to exert autocrine proliferative effects. On this basis, we evaluated whether the inhibition of the
tyrosine kinase (TK) activity of EGFR may control different mitogenic stimuli in
breast tumors using the EGFR-TK inhibitor
gefitinib to antagonize the proliferation induced by E2 in T47D human
breast cancer cells.
EGF, E2, and SDF-1 induced a dose-dependent T47D cell proliferation, that being nonadditive suggested the activation of common intracellular pathways.
Gefitinib treatment inhibited not only the
EGF-dependent proliferation and ERK1/2 activation but also the effects of SDF-1 and E2, suggesting that these activities were mediated by EGFR transactivation. Indeed, both SDF-1 and E2 caused EGFR
tyrosine phosphorylation. The molecular link between E2 and SDF-1 proliferative effects was identified because 1,1'-(1,4-phenylenebis(methylene))-bis-1,4,8,11-tetraazacyclotetradecane octahydrochloride (
AMD3100), a CXCR4 antagonist, inhibited SDF-1- and E2-dependent proliferation and EGFR and ERK1/2 phosphorylation. EGFR transactivation was dependent on c-Src activation. E2 treatment caused a powerful SDF-1 release from T47D cells. Finally, in SKBR3, E2-resistant cells, EGFR was constitutively activated, and
AMD3100 reduced EGFR phosphorylation and cell proliferation, whereas HER2-neu was transactivated by SDF-1 in SKBR3 but not in T47D cells. In conclusion, we show that activation of CXCR4 transduces proliferative signals from the E2 receptor to EGFR, whose inhibition is able to revert
breast cancer cell proliferation induced by multiple receptor activation.