Abstract
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 17β-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.
Footnotes
-
This work was supported by a research grant from Astra-Zeneca (Milano, Italy) and Italian Association for Cancer Research.
-
ABBREVIATIONS: ER, estrogen receptor; E2, 17β-estradiol; EGF, epidermal growth factor; EGFR, epidermal growth factor receptor; FBS, fetal bovine serum; GPCR, G protein-coupled receptors; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5, diphenyl tetrazolium bromide; SDF-1, stromal cell derived factor-1; PP1, 4-amino-5-methylphenyl-7-(t-buthyl)pyrazolo 3,4-[d]pyrimidine; TK, tyrosine kinase; AMD3100, 1,1′-(1,4-phenylenebis-(methylene))bis-1,4,8,11-tetraazacyclotetradecane octahydrochloride; MEK, mitogen-activated protein kinase kinase; DMEM, Dulbecco's modified Eagle's medium; dn, dominant negative; DMSO, dimethyl sulfoxide; ELISA, enzyme-linked immunosorbent assay; ERK1/2, extracellular signal-regulated kinases 1 and 2; PD98059, 2′-amino-3′-methoxyflavone; ICI 128,436, 3-(4-bromo-2-fluorobenzyl)-3,4-dihydro-4-oxo-1-phthalazineacetic acid; AZD0530, 4-(6-chloro-2,3-methylenedioxyanilino)-7-(2-(4-methylpiperazin-1-yl)ethoxy)-5-tetrahydropyran-4-yloxyquinazoline.
- Received July 18, 2007.
- Accepted October 23, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|