The epidermal growth factor receptor (EGFR) is frequently expressed in triple-negative breast cancer (TNBC) and is a marker of poor prognosis in this patient population. Because activating mutations in this kinase are very rare events in breast cancer, we screened breast tumor gene expression profiles to examine the distribution of EGFR ligand expression. Of the six known EGFR ligands, transforming growth factor alpha (TGFα) was expressed more highly in triple-negative breast tumors than in tumors of other subtypes. TGFα is synthesized as a transmembrane precursor requiring tumor necrosis factor alpha converting enzyme (TACE)/ADAM17-dependent proteolytic release to activate its receptor. In our study, we show that an inhibitor of this proteolytic release blocks invasion, migration and colony formation by several TNBC cell lines. Each of the effects of the drug was reversed upon expression of a soluble TGFα mutant that does not require TACE activity, implicating this growth factor as a key metalloproteinase substrate for these phenotypes. Together, these data demonstrate that TACE-dependent TGFα shedding is a key process driving EGFR activation and subsequent proliferation and invasion in TNBC cell lines.
Keywords: TACE/ADAM17; epidermal growth factor receptor; transforming growth factor alpha; triple-negative breast cancer.
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