A transforming Src mutant increases the bioavailability of EGFR ligands via stimulation of the cell-surface metalloproteinase ADAM17.

ADAM17 (a disintegrin and metalloproteinase 17, also referred to as TNFα converting enzyme or TACE) is a cell-surface metalloproteinase that regulates signaling via the epidermal growth factor receptor (EGFR) and has important roles in diseases such as cancer and rheumatoid arthritis. ADAM17 can be activated by stimulation of several tyrosine kinase receptors, raising questions about whether oncogenic tyrosine kinases could also enhance EGFR signaling and activation of extracellular signal-regulated kinase (ERK) via stimulation of ADAM17. The main goal of this study was to evaluate the role of Src in activating ADAM17. We provide evidence that a constitutively active transforming form of Src, the E378G mutant, as well as v-Src enhance ADAM17-mediated shedding of the EGFR ligand TGFα. Moreover, we demonstrate that constitutive shedding of TGFα can be reduced by inhibition of Src in several cell lines, including COS7, MCF7 (the human breast cancer cell line), PAE (a pig aortic endothelial cell line) and HaCaT (the human keratinocyte cell line) cells. Src(E378G)-stimulated shedding of TGFα is abolished in Adam17(-/-) cells, but can be rescued by wild-type (wt) ADAM17 and a mutant ADAM17 lacking its cytoplasmic domain. These findings demonstrate that ADAM17 is the principal TGFα sheddase that is activated by Src in a manner that does not require the cytoplasmic domain of ADAM17. Finally, we show that stimulation of ADAM17 by Src(E378G) leads to enhanced paracrine signaling via release of EGFR ligands into the culture supernatant. These results raise the possibility that activation of ADAM17 by oncogenic forms of Src can aid in promoting tumorigenesis by enhancing signaling via the EGFR and ERK in an autocrine and paracrine manner. Enhanced autocrine signaling could further activate tumor cells expressing oncogenic mutants of Src, whereas paracrine signaling could stimulate EGFR and ERK signaling in surrounding non-transformed cells such as stromal cells, thereby contributing to crosstalk between tumor cells and stromal cells.