Distinct Phosphotyrosine-dependent Functions of the ShcA Adaptor Protein Are Required for Transforming Growth Factor β (TGFβ)-induced Breast Cancer Cell Migration, Invasion, and Metastasis

The ErbB2 and TGFβ signaling pathways cooperate to promote the migratory, invasive, and metastatic behavior of breast cancer cells. We previously demonstrated that ShcA is necessary for these synergistic interactions. Through a structure/function approach, we now show that the phosphotyrosine-binding, but not the Src homology 2, domain of ShcA is required for TGFβ-induced migration and invasion of ErbB2-expressing breast cancer cells. We further demonstrate that the tyrosine phosphorylation sites within ShcA (Tyr239/Tyr240 and Tyr313) transduce distinct and non-redundant signals that promote these TGFβ-mediated effects. We demonstrate that Grb2 is required specifically downstream of Tyr313, whereas the Tyr239/Tyr240 phosphorylation sites require the Crk adaptor proteins to augment TGFβ-induced migration and invasion. Furthermore, ShcA Tyr313 phosphorylation enhances tumor cell survival, and ShcA Tyr239/Tyr240 signaling promotes endothelial cell recruitment into ErbB2-expressing breast tumors in vivo, whereas all three ShcA tyrosine residues are required for efficient breast cancer metastasis to the lungs. Our data uncover a novel ShcA-dependent signaling axis downstream of TGFβ and ErbB2 that requires both the Grb2 and Crk adaptor proteins to increase the migratory and invasive properties of breast cancer cells. In addition, signaling downstream of specific ShcA tyrosine residues facilitates the survival, vascularization, and metastatic spread of breast tumors. Background: ShcA integrates TGFβ and ErbB2 signaling in breast cancer. Results: Distinct motifs within ShcA facilitate TGFβ-induced effects in ErbB2-expressing cells. Conclusion: ShcA transduces distinct signals via Grb2 downstream of Tyr313 and Crk adaptors downstream of Tyr239/Tyr240, and all three residues are required for metastasis. Significance: ShcA is essential for the tumorigenesis and metastasis of ErbB2-expressing breast tumors with active TGFβ signaling.