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Background: There is growing evidence that integrins can cooperate with receptor protein tyrosine kinases (RPTKs) to transduce signals important for cell proliferation, survival, and migration. Not only do integrins and RPTKs act on parallel pathways to synergize ligand-induced responses, but growth factors have been shown to regulate integrin signaling, and certain pathways downstream of RPTKs are integrin dependent. Some aspects of epidermal growth factor receptor (EGFR) signaling in particular require integrin ligation, and EGF has been shown specifically to modulate integrin signaling. The α6β4 integrin appears to be important for tumor cell growth, survival, motility and invasion in breast carcinoma. MDA-MB-231 breast carcinoma cells have high α6β4 expression, and they are also known to have upregulated EGFR. We previously reported that cross-linking of the α6β4 integrin on MDA-MB-231 cells in suspension results in clustering of cell surface α6β4. We now report the effect of adhesion-independent α6β4 integrin cross-linking on EGFR distribution in breast carcinoma cells. Methods: Immunofluorescence microscopy was performed with FITC-labeled rat anti-EGFR on MDA-MB-231 cells treated with mouse anti-β4 on ice for 40 min, followed by rabbit anti-mouse IgG to induce cross-linking of β4 at 37°C for 30 min. Breast carcinoma cells isolated from surgical resection specimens were similarly treated with anti-β4 on ice for 40 min, followed by anti-IgG for 30 min at 37°C, and EGFR distribution was evaluated by immunofluorescence. Cross-linking of EGFR was performed as a control, and the effect of β4 cross-linking on the distribution of β1 integrins was also evaluated. Results: Cross-linking of the α6β4 integrin not only induced clustering of α6β4 but also induced clustering of EGFR. Cross-linking of EGFR produced no change in EGFR distribution. Moreover, in contrast to the clustering of α6β4 and EGFR observed after cross-linking cell surface α6β4, no change in the distribution of β1 integrins was observed. Of 36 breast carcinoma specimens with sufficient cellularity and viability to evaluate α6β4 and EGFR clustering after treatment, 16 (44%) underwent α6β4 clustering, and 12 (33%) underwent α6β4-induced EGFR clustering. Conclusion: These findings provide additional evidence of α6β4-EGFR crosstalk in breast carcinoma cell lines and breast carcinoma specimens. Integrin and EGFR signaling pathways in breast carcinoma specimens may be modulated by integrin-EGFR crosstalk.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]