ErbB2 stabilizes epidermal growth factor receptor (EGFR) expression via Erk and Sprouty2 in extracellular matrix-detached cells

Epithelial cells are dependent on extracellular matrix (ECM) attachment for maintenance of metabolic activity and suppression of apoptosis. Here we show that loss of ECM attachment causes down-regulation of epidermal growth factor receptor (EGFR) and β1 integrin protein and mRNA expression and that ErbB2, which is amplified in 25% of breast tumors, reverses these effects of ECM deprivation. ErbB2 rescue of β1 integrin mRNA and protein in suspended cells is dependent on EGFR, however, the rescue of EGFR expression does not require β1 integrin. We show that there is a significant decrease in the stability of EGFR in ECM-detached cells that is reversed by ErbB2 overexpression. Rescue of both EGFR and β1 integrin protein by ErbB2 is dependent on Erk activity and induction of its downstream target Sprouty2, a protein known to regulate EGFR protein stability. Interestingly, expression of EGFR and β1 integrin protein is more dependent on Erk/Sprouty2 in ECM-detached ErbB2-overexpressing cells when compared with ECM-attached cells. These results provide further insight into the ErbB2-driven anchorage independence of tumor cells and provide a new mechanism for regulation of EGFR and β1 integrin expression in ECM-detached cells.