HER2 expression defines unique requirements for flotillin and c-Src for EGFR signaling.

The epidermal growth factor receptor (EGFR) controls many cellular functions. Upon binding its ligand, the receptor undergoes dimerization, phosphorylation, and activation of signals including the phosphatidylinositol-3-kinase (PI3K)-Akt pathway. While some studies indicated that EGFR signaling may be controlled by signal enrichment within various membrane rafts such as flotillin nanodomains, others have found a limited effect of disruption of these nanodomains on EGFR signaling, suggesting that specific factor(s) may define context-specific control of EGFR signaling. Ligand-bound EGFR can homodimerize, or instead undergo heterodimerization with the related receptor HER2 when the latter is expressed. We examined how EGFR signaling in the presence of HER2 distinctly requires flotillin nanodomains. Induction of HER2 expression altered EGFR signaling duration consistent with EGFR/HER2 heterodimer formation. EGFR and c-Src localized within plasma membrane structures demarked by flotillin-1 more prominently in HER2-expressing cells. Consistently, HER2-expressing cells, but not cells lacking HER2, were dependent on flotillin-1 and c-Src for EGFR signaling leading to Akt activation and cell proliferation. Hence, HER2 expression establishes a requirement of EGFR signaling for flotillin membrane rafts and c-Src.