FIG. 3.

16E5 and bafilomycin A₁ enhance ligand-dependent EGFR activation. (A) Recombinant human EGF (100 ng/ml; Invitrogen) was prebound to EGF-starved HFKs expressing 16E5 (or harboring the empty pLXSN expression vector) for 60 min at 4°C. The levels of EGFR tyrosine phosphorylation subsequently were determined before (0 min) and up to 150 min after warming to 37°C using anti-phosphotyrosine immunoblots (IB) of EGFR immunoprecipitates (IP). For LXSN (+BfA), 0.33 μM bafilomycin A₁ was added to LXSN-HFKs as they were shifted to 37°C. Molecular mass marker (in kilodaltons) is shown on the right. (B) Quantitative analysis of panel A using densitometry.