Induction of EGFR tyrosine phosphorylation by intact Ln-5. Treatment of MDA-MB-231 cells with 1.7 nM EGF for 10 min at 37°C results in significant phosphorylation of 175 kD EGFR (lane 2, left panels) over control (lane 1, no ligand), whereas 2.5 nM purified Ln-5 causes only weak EGFR phosphorylation (lane 3). Stimulation of cells for 90 min (right panels) with Ln-5 (lane 3) results in an EGFR phosphorylation signal well above control (lane 1). In contrast, incubation of cells for 90 min in the presence of EGF (lane 2) diminished the signal toward background level (lane 1).