FIGURE 4.

Activation of Erk1/2 signaling by FL Reelin is independent of the ApoER2/VLDLR-Dab1 canonical pathway. A, Western blot analysis of Reelin-treated 5 DIV cortical neurons in the presence or absence of pharmacological inhibitors. The induction of phospho-Akt by Reelin was not affected by the MEK inhibitor U0126, but was abolished by the PI3K inhibitor LY294002 (30 μm) and by the SFK inhibitor PP2 (10 μm). The induction of phospho-Erk1/2 by Reelin was abolished by U0126 (10 μm) and PP2, but was not affected by LY294002. B, data were quantified from 4–5 independent experiments. C, WT and Dab1 KO cortical neurons were cultured for 5 DIV. FL Reelin induced Akt phosphorylation in WT cortical neurons, but not in Dab1-deficient neurons. Reelin-induced Erk1/2 phosphorylation in both, WT and Dab1 KO neurons. D, data were quantified from n = 3 WT, n = 5 KO independent cultures. E, binding to ApoER2/VLDLR receptors is not required for Reelin-induced Erk1/2 activation. Cortical neurons were treated with FL Reelin in the presence or absence of GST-bound lipoprotein receptor antagonist (RAP) or GST alone as control. Both proteins were added at the 50 μg/ml concentration 15 min prior to Reelin exposure. Akt activation by FL Reelin was completely blocked by RAP, whereas Erk1/2 activation was not affected. F, data were quantified from three independent experiments. G, diagram of the targets of the pharmacological inhibitors used in these experiments. All graphs show mean ± S.E.