Fig. 2

Characterization of heregulin-induced kinase activation in rat SCs. a-b Heregulin-induction of ERK phosphorylation in adult nerve-derived rat SCs as evidenced by immunofluorescence microscopy (a, 10 min post-stimulation) and Western blot (b, as indicated). c-d Heregulin-elicited rat SC proliferation as evidenced by BrdU incorporation (c) and induction of MCM2 expression (Western blot, d). Note the delay between the onset of MCM2 expression and the peaks of ErbB3, ERK and Akt phosphorylation (d). e,f Activity and specificity of RTK-induced signaling in response to assorted growth factors and serum at two early time points, as indicated. Note that β1-heregulin elicits the most potent and long-lasting activating signal when compared to other growth factors, serum and cAMP-stimulating agents. g-i Effect of a pharmacological ErbB inhibitor (ErbBi) on heregulin-induced SC proliferation (BrdU incorporation, g), ErbB3 tyrosine phosphorylation (h) and ERK activation (i). An antibody against total P-tyrosine (P-Tyr) was used to reveal generic changes associated with RTK activation in rat SCs (e-f and h). The phorbol ester PMA was used as a positive control for receptor-independent, PKC-mediated MEK and ERK phosphorylation (e,f). In panel d, the time course of expression of MCM2 is shown to confirm the expected β1-heregulin-associated changes in cell cycle progression under the same conditions used for kinase stimulation in the same batch of rat SCs. The β1-heregulin peptide was provided at 10 nM in all experiments