Fig. 7.

Activation of JNK in C2C12 myotubes by neuregulin. C2C12 myotubes were stimulated with 1 nm neuregulin for the indicated times (A) or with various concentrations of neuregulin for 10 min (B) and then harvested in the lysis buffer. To purify JNK, we incubated an aliquot of lysate with agarose beads containing the GST–c-JUN fusion protein at 4°C for 2 hr. After washing, the beads were incubated in the kinase assay buffer containing [γ-³²P]ATP at 30°C for 15 min. The kinase reaction was stopped by the addition of the sample-loading buffer and subjected to electrophoresis on a 10% SDS-polyacrylamide gel. Shown are means ± SD of five different samples. The JNK activity levels in the absence of neuregulin were considered to be 100%. The inset of eachpanel shows a representative radiogram. *p < 0.05; **p < 0.01.