Figure 3.

Both JNK1 and JNK2 are phosphorylated but only JNK1 exhibits c-Jun kinase activity on ConA/GalN treatment. A–B: Mice were treated and liver lysates were prepared as in Figure 2. Immunoblot assay was conducted using antibodies against phosphorylated JNK (p-JNK) and total JNK. Note that the majority of JNK1 are 46 kDa and the majority of JNK2 are 54KD as indicated. The minor band around 46 kDa seen in JNK1−/− liver represents the p46 isoform of JNK2. Conversely, the minor band around 54 kDa seen in JNK2−/− liver represents the p54 isoform of JNK1. Phosphorylated JNK could be both the major and the minor forms of JNK1 or JNK2 and are thus not specified other than the molecular weight. β-actin is 46 kDa. Asterisks indicated non-specific bands. C–D: The same cytosolic fraction was used for the in vitro JNK kinase assay with GST-c-Jun as the substrate. Phosphorylation of c-Jun by JNK was determined using the antibody against phosphorylated c-Jun (p-c-Jun, 35 kDa). The same membranes were immunoblotted with an anti-c-Jun antibody to confirm the protein loading.