FIG. 7.

Functional role of MEKK2 PB1 domain in JNK and ERK5 activation. (A) MEKK2 regulates both JNK and ERK5 activation. MEKK2^−/− MEF cells stably expressing empty vector or WT-MEKK2 which had been serum starved for 8 h were treated with 100 mM sorbitol for the indicated time periods. The activation of ERK5, ERK1/2, JNK, and p38 was measured with anti-phospho-specific Ab for each molecule (left). The total protein expression of each molecule was shown on the right. (B) The ⁴⁷K-A MEKK2 mutant abrogates the activation of ERK5 but enhances JNK activation. After serum starvation, MEKK2^−/− MEF cells stably expressing WT or ⁴⁷K-A MEKK2 were treated with 100 mM sorbitol for the indicated time periods. The cells collected were subjected to immunoblotting with anti-phospho-ERK5 and -JNK Abs. Total ERK5 or JNK expression was used to confirm the loading of equal amounts. MEKK2 expression is shown in the bottom panel.