Insights into the structural basis of the GADD45β-mediated inactivation of the JNK kinase, MKK7/JNKK2

NF-kappa B/Rel factors control programmed cell death (PCD), and this control is crucial to oncogenesis, cancer chemoresistance, and antagonism of tumor necrosis factor (TNF) alpha-induced killing. With TNF alpha, NF-kappa B-mediated protection involves suppression of the c-Jun-N-terminal kinase (JNK) cascade, and we have identified Gadd45 beta, a member of the Gadd45 family, as a pivotal effector of this activity of NF-kappa B. Inhibition of TNF alpha-induced JNK signaling by Gadd45 beta depends on direct targeting of the JNK kinase, MKK7/JNKK2. The mechanism by which Gadd45 beta blunts MKK7, however, is unknown. Here we show that Gadd45 beta is a structured protein with a predicted four-stranded beta-sheet core, five alpha-helices, and two acidic loops. Association of Gadd45 beta with MKK7 involves a network of interactions mediated by its putative helices alpha 3 and alpha 4 and loops 1 and 2. Whereas alpha 3 appears to primarily mediate docking to MKK7, loop 1 and alpha 4-loop 2 seemingly afford kinase inactivation by engaging the ATP-binding site and causing conformational changes that impede catalytic function. These data provide a basis for Gadd45 beta-mediated blockade of MKK7, and ultimately, TNF alpha-induced PCD. They also have important implications for treatment of widespread diseases.