A novel Jun N-terminal kinase (JNK)-binding protein that enhances the activation of JNK by MEK kinase 1 and TGF-beta-activated kinase 1

We have identified a novel Jun N-terminal kinase (JNK)-binding protein, ter med JNKBP1, and examined its binding affinity for JNK1, JNK2, JNK3, and ext racellular signal-regulated kinase 2 (ERK2) in COS-7 cells, JNKBP1 preferen tially interacted with the JNKs, but not with ERK2, Furthermore, we investi gated the effect of overexpressing JNKBP1 on the JNK and ERK signaling path ways in COS-7 cells. JNKBP1 alone had only a marginal effect on JNK activit y. However, the activation of JNK by MEK kinase 1 and TGF-beta-activated ki nase 1 was significantly enhanced in the presence of JNKBP1. In contrast, J NKBP1 had no or very little effect on the ERK signaling pathway. These resu lts suggest that JNKBP1 functions to facilitate the specific and efficient activation of the JNK signaling pathways. (C) 1999 Federation of European B iochemical Societies.