Axin Forms a Complex with MEKK1 and Activates c-Jun NH2-terminal Kinase/Stress-activated Protein Kinase through Domains Distinct from Wnt Signaling

Abstract

Axin negatively regulates the Wnt pathway during axis formation and plays a central role in cell growth control and tumorigenesis. We found that Axin also serves as a scaffold protein for mitogen-activated protein kinase activation and further determined the structural requirement for this activation. Overexpression of Axin in 293T cells leads to differential activation of mitogen-activated protein kinases, with robust induction for c-Jun NH 2 -terminal kinase (JNK)/stress-activated protein kinase, moderate induction for p38, and negligible induction for extracellular signal-regulated kinase. Axin forms a complex with MEKK1 through a novel domain that we term MEKK1-interacting domain. MKK4 and MKK7, which act downstream of MEKK1, are also involved in Axin-mediated JNK activation. Domains essential in Wnt signaling, i.e. binding sites for adenomatous polyposis coli, glycogen synthase kinase-3␤, and ␤-catenin, are not required for JNK activation, suggesting distinct domain utilization between the Wnt pathway and JNK signal transduction. Dimerization/oligomerization of Axin through its C terminus is required for JNK activation, although MEKK1 is capable of binding C terminus-deleted monomeric Axin. Furthermore, Axin without the MEKK1-interacting domain has a dominant-negative effect on JNK activation by wild-type Axin. Our results suggest that Axin, in addition to its function in the Wnt pathway, may play a dual role in cells through its activation of JNK/stress-activated protein kinase signaling cascade.

Axin negatively affects tau phosphorylation by glycogen synthase kinase 3β

“…Plasmids for transient transfection HA-axin, HA-axin-DGID (Zhang et al 1999), and the tau (T4L) plasmid encoding for full-length human tau (441 amino acids) (Tucholski et al 1999) were described previously. HA-GSK3b was a gift from Dr J. R. Woodgett.…”

“…To determine if this may be due to the fact that axin does not effectively interact with tau, co-immunoprecipitation assays were carried out. Cells were transfected with tau, GSK3b, and either axin or axin-DGID (Zhang et al 1999), and axin was immunoprecipitated from the cell lysates and the precipitates were blotted for axin, GSK3b, b-catenin or tau (Fig. 5).…”

Differential effects of inactivated Axin1 and activated β-catenin mutations in human hepatocellular carcinomas

“…Axin1 is a master scaffolding protein that can be a negative regulator of the Wnt pathway, but a positive regulator of the JNK, TGFb and p53 pathways (Zhang et al, 1999(Zhang et al, , 2000Furuhashi et al, 2001;Rui et al, 2004). Axin1 may thus act as a tumor suppressor by negatively controlling the Wnt pathway, and by facilitating JNK, TGFb signaling or p53 function in the liver.…”

The DIX Domain Protein Coiled-coil-DIX1 Inhibits c-Jun N-terminal Kinase Activation by Axin and Dishevelled through Distinct Mechanisms

“…It is interesting that Axin and Dvl both activate the c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SPAK) when overexpressed in a variety of cells even though they utilize different mechanisms for JNK activation (12,13). Axin and Dvl discriminate distinct pathways by differential domain utilizations (13)(14)(15).…”