GSK3β Is Involved in JNK2-Mediated β-Catenin Inhibition

Background: We have recently reported that mitogen-activated protein kinase(MAPK) JNK1 downregulates beta-catenin signaling and plays a critical role in regulating intestinal homeostasis and in suppressing tumor formation. This study was designed to determine whether JNK2, another MAPK, has similar and/or different functions in the regulation of beta-catenin signaling. Methodology and Principal Findings: We used an in vitro system with manipulation of JNK2 and beta-catenin expression and found that activated JNK2 increased GSK3 beta activity and inhibited beta-catenin expression and transcriptional activity. However, JNK2-mediated downregulation of beta-catenin was blocked by the proteasome inhibitor MG132 and GSK3 beta inhibitor lithium chloride. Moreover, targeted mutations at GSK3 beta phosphorylation sites(Ser33 and Ser37) of beta-catenin abrogated JNK2-mediated suppression of beta-catenin. In vivo studies further revealed that JNK2 deficiency led to upregulation of beta-catenin and increase of GSK3-beta phosphorylation in JNK2-/- mouse intestinal epithelial cells. Additionally, physical interaction and co-localization among JNK2, beta-catenin and GSK3 beta were observed by immunoprecipitation, mammalian two-hybridization assay and confocal microscopy, respectively. Conclusion and Significance: In general, our data suggested that JNK2, like JNK1, interacts with and suppresses beta-catenin signaling in vitro and in vivo, in which GSK3 beta plays a key role, although previous studies have shown distinct functions of JNK1 and JNK2. Our study also provides a novel insight into the crosstalk between Wnt/beta-catenin and MAPK JNKs signaling.