title: Phosphoprotein phosphatase-2A docks to Dishevelled and counterregulates Wnt3a/beta-catenin signaling.
abstract: BACKGROUND
  Wnt3a stimulates cellular trafficking of key signaling elements (e.g., Axin, Dishevelled-2, beta-catenin, and glycogen synthase kinase-3beta) and primitive endoderm formation in mouse F9 embryonic teratocarcinoma cells.
  
  
  RESULTS
  The role of phosphoprotein phosphatase-2A in signaling of the Wnt/beta-catenin/Lef-Tcf-sensitive gene activation pathway was investigated. Wnt3a action attenuates phosphoprotein phosphatase-2A activity and stimulates the Lef/Tcf-sensitive gene transcription. Inhibiting phosphoprotein phosphatase-2A by okadaic acid, by treatment with siRNA (targeting the C-subunit of the enzyme), or by expression of SV40 small t antigen mimics Wnt3a action, increasing the cellular abundance of Axin and phospho-glycogen synthase kinase-3beta as well as the trafficking of signaling elements in the Wnt/beta-catenin pathway. Although mimicking effects of Wnt3a on the cellular abundance and trafficking of key signaling elements in the Wnt canonical pathway, suppression of phosphatase-2A alone did not provoke activation of the Lef/Tcf-sensitive transcriptional response, but did potentiate its activation by Wnt3a. Phosphoprotein phosphatase-2A and the scaffold phosphoprotein Dishevelled-2 display similarities in cellular trafficking in response to either Wnt3a or suppression of the phosphatase. A docking site for phosphoprotein phosphatase-2A in the DEP domain of Dishevelled-2 was identified.
  
  
  CONCLUSIONS
  In current study, we showed new roles of phosphoprotein phosphatase-2A in Wnt/beta-catenin signaling pathway: effect on protein expression, effect on protein trafficking, retention of molecules in subcellular compartments, and regulation of enzymatic activity of several key players. Docking of phosphoprotein phosphatase-2A by Dishevelled-2 suppresses phosphatase activity and explains in part the central role of this phosphatase in the counterregulation of the Wnt/beta-catenin signaling pathway.
authors.affiliation: Department of Pharmacology, Health Sciences Center, State University of New York at Stony Brook, Stony Brook, NY 11794-8651, USA. noriko@pharm.stonybrook.edu.
authors.forename: Noriko
authors.initials: N
authors.lastname: Yokoyama
authors.forename: Craig C
authors.initials: CC
authors.lastname: Malbon