title: Protein phosphatase 2A (PP2A) holoenzymes regulate death-associated protein kinase (DAPK) in ceramide-induced anoikis.
abstract: The tumor suppressor, death-associated protein kinase (DAPK), is a Ca(2+)/calmodulin-regulated Ser/Thr kinase with an important role in regulating cytoskeletal dynamics. Autophosphorylation within the calmodulin-binding domain at Ser-308 inhibits DAPK catalytic activity. Dephosphorylation of Ser-308 by a previously unknown phosphatase enhances kinase activity and proteasome-mediated degradation of DAPK. In these studies, we identified two holoenzyme forms of protein phosphatase 2A (PP2A), ABalphaC and ABdeltaC, as DAPK-interacting proteins. These phosphatase holoenzymes dephosphorylate DAPK at Ser-308 in vitro and in vivo resulting in enhanced kinase activity of DAPK. The enzymatic activity of PP2A also negatively regulates DAPK levels by enhancing proteasome-mediated degradation of the kinase. Overexpression of wild type DAPK induces cell rounding and detachment in HEK293 cells; however, this effect is not observed following expression of an inactive DAPK S308E mutant. Finally, activation of DAPK by PP2A was found to be required for ceramide-induced anoikis. Together, our results provide a mechanism by which PP2A and DAPK activities control cell adhesion and anoikis.
authors.affiliation: Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
authors.forename: Ryan C
authors.initials: RC
authors.lastname: Widau
authors.forename: Yijun
authors.initials: Y
authors.lastname: Jin
authors.forename: Shelley A
authors.initials: SA
authors.lastname: Dixon
authors.forename: Brian E
authors.initials: BE
authors.lastname: Wadzinski
authors.forename: Patricia J
authors.initials: PJ
authors.lastname: Gallagher
mesh_terms: D019943:Amino Acid Substitution; D023102:Anoikis / Q000187:drug effects* / Q000235:genetics; D051017:Apoptosis Regulatory Proteins; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002448:Cell Adhesion / Q000187:drug effects / Q000235:genetics; D002518:Ceramides / Q000494:pharmacology*; D003599:Cytoskeleton / Q000235:genetics / Q000378:metabolism; D064550:Death-Associated Protein Kinases; D006367:HeLa Cells; D020035:Holoenzymes / Q000235:genetics / Q000378:metabolism; D006801:Humans; D020125:Mutation, Missense; D010766:Phosphorylation / Q000187:drug effects / Q000235:genetics; D054648:Protein Phosphatase 2 / Q000235:genetics / Q000378:metabolism*; D025521:Tumor Suppressor Proteins
chemical_list: D051017:Apoptosis Regulatory Proteins; D002518:Ceramides; D020035:Holoenzymes; D025521:Tumor Suppressor Proteins; D064550:Death-Associated Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D054648:Protein Phosphatase 2