Cyclic AMP-dependent protein kinase phosphorylates merlin at serine 518 independently of p21-activated kinase and promotes merlin-ezrin heterodimerization

J Biol Chem. 2004 Apr 30;279(18):18559-66. doi: 10.1074/jbc.M313916200. Epub 2004 Feb 23.

Abstract

Mutations in the NF2 tumor suppressor gene encoding merlin induce the development of tumors of the nervous system. Merlin is highly homologous to the ERM (ezrin-radixin-moesin) family of membrane/cytoskeleton linker proteins. However, the mechanism for the tumor suppressing activity of merlin is not well understood. Previously, we characterized a novel role for merlin as a protein kinase A (PKA)-anchoring protein, which links merlin to the cAMP/PKA signaling pathway. In this study we show that merlin is also a target for PKA-induced phosphorylation. In vitro [gamma-(33)P]ATP labeling revealed that both the merlin N and C termini are phosphorylated by PKA. Furthermore, both in vitro and in vivo phosphorylation studies of the wild-type and mutated C termini demonstrated that PKA can phosphorylate merlin at serine 518, a site that is phosphorylated also by p21-activated kinases (PAKs). Merlin was phosphorylated by PKA in cells in which PAK activity was suppressed, indicating that the two kinases function independently. Both in vitro and in vivo interaction studies indicated that phosphorylation of serine 518 promotes heterodimerization between merlin and ezrin, an event suggested to convert merlin from a growth-suppressive to a growth-permissive state. This study provides further evidence on the connection between merlin and cAMP/PKA signaling and suggests a role for merlin in the cAMP/PKA transduction pathway.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Binding Sites
  • Cell Line
  • Cyclic AMP-Dependent Protein Kinase Catalytic Subunits
  • Cyclic AMP-Dependent Protein Kinases / metabolism*
  • Cytoskeletal Proteins
  • Dimerization
  • Humans
  • Isoenzymes / metabolism*
  • Neurofibromin 2 / genetics
  • Neurofibromin 2 / metabolism*
  • Phosphoproteins / metabolism*
  • Phosphorylation
  • Protein Serine-Threonine Kinases
  • Serine / metabolism
  • Signal Transduction
  • Transfection
  • p21-Activated Kinases

Substances

  • Cytoskeletal Proteins
  • Isoenzymes
  • Neurofibromin 2
  • Phosphoproteins
  • ezrin
  • Serine
  • Protein Serine-Threonine Kinases
  • p21-Activated Kinases
  • Cyclic AMP-Dependent Protein Kinase Catalytic Subunits
  • Cyclic AMP-Dependent Protein Kinases
  • protein kinase A Calpha