Disruption of PKB signaling restores polarity to cells lacking tumor suppressor PTEN

Mol Biol Cell. 2011 Feb 15;22(4):437-47. doi: 10.1091/mbc.E10-06-0522. Epub 2010 Dec 17.

Abstract

By limiting phosphotidylinositol 3,4,5-triphosphate (PIP(3)) levels, tumor suppressor PTEN not only controls cell growth but also maintains cell polarity required for cytokinesis and chemotaxis. To identify the critical targets of PIP(3) that link it to the cytoskeleton, we deleted secondary genes to reverse the deficiencies of pten- cells in Dictyostelium. The polarity defects in pten- cells correlate with elevated phosphorylations of PKB substrates. Deletion of AKT orthologue, PkbA, or a subunit of its activator TORC2, reduced the phosphorylations and suppressed the cytokinesis and chemotaxis defects in pten- cells. In these double mutants, the excessive PIP(3) levels and, presumably, activation of other PIP(3)-binding proteins had little or no effect on the cytoskeleton. In bands with increased phosphorylation in pten- cells, we found PKB substrates, PI5K, GefS, GacG, and PakA. Disruption of PakA in pten- cells restored a large fraction of the cells to normal behavior. Consistently, expression of phosphomimetic PakA in pten- cells exacerbated the defects but nonphosphorylatable PakA had no effect. Thus, among many putative PTEN- and PIP(3)-dependent events, phosphorylation of PKB substrates is the key downstream regulator of cell polarity.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Cycle Proteins / metabolism
  • Cell Polarity / genetics*
  • Chemotaxis / genetics
  • Cyclic AMP / chemistry
  • Cytoskeleton / genetics
  • Cytoskeleton / metabolism
  • Dictyostelium / cytology
  • Dictyostelium / genetics
  • Dictyostelium / physiology
  • Gene Deletion
  • PTEN Phosphohydrolase / genetics*
  • PTEN Phosphohydrolase / metabolism
  • Phosphatidylinositol 3-Kinases / genetics
  • Phosphorylation
  • Protein Serine-Threonine Kinases / genetics
  • Protein Serine-Threonine Kinases / metabolism*
  • Proto-Oncogene Proteins c-akt / genetics*
  • Proto-Oncogene Proteins c-akt / metabolism*
  • Saccharomyces cerevisiae Proteins / metabolism
  • Signal Transduction
  • Tumor Suppressor Proteins / genetics
  • Tumor Suppressor Proteins / metabolism*

Substances

  • Cell Cycle Proteins
  • MEC3 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Tumor Suppressor Proteins
  • Cyclic AMP
  • PAKa protein, Dictyostelium discoideum
  • Protein Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • PTEN Phosphohydrolase
  • PTEN protein, human