Activation of ERM proteins in vivo by Rho involves phosphatidyl-inositol 4-phosphate 5-kinase and not ROCK kinases

Curr Biol. 1999 Nov 4;9(21):1259-62. doi: 10.1016/s0960-9822(99)80508-9.


When activated, ERM (ezrin, radixin, moesin) proteins are recruited to the plasma membrane, with concomitant carboxy-terminal threonine phosphorylation, where they crosslink actin filaments to the plasma membrane to form microvilli (reviewed in [1] [2] [3] [4] [5]). Here, we report that, when NIH3T3 or HeLa cells were transfected with a constitutively active mutant of the small GTPase RhoA (V14RhoA), microvilli were induced and the level of carboxy-terminal threonine-phosphorylated ERM proteins (CPERM) [6] [7] increased approximately 30-fold. This increase was not observed following transfection of constitutively active forms of two other Rho-family GTPases, Rac1 and Cdc42, or of a direct effector of Rho, Rho-kinase (also known as ROKalpha or ROCK-II) [8] [9] [10]. The V14RhoA-induced phosphorylation of ERM proteins was not suppressed by Y-27632, a specific inhibitor of ROCK kinases including Rho-kinase [11]. Overexpression of another direct effector of Rho, phosphatidylinositol 4-phosphate 5-kinase (PI4P5K) type Ialpha [12] [13] [14], but not a kinase-inactive mutant [15], increased approximately sixfold the level of CPERM, and induced microvilli. Together with the previous finding that the PI4P5K product phosphatidylinositol 4,5-bisphosphate (PIP(2)) activates ERM proteins in vitro [16], our data suggest that PIP(2), and not ROCK kinases, is involved in the RhoA-dependent activation of ERM proteins in vivo. The active state of ERM proteins is maintained through threonine phosphorylation by as yet undetermined kinases, leading to microvillus formation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3T3 Cells
  • Animals
  • Blood Proteins / metabolism*
  • Cytoskeletal Proteins*
  • HeLa Cells
  • Humans
  • Intracellular Signaling Peptides and Proteins
  • Membrane Proteins / metabolism*
  • Mice
  • Microfilament Proteins / metabolism*
  • Microvilli / physiology
  • Phosphoproteins / metabolism*
  • Phosphorylation
  • Phosphotransferases (Alcohol Group Acceptor) / metabolism*
  • Protein-Serine-Threonine Kinases / metabolism*
  • Threonine / metabolism
  • Transfection
  • rho-Associated Kinases
  • rhoA GTP-Binding Protein / metabolism*


  • Blood Proteins
  • Cytoskeletal Proteins
  • Intracellular Signaling Peptides and Proteins
  • Membrane Proteins
  • Microfilament Proteins
  • Phosphoproteins
  • ezrin
  • moesin
  • radixin
  • Threonine
  • Phosphotransferases (Alcohol Group Acceptor)
  • 1-phosphatidylinositol-4-phosphate 5-kinase
  • Protein-Serine-Threonine Kinases
  • rho-Associated Kinases
  • rhoA GTP-Binding Protein