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KSR1 is a functional protein kinase capable of serine autophosphorylation and direct phosphorylation of MEK1

Jeremy A Goettel1, Dongchun Liang, Valda C Hilliard

  • 1Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.

Experimental Cell Research
|December 15, 2010
PubMed

Insights

Kinase suppressor of Ras-1 (KSR1) is a functional protein kinase that activates the ERK/MAPK pathway. KSR1 and MEK1 catalytic activities are essential for cell survival downstream of TNF signaling.

Area of Science:

  • Cellular signaling
  • Molecular biology
  • Cancer research

Background:

  • The extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) pathway regulates cell differentiation, proliferation, and survival.
  • Kinase suppressor of Ras-1 (KSR1) facilitates ERK pathway activation but its kinase function is debated.

Purpose of the Study:

  • To investigate the hypothesis that KSR1 possesses functional protein kinase activity.
  • To determine if KSR1 directly phosphorylates MEK1.
  • To elucidate the role of KSR1's kinase activity in cell survival downstream of TNF.

Main Methods:

  • Production of recombinant wild-type and kinase-inactive KSR1 proteins in E. coli.
  • In vitro kinase assays using myelin basic protein (MBP) and MEK1 as substrates.
  • Analysis of KSR1 activity in KSR1(-/-) colon epithelial cells expressing wild-type or kinase-inactive KSR1.
  • Assessment of cell survival in response to TNF treatment.

Main Results:

  • Recombinant wild-type KSR1, but not kinase-inactive KSR1, exhibited autophosphorylation and phosphorylated MEK1 in vitro.
  • KSR1 immunoprecipitates from cells expressing wild-type KSR1 phosphorylated kinase-inactive MEK1.
  • Cells expressing wild-type KSR1 were resistant to TNF-induced apoptosis, unlike control cells or cells expressing kinase-inactive KSR1.
  • KSR1-mediated cell resistance to TNF was lost when MEK kinase activity was inhibited.

Conclusions:

  • KSR1 is a functional protein kinase.
  • MEK1 is a direct in vitro substrate of KSR1.
  • The catalytic activities of both KSR1 and MEK1 are critical for mediating cell survival responses to TNF signaling.

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