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Raf-independent, PP2A-dependent MEK activation in response to ERK silencing

Dongsoon Bae1, Susan Ceryak

  • 1Department of Pharmacology and Physiology, The George Washington University, Washington, DC 20037, USA.

Biochemical and Biophysical Research Communications
|May 26, 2009
PubMed

Insights

Silencing ERK1/2 in human lung fibroblasts revealed a feedback loop. ERK isoform silencing increased alternate ERK phosphorylation, and combined silencing led to MEK hyperactivation via PP2A downregulation.

Area of Science:

  • Cellular signaling
  • Molecular biology
  • Signal transduction pathways

Background:

  • The biological roles of Extracellular signal-regulated kinases (ERK) and Mitogen-activated protein kinase kinases (MEK) in cellular signaling are not fully understood.
  • The ERK-MAPK cascade is crucial for various cellular processes, but the specific functions of ERK isoforms remain debated.

Purpose of the Study:

  • To elucidate the precise role of ERK1/2 in the ERK-MAPK cascade signaling.
  • To investigate the interplay between ERK isoforms and MEK activation using RNA interference (RNAi).

Main Methods:

  • Utilized RNAi methodology, specifically transient transfection of erk1 or erk2 siRNA in human lung fibroblasts.
  • Quantified protein levels and phosphorylation status of ERK1/2 and MEK following siRNA-mediated gene silencing.

Main Results:

  • Individual silencing of ERK1 or ERK2 siRNA reduced respective protein levels to 3-8% and caused a reciprocal 2-fold increase in the phosphorylation of the alternate ERK isoform.
  • Combined silencing of ERK1 and ERK2 led to MEK hyperphosphorylation, while individual silencing did not affect MEK.
  • MEK hyperactivation was linked to Protein Phosphatase 2A (PP2A) downregulation, independent of Raf family member activation.

Conclusions:

  • ERK isoform silencing triggers a feedback mechanism involving decreased PP2A activity.
  • This feedback loop results in consequent MEK activation when ERK1/2 signaling is suppressed in normal cells.

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