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Akt negatively regulates translation of the ternary complex factor Elk-1
Claudia Figueroa1, Anne B Vojtek
1Department of Biological Chemistry, University of Michigan, Ann Arbor, MI 48109-0606, USA.
Abstract:
Cross-talk between signaling pathways plays an important role in regulation of cell growth, differentiation, survival, and death. Here, we show that Akt regulates the Elk-1 transcription factor, independent of its negative regulation of Raf kinases. Using a constitutively active Mek1 to bypass the regulation of Raf by Akt, we find that the Elk-1 and Sap1a proteins are dramatically decreased in the presence of activated Akt. Akt catalytic activity is required. Also, Mek-dependent activation of a TCF (Elk-1/Sap-1a)-dependent c-fos reporter is decreased by activated Akt. Neither the level of Elk-1 mRNA nor the stability of the Elk-1 protein is altered by activated Akt. Instead, the rate of incorporation of labeled methionine into Elk-1 protein is decreased in the presence of Akt. In addition, the level of the Elk-1 protein but not GFP is significantly decreased in the presence of activated Akt, when GFP is expressed from an IRES element in a bicistronic message with Elk-1. We conclude that Akt negatively regulates translation of the Elk-1 mRNA. A coding region determinant that maps within the first 279 nts of the Elk-1 message is necessary and sufficient for Akt-mediated regulation of Elk-1.
Insights
Activated Akt signaling negatively regulates the Elk-1 (Elk-1) transcription factor by inhibiting its translation, not its mRNA levels or protein stability. This regulation is mediated by a specific region within the Elk-1 mRNA.
Area of Science:
- Cellular signaling pathways
- Molecular biology
- Gene regulation
Background:
- Signaling pathway cross-talk is crucial for cellular processes like growth, differentiation, survival, and death.
- The Akt signaling pathway is a key regulator in cellular functions.
Purpose of the Study:
- To investigate the regulatory mechanism of the Elk-1 transcription factor by the Akt signaling pathway.
- To determine if Akt affects Elk-1 mRNA or protein levels, stability, or translation.
Main Methods:
- Utilized constitutively active Mek1 to bypass Akt's regulation of Raf kinases.
- Assessed Elk-1 and Sap1a protein levels, Elk-1 mRNA levels, and protein stability.
- Measured Mek-dependent activation of a TCF-dependent c-fos reporter.
- Investigated protein synthesis rates using labeled methionine incorporation.
- Employed bicistronic message expression with Elk-1 and GFP.
Main Results:
- Activated Akt significantly decreased Elk-1 and Sap1a protein levels, independent of Raf kinase regulation.
- Akt's catalytic activity was essential for this regulation.
- Mek-dependent reporter activation was reduced by activated Akt.
- Neither Elk-1 mRNA levels nor protein stability were affected by Akt.
- Akt reduced the rate of labeled methionine incorporation into Elk-1, indicating translational inhibition.
- A specific coding region within the first 279 nucleotides of Elk-1 mRNA was identified as necessary and sufficient for Akt-mediated translational regulation.
Conclusions:
- Akt negatively regulates the translation of Elk-1 mRNA.
- This translational control is mediated by a specific coding region determinant within the Elk-1 transcript.