Eukaryotic elongation factor 2 kinase activity is controlled by multiple inputs from oncogenic signaling

Area of Science:

• Cellular Biology
• Molecular Oncology
• Signal Transduction

Background:

• Eukaryotic elongation factor 2 kinase (eEF2K) is a calmodulin-dependent kinase that inhibits protein synthesis by phosphorylating eEF2.
• eEF2K is upregulated in some cancers and may promote cell survival under stress.
• Its role as a negative regulator of protein synthesis suggests cancer cells may have mechanisms to inhibit eEF2K for growth.

Purpose of the Study:

• To investigate how oncogenic signaling pathways regulate eEF2K activity.
• To identify specific phosphorylation sites on eEF2K and the kinases responsible for their regulation.
• To understand the impact of eEF2K regulation on cancer cell survival and growth.

Main Methods:

• Phosphorylation site mapping and mutagenesis of eEF2K.
• In vitro kinase assays using mTOR and ERK.
• Analysis of eEF2K activity in cancer cell lines under various signaling conditions.

Main Results:

• The mTORC1 and Ras/Raf/MEK/ERK pathways cooperate to inhibit eEF2K activity.
• Multiple novel phosphorylation sites on eEF2K regulated by mTORC1 and/or ERK were identified, including sites in the linker region.
• Specific phosphorylation sites were shown to be directly phosphorylated by mTOR or ERK, and glycogen synthase kinase 3 signaling also impacts eEF2 phosphorylation.
• Phosphorylation sites distant from the N-terminal calmodulin-binding motif regulate CaM binding, and mutations in these sites, found in cancer, activate eEF2K.

Conclusions:

• eEF2K activity is tightly regulated by a network of oncogenic signaling pathways, including mTORC1 and ERK.
• Regulation of eEF2K phosphorylation is crucial for controlling protein synthesis and cell growth in cancer.
• Dysregulation of eEF2K phosphorylation due to mutations can lead to its activation, potentially contributing to cancer progression.