Mitotic protein kinase CDK1 phosphorylation of mRNA translation regulator 4E-BP1 Ser83 may contribute to cell transformation
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Published on: September 5, 2017
Celestino Velásquez1, Erdong Cheng1, Masahiro Shuda1
1Cancer Virology Program, University of Pittsburgh Cancer Institute, Pittsburgh, PA 15213;
Abstract:
Mammalian target of rapamycin (mTOR)-directed eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) phosphorylation promotes cap-dependent translation and tumorigenesis. During mitosis, cyclin-dependent kinase 1 (CDK1) substitutes for mTOR and fully phosphorylates 4E-BP1 at canonical sites (T37, T46, S65, and T70) and the noncanonical S83 site, resulting in a mitosis-specific hyperphosphorylated δ isoform. Colocalization studies with a phospho-S83 specific antibody indicate that 4E-BP1 S83 phosphorylation accumulates at centrosomes during prophase, peaks at metaphase, and decreases through telophase. Although S83 phosphorylation of 4E-BP1 does not affect general cap-dependent translation, expression of an alanine substitution mutant 4E-BP1.S83A partially reverses rodent cell transformation induced by Merkel cell polyomavirus small T antigen viral oncoprotein. In contrast to inhibitory mTOR 4E-BP1 phosphorylation, these findings suggest that mitotic CDK1-directed phosphorylation of δ-4E-BP1 may yield a gain of function, distinct from translation regulation, that may be important in tumorigenesis and mitotic centrosome function.
Insights
Cyclin-dependent kinase 1 (CDK1) phosphorylates 4E-BP1 during mitosis, creating a unique isoform. This mitotic phosphorylation, distinct from mTOR
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Mammalian target of rapamycin (mTOR) pathway regulates protein synthesis and is implicated in cancer.
- Eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) is a key regulator of cap-dependent translation.
- Phosphorylation of 4E-BP1 by mTOR typically inhibits translation and promotes tumorigenesis.
Purpose of the Study:
- To investigate the role of 4E-BP1 phosphorylation during mitosis.
- To identify the kinase responsible for mitotic 4E-BP1 phosphorylation and its specific sites.
- To determine the functional consequences of mitotic 4E-BP1 phosphorylation, particularly its role in cell transformation and centrosome function.
Main Methods:
- Utilized phospho-specific antibodies to detect 4E-BP1 phosphorylation at serine 83 (S83).
- Performed colocalization studies using immunofluorescence to track 4E-BP1 S83 phosphorylation during different mitotic phases.
- Generated and expressed alanine substitution mutants (4E-BP1.S83A) in rodent cells to assess functional impact.
- Evaluated the effect of 4E-BP1 S83 phosphorylation on cell transformation induced by Merkel cell polyomavirus small T antigen.
Main Results:
- Identified cyclin-dependent kinase 1 (CDK1) as the kinase responsible for phosphorylating 4E-BP1 during mitosis.
- Discovered a mitosis-specific hyperphosphorylated isoform (δ-4E-BP1) resulting from phosphorylation at canonical sites and the noncanonical S83 site.
- Observed that 4E-BP1 S83 phosphorylation accumulates at centrosomes during prophase, peaks at metaphase, and declines by telophase.
- Demonstrated that S83 phosphorylation of 4E-BP1 does not affect general cap-dependent translation.
- Showed that expression of 4E-BP1.S83A partially reverses rodent cell transformation induced by Merkel cell polyomavirus small T antigen.
Conclusions:
- Mitotic CDK1-directed phosphorylation of 4E-BP1 generates a distinct isoform (δ-4E-BP1) with functions beyond translation regulation.
- Phosphorylation at S83 of 4E-BP1 by CDK1 appears to play a role in tumorigenesis, potentially through mechanisms independent of general translation control.
- Mitotic 4E-BP1 phosphorylation at S83 may be important for centrosome function during cell division.
