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Phosphorylation of the Src substrate Sam68 by Cdc2 during mitosis
R J Resnick1, S J Taylor, Q Lin
1Section of Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, NY 14853, USA.
Oncogene
|October 7, 1997
Summary
Sam68 protein is phosphorylated during mitosis by Cdc2 kinase, specifically on threonine residues. This finding reveals Sam68 as a direct target of Cdc2, potentially mediating its mitotic functions.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Sam68 (Src-associated in mitosis) is an RNA-binding protein involved in cell signaling.
- Sam68 associates with and is tyrosine phosphorylated by c-Src during mitosis.
Purpose of the Study:
- To investigate the phosphorylation patterns of Sam68 during the cell cycle.
- To identify the kinase responsible for mitotic threonine phosphorylation of Sam68.
Main Methods:
- Immunoprecipitation of Sam68 from HeLa S3 and NIH3T3 cells.
- Phosphorylation assays using recombinant Sam68 and cell lysates.
- Kinase identification via immunodepletion, inhibitor studies (olomoucine), and in vitro phosphorylation with purified Cdc2.
Main Results:
- Sam68 undergoes threonine phosphorylation exclusively during mitosis and serine phosphorylation during interphase and mitosis.
- Mitotic lysates induced significantly higher threonine and serine phosphorylation of recombinant Sam68 compared to unsynchronized lysates.
- Cdc2 was identified as the kinase responsible for mitotic threonine phosphorylation of Sam68.
Conclusions:
- Sam68 is a direct substrate of Cdc2 kinase.
- Sam68 phosphorylation by Cdc2 during mitosis suggests a role in mediating Cdc2's biological functions in cell division.