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p107 and p130 associated cyclin A has altered substrate specificity
1Department of Cell Biology, Vanderbilt University, Nashville, Tennessee 37240, USA.
Abstract:
We demonstrate that p107 and p130 immune complexes exhibit kinase activity. We have tested such immune complexes with four substrates commonly utilized to assay Cdk activity, including all three known members of the retinoblastoma family. Immunodepletion revealed this kinase activity could be abolished by removal of either cyclin A or Cdk2 but was unaffected by removal of Cdk4 or any D-type cyclin. The appearance of p107 associated activity followed the accumulation of p107 protein. In contrast, the kinase activity associated with p130 immune complexes became apparent after mid-G1, coincident with p130 hyperphosphorylation. GST-Rb, GST-p107, and GST-p130 (where GST indicates glutathione S-transferase) were equally suitable substrates in p107 and p130 immune complex kinase assays, yielding activity equal to 25% of the cyclin A activity present. The p107 and p130 associated activity was unable to phosphorylate histone H1, suggesting the p107 and p130 associated cyclin A/Cdk2 may represent a distinct pool with a distinct substrate specificity. The p107 and p130 associated activity was released from the immune complexes upon incubation with ATP and Mg2+ and exhibited the same substrate preference observed with the untreated immune complex. Our data suggest that p107 and p130 recognize, or form by association, a distinct pool of cyclin A/Cdk2 that preferentially phosphorylates retinoblastoma family members.
Insights
p107 and p130 proteins associate with cyclin A/Cdk2, exhibiting distinct kinase activity. This activity preferentially phosphorylates retinoblastoma family proteins, suggesting a specific role in cell cycle regulation.
Area of Science:
- Molecular Biology
- Cell Cycle Regulation
- Protein Kinase Activity
Background:
- p107 and p130 are proteins involved in cell cycle control.
- Cyclin-dependent kinases (Cdks) regulate cell cycle progression.
- Retinoblastoma family proteins are key regulators of the G1/S transition.
Purpose of the Study:
- To investigate the kinase activity associated with p107 and p130 immune complexes.
- To identify the specific cyclin and Cdk components responsible for this activity.
- To determine the substrate specificity of the p107/p130-associated kinase.
Main Methods:
- Immune complex kinase assays using p107 and p130.
- Testing activity against various substrates, including retinoblastoma family members.
- Immunodepletion experiments to identify essential cyclin and Cdk components.
- Analysis of substrate phosphorylation patterns.
Main Results:
- p107 and p130 immune complexes exhibit kinase activity.
- This activity is dependent on cyclin A and Cdk2, but not Cdk4 or D-type cyclins.
- GST-Rb, GST-p107, and GST-p130 are suitable substrates, with activity comparable to cyclin A.
- Histone H1 is not phosphorylated, indicating a distinct substrate specificity.
Conclusions:
- p107 and p130 associate with a specific pool of cyclin A/Cdk2.
- This distinct cyclin A/Cdk2 pool preferentially phosphorylates retinoblastoma family members.
- The findings suggest a specialized role for p107/p130-associated cyclin A/Cdk2 in regulating retinoblastoma family proteins.