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Mammalian p50Cdc37 is a protein kinase-targeting subunit of Hsp90 that binds and stabilizes Cdk4
L Stepanova1, X Leng, S B Parker
1Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77030, USA.
Insights
The molecular chaperone Hsp90 targets protein kinases via CDC37. This study reveals CDC37 stabilizes Cyclin-Dependent Kinase 4 (Cdk4), crucial for cell cycle progression and proliferation.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- CDC37 is an essential gene in yeast, interacting with protein kinases for Cdc28p/cyclin complex production.
- Mammalian p50Cdc37 is identified as a protein kinase-targeting subunit of the molecular chaperone Hsp90.
- p50 was previously observed with pp60v-src and Raf-1, but its function remained unclear.
Purpose of the Study:
- To elucidate the function of mammalian p50Cdc37 in protein kinase regulation.
- To investigate the role of the Cdc37/Hsp90 complex in cell cycle progression.
- To determine the mechanism by which Cdc37 influences Cdk4 activity and stability.
Main Methods:
- Identification of p50Cdc37 as an Hsp90-targeting subunit.
- Analysis of Cdc37's interaction with Cdk4 in mouse fibroblasts and insect cells.
- In vitro and in vivo association studies of Cdc37/Hsp90 with Cdk4.
- Pharmacological inactivation of Cdc37/Hsp90 function to assess Cdk4 half-life.
Main Results:
- p50Cdc37 targets Hsp90 to Cdk4, particularly the cyclin D-unbound fraction.
- Cdc37 is coexpressed with cyclin D1 during proliferation, suggesting a role in cell cycle progression.
- Inactivation of Cdc37/Hsp90 reduces the half-life of newly synthesized Cdk4.
Conclusions:
- p50Cdc37 acts as a scaffold, bringing the Hsp90 chaperone to protein kinases like Cdk4.
- The Cdc37/Hsp90 complex is essential for stabilizing Cdk4, promoting cell cycle progression.
- This reveals a novel chaperone-dependent mechanism in the production of Cdk4/cyclin D complexes.
Abstract:
CDC37, an essential gene in Saccharomyces cerevisiae, interacts genetically with multiple protein kinases and is required for production of Cdc28p/cyclin complexes through an unknown mechanism. We have identified mammalian p50Cdc37 as a protein kinase-targeting subunit of the molecular chaperone Hsp90. Previously, p50 was observed in complexes with pp60v-src and Raf-1, but its identity and function have remained elusive. In mouse fibroblasts, a primary target of Cdc37 is Cdk4. This kinase is activated by D-type cyclins and functions in passage through G1. In insect cells, Cdc37 is sufficient to target Hsp90 to Cdk4 and both in vitro and in vivo, Cdc37/Hsp90 associates preferentially with the fraction of Cdk4 not bound to D-type cyclins. Cdc37 is coexpressed with cyclin Dl in cells undergoing programmed proliferation in vivo, consistent with a positive role in cell cycle progression. Pharmacological inactivation of Cdc37/Hsp90 function decreases the half-life of newly synthesized Cdk4, indicating a role for Cdc37/Hsp90 in Cdk4 stabilization. This study suggests a general role for p50Cdc37 in signaling pathways dependent on intrinsically unstable protein kinases and reveals a previously unrecognized chaperone-dependent step in the production of Cdk4/cyclin D complexes.