Hsc70 regulates accumulation of cyclin D1 and cyclin D1-dependent protein kinase.
The cyclin D-dependent kinase is a critical mediator of mitogen-dependent G1 phase progression in mammalian cells. Given the high incidence of cyclin D1 overexpression in human neoplasias, the nature and complexity of cyclin D complexes in vivo have been subjects of intense interest. Besides its catalytic partner, the nature and complexity of cyclin D complexes in vivo remain ambiguous. To address this issue, we purified native cyclin D1 complexes from proliferating mouse fibroblasts by affinity chromatography and began to identify and functionally characterize the associated proteins. In this report, we describe the identification of Hsc70 and its functional importance for cyclin D1 and cyclin D1-dependent kinase maturation. We demonstrate that Hsc70 associates with newly synthesized cyclin D1 and is a component of a mature, catalytically active cyclin D1/CDK4 holoenzyme complex. Our data suggest that Hsc70 promotes stabilization of newly synthesized cyclin D1, thereby increasing its availability for assembly with CDK4. In addition, our data demonstrate that Hsc70 remains bound to cyclin D1 following its assembly with CDK4 and Cip/Kip proteins, where it ensures the formation of a catalytically active complex.
Diehl
J Alan
JA
The Leonard and Madlyn Abramson Family Cancer Research Institute, Department of Cancer Biology, Abramson Cancer Center at the University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA. adiehl@mail.med.upenn.edu
Yang
Wensheng
W
Rimerman
Ronald A
RA
Xiao
Hua
H
Emili
Andrew
A
D016475:3T3 Cells; D000818:Animals; D002384:Catalysis; D002455:Cell Division; D002845:Chromatography; D002850:Chromatography, Gel; D019938:Cyclin D1 / Q000378:metabolism*; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006133:Growth Substances / Q000378:metabolism; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism / Q000502:physiology*; D015151:Immunoblotting; D051379:Mice; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D011233:Precipitin Tests; D011485:Protein Binding; D011518:Proto-Oncogene Proteins; D013997:Time Factors
D006133:Growth Substances; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; C494372:Hspa8 protein, mouse; D011518:Proto-Oncogene Proteins; D019938:Cyclin D1; C495902:Cdk4 protein, mouse; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases