NGF regulates the PC12 cell cycle machinery through specific inhibition of the Cdk kinases and induction of cyclin D1.
We have examined the effects of NGF on components of the PC12 cell cycle machinery. We show that NGF represses over 6-8 d the levels of specific cdk kinase proteins and the G2-M phase specific cyclin B1 and the S phase marker PCNA as well as the level of phosphorylation of the retinoblastoma (Rb) protein. All of these changes may provide a basis for a NGF block to cell cycling. Unexpectedly, the G1 phase-specific cyclin D1 was dramatically increased by inducers of differentiation (NGF and FGF), but not by inducers of proliferation (EGF and insulin). Although the levels of cyclin D1/cdk2 and cyclin D1/cdk4 complexes increased following NGF treatment, as did cyclin D1/Rb complexes, the associated kinase activities declined, indicating that NGF also induces an inhibitor of cdk kinase activity. In agreement, NGF induced the cdk inhibitory protein, p21, which was found in cyclin D1/cdk kinase complexes after NGF treatment. We show that vector over expression of cyclin D1 in PC12 is sufficient on its own to arrest the cells in G1 phase and inhibit expression of PCNA. These results indicate that NGF induction of cyclin D1 and inactivation of cdk kinases, the latter possibly by increase of p21, play a central role in the NGF block of PC12 cell cycling.
Yan
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GZ
Howard Hughes Medical Institute, Department of Biochemistry, New York University Medical Center, New York 10016, USA.
Ziff
E B
EB
D000818:Animals; D042846:CDC2-CDC28 Kinases; D002453:Cell Cycle / Q000187:drug effects; D002454:Cell Differentiation; D019938:Cyclin D1; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism*; D016193:G1 Phase; D009414:Nerve Growth Factors / Q000494:pharmacology*; D009474:Neurons / Q000166:cytology; D015513:Oncogene Proteins / Q000378:metabolism*; D016716:PC12 Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010766:Phosphorylation; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D051381:Rats; D016160:Retinoblastoma Protein / Q000378:metabolism
D016213:Cyclins; D009414:Nerve Growth Factors; D015513:Oncogene Proteins; D018809:Proliferating Cell Nuclear Antigen; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein; D019938:Cyclin D1; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495892:Cdk2 protein, rat; C495903:Cdk4 protein, rat; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases