FGF inhibits the activity of the cyclin B1/CDK1 kinase to induce a transient G₂arrest in RCS chondrocytes.
Fibroblast growth factors (FGFs) negatively regulate long bone development by inhibiting the proliferation of chondrocytes that accumulate in the G₁ phase of the cycle following FGF treatment. Here we report that FGF also causes a striking but transient delay in mitotic entry in RCS chondrocytes by inactivating the cyclin B1-associated CDK1(CDC2) kinase. As a consequence of this inactivation, cells accumulate in the G₂ phase of the cycle for the first 4-6 hours of the treatment. Cyclin B1/CDK1 activity is then restored and cells reach a G₁ arrest. The reduced cyclin B1/CDK1 activity was accompanied by increased CDK1 inhibitory phosphorylation, likely caused by increased activity and expression of the Myt1 kinase. FGF1 also caused dephosphorylation of the CDC25C phosphatase, that however appears due the inactivation of cyclin B1/CDK1 complex in the CDK1 feedback loop, and not the activation of specific phosphatases. the inactivation of the cyclin B1/CDK1 complex is a direct effect of FGF signaling, and not a consequence of the G₂ arrest as it can be observed also in cells blocked at mitosis by Nocodazole. The Chk1 and AtM/ATR kinase are known to play essential roles in the G₂ checkpoint induced by DNA damage/genotoxic stress, but inhibition of Chk1 or ATM/ATR not only did not prevent, but rather potentiated the FGF-induced G₂ arrest. Additionally our results indicate that the transient G₂ arrest is induced by FGF in RCS cell through mechanisms that are independent of the G₁ arrest, and that the G₂ block is not strictly required for the sustained G₁ arrest but may provide a pausing mechanism that allows the FGF response to be fully established.
NYU School of Medicine, New York, USA.
Tri
T
Tran
Victoria
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Kolupaeva
Claudio
C
Basilico
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D064007:Ataxia Telangiectasia Mutated Proteins; D016203:CDC2 Protein Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D019902:Chondrocytes / Q000201:enzymology* / Q000378:metabolism; D056744:Cyclin B1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D015536:Down-Regulation; D016220:Fibroblast Growth Factor 1 / Q000494:pharmacology*; D016195:G2 Phase; D008938:Mitosis; D015739:Nocodazole / Q000494:pharmacology; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D020687:cdc25 Phosphatases / Q000378:metabolism
D000970:Antineoplastic Agents; D018797:Cell Cycle Proteins; D056744:Cyclin B1; D004268:DNA-Binding Proteins; D025521:Tumor Suppressor Proteins; D016220:Fibroblast Growth Factor 1; D011494:Protein Kinases; C576887:ataxia telangiectasia and Rad3-related kinase, rat; C490680:Myt1 kinase, rat; D011505:Protein-Tyrosine Kinases; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; D016203:CDC2 Protein Kinase; D020687:cdc25 Phosphatases; D015739:Nocodazole