Fibroblast growth factor inhibits chondrocytic growth through induction of p21 and subsequent inactivation of cyclin E-Cdk2.
Fibroblast growth factor (FGF) and its receptor (FGFR) are thought to be negative regulators of chondrocytic growth, as exemplified by achondroplasia and related chondrodysplasias, which are caused by constitutively active mutations in FGFR3. To understand the growth-inhibitory mechanisms of FGF, we analyzed the effects of FGF2 on cell cycle-regulating molecules in chondrocytes. FGF2 dramatically inhibited proliferation of rat chondrosarcoma (RCS) cells and arrested their cell cycle at the G(1) phase. FGF2 increased p21 expression in RCS cells, which assembled with the cyclin E-Cdk2 complexes, although the expression of neither cyclin E nor Cdk2 increased. In addition, the kinase activity of immunoprecipitated cyclin E or Cdk2, assessed with retinoblastoma protein (pRb) as substrate, was dramatically reduced by FGF-2. Moreover, FGF2 shifted pRb to its underphosphorylated, active form in RCS cells. FGF2 not only induced p21 protein expression in proliferating chondrocytes in mouse fetal limbs cultured in vitro but also decreased their proliferation as assessed by the expression of histone H4 mRNA, a marker for cells in S phase. Furthermore, inhibitory effects of FGF2 on chondrocytic proliferation were partially reduced in p21-null limbs, compared with those in wild-type limbs in vitro. Taken together, FGF's growth inhibitory effects of chondrocytes appear to be mediated at least partially through p21 induction and the subsequent inactivation of cyclin E-Cdk2 and activation of pRb.
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Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
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D000818:Animals; D042846:CDC2-CDC28 Kinases; D002356:Cartilage / Q000187:drug effects / Q000196:embryology*; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology*; D002455:Cell Division / Q000187:drug effects; D019902:Chondrocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D002813:Chondrosarcoma; D019927:Cyclin E / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D016213:Cyclins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000378:metabolism; D005333:Fetus; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology*; D016193:G1 Phase; D006657:Histones / Q000235:genetics; D018878:Limb Buds / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D009924:Organ Culture Techniques; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D016196:S Phase; D014158:Transcription, Genetic / Q000187:drug effects; D014407:Tumor Cells, Cultured
C493957:Cdkn1a protein, mouse; C493958:Cdkn1a protein, rat; D019927:Cyclin E; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D006657:Histones; D012333:RNA, Messenger; D016222:Fibroblast Growth Factor 2; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495893:Cdk2 protein, mouse; C495892:Cdk2 protein, rat; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases