RANKL coordinates cell cycle withdrawal and differentiation in osteoclasts through the cyclin-dependent kinase inhibitors p27KIP1 and p21CIP1.
The coordination of cell cycle progression and osteoclast differentiation by RANKL signaling was studied. Experiments with mouse genetic models revealed that RANKL promoted cell cycle withdrawal of osteoclast precursors dependent on the cyclin kinase inhibitor p27-KIP1, but that both p27-KIP1 and p21-CIP1 were required for osteoclast differentiation. These cyclin inhibitors may directly regulate osteoclast differentiation in addition to regulating cell cycle withdrawal.


BACKGROUND
RANKL stimulates mononuclear precursor cells of the myeloid lineage to differentiate into multinuclear osteoclasts, thus providing a system to study the fundamental problem of coordination of cell cycle progression with cell differentiation.


METHODS
Mice that lack expression of functional cyclin inhibitors p27KIP1and p21CIP1 were used to study cell cycle progression and differentiation of osteoclast precursors in vitro and in vivo.


CONCLUSIONS
Experiments with cells derived from p27KIP1- and p21CIP1-deficient mice indicated that p27KIP1 function alone was necessary for RANKL-mediated cell cycle withdrawal by osteoclast precursors, but osteoclasts from mice with single mutations in either of these two genes differentiated normally. In contrast, p21/p27 double knockout mice developed osteopetrosis, with fewer osteoclasts that exhibited lower TRACP activity and abnormal cell morphology present in long bone. Moreover, isolated osteoclast progenitors from p21/p27 double knockout mice were defective in RANKL-mediated differentiation in vitro, expressing low levels of osteoclast-specific genes like TRACP and cathepsin K. Taken together, these data suggest p27KIP1 and p21CIP1 play roles in osteoclast differentiation in response to RANKL signaling distinct from their roles in promoting cell cycle withdrawal.
Sankar
Uma
U
Department of Molecular Genetics, The Ohio State University, Columbus, Ohio 43210, USA.
Patel
Krupen
K
Rosol
Thomas J
TJ
Ostrowski
Michael C
MC
D000135:Acid Phosphatase / Q000235:genetics / Q000378:metabolism; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D001854:Bone Marrow Cells / Q000187:drug effects / Q000378:metabolism; D042846:CDC2-CDC28 Kinases / Q000378:metabolism; D002352:Carrier Proteins / Q000494:pharmacology*; D056657:Cathepsin K; D002403:Cathepsins / Q000235:genetics / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects* / Q000235:genetics; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects* / Q000235:genetics; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D051357:Cyclin-Dependent Kinase 2; D050763:Cyclin-Dependent Kinase Inhibitor p18; D050764:Cyclin-Dependent Kinase Inhibitor p19; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005269:Femur / Q000000981:diagnostic imaging / Q000201:enzymology / Q000473:pathology; D005419:Flavonoids / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D007093:Imidazoles / Q000494:pharmacology; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D016173:Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009025:Morpholines / Q000494:pharmacology; D010010:Osteoclasts / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D010022:Osteopetrosis / Q000235:genetics / Q000473:pathology; D011725:Pyridines / Q000494:pharmacology; D053245:RANK Ligand; D011859:Radiography; D053246:Receptor Activator of Nuclear Factor-kappa B; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000071681:Tartrate-Resistant Acid Phosphatase; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
D002352:Carrier Proteins; C493957:Cdkn1a protein, mouse; C493961:Cdkn1b protein, mouse; C493972:Cdkn2c protein, mouse; C493975:Cdkn2d protein, mouse; D018797:Cell Cycle Proteins; D002867:Chromones; D050763:Cyclin-Dependent Kinase Inhibitor p18; D050764:Cyclin-Dependent Kinase Inhibitor p19; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004791:Enzyme Inhibitors; D005419:Flavonoids; D007093:Imidazoles; D007527:Isoenzymes; D008562:Membrane Glycoproteins; D009025:Morpholines; D011725:Pyridines; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; C505687:Tnfrsf11a protein, mouse; C505689:Tnfsf11 protein, mouse; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D016173:Macrophage Colony-Stimulating Factor; D042846:CDC2-CDC28 Kinases; C495893:Cdk2 protein, mouse; D051357:Cyclin-Dependent Kinase 2; D000469:Alkaline Phosphatase; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase; D002403:Cathepsins; D056657:Cathepsin K; C534132:Ctsk protein, mouse; C093642:SB 203580; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one