Impaired cell cycle regulation of the osteoblast-related heterodimeric transcription factor Runx2-Cbfbeta in osteosarcoma cells.
Bone formation and osteoblast differentiation require the functional expression of the Runx2/Cbfbeta heterodimeric transcription factor complex. Runx2 is also a suppressor of proliferation in osteoblasts by attenuating cell cycle progression in G(1). Runx2 levels are modulated during the cell cycle, which are maximal in G(1) and minimal beyond the G(1)/S phase transition (S, G(2), and M phases). It is not known whether Cbfbeta gene expression is cell cycle controlled in preosteoblasts nor how Runx2 or Cbfbeta are regulated during the cell cycle in bone cancer cells. We investigated Runx2 and Cbfbeta gene expression during cell cycle progression in MC3T3-E1 osteoblasts, as well as ROS17/2.8 and SaOS-2 osteosarcoma cells. Runx2 protein levels are reduced as expected in MC3T3-E1 cells arrested in late G(1) (by mimosine) or M phase (by nocodazole), but not in cell cycle arrested osteosarcoma cells. Cbfbeta protein levels are cell cycle independent in both osteoblasts and osteosarcoma cells. In synchronized MC3T3-E1 osteoblasts progressing from late G1 or mitosis, Runx2 levels but not Cbfbeta levels are cell cycle regulated. However, both factors are constitutively elevated throughout the cell cycle in osteosarcoma cells. Proteasome inhibition by MG132 stabilizes Runx2 protein levels in late G(1) and S in MC3T3-E1 cells, but not in ROS17/2.8 and SaOS-2 osteosarcoma cells. Thus, proteasomal degradation of Runx2 is deregulated in osteosarcoma cells. We propose that cell cycle control of Runx2 gene expression is impaired in osteosarcomas and that this deregulation may contribute to the pathogenesis of osteosarcoma.
San Martin
Inga A
IA
Faculty of Medicine, Institute of Biomedical Sciences ICBM, University of Chile, Santiago, Chile.
Varela
Nelson
N
Gaete
Marcia
M
Villegas
Karina
K
Osorio
Mariana
M
Tapia
Julio C
JC
Antonelli
Marcelo
M
Mancilla
Edna E
EE
Pereira
Barry P
BP
Nathan
Saminathan S
SS
Lian
Jane B
JB
Stein
Janet L
JL
Stein
Gary S
GS
van Wijnen
Andre J
AJ
Galindo
Mario
M
D000818:Animals; D002453:Cell Cycle / Q000502:physiology*; D002460:Cell Line; D045744:Cell Line, Tumor; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics / Q000378:metabolism*; D050658:Core Binding Factor beta Subunit / Q000235:genetics / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors; D016193:G1 Phase / Q000502:physiology; D015870:Gene Expression / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology*; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D051379:Mice; D008938:Mitosis / Q000502:physiology; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism; D012516:Osteosarcoma / Q000378:metabolism* / Q000473:pathology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D051381:Rats; D054875:Ubiquitination / Q000187:drug effects
D050659:Core Binding Factor Alpha 1 Subunit; D050658:Core Binding Factor beta Subunit; D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; D061988:Proteasome Inhibitors; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde