Constitutive activation of MKK6 in chondrocytes of transgenic mice inhibits proliferation and delays endochondral bone formation.
Accumulating in vitro evidence suggests that the p38 mitogen-activated protein kinase (MAPK) pathway is involved in endochondral ossification. To investigate the role of this pathway in endochondral ossification, we generated transgenic mice with expression in chondrocytes of a constitutively active mutant of MKK6, a MAPK kinase that specifically activates p38. These mice had a dwarf phenotype characterized by reduced chondrocyte proliferation, inhibition of hypertrophic chondrocyte differentiation, and a delay in the formation of primary and secondary ossification centers. Histological analysis with in situ hybridization showed reduced expression of Indian hedgehog, PTH/PTH-related peptide receptor (PTH, parathyroid hormone), cyclin D1, and increased expression of p21 in chondrocytes. In addition, both in vivo and in transfected cells, p38 signaling increased the transcriptional activity of Sox9, a transcription factor essential for chondrocyte differentiation. In agreement with this observation, transgenic mice that express a constitutively active mutant of MKK6 in chondrocytes showed phenotypes similar to those of mice that overexpress SOX9 in chondrocytes. These observations are consistent with the notion that increased activity of Sox9 accounts at least in part for the phenotype caused by constitutive activation of MKK6 in chondrocytes. Therefore, our study provides in vivo evidence for the role of p38 in endochondral ossification and suggests that Sox9 is a likely downstream target of the p38 MAPK pathway.
Zhang
Ren
R
Department of Molecular Genetics, Graduate Program in Genes and Development, University of Texas, M. D. Anderson Cancer Center, Houston, TX 77030, USA.
Murakami
Shunichi
S
Coustry
Françoise
F
Wang
Ying
Y
de Crombrugghe
Benoit
B
D000818:Animals; D002454:Cell Differentiation / Q000235:genetics; D049109:Cell Proliferation; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D019902:Chondrocytes / Q000166:cytology* / Q000378:metabolism*; D004622:Embryo, Mammalian / Q000196:embryology / Q000378:metabolism; D004789:Enzyme Activation / Q000235:genetics; D006609:High Mobility Group Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D048669:MAP Kinase Kinase 6 / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation / Q000235:genetics; D010012:Osteogenesis; D055758:SOX9 Transcription Factor; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000235:genetics; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D006609:High Mobility Group Proteins; D055758:SOX9 Transcription Factor; C527932:SOX9 protein, human; C527933:Sox9 protein, mouse; D014157:Transcription Factors; D048051:p38 Mitogen-Activated Protein Kinases; D048669:MAP Kinase Kinase 6; C482567:Map2k6 protein, mouse