Parathyroid hormone-related peptide represses chondrocyte hypertrophy through a protein phosphatase 2A/histone deacetylase 4/MEF2 pathway.
The maturation of immature chondrocytes to hypertrophic chondrocytes is regulated by parathyroid hormone-related peptide (PTHrP). We demonstrate that PTHrP or forskolin administration can block induction of collagen X-luciferase by exogenous Runx2, MEF2, and Smad1 in transfected chondrocytes. We have found that PTHrP/forskolin administration represses the transcriptional activity of MEF2 and that forced expression of MEF2-VP16 can restore expression of the collagen X reporter in chondrocytes treated with these agents. PTHrP/forskolin induces dephosphorylation of histone deacetylase 4 (HDAC4) phospho-S246, which decreases interaction of HDAC4 with cytoplasmic 14-3-3 proteins and promotes nuclear translocation of HDAC4 and repression of MEF2 transcriptional activity. We have found that forskolin increases the activity of an HDAC4 phospho-S246 phosphatase and that forskolin-induced nuclear translocation of HDAC4 was reversed by the protein phosphatase 2A (PP2A) antagonist, okadaic acid. Finally, we demonstrate that knockdown of PP2A inhibits forskolin-induced nuclear translocation of HDAC4 and attenuates the ability of this signaling molecule to repress collagen X expression in chondrocytes, indicating that PP2A is critical for PTHrP-mediated regulation of chondrocyte hypertrophy.
Kozhemyakina
Elena
E
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Ave., Boston, MA 02115, USA.
Cohen
Todd
T
Yao
Tso-Pang
TP
Lassar
Andrew B
AB
D048948:14-3-3 Proteins / Q000378:metabolism; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D002645:Chickens; D019902:Chondrocytes / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology*; D005576:Colforsin / Q000494:pharmacology; D024121:Collagen Type X / Q000235:genetics / Q000378:metabolism; D050659:Core Binding Factor Alpha 1 Subunit / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D017930:Genes, Reporter; D006655:Histone Deacetylases / Q000378:metabolism*; D006984:Hypertrophy; D008156:Luciferases / Q000378:metabolism; D064326:MEF2 Transcription Factors; D051379:Mice; D018006:Myogenic Regulatory Factors / Q000378:metabolism*; D019319:Okadaic Acid / Q000494:pharmacology; D044162:Parathyroid Hormone-Related Protein / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D054648:Protein Phosphatase 2 / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D051898:Smad1 Protein / Q000235:genetics; D051901:Smad4 Protein / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects
D048948:14-3-3 Proteins; D024121:Collagen Type X; D050659:Core Binding Factor Alpha 1 Subunit; D064326:MEF2 Transcription Factors; C578041:Mef2c protein, mouse; D018006:Myogenic Regulatory Factors; D044162:Parathyroid Hormone-Related Protein; D011993:Recombinant Fusion Proteins; D051898:Smad1 Protein; D051901:Smad4 Protein; D005576:Colforsin; D019319:Okadaic Acid; D008156:Luciferases; D054648:Protein Phosphatase 2; C498618:Hdac5 protein, mouse; D006655:Histone Deacetylases
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