| 0591 PP2A, a negative regulator of Akt-mediated osteoblast differentiation | ||
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C.A. BARWACZ, and S. STRACK, University of Iowa, Iowa City, USA Objectives: Bone morphogenic protein-2 (BMP-2), a member of the TGFbeta superfamily, has been shown to be a very potent osteoinductive cytokine that induces osteoblast differentiation. BMP-2 induced signaling is mediated via the BMP type I and type II receptors (BMPR-IA/B and BMPR-II). Involvement of the PI 3-kinase/Akt pathway has recently been shown to be necessary in the process of BMP-2 mediated osteoblast differentiation. While much information has been garnered regarding the role of kinases in the BMP-2 induced signal transduction cascade, considerably less is known regarding the role that phosphatases play in the regulation of osteoblast differentiation. Subsequent experiments sought to examine the regulation of BMP-2 induced PI 3-kinase/Akt by the heterotrimeric protein phosphatase 2A (PP2A). Methods: The MC3T3-E1 osteoblast cell line was utilized as a model system in which to investigate the BMP-2 – PI 3 kinase/Akt differentiation pathway. MC3T3-E1 cells were stimulated with rhBMP-2, and Akt kinase was examined for activation both in the absence and presence of the PP2A-specific inhibitor okadaic acid (OA). RTPCR analysis was carried out in order to establish which PP2A regulatory B-subunits MC3T3-E1 osteoblasts express. Results: Data in which MC3T3-E1 osteoblasts were stimulated with rhBMP-2 shows that PP2A acts as a negative regulator of Akt. Under native conditions, MC3T3-E1 osteoblasts showed an increase in PI 3-kinase/Akt phosphorylation as a result of BMP-2 treatment. Osteoblasts devoid of BMP-2 treatment showed a lack of Akt phosphorylation. MC3T3-E1 osteoblasts pre-treated with okadaic acid showed an increase in Akt phosphorylation, including cells devoid of BMP-2 treatment. Conclusion: PP2A acts as a negative regulator of Akt, maintaining Akt in a dephosphorylated state in the absence of the differentiation cytokine BMP-2. Thus PP2A acts as a checkpoint in the signal transduction cascade partially responsible for osteoblast differentiation and survival. | ||
| Seq #87 - Cell differentiation 2:00 PM-3:15 PM, Thursday, March 22, 2007 Ernest N. Morial Convention Center Exhibit Hall I2-J | ||
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