Activation of Caspases Is Required for Osteoblastic Differentiation

• Published in: The Journal of biological chemistry 2003-11, Vol.278 (48), p.47477-47482
• Main Authors: Mogi, Makio, Togari, Akifumi
• Format: Article
• Language: English
• Subjects: Alkaline Phosphatase - metabolism; Animals; Apoptosis; Blotting, Western; Bone Morphogenetic Protein 4; Bone Morphogenetic Proteins - metabolism; Caspase 2; Caspase 3; Caspase 8; Caspase 9; Caspases - metabolism; Cell Cycle; Cell Differentiation; Cell Division; Cell Line; Cell Separation; Cyclic AMP - metabolism; Enzyme Activation; Enzyme-Linked Immunosorbent Assay; Flow Cytometry; Mice; Osteoblasts - cytology; Parathyroid Hormone - metabolism; Phenotype; Time Factors
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M307055200

Previous studies have shown that mouse osteoblastic MC3T3-E1 cells undergo apoptosis when exposed to a mixture of proinflammatory cytokines. Bone morphogenetic protein (BMP)s are important regulators of osteoblast differentiation. Because regulation of osteoblastic differentiation is poorly understood, we sought to determine if BMP-4-induced differentiation of osteoblastic cells depends on the activity of the key apoptotic proteases, i.e. the caspases. BMP-4 induced the growth arrest and differentiation of osteoblastic cell line MC3T3-E1, as evidenced by the appearance of osteoblastic phenotypes such as alkaline phosphatase (ALP) activation and parathyroid hormone (PTH)-dependent production of cAMP. Surprisingly, BMP-4 induced transient and potent activation of caspase-8, caspase-2, and caspase-3, in this order. However, no apoptosis or necrosis in BMP-4-treated cells could be detected by FACS using annexin-V/propodium iodine double staining. Peptide inhibition of caspase activity led to a dramatic reduction in ALP activation and PTH-induced production of cAMP in BMP-4-treated cells. Although BMP-4 treatment resulted in cell-cycle G 0 /G 1 arrest as detected by FACS cell-cycle analysis, caspase inhibitors (caspase-8, caspase-2, and caspase-3 inhibitors) could block the G 0 /G 1 arrest in MC3T3-E1 cells. Taken together, these results confirm a unique and unanticipated role for the caspase-mediated signal cascade in the differentiation of osteoblasts.