Notch receptors participate in a conserved signaling pathway that controls the development of diverse tissues and cell types. In the present study we investigated the expression of four Notch genes in primary human osteoblasts and in human osteoblastic osteosarcoma cell line SaOS-2 by RT-PCR. We found a strong constitutive expression of Notch-1 and a weak constitutive expression of Notch-2 in both cell types. After stimulation with Dexamethasone or Vitamin D3, two factors known to induce differentiation in osteogenic cells, both Notch receptors were downregulated, however, with a different time course. Notch-1 and Notch-2 showed a transient induction after 2 days and a decrease after 7 days in osteoblasts and after 28 days in SaOS-2 cells. Notch-4 expression could only be detected after stimulation with Dexamethasone and Vitamin D3. However, in osteoblasts a transient induction after 2 days could be detected in osteoblasts, whereas Notch-4 expression increased after 14 and 28 days in SaOS-2 cells. In contrast, Notch-3 was not expressed in human osteoblasts and SaOS-2 osteosarcoma cells. These data show, that Notch genes are expressed in human osteoblastic cells and that the expression is differentially regulated upon stimulation with osteogenic factors.

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