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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 D(3), 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 D(3). 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.

The aim of the present study was to detect differentially expressed genes in the human osteoblast-like osteosarcoma cell line SaOS-2 using non-radioactive RNA fingerprinting (RNA arbitrarily primed polymerase chain reaction, RAP-PCR). RNA was isolated at different time points from SaOS-2 cells grown with and without dexamethasone (DEX). By RAP-PCR we detected changes in band patterns of cells treated with DEX compared with untreated cells. PCR fragments further characterized and sequences from three of these gave perfect matches to the coding sequences of the human nucleophosmin gene B23, cDNA clone 4_c6 from P1 H25 and the human TRA1 gene, respectively. differential regulation of these genes in DEX-stimulated SaOS-2 cells could be demonstrated by RT-PCR.