Epidermal growth factor receptor-mediated expression of NF-χB transcription factor in osteoblastic MC3T3-E1 cells cultured under a low-calcium environment

We examined the effect of a low calcium environment on DNA-protein binding reaction activity of the transcription factor, NF-xB in osteoblastic MC3T3-E1 cells, using an electrophoretic mobility shift assay. Binding sites for the NF-xB sequence in DNA in nuclear protein in MC3T3-E1 cells are present. This DNA-protein binding reaction activity increased in MC3T3-E1 cells with EGF treatment, compared with those with no treatment. When MC3T3-E1 cells were placed in a low calcium environment, DNA-protein binding reaction activity seemed to decrease. This suggests that the phosphorylation of IxB is less active in a low calcium environment as compared with that in a normal calcium environment, because the activation of NF-xB is required for the dissociation of the cytoplasmic heterodimer after the phosphorylation of IxB. From these facts, it was suggested that gene transcription factor NF-xB is intimately associated with inhibitory bone formation in osteoblastic cells.