Transcriptional Regulatory Mechanism for Ca^<2+>-Signaling Regulatory Protein Regucalcin Gene Which Is Expressed Specifically in Liver Cells

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Regucalcin (RC) is a regulatory protein in Ca^<2+> signaling in cells, and it is mainly expressed in liver cells. This study was undertaken to clarify the transcriptional mechanism for the regucalcin gene in liver cells. Firstly, the involvement of signaling factors, which are related to serum component, on the regucalcin mRNA expression in the cloned rat hepatoma cells (H4-II-E) was examined. The regucalcin mRNA expression was found to be mediated through signaling pathway which are partly involved in Ca^<2+>-dependent protein kinase and tyrosine kinase in H4-II-E hepatoma cells. To understand the mechanism underlying the regulation of the regucalcin gene was the 5'-flanking region of the rat regucalcin gene was characterized, and it was found that nuclear proteins from H4-II-E cells specifically bind to the 5'-flanking region of the rat regucalcin gene. Then, the characterization of the binding of nuclear protein on the 5'-flanking resion of the rat regucalcin gene was investigated. It was found of that the specific nuclear factor binds to the NFI-like sequence, which can stimulate the transcriptional activity in the promoter region of regucalcin gene in liver cells. Moreover, it was demonstrated that hepatic nuclear protein can specifically bind to the TTGGC sequence in rat regucalcin gene promoter resion, and that this binding is enhanced by inttacellular signaling factors which are pathway mediated through protein phosphorylation. Liver nuclear proteins which can bind to the TTGGC sequence were clonining with one-hybrid method. It was found that two nuclear proteins can specifically bind to the TTGGC in the promoter region of regucalcin gene in liver cells. One was NFI (a2), and other was a novel protein.