A redox factor protein, ref1, is involved in negative gene regulation by extracellular calcium.

A rise in extracellular calcium (CaZ+J suppresses not only secretion of parathyroid hormone (PTH) but also expression of the PTH gene to ensure constant plasma Ca2+ level.A nuclear protein(s) in a wide variety of cells bound to the specific DNA elements (negative Ca' responsive elements, nCaREs) in the human PTH gene in sequence-specific and CaZ+, concentration-dependent manners.Our Southwestern cloning revealed that a redox factor protein (refl), which was known to activate several transcription factors via alterations of their redox state, belonged to an nCaRE binding protein.The level of refl mR.NA as well as of its protein was elevated by an increase in CaZ+, concentration.In gel shift assay, anti-refl antibody eliminated formation of the nCaREprotein complex.We also found that there was another protein(s1 interacting with nCaREs and refl.Further, experiments with an antisense-ref cDNA expression vector introduced into cultured cells suggested that DNA (nCaRE)-refl interaction led to Ca'+,-mediated transcriptional suppression.Thus, it is concluded that refl possesses transcription repressor activity in addition to its function as a transcriptional auxiliary protein.Recently, the mechanism of gene regulation by signal transduction molecules such as the cyclic AMP (CAMPI-protein kinase A or the phorbol ester-protein kinase C systems has been studied extensively (1, 2).Among them, nuclear transcription factors CREW (CAMP response element binding protein (3,411 and A P l (5) were cloned, and their molecular characteristics including structure, dimerization, subcellular localization, phosphorylation, and protein-protein interactions have been vigorously clarified 11-81.