Binding of kidney nuclear proteins to the 5'-flanking region of the rat gene for Ca2+-binding protein regucalcin: involvement of Ca2+/calmodulin signaling.

Ca2+-binding protein regucalcin is expressed in the kidney cortex of rats, as assayed by Northern blot analysis. The existence of kidney nuclear factor which binds to the 5'-flanking region of the rat regucalcin gene was investigated. When nuclear extracts obtained from the kidney cortex of rats were used in gel mobility-shift assays, two protein-DNA complexes were uniquely formed with the DNA fragment containing the 5'-flanking region of the rat regucalcin gene. Competition gel shift experiments indicated the specific binding region of kidney cortex nuclear proteins in the 5'-flanking region of the rat regucalcin gene. The two nuclear protein-DNA complexes were formed with the same mobility in rat kidney cortex and liver, which possess detectable amounts of regucalcin mRNA in Northern blot analysis. The binding activities of nuclear factors from kidney cortex to the 5'-flanking region of the rat regucalcin gene were inhibited by a single intraperitoneal administration of trifluoperazine, an antagonist of calmodulin, to rats. The present study demonstrates that kidney cortex nuclear proteins specifically bind to the 5'-flanking region of the rat regucalcin gene, and that the binding activity may be partly mediated through the Ca2+/calmodulin-dependent process.