The rat angiotensin II type 1a receptor (AT1a-R) gene is expressed in a cell-specific manner. We demonstrated that the negative regulatory element (NRE) between -489 and -331 is active in PC12 cells (Murasawa, S., Matsubara, H., Urakami, M., and Inada, M. (1993) J. Biol. Chem. 268, 26996-27003). Gel retardation assays confirmed that PC12 cells have a trans-acting factor bound to the NRE. By means of a DNase I footprint assay we identified the core of the NRE as an (A + T)-rich sequence (TAATCTTTTATTTTA) located at nucleotides -456 to -442. Oligonucleotides corresponding to the NRE core sequence bound to nuclear protein. Site-directed mutagenesis at nucleotides -451 to -448 eliminated the specific protein/DNA binding and restored expression of the AT1a-R in transient transfection assays (2.7-fold increase). The NRE did not negatively affect the thymidine kinase promoter. No homology was found with known NREs, suggesting that this is a novel NRE. Southwestern blotting revealed a 53-kDa, specific binding protein in PC12 cells and the rat brain, but not in the liver, spleen, adrenal gland, and kidney. These findings demonstrate that the NRE of the rat AT1a-R is an (A + T)-rich sequence located at nucleotides -456 to -442 and the 53-kDa protein is a specific binding protein, and suggest that this protein may be a trans-acting factor which determines the neuron-specific down-regulation of the AT1a-R gene.

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