Nuclear Factor B Functions as a Negative Regulator for the Rat Androgen Receptor Gene and NF-B Activity Increases during the Age-dependent Desensitization of the Liver

• Published in: The Journal of biological chemistry 1995-01, Vol.270 (2), p.837
• Main Authors: Prakash C. Supakar, Myeong H. Jung, Chung S. Song, Bandana Chatterjee, Arun K. Roy
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.270.2.837

Transcriptional regulation of the steroid hormone receptor genes plays a central role in temporal changes of target cell sensitivity during development, maturation, and aging. Sequence-specific DNA-protein interactions mediate these regulatory functions. Progressive 5′ deletion of the rat androgen receptor (rAR) gene immediately beyond the −572 base pair (bp) region causes a marked increase in its promoter activity. DNase I footprinting with nuclear proteins revealed a protected area encompassing −574- to −554-bp positions that begins with a perfectly palindromic nuclear factor κB (NF-κB) motif. Electrophoretic mobility shift analyses (EMSA) showed that the decameric rAR NF-κB site at positions −574 to −565 cross-competes with the authentic κ immunoglobulin light chain enhancer for specific protein binding. Supershift with specific antibodies to NF-κB subunits confirmed that the two retarded bands observed in the EMSA with the labeled rAR probe are due to p50/p65 and p50/p50 dimers of the NF-κB/Rel proteins. Fragments of rAR promoter with either deletion or point mutation of the NF-κB site are found to be about 2- to 3-fold more effective as compared to the wild type control in driving a heterologous reporter gene in cellulo. Thus, unlike most other known cases, NF-κB acts as a negative regulator for the rAR gene. The physiological relevance of this repressor function is evident from a 10-fold increase in the p50/p50 form of the NF-κB activity in the liver of aged rats exhibiting hepatic androgen desensitization. The newly identified repressor element is a rare example of a naturally occurring perfect palindromic binding motif for the NF-κB/Rel family of transcription factors. This repressor factor and the positively acting age-dependent factor, ADF, described earlier (Supakar, P. C., Song, C. S., Jung, M. H., Slomczynska, M. A., Kim, J.-M., Vellanoweth, R. L., Chatterjee, B. & Roy, A. K.(1993) J. Biol. Chem. 268, 26400-26408) function to coordinate the tissue-specific down-regulation of the rAR gene during aging.