Interaction of nuclear factors from young and old rat brain regions with regulatory sequences of the D2 dopamine receptor gene promoter.

Abstract

Alterations in the number or functional state of D2 dopamine receptors have been implicated in the decreased motor abilities associated with normal aging, Parkinson's disease and other neurodegenerative diseases. Previous work has demonstrated a substantial decrease in D2 receptor-containing neurons, receptor proteins, steady-state mRNA levels, and the rate of mRNA synthesis with age in the rat striatum in particular and in mammalian brains in general. These observations suggest that one key area of regulatory control is at the level of transcriptional initiation and/or elongation. In the present study gel mobility shift experiments were used to assess the interaction of nuclear proteins from different rat brain regions with DNA containing putative DNA regulatory sites of the transcriptionally active rat D2 receptor gene promoter. Oligonucleotides containing either of the two SP1 binding sites immediately upstream of the primary transcriptional start site were bound by proteins found in nuclear extracts obtained from rat striatum, hippocampus, cortex, and cerebellum. Extracts from striatum and hippocampus formed predominantly low molecular weight complexes which do not contain SP1, as well as a small amount of high molecular weight complexes which may contain SP1 or an SP1-related protein. Cerebellar extracts formed two similar sets of complexes, but they were formed in roughly equal amounts. Extracts from cortex produced a more involved pattern of complexes, but still formed both high molecular weight complexes which contain SP1 and low molecular weight complexes which do not contain SP1. There were differences in the gel mobility as well as the relative amounts of complexes formed with the two SP1-specific oligonucleotides among different brain regions. With respect to possible age-related changes in transcription of the D2 dopamine receptor gene, there appeared to be no statistically significant difference in the DNA-protein complexes formed with striatal nuclear proteins from a population of young rats versus a population of old rats.