Steroid Receptor Coactivator-1 from Brain Physically Interacts Differentially with Steroid Receptor Subtypes

Abstract

In vitro studies reveal that nuclear receptor coactivators enhance the transcriptional activity of steroid receptors, including estrogen (ER) and progestin receptors (PR), through ligand-dependent interactions. Whereas work from our laboratory and others shows that steroid receptor coactivator-1 (SRC-1) is essential for efficient ER and PR action in brain, very little is known about receptor-coactivator interactions in brain. In the present studies, pull-down assays were used to test the hypotheses that SRC-1 from hypothalamic and hippocampal tissue physically associate with recombinant PR or ER in a ligand-dependent manner. SRC-1, from hypothalamus or hippocampus, interacted with PR-A and PR-B in the presence of an agonist, but not in the absence of ligand or in the presence of a selective PR modulator, RU486. Interestingly, SRC-1 from brain associated more with PR-B, the stronger transcriptional activator, than with PR-A. In addition, SRC-1 from brain, which was confirmed by mass spectrometry, interacted with ERalpha and ERbeta in the presence of agonist but not when unliganded or in the presence of the selective ER modulator, tamoxifen. Furthermore, SRC-1 from hypothalamus, but not hippocampus, interacted more with ERalpha than ERbeta, suggesting distinct expression patterns of other cofactors in these brain regions. These findings suggest that interactions of SRC-1 from brain with PR and ER are dependent on ligand, receptor subtype, and brain region to manifest the pleiotropic functional consequences that underlie steroid-regulated behaviors. The present findings reveal distinct contrasts with previous cell culture studies and emphasize the importance of studying receptor-coactivator interactions using biologically relevant tissue.

Nuclear Receptor Coactivators Are Coexpressed with Steroid Receptors and Regulated by Estradiol in Mouse Brain

“…In support of this idea, ER and other steroid receptors have distinct affinities for nuclear receptor coactivators. For example, SRC-1 and SRC-2 from the rat hypothalamus and hippocampus physically associate with ER and PR in a receptor subtype- and brain region-specific manner [58,65]. Interestingly, SRC-1 from the hypothalamus interacts more with ERα than ERβ, while SRC-2 associates with ERα but shows virtually no interaction with ERβ [58,65].…”

“…For example, SRC-1 and SRC-2 from the rat hypothalamus and hippocampus physically associate with ER and PR in a receptor subtype- and brain region-specific manner [58,65]. Interestingly, SRC-1 from the hypothalamus interacts more with ERα than ERβ, while SRC-2 associates with ERα but shows virtually no interaction with ERβ [58,65]. In addition, receptor-coactivator interactions are influenced by different ligands and response elements on DNA [90,91,92,93].…”

“…Our laboratory and others have found that SRC-1 and SRC-2 are important for hormone-dependent sexual differentiation of the brain [53], gene expression in brain [54,61,62,63] and sexual behavior [54,61,62,63,64]. Finally, SRC-1 and SRC-2 from rodent brain physically interact with ER and PR in a receptor subtype- and brain region-specific manner [58,65]. …”

Silencing steroid receptor coactivator-1 in the nucleus of the solitary tract reduces estrogenic effects on feeding and apolipoprotein A-IV expression

“…the apoA-IV promoter-While SRC-1 has been reported to form a protein complex with ERα in the hypothalamus in an in vitro study (17), it is unknown whether ERα and SRC-1 interact with the ERE located at the 5′-upstream region of the apo A-IV promoter in the NTS. We therefore examined this possibility using a sequential biotinylated double-stranded DNA pull-down assay and immunoblot approach, as described previously (18)(19)(20).…”

Role of Progesterone Receptor Isoforms in Female Sexual Behavior Induced by Progestins in Rats

“…The differential transcriptional activity of PR-A and PR-B has been associated with the presence of an activation function in the N-terminal of PR-B that is absent in PR-A, and the distinct affinity for coregulators: PR-A has a higher affinity for corepressors such as the silencing mediator of retinoid and thyroid hormone receptor (SMRT) whereas PR-B exhibits a higher affinity for coactivators such as steroid receptor coactivator-1 (SRC-1) [19, 20]. In the rat brain, PR isoform expression ratio and regulation vary among different cerebral regions, through the estrous cycle, and in a sex- and age-specific manner [21,22,23,24].…”