Acute Disruption of Select Steroid Receptor Coactivators Prevents Reproductive Behavior in Rats and Unmasks Genetic Adaptation in Knockout Mice

Abstract

Estrogen (E) and progesterone exert profound influence on development and reproduction. In vitro, steroid receptor coactivators (SRCs) are nuclear proteins that interact with DNA-bound steroid receptors to potentiate their transcriptional efficiency. We examined the effects of antisense oligonucleotides to SRC-1, SRC-2, and SRC-3 on female sexual behavior and steroid receptor-mediated transcription. Rat (r) SRC-1, rSRC-2, and rSRC-3 genes were cloned. Our results reveal a significant inhibitory effect by antisense (AS) to SRC-1 and SRC-2, but not SRC-3, on hormone-induced reproductive behavior. Importantly, sexual behavior was attenuated through estrogen receptor alpha (ERalpha)-dependent, rather than progesterone receptor (PR)-dependent, transcription, as E failed to induce the synthesis of PR content in the medial basal hypothalamus, and immunoreactive PR in the ventromedial nucleus were depleted in tissue from rSRC-1-AS- and rSRC-2-AS-treated, but not rSRC-3-AS-treated, rats primed with E. Consistent with interruption of ERalpha-induced transcription, high dose of E and epidermal growth factor alone failed to induce sexual behavior in females treated with either rSRC-1-AS or SRC-2-AS. Immunoreactive SRC-1 and SRC-2, but not SRC-3, proteins were abundant in the ventromedial nucleus, thus demonstrating that the biological activities of hypothalamic steroid receptors are selectively regulated by regional distribution of specific SRCs. As SRC-1 knockout mice have only a slight loss in reproductive function, the possibility that genetic adaptation occurs during development was tested. Mouse (m) SRC-1-AS suppressed lordosis in wild-type, but not SRC-1, knockout mice, whereas mSRC-2-AS suppressed behavior in both genotypes. mSRC-3-AS had no effect in either genotype, and SRC-3 knockout mice exhibited full receptivity. Collectively, the findings clearly implicate dual regulation of ERalpha-dependent function by SRC-1 and SRC-2 in the intact female brain. In the genetic, but not acute, absence of SRC-1, up-regulation of SRC-2 serves as a critical adaptive mechanism during female development.

Inhibition of Steroid Receptor Coactivator-1 Blocks Estrogen and Androgen Action on Male Sex Behavior and Associated Brain Plasticity

“…In a previous study that investigated the actions of coactivators for adult sexual behaviors, both SRC-1 and CBP were blocked and only moderate effects were observed on the ability of estrogen to facilitate the lordosis response (intensity only), as well as to induce the expression of the progesterone receptor in female rats (Molenda et al, 2002). Another study, however, demonstrated a profound inhibition of lordosis in female rats treated with SRC-1 antisense (Apostolakis et al, 2002). Studies of SRC-1 knock-out mice also found no effect on the development of the androgen-dependent motoneurons within the spinal nucleus of the bulbocavernosus (Monks et al, 2003), suggesting that this cofactor may not be important for androgendependent neuroendocrine processes.…”

“…SRC-1 may also play a role in the estrogenic activation of female sexual behaviors (Molenda et al, 2002). Studies with SRC-1 knock-out mice found no significant effects on female sexual responding, but it was demonstrated that developmental compensation had occurred based on the upregulation of other coactivators (Apostolakis et al, 2002). We wanted to establish whether SRC-1 is necessary for the behavioral activation by testosterone of male-typical sexual responding in adult animals and for the associated neural changes that are regulated by this steroid.…”

Steroid receptor coactivator-1 is necessary for regulation of corticotropin-releasing hormone by chronic stress and glucocorticoids

“…However, earlier studies with these mice have shown that increased SRC-2 expression can compensate and therefore mask certain phenotypes, such as involvement of SRC-1 in estrogen receptor signaling in the hypothalamus (13,19). The complexity of the HPA axis, and the number of check points that lie between mRNA expression of the secretagogues CRH and ACTH and actual secretion of biologically active peptides (41, 42) may allow genomic compensation that is almost complete under basal conditions.…”

“…The p160 coregulator Steroid Receptor Coactivator (SRC-1) is strongly expressed in brain (11), can affect neuronal differentiation (12), and mediates effects of androgens and estrogens in brain areas involved in sexual behavior (13)(14)(15). SRC-1 is a multimodal protein that can also interact with nonnuclear receptor transcription factors (16,17), but to date these have not been shown to be relevant in the brain.…”

Hypothalamic progesterone receptor-A mediates gonadotropin surges, self priming and receptivity in estrogen-primed female mice

“…Tactile stimulation that accompanies mounting activates the ascending portion of this circuitry for the initiation of PR-mediated lordosis (Pfaff & Schwartz--Giblin 1998). Although we (Apostolakis et al 1996(Apostolakis et al , 2000(Apostolakis et al , 2002(Apostolakis et al , 2004(Apostolakis et al , 2005 and others (Blaustein 2004) have reported steroid-and/or steroid receptor-independent lordosis induced by select neurotransmitters, neuropeptides, and growth factors, the present study focused on Prog-and PR-mediated sexual behavior. Therefore, we used mice in which PR-A and PR-B were selectively disrupted to analyze the functional role of hypothalamic PR isoforms in female reproduction.…”