This application investigates three new and discrete aspects of the GnRH transcriptional network.
Aim 1 should reveal to what extent post-transcriptional and post-translational mechanisms interface with GnRH regulated transcription of Egr1. While these mechanisms have been studied for IEGs in other systems, their role in gonadotropes remains unknown. We are convinced that the combination of post-transcriptional and post-translational contributions will provide a powerful one, two punch that ensures Egr1 mRNA and EGR1 protein reach maximally effective concentrations after transcriptional stimulation by GnRH.
Aim 2 draws upon steadily emerging evidence, including our own, indicating that 2-catenin may be viewed as a new member of the GnRH signaling pathway that plays an instrumental role in regulating hormone stimulated expression of Jun mRNA and possibly Atf3 and Egr1 mRNA. Almost nothing is known about the signaling pathways GnRH uses to regulate transcription of Jun. Our approach addresses the role of 2-catenin as well as major pathway components such as PKC, PKA, and PI3K. Thus, Aim 2 is comprehensive and addresses a timely and important topic. The studies in Aim 3 address another novel feature of 2-catenin, namely its role as a required co-activator for SF1, certainly in acting permissively to allow Lhb to respond to transcriptional cues that flow from GnRH through Egr1. We suspect that the role of 2-catenin is broader and will extend to the other three signature genes that depend on SF1 for their expression.
While Aims 1 and 2 are heavy on molecular detail and reliant on a gonadotrope cell line, Aim 3 uses transgenic technology to determine whether the requirement for 2-catenin and SF1 occurs in vivo and within the setting of a functional HPG axis. Most importantly, the transgenic approaches described in Aim 3 provide an exciting future direction that will be used to determine whether post-transcriptional and post-translational modifications uncovered for Egr1 have a significant impact when studied in vivo and in the context of a functional HPG axis. In short, we have charted an exciting new course that will deepen our mechanistic understanding of how GnRH controls gonadotrope homeostasis when signaling through a complex transcriptional network. Project Narrative: Normal reproductive function requires precise hypothalamic-gonadal control of the pituitary gonadotropins, LH and FSH. Too much or too little of either hormone disrupts gonadal function causing a spectrum of diseases ranging from infertility to endocrine cancer. This application focuses on GnRH, the hypothalamic hormone that signals through a cascade of protein kinases to regulate transcription, translation and ultimately secretion of LH and FSH from gonadotropes. Within this context, we consider how a tiered network of primary, secondary, and tertiary genes respond to the GnRH signal as well as contributions from components that act independently of GnRH. Completing these aims will deepen our understanding of the mechanistic coordination of gonadotrope gene expression required for maintaining reproductive homeostasis within the hypothalamic-pituitary-gonadal axis. Such an understanding is required for identifying new therapeutic targets and agents that can be used to either promote fertility or treat infertility and other endocrine disorders including hormone-dependent cancer.
|Binder, April K; Grammer, Jean C; Herndon, Maria K et al. (2012) GnRH regulation of Jun and Atf3 requires calcium, calcineurin, and NFAT. Mol Endocrinol 26:873-86|
|Chauvin, Theodore R; Herndon, Maria K; Nilson, John H (2012) Cold-shock-domain protein A (CSDA) contributes posttranscriptionally to gonadotropin-releasing hormone-regulated expression of Egr1 and indirectly to Lhb. Biol Reprod 86:53|
|Salisbury, Travis B; Binder, April K; Grammer, Jean C et al. (2009) GnRH-regulated expression of Jun and JUN target genes in gonadotropes requires a functional interaction between TCF/LEF family members and beta-catenin. Mol Endocrinol 23:402-11|