CREB Binding Protein (CBP) Activation Is Required for Luteinizing Hormone Beta Expression and Normal Fertility in Mice

Abstract

Normal function of the hypothalamic-pituitary-gonadal axis is dependent on gonadotropin-releasing hormone (GNRH)-stimulated synthesis and secretion of luteinizing hormone (LH) from the pituitary gonadotroph. While the transcriptional coactivator CREB binding protein (CBP) is known to interact with Egr-1, the major mediator of GNRH action on the Lhb gene, the role of CBP in Lhb gene expression has yet to be characterized. We show that in the L␤T2 gonadotroph cell line, overexpression of CBP augmented the response to GNRH and that knockdown of CBP eliminated GNRH responsiveness. While GNRH-mediated phosphorylation of CBP at Ser436 increased the interaction with Egr-1 on the Lhb promoter, loss of this phosphorylation site eliminated GNRH-mediated Lhb expression in L␤T2 cells. In vivo, loss of CBP phosphorylation at Ser436 rendered female mice subfertile. S436A knock-in mice had disrupted estrous cyclicity and reduced responsiveness to GNRH. Our results show that GNRHmediated phosphorylation of CBP at Ser436 is required for Egr-1 to activate Lhb expression and is a requirement for normal fertility in female mice. As CBP can be phosphorylated by other factors, such as insulin, our studies suggest that CBP may act as a key regulator of Lhb expression in the gonadotroph by integrating homeostatic information with GNRH signaling. Reproductive viability in humans is dependent on normal function of the hypothalamic-pituitary-gonadal axis. Gonadotropin-releasing hormone (GNRH) is produced by hypothalamic neurosecretory cells and released in a pulsatile manner into the hypothalamo-hypophyseal portal circulation, through which the hormone is transported to the anterior pituitary gland. GNRH bound to its receptor on pituitary gonadotrophs results in an increase in GNRH receptor density and stimulates the synthesis and secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) into the circulation (14,30,41). LH and FSH are heterodimeric glycoproteins consisting of a common ␣-subunit and hormone-specific ␤-subunit encoded by the Lhb and Fshb genes, respectively. Lhb and Fshb gene expression in the anterior pituitary is dependent on pulsatile GNRH secretion. Rapid, highamplitude GNRH pulses stimulate an increase in Lhb mRNA levels, leading to an increase in LH synthesis and release from the gonadotroph (11,18,45,51).At least three major transcription factors are important for Lhb gene expression: steroidogenic factor 1 (SF-1), pituitary homeobox factor 1 (Pitx1), and early growth response factor 1 (Egr-1). GNRH stimulates the expression of Egr-1, resulting in Egr-1 binding to two conserved cis elements of the proximal Lhb promoter (5, 43, 49). Egr-1 is rapidly and markedly induced by GNRH, while SF-1 and Pitx1 expression levels are unchanged following GNRH administration (43, 49). In rat, Egr-1 expression increases in proestrous, suggesting that it may be an important signal for ovulation (39). Loss of Egr-1 in the gonadotroph, unlike loss of SF-1 or Pitx1, renders the cell unable to respond to GNRH, and Egr-1...

The Myb-p300-CREB axis modulates intestine homeostasis, radiosensitivity and tumorigenesis

“…To further investigate the creb KO colon and SI architecture, we explored the relative numbers of Chromogranin A+ve cells, as CREB regulates the ChrA gene 27, 28 and neuroendocrine cell function. 29, 30, 31, 32 However, the number of these cells appeared elevated in the SI and significantly increased in the colon in creb KO mice. Goblet cells and mucin production, as judged by period acid shift (PAS) histochemistry, was more intense in the creb KO colons (Supplementary Figure 2).…”

Systematic Analysis of Protein Interaction Network Associated with Azoospermia

“…Nephrocystin is involved in spermatogenesis and is required for the differentiation of early elongating spermatids into spermatozoa [21]. Previously, it has been reported that knockdown CREBBP eliminated gnrh; thus, CREBBP may function to regulate the reproductive process [22]. The rest of the proteins identified as hub and key nodes are those previously associated with azoospermia.…”

The regulation of reproductive neuroendocrine function by insulin and insulin-like growth factor-1 (IGF-1)

“…2005), and may be necessary to regulate an especially large number of separate processes including LH and FSH synthesis and secretion (Stanislaus et al 1998a), GnRH receptor expression and GnRH receptor desensitization. GnRHR can couple with Gαq/11, GαI, and Gαs (Hawes et al 1993, Stanislaus et al 1998b), and has been shown to exert effects through known insulin targets such as ERK (Bliss et al 2009), PI3K (Navratil et al 2009), FOXO1 (Arriola et al 2012) and CBP (Miller et al 2012). …”