Differential Regulation of Two Forms of Gonadotropin-Releasing Hormone Messenger Ribonucleic Acid in Human Granulosa-Luteal Cells**This work was supported by grants from the Medical Research Council of Canada.

Abstract

Until recently, the primate brain was thought to contain only one form of GnRH known as mammalian GnRH (GnRH-I). The recent cloning of a second form of GnRH (GnRH-II) with characteristics of chicken GnRH-II in the primate brain has prompted a reevaluation of the role of GnRH in reproductive functions. In the present study, we investigated the hormonal regulation of GnRH-II messenger RNA (mRNA) and its functional role in the human granulosa-luteal cells (hGLCs), and we provided novel evidence for differential hormonal regulation of GnRH-II vs. GnRH-I mRNA expression. Human GLCs were treated with various concentrations of GnRH-II, GnRH-II agonist (GnRH-II-a), or GnRH-I agonist (GnRH-I-a; leuprolide) in the absence or presence of FSH or human CG (hCG). The expression levels of GnRH-II, GnRH-I, and GnRH receptor (GnRHR) mRNA were investigated using semiquantitative or competitive RT-PCR. A significant decrease in GnRH-II and GnRHR mRNA levels was observed in cells treated with GnRH-II or GnRH-II-a. In contrast, GnRH-I-a revealed a biphasic effect (up- and down-regulation) of GnRH-I and GnRHR mRNA, suggesting that GnRH-I and GnRH-II may differentially regulate GnRHR and their ligands (GnRH-I and GnRH-II). Treatment with FSH or hCG increased GnRH-II mRNA levels but decreased GnRH-I mRNA levels, further indicating that GnRH-I and GnRH-II mRNA levels are differentially regulated. To investigate the physiological role of GnRH-II, hGLCs were treated with GnRH-II or GnRH-II-a in the presence or absence of hCG, for 24 h, and progesterone secretion was measured by RIA. Both GnRH-II and GnRH-II-a inhibited basal and hCG-stimulated progesterone secretion, effects which were similar to the effects of GnRH-I treatment on ovarian steroidogenesis. Next, hGLCs were treated with various concentrations of GnRH-II, GnRH-II-a, or GnRH-I-a; and the expression levels of FSH receptor and LH receptor were investigated using semiquantitative RT-PCR. A significant down-regulation of FSH receptor and LH receptor was observed in cells treated with GnRH-II, GnRH-II-a, and GnRH-I-a, demonstrating that GnRH-II and GnRH-I may exert their antigonadotropic effect by down-regulating gonadotropin receptors. Interestingly, GnRH-II and GnRH-II-a did not affect basal and hCG-stimulated intracellular cAMP accumulation, suggesting that the antigonadotropic effect of GnRH-II may be independent of modulation of cAMP levels. Taken together, these results suggest that GnRH-II may have biological effects similar to those of GnRH-I but is under differential hormonal regulation in the human ovary.

Differential role of gonadotropin-releasing hormone on human ovarian epithelial cancer cell invasion

“…The classical mammalian GnRH (now referred to as GnRH-I) as well as a second form of GnRH (GnRH-II) that is identical to chicken GnRH-II are expressed in humans [5,6]. In addition to the well-established function of GnRH in the control of gonadotropin secretion from the pituitary, both GnRH-I and GnRH-II have been shown to exert autocrine and/or paracrine effects in extrapituitary tissues, including the ovary [7,8]. GnRH-I and its receptor are expressed in 80% of human ovarian epithelial tumors, ovarian surface epithelial (OSE) cells, and ovarian cancer cell lines [9,10], suggesting that this decapeptide hormone may be an autocrine and/or paracrine regulator of the OSE and play a role in the pathophysiology of ovarian cancer [11][12][13][14][15].…”

Role of gonadotropin‐releasing hormone‐II and its receptor in swine reproduction

“…Cellular signaling differences have been reported between the cognate receptors for GnRH‐I and GnRH‐II. Consistent with GnRHR1, GnRHR2 couples to G αq/11 to initiate inositol triphosphate production, mobilization of calcium and protein kinase C (PKC) activation (Kang et al, 2001; Liu et al, 2009; Millar, 2003). Although limited studies exist, signaling pathways downstream of PKC differ following ligand binding to either GnRHR‐I and GnRHR‐II.…”

“…GnRH‐II and its receptor are present in many cells and tissues of the female reproductive tract (Millar, 2003); however, very little research has been performed to elucidate how this ligand‐receptor interaction mediates female reproductive processes. Although data is limited, GnRH‐II and/or GnRHR‐II have been implicated in ovarian steroidogenesis, including the regulation of progesterone synthesis in humans (Kang et al, 2001), rhesus macaques (Siler‐Khodr et al, 2004, 2006) and baboons (Siler‐Khodr et al, 2003). Therefore, we sought to examine the effect of GnRHR‐II KD on progesterone production in gilts.…”

Gonadotropin-releasing hormone II: a multi-purpose neuropeptide

“…Molecular analysis has shown that the human type-2 GnRH receptor contains a stop codon and is thought to be inactive (Faurholm et al 2001;Neill 2002). This is odd in light of the wide distribution of GnRH II mRNA in many human tissues including the brain, prostate, ovary, kidney, and bone marrow (White et al 1998;Choi et al 2001;Kang et al 2001). The high affinity of GnRH II for the type-1 GnRH receptor suggests that, despite the type-2 GnRH receptor in humans being nonfunctional, GnRH II could act through the type-1 GnRH receptor (Millar 2003).…”