Proliferation of TSU-Pr1, a human prostatic carcinoma cell line is stimulated by gonadotropin-releasing hormone

Anti-cancer effect of GV1001 for prostate cancer: function as a ligand of GnRHR

GV1001, a 16-amino acid fragment of the human telomerase reverse transcriptase catalytic subunit (hTERT), has been developed as an injectable formulation of cancer vaccine. Here, we revealed for the first time that GV1001 is a novel ligand for gonadotropin-releasing hormone receptor (GnRHR). The docking prediction for GV1001 against GnRHR showed high binding affinity. Binding of GV1001 to GnRHR stimulated the Gαs-coupled cAMP signaling pathway and antagonized Gαq-coupled Ca2+ release by leuprolide acetate (LA), a GnRHR agonist. Repeated injection of GV1001 attenuated both serum testosterone level and seminal vesicle weight via desensitization of hypothalamic-pituitary-gonadal (HPG) axis. We then tested whether GV1001 has an inhibitory effect on tumor growth of LNCaP cells, androgen receptor-positive human prostate cancer (PCa) cells. GV1001 significantly inhibited tumor growth and induced apoptosis in LNCaP-implanted xenografts. Interestingly, mRNA expressions of matrix metalloproteinase 2 and matrix metalloproteinase 9 were suppressed by GV1001, but not by LA. Moreover, GV1001 significantly inhibited the proliferation and migration of PCa cells and induced apoptosis in a concentration-dependent manner. Our findings suggest that GV1001 functions as a biased GnRHR ligand to selectively stimulate the Gαs/cAMP pathway, with anti-proliferative and anti-migratory effects on human PCa.

Regulation of the cell proliferation and migration as extra-pituitary functions of GnRH

GnRH was originally identified as a hypothalamic factor which promotes gonadotropin release from the pituitary and was named gonadotropin-releasing hormone (GnRH). However, broad tissue distributions of GnRH and the GnRH receptor in various extrapituitary tissues and organs have been revealed and it has been suggested that GnRH has extrapituitary effects such as neuromodulation, immunomodulation, and regulation of follicular atresia and ovulation. Although a number of studies have been performed on these effects, little is known about the molecular mechanisms and physiological settings in which GnRH exerts its activities in extrapituitary organs or tissues. Our recent studies had demonstrated that GnRH is able to regulate both cell proliferation and cell migration at much lower concentration than that in the peripheral circulation by using human carcinoma cell lines. Moreover, stimulating activity of GnRH on the developing chick embryonic GnRH neurons was also demonstrated and strongly suggests possible involvement of GnRH in some of extrapituitary functions. This mini-review intends to provide solid evidence of GnRH activity in the regulation of cell proliferation and migration and its physiological relevance in extra-pituitary functions. Recent other research, including that in various invertebrates, provides new insight into the evolutionary scenarios of GnRH signaling systems, and GnRH functions. Both proliferating and migrating activities are important fundamental cellular activities and could provide an important clue into understanding what the driving force behind the evolution of the GnRH signaling system was.

Gonadotropin-releasing hormone receptor system: modulatory role in aging and neurodegeneration

Receptors for hormones of the hypothalamic-pituitary-gonadal axis are expressed throughout the brain. Age-related decline in gonadal reproductive hormones cause imbalances of this axis and many hormones in this axis have been functionally linked to neurodegenerative pathophysiology. Gonadotropin-releasing hormone (GnRH) plays a vital role in both central and peripheral reproductive regulation. GnRH has historically been known as a pituitary hormone; however, in the past few years, interest has been raised in GnRH actions at non-pituitary peripheral targets. GnRH ligands and receptors are found throughout the brain where they may act to control multiple higher functions such as learning and memory function and feeding behavior. The actions of GnRH in mammals are mediated by the activation of a unique rhodopsin-like G protein-coupled receptor that does not possess a cytoplasmic carboxyl terminal sequence. Activation of this receptor appears to mediate a wide variety of signaling mechanisms that show diversity in different tissues. Epidemiological support for a role of GnRH in central functions is evidenced by a reduction in neurodegenerative disease after GnRH agonist therapy. It has previously been considered that these effects were not via direct GnRH action in the brain, however recent data has pointed to a direct central action of these ligands outside the pituitary. We have therefore summarized the evidence supporting a central direct role of GnRH ligands and receptors in controlling central nervous physiology and pathophysiology.

Gonadotropin-releasing hormone: GnRH receptor signaling in extrapituitary tissues

Gonadotropin-releasing hormone (GnRH) has historically been known as a pituitary hormone; however, in the past few years, interest has been raised in locally produced, extrapituitary GnRH. GnRH receptor (GnRHR) was found to be expressed in normal human reproductive tissues (e.g. breast, endometrium, ovary, and prostate) and tumors derived from these tissues. Numerous studies have provided evidence for a role of GnRH in cell proliferation. More recently, we and others have reported a novel role for GnRH in other aspects of tumor progression, such as metastasis and angiogenesis. The multiple actions of GnRH could be linked to the divergence of signaling pathways that are activated by GnRHR. Recent observations also demonstrate cross-talk between GnRHR and growth factor receptors. Intriguingly, the classical G(alphaq)-11-phospholipase C signal transduction pathway, known to function in pituitary gonadotropes, is not involved in GnRH actions at nonpituitary targets. Herein, we review the key findings on the role of GnRH in the control of tumor growth, progression, and dissemination. The emerging role of GnRHR in actin cytoskeleton remodeling (small Rho GTPases), expression and/or activity of adhesion molecules (integrins), proteolytic enzymes (matrix metalloproteinases) and angiogenic factors is explored. The signal transduction mechanisms of GnRHR in mediating these activities is described. Finally, we discuss how a common GnRHR may mediate different, even opposite, responses to GnRH in the same tissue/cell type and whether an additional receptor(s) for GnRH exists.

Gonadotropin-releasing hormone induces actin cytoskeleton remodeling and affects cell migration in a cell-type-specific manner in TSU-Pr1 and DU145 cells

GnRH was first identified as the hypothalamic decapeptide that promotes gonadotropin release from pituitary gonadotropes. Thereafter, direct stimulatory and inhibitory effects of GnRH on cell proliferation were demonstrated in a number of types of primary cultured cells and established cell lines. Recently, the effects of GnRH on cell attachment, cytoskeleton remodeling, and cell migration have also been reported. Thus, the effects of GnRH on various cell activities are of great interest among researchers who study the actions of GnRH. In this study, we demonstrated that GnRH induces actin cytoskeleton remodeling and affects cell migration using two human prostatic carcinoma cell lines, TSU-Pr1 and DU145. In TSU-Pr1, GnRH-I and -II induced the filopodia formation of the cells and promoted cell migration, whereas in DU145, GnRH-I and -II induced the formation of the cells with stress fiber and inhibited cell migration. In our previous studies, we reported the stimulatory and inhibitory effects of GnRH on the cell proliferation of TSU-Pr1 and DU145 cells. This study provides the first evidence for the effects of GnRH on actin cytoskeleton remodeling and cell migration of cells in which cell proliferation was affected by GnRH at the same time. Moreover, we also demonstrated that the same human GnRH receptor subtype, human type I GnRH receptor, is essential for the effects of GnRH-I and -II on actin cytoskeleton remodeling and cell migration in both TSU-Pr1 and DU145 cells using the technique of gene knock-down by RNA interference.

Regulation of expression of mammalian gonadotrophin-releasing hormone receptor genes

Gonadotrophin-releasing hormone (GnRH), acting via its cognate GnRH receptor (GnRHR), is the primary regulator of mammalian reproductive function, and hence GnRH analogues are extensively used in the treatment of hormone-dependent diseases, as well as for assisted reproductive techniques. In addition to its established endocrine role in gonadotrophin regulation in the pituitary, evidence is rapidly accumulating to support the expression and functional roles for two forms of GnRHR (GnRHR I and GnRHR II) in multiple and diverse extra-pituitary mammalian tissues and cells. These findings, together with findings indicating that mutations of the GnRHR are linked to the disease hypogonadotrophic hypogonadism and that GnRHRs play a direct role in neuronal migration and reproductive cancers, have presented new therapeutic targets and intensified research into the structure, function and mechanisms of regulation of expression of GnRHR genes. The present review focuses on the current knowledge on tissue-specific and hormonal regulation of transcription of mammalian GnRH receptor genes. Emerging insights, such as the discovery of diverse regulatory mechanisms in pituitary and extra-pituitary cell types, nonclassical mechanisms of steroid regulation, the use of composite elements for cell-specific expression, the increasing profile of hormones involved in regulation, the complexity of kinase pathways that target the GnRHR I gene, as well as species-differences, are highlighted. Although further research is necessary to understand the mechanisms of regulation of expression of GnRHR I and GnRHR II genes, the GnRHR is emerging as a potential target gene for facilitating cross-talk between neuroendocrine, immune and stress-response systems in multiple tissues via autocrine, paracrine and endocrine signalling.