Metastin receptor is overexpressed in papillary thyroid cancer and activates MAP kinase in thyroid cancer cells

Role of the tumor microenvironment in regulating the anti-metastatic effect of KISS1

KISS1, a metastasis suppressor gene, has been shown to block metastasis without affecting primary tumor formation. Loss of KISS1 leads to invasion and metastasis in multiple cancers, which is the leading cause of cancer morbidity and mortality. The discovery of KISS1 has provided a ray of hope for early clinical diagnosis and for designing effective treatments targeting metastatic cancer. However, this goal requires greater holistic understanding of its mechanism of action. In this review, we go back into history and highlight some key developments, from the discovery of KISS1 to its role in regulating multiple physiological processes including cancer. We discuss key emerging roles for KISS1, specifically interactions with tissue microenvironment to promote dormancy and regulation of tumor cell metabolism, acknowledged as some of the key players in tumor progression and metastasis. We finally discuss strategies whereby KISS1 might be exploited clinically to treat metastasis.

Molecular evolution of GPCRs: Kisspeptin/kisspeptin receptors

Following the discovery of kisspeptin (Kiss) and its receptor (GPR54 or KissR) in mammals, phylogenetic studies revealed up to three Kiss and four KissR paralogous genes in other vertebrates. The multiplicity of Kiss and KissR types in vertebrates probably originated from the two rounds of whole-genome duplication (1R and 2R) that occurred in early vertebrates. This review examines compelling recent advances on molecular diversity and phylogenetic evolution of vertebrate Kiss and KissR. It also addresses, from an evolutionary point of view, the issues of the structure-activity relationships and interaction of Kiss with KissR and of their signaling pathways. Independent gene losses, during vertebrate evolution, have shaped the repertoire of Kiss and KissR in the extant vertebrate species. In particular, there is no conserved combination of a given Kiss type with a KissR type, across vertebrate evolution. The striking conservation of the biologically active ten-amino-acid C-terminal sequence of all vertebrate kisspeptins, probably allowed this evolutionary flexibility of Kiss/KissR pairs. KissR mutations, responsible for hypogonadotropic hypogonadism in humans, mostly occurred at highly conserved amino acid positions among vertebrate KissR. This further highlights the key role of these amino acids in KissR function. In contrast, less conserved KissR regions, notably in the intracellular C-terminal domain, may account for differential intracellular signaling pathways between vertebrate KissR. Cross talk between evolutionary and biomedical studies should contribute to further understanding of the Kiss/KissR structure-activity relationships and biological functions.

Kisspeptin-10 inhibits cell migration in vitro via a receptor-GSK3 beta-FAK feedback loop in HTR8SVneo cells

Kisspeptin inhibits cancer cell metastasis and placental trophoblast cell migration. Kisspeptin gene expression in the placenta and circulating kisspeptin levels change during normal pregnancy and they are altered in preeclampsia. We therefore assessed the effect of kisspeptin-10 on the in vitro migration of a human placental cell line derived from first trimester extravillious trophoblasts (HTR8SVneo). HTR8SVneo cells specifically bound 125I-Kisspeptin-10 but kisspeptin-10 did not induce inositol phosphate production. Cell migration was inhibited by kisspeptin-10 with a maximal inhibition at 100nM. The signaling pathways involved in inhibition of cell migration were examined. Treatment with kisspeptin-10 elicited phosphorylation of GSK3 beta at Ser9 (which inhibits activity), with a 3-fold increase at 5 min. Transient phosphorylation of ERK1/2 and p38MAPK peaked at 10min. Phosphorylation of focal adhesion kinase (FAK) at Tyr925 increased 3-fold at 10 min. Inhibition of GSK3 beta correlated with release of beta-catenin into the cytoplasm. These signaling events were differentially blocked by inhibitors of G(q/11), Src, EGFR, PI(3)K, PKC and MEK. The data suggest that kisspeptin/GPR54 EGF-receptor transactivation leads to phosphorylation of ERK1/2, causing activation of p90rsk which in turn inhibits GSK3 beta via Ser9 phosphorylation. Inactivation of GSK3 beta results in release of beta-catenin into the cytoplasm, affecting cell-cell adhesion and Tyr925 phosphorylation of FAK, which increases phosphorylation of ERK1/2 via RAS/Raf-1 creating a feedback loop to enhance the effects on migration. These findings indicate that kisspeptin-10 inhibits the migration of human placental trophoblast-derived HTR8SVneo cells by stimulating complex ERK1/2-p90rsk-GSK3 beta-FAK feedback interactions.

Q36R polymorphism of KiSS-1 gene in Brazilian head and neck cancer patients

The KiSS-1 metastasis-suppressor gene (KiSS-1) product (metastin, kisspeptin) is reported to act after binding with the natural ligand of a G-protein coupled receptor and this gene product inhibits chemotaxis, invasion, and metastasis of cells. The aim of this study was to evaluate the Q36R polymorphism of KiSS-1 in patients with head and neck cancer and to compare the results with healthy individuals and its association with clinicopathological parameters. Gender, age, smoking and alcohol consumption were analyzed for 744 individual (252 head and neck cancer patients and in 522 control individuals). The molecular analysis of these individuals was made after extraction of genomic DNA using the SSCP-PCR technique. This study did not reveal any significant differences in genotype frequencies between healthy individuals and patients with head and neck cancer or with the clinical parameters. This study showed an increase frequency of the Q36R polymorphism in pharyngeal cancer.

Relation between (99m)Tc-tetrofosmin thyroid scintigraphy and mitogen-activated protein kinase in papillary thyroid cancer patients

PURPOSE

The aim of this study was to investigate the relation between (99m)Tc-tetrofosmin uptake and extracellular signal-regulated kinase mitogen-activated protein kinase (ERK MAPK) expression in papillary thyroid cancer patients.

MATERIALS AND METHODS

Our study population consisted of 14 patients. The histopathological findings for all patients were confirmed by surgery. Patients were administ 740 MBq of (99m)Tc-tetrofosmin. The tumor/background (T/B) ratios in regions of interest (ROIs) were measured at 10 min, 1 h, and 3 h to determine the uptake by papillary cancer. Immunohistopathological staining was performed, and the expression of phospho-ERK MAPK in papillary cancer was investigated. The relation between the expression of phospho-ERK MAPK and the T/B ratio was examined using the Mann-Whitney U-test.

RESULTS

(99m)Tc-tetrofosmin uptake was positive in all patients. There was a statistically significant relation between the T/B ratio (at 3 h) and the expression of phospho-ERK MAPK but not with the T/B ratio at 10 min or 1 h: T/B ratio at 10 min (P = 0.32), at 1 h (P = 0.62), and at 3 h (P = 0.0072).

CONCLUSION

Our results suggest that the relation between (99m)Tc-tetrofosmin uptake (3 h T/B ratio) may lead us to assume cell proliferation of papillary cancer.

Metastatic dormancy and progression in thyroid cancer: targeting cells in the metastatic frontier

BACKGROUND

Metastatic dormancy, or the ability of cancer cells to survive but not progress in metastatic environments, is now recognized to be a common occurrence in cancer.

SUMMARY

From a clinical perspective, this phenomenon is common in metastatic well-differentiated thyroid cancer, whereby patients often present with distant metastases that remain stable for years after removal of the primary tumor and subsequent treatment. Experimental data suggest that metastases can develop throughout the life of a cancer and that progression in the distant environment depends on the biology of the cancer cells that metastasize as well as that of the various microenvironments they encounter. A firm understanding of how thyroid cancer cell progression is regulated in different metastatic environments is necessary to devise effective therapies targeting progressive metastatic thyroid cancer.

CONCLUSION

In this review, current models of metastatic progression and factors that regulate late-stage metastatic progression that are particularly relevant for thyroid cancer are discussed.

International Union of Basic and Clinical Pharmacology. LXXVII. Kisspeptin receptor nomenclature, distribution, and function

Kisspeptins are members of the Arg-Phe amide family of peptides, which have been identified as endogenous ligands for a G-protein-coupled receptor encoded by a gene originally called GPR54 (also known as AXOR12 or hOT7T175). After this pairing, the gene has been renamed KISS1R. The International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification recommends that the official name for the receptor is the kisspeptin receptor to follow the convention of naming the receptor protein after the endogenous ligand. The endogenous ligand was initially called metastin, after its role as a metastasis suppressor, and is now referred to as kisspeptin-54 (KP-54), a C-terminally amidated 54-amino acid peptide cleaved from the 145-amino acid gene product. Shorter C-terminal cleavage fragments [KP-14, KP-13 and KP-10 (the smallest active fragment)] are also biologically active. Both receptor and peptide are widely expressed in human, rat, and mouse; the receptor sequence shares more than 80% homology in these species. Activation of the kisspeptin receptor by kisspeptin is via coupling to G(q/11) and the phospholipase C pathway, causing Ca(2+) mobilization. Mutations in the KISS1R gene result in hypogonadotropic hypogonadotropism, and targeted disruption of Kiss1r in mice reproduces this phenotype, which led to the discovery of the remarkable ability of the kisspeptin receptor to act as a molecular switch for puberty. In addition to regulating the reproductive axis, the kisspeptin receptor is also implicated in cancer, placentation, diabetes, and the cardiovascular system.

Relationship of kiss-1 gene expression with the TNM stage and prognosis in gastric cancer

AIM: To investigate the clinical value of the expression of kiss-1 (a metastasis suppressor gene) in gastric cancer.

METHODS: The expression of kiss-1 mRNA in gastroscopic biopy specimens taken from 30 gastric cancer patients was detected by reverse transcription-polymerase chain reaction. Based on kiss-1 expression level, the patients were divided into two groups: those with high and low expression of kiss-1 mRNA. The clinicopathologic characteristics of gastric cancer were then compared between the two groups.

RESULTS: The expression levels of kiss-1 mRNA in stage III-IV (TNM) gastric cancer patients (t = 1.87, F = 1.00, P = 0.025) and those with frequent venous invasion (t = 3.51, F = 1.22, P = 0.009) or frequent distant lymph node metastasis (t = 2.26, F= 2.17, P = 0.009) were significantly lower than those in stage I-II (TNM) gastric cancer patients and those without venous invasion or distant lymph node metastasis, respectively.

CONCLUSION: The expression level of kiss-1 mRNA can be used as an important biological marker for evaluating the TNM stage and prognosis of gastric cancer.

Kisspeptin increases GnRH mRNA expression and secretion in GnRH secreting neuronal cell lines

Kisspeptins, and their G-protein coupled receptor 54 (GPR54), are key components in the regulation of gonadotropin-releasing hormone (GnRH) secretion in humans and other mammals. Several studies demonstrate that the central or systemic administration of kisspeptin increases GnRH and gonadotropin secretion in both prepubertal and adult animals; however, the cellular targets and intracellular mechanisms of action in the central reproductive axis are unclear. In this study, we documented the presence of GPR54 in two GnRH secreting neuronal cell lines (GT1-7 and GN11). Kisspeptin treatment increases GnRH secretion and GnRH mRNA levels in a dose and time dependent manner. 10(-9)M kisspeptin maximally stimulated GnRH secretion by 2-fold and GnRH mRNA levels up to 4-fold after 4h of treatment in both cell lines. Negative regulation by 17beta-estradiol of GnRH secretion and GnRH mRNA was antagonized by kisspeptin. Co-treatment with kisspeptin and 17beta-estradiol increased GnRH secretion by 2-fold and GnRH mRNA by 4-fold over estradiol alone in both cell lines. Intracellular signaling pathway studies showed that an ERK1/2 MAPK inhibitor (PD98059) and a PI3K inhibitor, LY29402, attenuated the effects of kisspeptin on GnRH mRNA modulation. Furthermore, Western blot analysis showed that phosphorylation of both MAPK and Akt substrates increased with kisspeptin treatment. This work demonstrates that the kisspeptin-GPR54 system plays a significant role stimulating GnRH secretion and positive regulation of GnRH mRNA levels in GnRH neurons in culture, and also, demonstrates the activation of MAPK and Akt signaling pathways by kisspeptin in GT1-7 and GN11 cell lines.

Gene expression of the invasive phenotype of TNF-alpha-treated MCF-7 cells

BACKGROUND AND OBJECTIVES

TNF-alpha secreted by tumor cells and macrophages that have infiltrated into the micro-environment of a tumor may promote the metastasis of a variety of malignant cancers, including breast cancer. The present study was designed to detect gene expression changes in metastatic MCF-7 cells treated with a low dose of TNF-alpha (20ng/mL), and to further explore the mechanisms by which TNF-alpha can contribute to metastasis.

METHODS

Transwell assays were performed to evaluate the invasive phenotype of MCF-7 cells. Samples for cDNA array analysis were collected 3h and 24h after pre-treatment with TNF-alpha and changes in gene expression were quantitated.

RESULTS

The invasive phenotype of MCF-7 cells was enhanced by the exposure of MCF-7 cells to a low dose of TNF-alpha. Gene expression profiles of 39 genes significantly increased or decreased after treatment with TNF-alpha, 6 of which were genes not previously associated with regulation by TNF-alpha. Genes to promote metastasis, as well as to inhibit metastasis, were identified with some changes being time dependent.

CONCLUSIONS

TNF-alpha can enhance the invasive capacity of MCF-7 cells by affecting the expression of a group of genes that have roles in various steps of metastasis. Mechanistic insights into the role of TNF-alpha in tumor cell metastasis are discussed.

From KISS1 to kisspeptins: An historical perspective and suggested nomenclature

The cancer suppressor gene, KISS1, was initially described as having an important role in inhibiting cancer metastasis. Since then, KISS1 and its receptor, KISS1R, have been shown to play a key role in controlling the onset of puberty of reproductive physiology in the human and other species. Recent studies have also linked KISS1/kisspeptin/KISS1R to other processes, such as vasoconstriction, aging, adipocyte physiology, and perhaps as a molecular conduit linking metabolism and reproduction. This article highlights the history of KISS1/kisspeptin/KISS1R biology and proposes a consensus for nomenclature of the key molecules in this signaling pathway.

Molecular cloning of the bullfrog kisspeptin receptor GPR54 with high sensitivity to Xenopus kisspeptin

Kisspeptin and its receptor, GPR54, play important roles in mammalian reproduction and cancer development. However, little is known about their function in nonmammalian species. In the present study, we have isolated the cDNA encoding the kisspeptin receptor, GPR54, from the bullfrog, Rana catesbeiana. The bullfrog GPR54 (bfGPR54) cDNA encodes a 379-amino acid heptahelical G protein-coupled receptor. bfGPR54 exhibits 45-46% amino acid identity with mammalian GPR54s and 70-74% identity with fish GPR54s. RT-PCR analysis showed that bfGPR54 mRNA is highly expressed in the forebrain, hypothalamus and pituitary. Upon stimulation by synthetic human kisspeptin-10 with Phe-amide residue at the C-terminus (h-Kiss-10F), bfGPR54 induces SRE-luc activity, a PKC-specific reporter, evidencing the PKC-linked signaling pathway of bfGPR54. Using a blast search, we found a gene encoding a kisspeptin-like peptide in Xenopus. The C-terminal decapeptide of Xenopus kisspeptin shows higher amino acid sequence identity to fish Kiss-10s than mammalian Kiss-10s. A synthetic Xenopus kisspeptin peptide (x-Kiss-12Y) showed a higher potency than mammalian Kiss-10s in the activation of bfGPR54. This study expands our understanding of the physiological roles and molecular evolution of kisspeptins and their receptors.

Intracellular signaling pathways activated by kisspeptins through GPR54: do multiple signals underlie function diversity?

Kisspeptins, a family of peptide products derived from the KiSS-1 gene, activate their cognate receptor GPR54 in various target tissues to exert disparate functions, including inhibition of tumor metastasis and control of reproductive function. In contrast to the plethora of studies that have analyzed in recent years the regulatory functions of the KiSS-1/GPR54 system, only a limited number of reports have been primarily focused on delineating the intracellular signaling pathways involved. Nevertheless, there is solid evidence indicating that kisspeptin can activate a wide variety of signals via GPR54. These include typical G-protein (Galphaq/11)-coupled cascades, such as activation of phospholipase C (PLC), and subsequent accumulation of inositol-(1,4,5)-triphosphate (IP3), intracellular Ca(2+) mobilization, and activation of protein kinase C. However, kisspeptin also activates pathways related to mitogen activated protein kinases (MAPK), especially ERK1/2, and p38 and phosphatidylinositol-3-kinase (PI3K)/Akt. Additionally, the kisspeptin/GPR54 pair can also influence cell signaling by interacting with other receptors, such as chemokine receptor CXCR4, and GnRH receptor. Kisspeptin can also affect other signaling events, like expression of matrix metalloproteinase 9 (via NFkappaB), and that of calcineurin. The information gathered hitherto clearly indicates that activation of a specific set of interconnected signals is selectively triggered by kisspeptin via GPR54 in a cell type-dependent manner to precisely regulate functions as distinct as hormone release and cell migration. In this scenario, it will be important to decipher kisspeptin/GPR54 signaling mechanisms in reproductive and non-reproductive tissues by studying additional models, especially on natural kisspeptin targets expressing endogenous GPR54.

The role of kisspeptin and GPR54 in the hippocampus

The granule cells of the dentate gyrus form the input stage of the hippocampal trisynaptic circuit and their function is strongly influenced by peptidergic systems. GPR54 is highly and discretely expressed in these cells. We have found that activation of GPR54 with kisspeptin-10 causes a rapid and large increase in the amplitude of excitatory synaptic responses in granule cells, without changing membrane properties. The effect was suppressed by the G-protein inhibitor GDP-beta-S and the calcium chelator BAPTA, and analysis of miniature EPSCs revealed an increase in mean amplitude but not event frequency, indicating that GPR54 and the mechanisms for enhancing EPSCs are postsynaptic, possibly involving changes in AMPA receptor number or conductance. The kisspeptin-induced synaptic potentiation was abolished by inhibitors of ERK1/2, tyrosine kinase, and CaMKII. RT-PCR experiments showed that KiSS-1 is expressed in the dentate gyrus. KiSS-1 mRNA was significantly increased by seizure activity in rats and when neuronal activity in organotypic hippocampal slice cultures was enhanced by kainate or picrotoxin, while mRNA for GPR54 remained essentially unchanged. These results suggest that kisspeptin may be locally synthesized and act as an autocrine factor. In separate experiments, hippocampal KiSS-1 mRNA in male rats was increased after gonadectomy. In summary, kisspeptin is a novel endogenous factor which is dynamically regulated by neuronal activity and which, in marked distinction from other neuropeptides, increases synaptic transmission in dentate granule cells through signaling cascades possibly linked to the MAP kinase system. This novel peptide system may play a role in cognition and in the pathogenesis of epilepsy.

Regulation of KiSS1 gene expression

Kisspeptins are the protein products encoded by KiSS1 gene, an important tumor metastatic suppressor and pivotal master hormone of puberty. Although KiSS1 gene is expressed in both central and peripheral tissues, the molecular mechanisms that determine the temporal and spatial expression of KiSS1 gene are not well understood. This review provides an update on the latest studies and ideas about the expression of KiSS1 gene as a puberty gatekeeper and a metastasis suppressor, with special emphasis on the molecular mechanisms for the transcriptional regulation of KiSS1 gene expression.

GPR54 and kisspeptins

The G-protein coupled receptor GPR54 has an essential role in the initiation and maintenance of mammalian fertility. Humans and mice with mutations in GPR54 have hypogonadotropic hypogonadism characterized by absence of sexual maturation and low levels of gonadotropic hormones (LH and FSH). The ligand for GPR54 is encoded by the KISS1 gene, which produces a 54-amino-acid peptide (metastin or kisspeptin-54) that can be cleaved into shorter peptides (kisspeptins 14, 13 and 10) with similar potencies. Kisspeptin administration stimulates gonadotropin release in several species by inducing GnRH secretion from hypothalamic GnRH neurons expressing GPR54. Kisspeptins are produced by neurons located in the AVPV and ARC regions of the hypothalamus. Expression of Kiss1 in these neurons is differentially regulated by sex steroids providing a mechanism by which testosterone or estrogen can regulate GnRH release. The AVPV region is sexually dimorphic with highest expression of kisspeptin in females. Positive feedback by estrogen on expression of Kiss1 in the AVPV region may be responsible for the pre-ovulatory LH surge during the estrus cycle. Central administration of kisspeptin to immature female rats can induce precocious activation of the gonadotropic axis, causing advanced vaginal opening, elevated uterus weight, increased serum levels of LH and estrogen and induce ovulation. Kisspeptins/GPR54 have also been implicated in regulating the estrus cycle of seasonal breeders and in the control of lactational amenorrhea. Expression of Gpr54 and Kiss1 have also been reported in several peripheral tissues including the pituitary, ovary, testes and the placenta raising the possibility that these genes may have additional functions in these tissues. Regulation of kisspeptin expression by peripheral factors such as leptin may be involved in coordinating metabolic status with the reproductive axis.

Drug development against metastasis-related genes and their pathways: a rationale for cancer therapy

It is well recognized that the majority of cancer related deaths is caused by metastatic diseases. Therefore, there is an urgent need for the development of therapeutic intervention specifically targeted to the metastatic process. In the last decade, significant progress has been made in this research field, and many new concepts have emerged that shed light on the molecular mechanism of metastasis cascade which is often portrayed as a succession of six distinct steps; localized invasion, intravasation, translocation, extravasation, micrometastasis and colonization. Successful metastasis is dependent on the balance and complex interplay of both the metastasis promoters and suppressors in each step. Therefore, the basic strategy of our interventions is aimed at either blocking the promoters or potentiating the suppressors in this disease process. Toward this goal, various kinds of antibodies and small molecules have been designed. These include agents that block the ligand-recepter interaction of metastasis promoters (HGF/c-Met), antagonize the metastasis-promoting enzymes (AMF, uPA and MMP) and inhibit the transcriptional activity of metastasis promoter (beta-Catenin). On the other hand, the intriguing roles of metastasis suppressors and their signal pathways have been extensively studied and various attempts have been made to potentiate these factors. Small molecules have been developed to restore the expression or mimic the function of metastasis-suppressor genes such as NM23, E-cadherin, Kiss-1, MKK4 and NDRG1, and some of them are under clinical trials. This review summarizes our current understanding of the molecular pathway of tumor metastasis and discusses strategies and recent development of anti-metastatic drugs.

The kisspeptin (KiSS-1)/GPR54 system in cancer biology

Kisspeptin (KiSS-1) gene, initially described as a melanoma metastasis suppressor gene, encodes a number of peptides (kp-54, kp-14, kp-13, kp-10), which are endogenous ligands to a G protein-coupled receptor, referred as hOT7T175 or AXOR12 or GPR54. So far intensive investigation has provided substantiate evidence supporting the role of KiSS-1/GPR54 system in cancer biology as well as in the regulation of the reproductive function and trophoblast invasion. The precise mechanism by which KiSS-1/GPR54 system is affecting cancer cell growth and metastasis includes complex endocrine, paracrine and autocrine actions. Nevertheless, the detail mechanism of such actions is still under intensive investigation. Herein we review the evidence which support the role of KiSS-1/GPR54 system in cancer biology.

Expression of metastin and a G-protein-coupled receptor (AXOR12) in epithelial ovarian cancer

BACKGROUND

Metastin, a product of the KiSS-1 gene, is a ligand for a G-protein-coupled receptor (AXOR12) and is a strong suppressant of metastasis. The aim of this study was to evaluate whether metastin and AXOR12 gene expressions affect prognosis of patients with epithelial ovarian cancer.

METHODS

The expression levels of metastin, AXOR12 and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene expression were analysed by the real-time quantitative reverse transcription-polymerase chain reaction in 76 epithelial ovarian cancer surgical specimens. Their expression (metastin/GAPDH and AXOR12/GAPDH ratios) was correlated with the clinical findings. Furthermore, cellular distribution of metastin and AXOR12 mRNA was examined by in situ hybridisation on tissue sections.

RESULTS

The median and range of mRNA expression for metastin and AXOR12 were 0.047 and 0.01-13.57, and 4.00 and 0.011-135.13, respectively. Patients were dichotomised into two groups having low and high expressions by using the median value as the cutoff. A good agreement was noticed between metastin and AXOR12 gene expression levels (kappa coefficient; 0.74). The presence of residual tumour following resection was negatively associated with metastin (P=0.0084) and AXOR12 (P=0.0148) gene expressions indicating an association of low expression of these genes in more aggressive, and advanced tumours. By univariate Cox regression analysis, the prognosis of the patients with low AXOR12 gene expression was significantly worse than those with high AXOR12 gene expression (P=0.030). The combination of metastin and AXOR12 gene expression level was also significantly associated with the prognosis (P=0.049). Transcripts for both metastin and AXOR12 were detected in the epithelial ovarian carcinoma cells.

CONCLUSIONS

These results present a new insight into the understanding of the biological behaviour of epithelial ovarian cancer. Metastin/AXOR12 signalling may suppress the invasive phenotype of epithelial ovarian cancer.

Requirement of KISS1 secretion for multiple organ metastasis suppression and maintenance of tumor dormancy

BACKGROUND

The KISS1 protein suppresses metastasis of several tumor models without blocking orthotopic tumor growth, but the mechanism remains elusive. For its role in human sexual maturation, KISS1 protein is secreted and processed to kisspeptins, which bind to the G protein-coupled receptor GPR54. We tested the hypothesis that KISS1 secretion is required for metastasis suppression via GPR54.

METHODS

KISS1 containing an internal FLAG epitope with (KFM) or without (KFMdeltaSS) a signal sequence was transfected into C8161.9 human melanoma cells, which do not express endogenous KISS1. Whole-cell lysates and conditioned medium from C8161.9(KFM) and C8161.9(KFMdeltaSS) cells were collected and analyzed for kisspeptins by immunoprecipitation and enzyme-linked immunosorbent assay. GPR54 levels were measured using real-time reverse transcription-polymerase chain reaction. The ability of conditioned medium from C8161.9(KFM) and C8161.9(KFMdeltaSS) cells to stimulate calcium mobilization in GPR54-expressing Chinese hamster ovary cells (CHO-G) and in C8161.9 cells was evaluated. Metastasis was monitored in athymic mice (groups of 10 per experiment) that were injected with C8161.9(KFM) or C8161.9(KFMdeltaSS) cells labeled with enhanced green fluorescent protein. Survival of mice injected with C8161.9 or C8161.9(KFM) cells was analyzed by Kaplan-Meier methods.

RESULTS

Full-length KFM and KFMdeltaSS were detected in whole-cell lysates of C8161.9(KFM) and C8161.9(KFMdeltaSS) cells, respectively, but kisspeptins were detected only in conditioned medium of C8161.9(KFM) cells. In vivo, C8161.9(KFM), but not C8161.9(KFMdeltaSS), cells were suppressed for metastasis to lung, eye, kidney, and bone, with corresponding differences in mouse survival (median > 120 versus 42 days). C8161.9(KFM) cells seeded mouse lungs but did not form macroscopic metastases. Conditioned medium from C8161.9(KFM), but not C8161.9(KFMdeltaSS), cells stimulated calcium mobilization in CHO-G cells. GPR54 expression was low in C8161.9 cells, which were not stimulated by conditioned medium from C8161.9(KFM) cells.

CONCLUSIONS

KISS1 secretion was required for multiple organ metastasis suppression and for maintenance of disseminated cells in a dormant state. The absence of GPR54 expression in C8161.9 cells (whose metastatic spread was suppressed by KFM) suggests that metastasis suppression is not mediated through this receptor. The results imply the existence of another KISS1 receptor and/or paracrine signaling. The findings raise the possibility that soluble KISS1, kisspeptins, or mimetics could be used to maintain tumor dormancy, rendering treatment of already disseminated tumor cells (i.e., micrometastases) a legitimate target.

Ontogeny and mechanisms of action for the stimulatory effect of kisspeptin on gonadotropin-releasing hormone system of the rat

Kisspeptins have recently emerged as essential regulators of gonadotropin secretion and puberty onset. These functions are primarily conducted by stimulation of hypothalamic gonadotropin-releasing hormone (GnRH) secretion. However, relevant aspects of KiSS-1 physiology, including the ontogeny and major signaling systems of its stimulatory action, remain to be fully elucidated. To cover these issues, the effects of kisspeptin-10 on GnRH and LH secretion were monitored at early stages of postnatal maturation, and potential changes in the sensitivity to kisspeptin were assessed along the pubertal transition in the rat. In addition, the signaling cascades involved in kisspeptin-induced GnRH secretion were explored by means of pharmacological blockade using rat hypothalamic explants. Despite sexual immaturity, kisspeptin-10 potently elicited GnRH release ex vivo and LH secretion in vivo at early stages (neonatal to juvenile) of postnatal development. Yet, LH responsiveness to low doses of kisspeptin was enhanced in peri-pubertal animals. Concerning GnRH secretion, the stimulatory action of kisspeptin-10 required activation of phospholipase-C, mobilization of intracellular Ca2+ and recruitment of ERK1/2 and p38 kinases, but was preserved after blockade of type 2 cyclo-oxygenase and prostaglandin synthesis. In summary, our present data document the ontogeny, sensitivity and intracellular signals for the stimulatory action of kisspeptin on the GnRH/LH axis in the rat. Although LH responses to low doses of kisspeptin appeared to be enhanced at puberty, kisspeptin was able to readily activate the GnRH system at early stages of postnatal maturation. These observations further stress the essential role of kisspeptin in normal, and eventually pathological, timing of puberty.

Kisspepeptin-GPR54 signaling in the neuroendocrine reproductive axis

Kisspeptins, which are products of the Kiss1 gene, and their receptor, GPR54, have emerged as key players in the regulation of gonadotropin-releasing hormone (GnRH) secretion. Mutations or targeted deletions of GPR54 produce isolated hypogonadotropic hypogonadism in humans and mice, indicating that signaling through this receptor is a prerequisite for sexual maturation. Centrally administered kisspeptins stimulate GnRH and gonadotropin secretion in prepubertal and adult animals. Kisspeptin-expressing neurons are direct targets for the negative and positive feedback actions of sex steroids, which differentially regulate the expression of KiSS-1 mRNA in various regions of the forebrain. This review highlights what is currently known about kisspeptin-GPR54 signaling in the regulation of the neuroendocrine reproductive axis.

Activation of protein kinase C delta induces growth arrest in NPA thyroid cancer cells through extracellular signal-regulated kinase mitogen-activated protein kinase

Protein kinase C (PKC) is a family of serine-threonine kinases that regulate many cell processes. To study the role of PKCdelta in thyroid cancer cells, we used a replication-deficient adenovirus (PKCdeltaAdV), to tightly control PKCdelta expression. In NPA cells, activation of wild-type (WT) PKCdelta with phorbol 12-myristate 13-acetate (PMA) induced an arrest in cell growth at G(1) phase, which was itself inhibited by the PKCdelta inhibitor rottlerin. Furthermore, overexpression of a dominant negative PKCdelta did not induce G(1) arrest. These findings strongly suggested that PKCdelta induced cell growth arrest in NPA cells. We investigated the mechanism of G1 arrest by examining G(1)-related proteins and mitogen-activated protein kinase (MAPK) by Western blotting. After activation of WTPKCdelta with PMA, cyclin E expression and retinoblastoma protein (Rb) phosphorylation decreased; the expression of p27(Kip1) increased and the phosphorylation of extracellular signal-regulated kinase (ERK) MAPK decreased. These results indicated that the activation of PKCdelta induced cell growth arrest in NPA cells, through an ERK MAPK-p27(Kip1)-cyclin E-pRb pathway. PKCdelta may therefore be an effective molecular target for novel therapy in thyroid cancer.

Kisspeptins: regulators of metastasis and the hypothalamic-pituitary-gonadal axis

The kisspeptins are the peptide products of the KiSS-1 gene and the endogenous agonists for the GPR54 receptor. Although KiSS-1 was initially discovered as a metastasis suppressor gene, recent evidence suggests the kisspeptin/GPR54 system is a key regulator of the reproductive system. Disrupted GPR54 signalling causes hypogonadotrophic hypogonadism in rodents and man. Central or peripheral administration of kisspeptin potently stimulates the hypothalamic-pituitary-gonadal axis, increasing circulating gonadotrophin concentrations in a number of animal models. These effects appear likely to be mediated via the hypothalamic gonadotrophin-releasing hormone system, although kisspeptins may have direct effects on the anterior pituitary gland. Hypothalamic KiSS-1 expression is regulated by circulating sex steroids. The precise physiological role of the kisspeptin system in the regulation of reproductive function remains to be elucidated.

GPR54 and puberty

At puberty, pulsatile secretion of hormones initiates sexual maturation of the gonads. The G-protein-coupled receptor GPR54 is crucially involved in the initiation of puberty, along with its ligand metastin. Mice lacking GPR54 fail to undergo puberty and have immature reproductive organs and low levels of sex steroids and gonadotrophic hormones, but have normal levels of gonadotrophin-releasing hormone in the hypothalamus. In humans, several cases of hypogonadism have been ascribed to mutations in GPR54. Production of metastin and, to a lesser extent, GPR54 are negatively regulated by testosterone and oestrogen, and injecting GPR54 ligands can increase hormone secretion in rodents. Thus, GPR54 is required for normal functioning of the hypothalamic-pituitary-gonadal axis, probably at the level of gonadotrophin-releasing-hormone secretion.

Metastasis suppressor pathways--an evolving paradigm

A greater understanding of the processes of tumor invasion and metastasis, the principal cause of death in cancer patients, is essential to determine newer therapeutic targets. Metastasis suppressor genes, by definition, suppress metastasis without affecting tumorigenicity and, hence, present attractive targets as prognostic or therapeutic markers. This short review focuses on those twelve metastasis suppressor genes for which functional data exist. We also outline newly identified genes that bear promising traits of having metastasis suppressor activity, but for which functional data have not been completed. We also summarize the biochemical mechanism(s) of action (where known), and present a working model assembling potential metastasis suppression pathways.

Tumor suppressor role of KiSS-1 in bladder cancer: loss of KiSS-1 expression is associated with bladder cancer progression and clinical outcome

The expression profiles of nine bladder cancer cell lines were compared against a pool containing equal total RNA quantities of each of them. Lower expression of KiSS-1 was revealed in cells derived from the most advanced bladder tumors. When comparing 15 primary bladder tumors versus a pool of four bladder cancer cell lines, lower transcript levels of KiSS-1 were observed in the invasive bladder carcinomas as compared to superficial tumors. KiSS-1 expression ratios provided prognostic information. The expression pattern of KiSS-1 transcripts was analyzed using in situ hybridization in nine bladder cancer cells, paired normal urothelium and bladder tumor samples (n = 25), and tissue microarrays of bladder tumors (n = 173). We observed complete loss of KiSS-1 in all invasive tumors under study as compared to their respective normal urothelium. The expression of KiSS-1 was found to be significantly associated with histopathological stage. Patients with lower KiSS-1 expression showed a direct correlation with overall survival in a subset of bladder tumors whose follow-up was available (n = 69). We did not observe any significant differential KiSS-1 expression along cell cycle by sorting analysis. A potential tumor suppressor role in bladder cancer was revealed for KiSS-1. Moreover, it showed predictive value by identifying patients with poor outcome.