Gastrin-releasing peptide is produced in the pregnant ovine uterus

A sexually dimorphic peptidergic system in the lower spinal cord controlling penile function in non-human primates

STUDY DESIGN

Experimental animal study.

OBJECTIVES

Although a population of gastrin-releasing peptide (GRP) neurons in the lumbar spinal cord has an important role in erection and ejaculation in rats, little information exists on this GRP system in primates. To identify the male-specific GRP system in the primate spinal cord, we studied the lumbosacral cord in macaque monkeys as a non-human primate model.

SETTING

University laboratory in Japan.

METHODS

To determine the gene sequence of GRP precursors, the rhesus macaque monkey genomic sequence data were searched, followed by phylogenetic analysis. Subsequently, immunocytochemical analysis for GRP was performed in the monkey spinal cord.

RESULTS

We have used bioinformatics to identify the ortholog gene for GRP precursor in macaque monkeys. Phylogenetic analysis suggested that primate prepro-GRP is separated from that of other mammalian species and clustered to an independent branch as primates. Immunocytochemistry for GRP further demonstrated that male-dominant sexual dimorphism was found in the spinal GRP system in monkeys as in rodents.

CONCLUSION

We have demonstrated in macaque monkeys that the GRP system in the lower spinal cord shows male-specific dimorphism and may have an important role in penile functions not only in rodents but also in primates.

SPONSORSHIP

Tissues of Nihonzaru (Japanese macaque monkeys) were provided in part by National Institutes of Natural Sciences (NINS) through the National Bio-Resource Project (NBRP) of the MEXT, Japan. This work was supported in part by KAKENHI from the Japan Society for the Promotion of Science (JSPS) (to KT; 15KK0343, 15J40220 and HS; 15K15202, 15KK0257, 15H05724).

Extracellular vesicles in luminal fluid of the ovine uterus

Microvesicles and exosomes are nanoparticles released from cells and can contain small RNAs, mRNA and proteins that affect cells at distant sites. In sheep, endogenous beta retroviruses (enJSRVs) are expressed in the endometrial epithelia of the uterus and can be transferred to the conceptus trophectoderm. One potential mechanism of enJSRVs transfer from the uterus to the conceptus is via exosomes/microvesicles. Therefore, studies were conducted to evaluate exosomes in the uterine luminal fluid (ULF) of sheep. Exosomes/microvesicles (hereafter referred to as extracellular vesicles) were isolated from the ULF of day 14 cyclic and pregnant ewes using ExoQuick-TC. Transmission electron microscopy and nanoparticle tracking analysis found the isolates contained vesicles that ranged from 50 to 200 nm in diameter. The isolated extracellular vesicles were positive for two common markers of exosomes (CD63 and HSP70) by Western blot analysis. Proteins in the extracellular vesicles were determined by mass spectrometry and Western blot analysis. Extracellular vesicle RNA was analyzed for small RNAs by sequencing and enJSRVs RNA by RT-PCR. The ULF extracellular vesicles contained a large number of small RNAs and miRNAs including 81 conserved mature miRNAs. Cyclic and pregnant ULF extracellular vesicles contained enJSRVs env and gag RNAs that could be delivered to heterologous cells in vitro. These studies support the hypothesis that ULF extracellular vesicles can deliver enJSRVs RNA to the conceptus, which is important as enJSRVs regulate conceptus trophectoderm development. Importantly, these studies support the idea that extracellular vesicles containing select miRNAs, RNAs and proteins are present in the ULF and likely have a biological role in conceptus-endometrial interactions important for the establishment and maintenance of pregnancy.

Isolation, identification and biological activity of gastrin-releasing peptide 1-46 (oGRP 1-46), the primary GRP gene-derived peptide product of the pregnant ovine endometrium

We have previously demonstrated that pregnant ovine endometrium expresses the gastrin-releasing peptide (GRP) gene at a high level following conceptus implantation. Here we report the isolation, characterization and biological activity of ovine GRP 1-46, the primary product of this gene in the pregnant endometrium. Full thickness 125-140-day pregnant sheep uterus (term is 145 day) was homogenized in 80% acetonitrile/2% trifluoroacetic acid (1:7 ACN/TFA), concentrated on reverse-phase C18 cartridges and chromatographed successively on gel filtration (Sephadex G-50) and reverse-phase HPLC (C18 muBondapak). Purification was monitored by RIA. Purified GRP peptide was analysed by mass spectrometry giving a major mass ion at 4963 which corresponds exactly to GRP 1-46. Other mass ions from pro-GRP did not contain a biologically active N-terminus or antigenic determinant. Proteolytic cleavage of pro-GRP to give rise to GRP(1-46) would require preferential cleavage at the Glu-Glu bond by a Glu-C2-like enzyme, rather than the trypsin-like and C-terminal amidation enzymes (PAM) that produce GRP(18-27) and GRP(1-27) in other tissues. GRP 1-46 was synthesized and receptor binding and biological activity tested on a range of rodent and human cell lines that express GRP-related receptors GRPR, NMBR and BRS3. GRP 1-46 bound GRPR and NMBR with low affinity, and mobilized inositol phosphate in cell lines expressing the GRPR and NMBR, but not BRS-3. This study describes a new processed product of the GRP gene, GRP 1-46, which is highly expressed in the pregnant sheep endometrium and which acts as a weak agonist at the GRPR and NMBR.

Gastrin-releasing peptide (GRP) in the ovine uterus: regulation by interferon tau and progesterone

Gastrin-releasing peptide (GRP) is abundantly expressed by endometrial glands of the ovine uterus and processed into different bioactive peptides, including GRP1-27, GRP18-27, and a C-terminus, that affect cell proliferation and migration. However, little information is available concerning the hormonal regulation of endometrial GRP and expression of GRP receptors in the ovine endometrium and conceptus. These studies determined the effects of pregnancy, progesterone (P4), interferon tau (IFNT), placental lactogen (CSH1), and growth hormone (GH) on expression of GRP in the endometrium and GRP receptors (GRPR, NMBR, BRS3) in the endometrium, conceptus, and placenta. In pregnant ewes, GRP mRNA and protein were first detected predominantly in endometrial glands after Day 10 and were abundant from Days 18 through 120 of gestation. Treatment with IFNT and progesterone but not CSH1 or GH stimulated GRP expression in the endometrial glands. Western blot analyses identified proGRP in uterine luminal fluid and allantoic fluid from Day 80 unilateral pregnant ewes but not in uterine luminal fluid of either cyclic or early pregnant ewes. GRPR mRNA was very low in the Day 18 conceptus and undetectable in the endometrium and placenta; NMBR and BRS3 mRNAs were undetectable in ovine uteroplacental tissues. Collectively, the present studies validate GRP as a novel IFNT-stimulated gene in the glands of the ovine uterus, revealed that IFNT induction of GRP is dependent on P4, and found that exposure of the ovine uterus to P4 for 20 days induces GRP expression in endometrial glands.

Immunohistochemical localization of gastrin-releasing peptide, neuronal nitric oxide synthase and neurone-specific enolase in the uterus of the North American opossum, Didelphis virginiana

The present study has demonstrated the immunohistochemical localization of gastrin-releasing peptide (GRP), neuronal nitric oxide synthase (nNOS) and neurone-specific enolase (NSE) in the uterus of the North American opossum. Although the presence of GRP, nNOS and NSE has been reported recently in the uterus of eutherian species this is the first description of these peptides in a metatherian species. Metatherian mammals are of interest because in these species it is the prolonged lactation phase of development that is the period of primary reproductive investment rather than intrauterine development as is true of eutherian mammals. The opossum, like other marsupial species, has a very abbreviated gestation period which in Didelphis lasts only 12.5 days. GRP was localized in the cytoplasm of cells forming the surface lining epithelium and the glandular epithelium of the opossum endometrium late in pregnancy, at 11.5 days of gestation. Likewise, immunoreactivities of nNOS and NSE were found primarily within the epithelial cells of the endometrium at 11.5 days of gestation. As these peptides and enzymes appear primarily at the time of establishment of the yolk sac placenta (between day 10 and day 12.5 gestation), the present results strongly suggest that these factors may play a fundamental role in the placentation of the opossum.

Transient upregulation of GRP and its receptor critically regulate colon cancer cell motility during remodeling

Gastrin-releasing peptide (GRP) is typically viewed as a growth factor in cancer. However, we have suggested that in colon cancer, GRP acts primarily as a morphogen when it and its receptor (GRP-R) are aberrantly upregulated. As such, GRP/GRP-R act(s) primarily to modulate processes contributing to the assumption or maintenance of tumor differentiation. One of the most important such processes is the ability of tumor cells to achieve directed motility in the context of tissue remodeling. Yet the cellular conditions affecting GRP/GRP-R expression, and the biochemical pathways involved in mediating its morphogenic properties, remain to be established. To study this, we evaluated the human colon cancer cell lines Caco-2 and HT-29 cells. We found that confluent cells do not express GRP/GRP-R. In contrast, disaggreation and plating at subconfluent densities results in rapid GRP/GRP-R upregulation followed by their progressive decrease as confluence is achieved. GRP/GRP-R coexpression correlated with that of focal adhesion kinase (FAK) phosphorylation of Tyr(397), Tyr(407), Tyr(861), and Tyr(925) but not Tyr(576) or Tyr(577). To more specifically evaluate the kinetics of GRP/GRP-R upregulation, we wounded confluent cell monolayers. At t = 0 h GRP/GRP-R were not expressed, yet cells immediately began migrating into the gap created by the wound. GRP/GRP-R were first detected at approximately 2 h, and maximal levels were observed at approximately 6 h postwounding. The GRP-specific antagonist [d-Phe(6)]-labeled bombesin methyl ester had no effect on cell motility before GRP-R expression. In contrast, this agent increasingly attenuated cell motility with increasing GRP-R expression such that from t = 6 h onward no further cell migration into the gap was observed. Overall, these findings indicate the existence of GRP-independent and -dependent phases of tumor cell remodeling with the latter mediating colon cancer cell motility during remodeling via FAK.

Phosphorylation of focal adhesion kinase tyrosine 397 critically mediates gastrin-releasing peptide's morphogenic properties

We have proposed that gastrin-releasing peptide (GRP) and its receptor (GRP-R) are morphogens that when aberrantly re-expressed in colon cancer promote tumor cell differentiation and retard metastasis. Because circumstantial evidence suggested that these properties were mediated via focal adhesion kinase (FAK), the purpose of this study was to elucidate the role of GRP-induced activation of this enzyme on properties fundamental to metastasis including cell attachment, motility, and deformability. To do this, we studied 293 cells, a non-malignant epithelial cell line that we show expresses GRP and GRPR. To dissect out the role of FAK, 293 cells were modified to inducibly express the dominant negative enzyme FAK-related non-kinase (FRNK) under control of a Tet-On (i.e., doxycycline-sensitive) promoter. Under serum-free conditions, GRP acting in an autocrine manner caused FAK to be phosphorylated at Y397; and this could be completely inhibited either by incubating with the specific GRP-R antagonist D-Phe(6)(bombesin) methyl ester, or by upregulating FRNK using doxycycline. To measure cell attachment, we designed a cone-plate viscometer that recorded the shear stress required to detach cells from their underlying matrix. To assess motility, confluent cells were wounded and behavior assessed by time-lapse photography. To measure deformability, we recorded the ability of cells to be completely drawn into a micropipette <50% the size of the non-deformed cell. Control 293 cells adhered more avidly to their underlying matrix, rapidly remodeled wounded tissues without any increase in overall proliferation, and were less distensible than cells treated with antagonist or doxycycline. Thus, these findings suggest that expression of GRP/GRPR in cancer inhibits metastasis by enhancing cell attachment to the matrix, regulating motility in the context of remodeling, and decreasing deformability.

Contribution of gastrin-releasing peptide and its receptor to villus development in the murine and human gastrointestinal tract

Recent studies have shown that aberrantly expressed gastrin-releasing peptide (GRP) and its receptor (GRP-R) critically regulate tumor cell differentiation in colon cancers developing in humans and mice. This finding suggested that the ability of GRP/GRP-R to promote a well-differentiated phenotype in colon cancer might reflect a re-capitulation of a normal role in regulating intestinal organogenesis. To determine if this was the case, we compared and contrasted intestinal development in GRPR-/- mice with their wild type littermates. GRP/GRP-R co-expression in wild type mice was only observed in villous enterocytes between N-1 and N-12. During this time frame villous growth was completely attenuated in GRPR-/- mice. The contribution of GRP/GRP-R to villous growth was due to their act in increasing enterocyte proliferation prior to N-8 but increasing enterocyte size thereafter. From N-12 onwards, small intestinal villous growth in GRPR-/- mice resumed such that no difference in this structure could be detected at adulthood between mice of either genotype. We next studied GRP/GRP-R expression in human abortuses. These proteins were co-expressed by villous enterocytes only between weeks 14 and 20 post-conception, a time frame analogous to when they are expressed in the murine intestine. Thus, this study shows for the first time that GRP/GRP-R play a transient and non-critical role in intestinal development, yet provides a rationale for their re-appearance in colon cancer.

A new cause of Zollinger-Ellison syndrome: non-small cell lung cancer

Numerous epidemiologic studies suggest a relationship between lung cancer and peptic ulcer disease. Furthermore, various lung cancers synthesize and release a number of peptides such as gastrin and gastrin-releasing peptide that could cause acid hypersecretion; however, Zollinger-Ellison syndrome (ZES), because of a lung tumor, has never been described. We report such a patient for the first time. A 60-year-old man with a non-small cell lung carcinoma (large cell type) presented with diarrhea, heartburn, abdominal pain, and duodenal ulcers. Evaluation showed ZES was present (fasting hypergastrinemia, hyperchlorhydria) and control of all symptoms by omeprazole. No abdominal or cardiac tumor, the other known locations of gastrinomas causing ZES, was found on detailed tumor imaging studies. Resection of the lung tumor resulted in a decrease in gastrin levels to normal values. Plasma radioimmunoassays showed elevated gastrin, chromogranin A and normal levels of gastrin-releasing peptide, and 9 other hormones. The tumor showed similar immunocytochemical results. The characteristics of this case are compared with 100 cases of sporadic abdominal gastrinomas, and the evidence reviewed suggests why ZES should be considered in patients with lung cancer with peptic symptoms.

Aberrant expression of gastrin-releasing peptide and its receptor by well-differentiated colon cancers in humans

Epithelial cells lining the adult human colon do not normally express gastrin-releasing peptide (GRP) or its receptor (GRPR). In contrast, approximately one-third of human colon cancers and cancer cell lines have been shown to express GRP-binding sites. Because GRPR activation causes the proliferation of many cancer cell lines, GRP has been presumed to act as a clinically significant growth factor. Yet GRP has not been shown to be expressed by colon cancers in humans nor has the effect of GRP and/or GRPR coexpression on tumor behavior been investigated. We therefore determined GRP and GRPR expression by immunohistochemistry in 50 randomly selected colon cancers resected between 1980 and 1997, all 37 associated lymph node and liver metastases, and 20 polyps. Tumor sections studied were those that contained the margin and adjacent nonmalignant epithelium. Overall, 84% of cancers aberrantly expressed GRP or GRPR, with 62% expressing both ligand and receptor, whereas expression was not observed in adjacent normal epithelium. Consistent with the previously established mitogenic capabilities of GRP, tissues coexpressing GRP and GRPR were more likely to express proliferating cell nuclear antigen than tissues not expressing both ligand and receptor. Yet GRP/GRPR coexpression was seen with equal frequency in stage A as in stage D cancers and was only detected in 1 in 37 metastases. Furthermore, Kaplan-Meier analysis did not reveal any difference in patient survival between those whose tumors did or did not express GRP/GRPR. In contrast, GRP/GRPR coexpression was found in all well-differentiated tumor regions, whereas poorly differentiated tissues never coexpressed GRP/GRPR. Overall, these data indicate that, although GRP is a mitogen, it is not a clinically significant growth factor in human colon cancers. Rather, the strong association of GRP/GRPR coexpression with tumor differentiation raises the possibility that these proteins primarily act in vivo as morphogens.

Mechanisms of electrolyte transport across the endometrium. II. Regulation by GRP and substance P

The purpose of this study was to investigate the regulation of electrolyte transport across the porcine endometrium by gastrin-releasing peptide (GRP) and substance P (SP). Luminal addition of GRP, neuromedin B (NMB), SP, or neurokinin A(NKA) to mucosal tissues mounted in Ussing chambers produced a multiphasic change in short-circuit current (Isc) characterized by an initial rapid increase and subsequent decrease in current. A similar response was obtained after addition of ionomycin or thapsigargin to the tissues. The Isc response to the peptides or Ca ionophore was inhibited by pretreatment of the tissues with luminal amiloride or benzamil. GRP and SP were more potent [50% effective concentration (EC50) of 3 nM] than NMB or NKA (EC50 values of 46 and 26 nM, respectively) in producing the decrease in Isc. Pretreatment with the GRP receptor antagonist 3-Phe-His-Trp-Ala-Val-D-Ala-His-D-Pro-psi Phe-NH2 blocked the Isc response to GRP and NMB but not to SP or NKA, whereas the NMB receptor antagonist D-Nal-[Cys-Try-D-Trp-Orn-Val-Cys]-Nal-NH2 was ineffective in inhibiting the Isc response to any of the peptides. In contrast, pretreatment of the tissue with the nonpeptide SP receptor antagonist CP-99,994 blocked the Isc response to SP and NKA but not to GRP or NMB. Experiments with amphotericin B-permeabilized tissues showed that GRP, SP, ionomycin, and thapsigargin increased current through an outwardly rectifying K conductance located on the apical membrane of the cells. The K-to-Na selectivity ratio of this conductance was calculated to be 2.5:1. These experiments showed that GRP and SP, acting through different receptors, produced an increase in K efflux through a Ca-dependent K conductance present in the apical membrane of surface endometrial epithelial cells. In addition, immunohistochemistry data showed that GRP-like immunoreactivity was localized to surface and glandular epithelial cells, whereas GRP receptor antibody labeling was observed in both epithelial and stromal cells. These results suggest that GRP functions as both an autocrine and paracrine regulatory peptide in the endometrium.

Systemic and luminal influences on the perinatal development of the gut

At birth, the mammalian gastrointestinal tract (GIT) must be able to support a shift from mainly parenteral nutrition in the fetus (via the placenta) to enteral nutrition in the neonate. In the perinatal period the GIT therefore undergoes enhanced growth as well as morphological and functional differentiation, and this maturational programme is influenced by a complex interplay of local, systemic and luminal factors. This review shows how systemic and luminal factors may influence GIT development in the perinatal period of the pig and sheep, two long-gestation species. Adrenocortical hormones play a pivotal role in the prepartum maturation of the GIT in addition to their better known effects on the development of many other tissues and body systems. More particularly, in the fetal pig and sheep, the prenatal development of gastric acid and gastrin secretion, and of GIT hydrolase activities (chymosin, pepsin, amylase, lactase, aminopeptidases) is influenced by cortisol. Additionally, glucocorticoids exert effects throughout the GIT by influencing morphological, cytological, and functional differentiation. Since the GIT epithelial cells comprise a renewing cell population there are also changes in cell kinetics. In addition to systemic factors, the presence of growth factors, hormones and nutrients from swallowed amniotic fluid (fetus) and colostrum (neonate) may influence GIT development. In utero, fetal fluid ingestion has been shown to modulate tissue growth, macromolecule and immunoglobulin transport, enterocyte differentiation, cell turnover and activity of brush-border hydrolases. These effects may be mediated via regulatory peptides (e.g. insulin-like growth factor I, gastrin-releasing peptides, insulin, epidermal growth factor, gastrin). A physiological role of luminally derived growth factors is supported by a number of unique structural and functional adaptations of the GIT in the fetus and neonate (low luminal proteolysis, intestinal macromolecule transport). Thus, in the pig and sheep, both systemic and luminal factors appear to play critical roles in GIT development in the perinatal period.