1Laboratory of Pharmacology, Faculty of Medicine, Democritus University of Thrace, Alexandroupolis, 2Department of General Surgery, General Hospital of Drama, 3Laboratory of Histology-Embryology, Faculty of Medicine, Democritus University of Thrace, Alexandroupolis, Greece
The corticotropin-releasing factor (CRF) system plays a crucial regulatory role in the adaptation to exogenous and endogenous stress stimuli, as well as homeostasis. Apart from the central nervous system (CNS), the members of this neuropeptide family extend their actions in the periphery, where they may affect various body systems independently, stimulating peripheral CRF receptors via vagal and/or autocrine/paracrine pathways. Here, we review all findings concerning the expression and role of the CRF system in human liver, but also in other species. Direct and indirect regulatory data are also analyzed in order to draw conclusions about possible physiological/pathophysiological implications. Although data supporting any clinical significance are still limited and further research in the field is necessary, scientific interest in the CRF system is particularly active, with multiple ongoing clinical studies evaluating the activity of CRF ligands in medical conditions involving other organs. Thus, new knowledge with therapeutic potential appears to be steadily accumulating.
Cancer, Corticotropin Releasing Factor, Hepatic, Liver, Neuropeptide, Receptor, Urocortin
In the mid 1950s two Nobel laureates, Dr Schally and Dr Guillemin, discovered independently the existence of a compound with stimulatory action on adrenocorticotropin hormone (ACTH) secretion from the pituitary gland in rats and named it corticotropin-releasing factor (CRF).1,2 Its structure remained unclear for almost three more decades, until Vale and his associates identified CRF as a 41-residue amino acid peptide, isolated from ovine hypothalami.3 Scientists from the same research group cloned two CRF receptors, CRF14 and CRF2,5 described urocortins (additional members of the CRF family)6-9 and synthesized peptide antagonists of CRF receptors; the latter substantially contributed to elucidating molecular mechanisms regulated by the CRF system.10-12
THE CRF FAMILY: NEUROPEPTIDES AND RECEPTORS
The CRF family consists of four peptides, including CRF, urocortin 1 (Ucn 1), Ucn 2, Ucn 3 and their binding sites.13 The 41 aa peptide CRF has a common primary structure among mammals, such as humans, primates, dogs and rodents14 and mediates neuroendocrine and behavioral stress responses through the regulation of ACTH secretion by the pituitary gland. Ucn 1 is a 40 aa peptide that displays highly conserved primary structure among mammalian species, such as sheep, rat and mouse; it shares 45% sequence homology with CRF.15,16 Ucn 1 may be traced in the pituitary, hypothalamus, the Edinger-Westphal locus and the periphery, including the gastrointestinal system, thymus, heart, spleen, kidneys and testis.16-19 Ucn 2, a 38 aa peptide, and Ucn 3 are both expressed in multiple sites of the central nervous system (CNS), similarly to CRF and Ucn 1. Concurrently, Ucn 2 may be identified in the heart, adrenals and blood cells and Ucn 3 in the skin, muscles, adrenals and gut.7,9,20
The aforementioned four neuropeptides of the CRF system act through two receptors, CRF1 and/or CRF2, which have been cloned from two separate genes that present 70% identity at the aa level.21 Both CRF receptors belong to class B1 of the G-protein-coupled receptor superfamily5,22-24 and, due to their extensive splicing, CRF1 and CRF2 present various isoforms. With regard to CRF1, CRF1a, primarily expressed in the pituitary and the brain, appears to be the unique isoform, which is coupled directly to adenylate cyclase, although new splicing variants are emerging and may play a critical role in CRF signaling.25-28 Alternatively, CRF2 has three functional splice variants (CRF2a, CRF2b and CRF2c) differing in their extracellular N-terminal domain. They are located in the CNS, skeletal muscles, heart and testis.5,13,22,29-31 The CRF system receptors display different binding characteristics with their ligands. The CRF1a has high affinity to CRF and Ucn 1 and no affinity to Ucn 2 and Ucn 3. On the contrary, the CRF2a and CRF2b display high affinity to Ucn 1, Ucn 2 and Ucn 3 and lower affinity to CRF.8,9,13,23,32,33 Although Ucn 2 and Ucn 3 have been identified as selective endogenous ligands for CRF2, so far, no endogenous ligand exclusively binding to the CRF1 has been identified.34 Finally, CRF-BP is a 37kDa glycoprotein that was initially identified in the human plasma, dimerizing upon binding to both CRF and Ucn 1 and thus controlling the bioavailability of these peptides.35
CRF NEUROPEPTIDES AND RECEPTORS IN THE PERIPHERY
The neuropeptides of the CRF system were initially thought to be restricted to the pituitary and brain; however, subsequent research discovered that they were widely expressed in the periphery, including multiple non-neuronal sites.36 In the human periphery, CRF is expressed in adrenals (cortex and core), testis, placenta,36,37 intestines, spleen, thymus, skin, pancreas, leucocytes,38,39 endometrium,40 ovaries41 and heart.42 In the rat, extra-hypothalamic CRF has been detected in the myenteric plexus and nervous fibers of the submucosal plexus in intestines and other tissues, such as testis,43 ovaries,44 thymus, spleen45 and adrenals.46,47 Furthermore, CRF has been discovered in mice,48 dogs,49 cows,50 baboons51 and monkeys.52 Nonetheless, it should be noted that all studies conducted prior to the characterization of the homologue Ucns should be confirmed by selective CRF antibodies.
In addition to the brain and the pituitary, Ucn 1 is reported to be expressed in the heart, blood and lymph vessels, the reproductive organs and the gastrointestinal tract.14-18,53-55 Moreover, Ucn 1 was identified in the rat autonomous nervous system of the gut at the peptide and the gene level.56,57 Using RT-PCR in human tissues, Ucn 2 transcripts were detected in most sites, with higher expression levels in the heart, lung, muscle, stomach, adrenals and peripheral blood, but not in the intestine.20 More recently, Ucn 2 was found in human skin,28 placenta and embryonic membranes.58 Ucn 3 has been identified in human CNS, heart, kidney and reproductive organs as well as the gastrointestinal system.19-21
CRF ligands and receptors were detected in the gastrointestinal tract,59,60 lung, heart, spleen, testis and connective tissue61 in humans and animals. In humans, CRF2b and CRF2c were identified primarily in the brain, whereas CRF2a was expressed peripherally and centrally.22,62 Ucn 1 was detected by immunostaining in the heart,63 along with CRF2a and CRF1.30 In contrast, in rodents, CRF1 expression was reported in the submucosal and myenteric nervous plexus of the distal bowel,53,64 whereas CRF2 expression was predominantly detected on the luminal surface of the enteric crypts, on blood vessels of the submucosal layer53 as well as on myenteric neurons.65 Interestingly, CRF2a appears to be the main receptor expressed in the rat brain, whereas CRF2b is expressed in non-neuronal tissues in the brain and the periphery.66
Abundant evidence suggests the involvement of the CRF system in the inflammatory process as well as its regulatory role in the apoptotic process of macrophages,67 cardiac myocytes,63,68,69 adrenals,70 endometrium,71 colon72 and kidney.73 Chatzaki et al, as well as other research groups, have described the expression of Ucn and CRF receptor in both the upper and the lower human gastrointestinal tract,19,53,74,75 where it appears to regulate the pathogenesis of stress-related disorders.59,76
THE CRF SYSTEM IN THE LIVER
The expression of CRF ligands and receptors in the liver has been addressed in some studies and species differences have emerged. Simopoulos et al77 examined the expression of the CRF system in normal human liver tissue at gene and protein levels. Transcripts of Ucn 1, the two-receptor proteins CRF1 and CRF2α and the CRF-BP genes were detected in total RNA liver extracts by RT-PCR. The CRF and CRF2β genes were not expressed. The immunohistochemistry study showed localization of immunoreactive Ucn 1, CRF1 and CRF2 receptor proteins in the cytoplasm and cell membrane of hepatocytes, blood vessels and bile ducts in the portal triad. Additionally, Ucn 1 and CRF receptor expression was described in hepatic biopsies from a variety of liver pathologies, including primary or metastatic liver carcinoma and cirrhosis. A similar expression pattern of the CRF system was observed in liver cancer. Malignant cells expressed Ucn 1 and its receptors in primary hepatocarcinomas, cholangiocarcinomas and metastatic adenocarcinomas. One cirrhotic liver biopsy was also examined and indicated Ucn 1 and CRF1 expression, but not CRF2. It was concluded that the CRF system is expressed in human liver under normal and pathological conditions, with Ucn 1 being the major ligand that may act in an autocrine manner through activation of the local CRF receptors.
The expression of Ucn 1 and its receptors was also depicted in Kupffer cells (KCs), the resident macrophages that play a crucial role in the antigen-specific immune response, although in a variable way. The latter was attributed to the dissimilar degrees of maturation of KCs. The importance of the CRF system in KC activation and consequently in the hepatic immune response to noxious stimuli should be further investigated, since Ucn 1 also appeared to suppress lipopolysaccharide (LPS)-induced tumor necrosis factor alpha (TNF-α) secretion by rat KCs (Figure 1).78 CRF, Ucn 2 and Ucn 3 were not detected in liver cells.77 Concordant with these findings, research on baboon livers showed that CRF expression is prominent at term but declines towards adulthood.79
Figure 1. The effects of Ucn 1 via its receptors on liver cells.76-78,101
CRF: Corticotropin Releasing Factor, HCC: HepatoCellular Carcinoma, HGF: Hepatocyte Growth Factor, TNFα: Tumour Necrosis Factor alpha, Ucn: Urocortin.
In the study by Simopoulos et al, the presence of CRF binding protein (CRF-BP) was also discovered at the gene and protein levels in the human liver.77 CRF-BP is a 37kDa glycoprotein that was firstly identified in the human plasma, dimerizing upon binding to both CRF and Ucn 1.35 CRF-BP gene expression has been revealed in the brain, placenta and liver in the primates and the latter is believed to be a major source of CRF-BP secretion in the human plasma.80 Nevertheless, CRF-BP was described in neither the liver nor the placenta of any of the other species examined, although it was expressed in their brain, a finding that still lacks a satisfactory explanation.81 Simopoulos et al have indicated low levels of protein expression in the human liver, localized in the parenchymal hepatocytes, in addition to gene expression. It is likely that most CRF-BP synthesized in the liver is secreted into the general circulation. Through its connection with CRF and Ucn, CRF-BP may affect their bioavailability, hindering binding to CRF receptors and in that way regulating in a fast and transient way the concentration of the free peptides.82 Therefore, in both neural and peripheral sites, it seems that there is a connection between CRF-BP expression and CRF or Ucn expression, as indicated in placenta81 and in rat adrenals;83 this may be an integral part of functional CRF-based paracrine mechanisms, since CRF-BP can bind locally secreted neuropeptides and is regulated by CRF, glucocorticoids and cytokines.
While Ucn 1 expression in the human liver was clarified,77 it remains unclear in rodent livers. Rat KCs express Ucn and all its receptors, including CRF1, CRF2 and the pseudoreceptor CRF-BP; consequently, KCs appear to possess a strong neuroendocrine phenotype and, reversely, the CRF system appears to influence the hepatic immunological functions.78 Data from RT-PCR or Rnase protection assays suggested Ucn 1 gene expression in crude liver extracts,18,84 although other investigators failed to detect this neuropeptide in rat lives.85 Interestingly, differential expression patterns of the CRF system among species have also been demonstrated in other tissues and organs, such as the colon;53,74 this fact may contribute to a possible explanation of the differential findings in human and rodent livers.
THE CRF SYSTEM IN THE LIVER: FUNCTIONAL DATA
It appears that CRF and Ucn enhances the CCl4-induced hepatic injury in rats through central receptors, while CRF antagonists alleviate this action; these observations may have clinical prospects, because they suggest that both neuropeptides are involved in the sympathetic regulation of hepatic pathophysiology.86,87 These effects were canceled through sympathectomy, although not by vagotomy of the hepatic branch; it could be concluded that they were predominantly mediated centrally.
Peripherally produced Ucn 1 within the liver may exert immediate autocrine or/and paracrine modulatory effects on the local immune response to various stimuli, promoting a different, potentially adjunct pathway in immunity. The concomitant presence of CRF1 and CRF2, through which Ucn1 acts, further support the autocrine role of this neuropeptide. In fact, many reports associate CRF receptor signaling with immune and either pro- or anti-inflammatory responses in various conditions such as inflammatory bowel disease56,72 and H. pylori-induced gastritis.19 These data taken together with the expression of CRF receptors and their ligands by both KCs and hepatocytes77,78 could suggest a potential role of CRF peptides as mediators of the crosstalk between liver cells and infiltrating immune cells in hepatic disorders, such as hepatitis and cancer. This hypothesis is strongly supported by the ability of CRF receptor ligands to suppress the LPS-induced production of inflammatory TNF-α by rat KCs77,92 and other reported actions on macrophages,67,89,90 suggesting a protective, anti-inflammatory role. Ucn 1 in the hepatic parenchyma may be related to defense mechanisms activated locally to protect the liver from noxious stimuli. In fact, KCs possess important functions in the antigen-specific immune response, acting as antigen-presenting cells, interacting with hepatocytes via locally produced cytokines and/or adhesion molecule expression, and leading to a mutual influence of immunological functions. It becomes evident that Ucns’ 1 role as an immune mediator in liver pathophysiology is not yet elucidated and it comprises an interesting field for further investigation.
In the rat pheochromocytoma cell line PC12, CRF favors apoptosis via CRF1, through the induction of p38-mediated Fas ligand production, possibly in a paracrine manner.91 Such a Ucn/CRF-mediated paracrine regulatory loop in the liver would attract intense research interest, since it is well established that Fas ligand-mediated apoptosis is important in the pathogenesis of certain hepatic diseases, including chronic viral hepatitis and acute liver failure.92,93 Further research is mandatory to investigate such involvement of the CRF system in liver pathophysiology, because it may lead to useful and important clinical discoveries.
Indeed, in order to unfold a functional biological role of these effectors in liver physiology and pathogenesis, we tested the effects of the CRF system in the hepatocellular apoptotic process, using a rat experimental model of common bile duct surgical ligation, leading to obstructive jaundice, cholestasis and apoptosis induction in the hepatic parenchyma.76 Administration of selective and non-selective CRF antagonists showed that the endogenous CRF system promotes the cholestasis-induced apoptotis via CRF1 activation. In contrast, CRF2 seems to mediate an early and a late apoptosis-preventing phenomenon, i.e. elevated gene transcript levels of the anti-apoptotic bcl-2 at the first postoperative day and increased rat serum hepatocyte growth factor (HGF) levels94 on the third postoperative day, acting opposed to CRF1. Interestingly, no activity of CRF antagonists was observed under basal hepatic function, a finding that may imply that the CRF system plays a minimum role in the physiological turnover of the liver. Our data point to a CRF-based apoptosis-regulating mechanism in the liver: CRF1 activation resulted in apoptosis-inducing effects, whereas CRF2 mediated antiapoptotic cytoprotective actions. Opposing effects of the two receptors have also been documented in other physiological pathways, such as the catecholamine secretion by adrenals.47 Moreover, it has been suggested that CRF1 receptor activation initiated fear and anxiety-like responses in the CNS, whereas CRF2 receptor activation reestablished homeostasis by counteracting the aversive effects of CRF1 receptor signaling.95
The potential regulatory activity of CRF, Ucn and their receptors in the oncogenic and carcinogenic process has been studied during the last decade with interesting results, revealing a new exciting field for CRF system-related research.96 Ample experimental data have reported considerable antitumor effects of the CRF and Ucn; they appeared to inhibit the proliferation of melanoma and endometrial tumor cells, keratinocytes and human mammary cancer cells via CRF1.97-100 These antitumor findings were also tested in a study showing a role of hepatic CRF receptors on tumor growth and angiogenesis.101 Both in vivo and in vitro effects of Ucn1 were evaluated in human hepatoma cell lines SMMC-7721 and HepG2, human umbilical vein endothelial cells (HUVECs) and human hepatocellular carcinoma tissues. Ucn 1 inhibited the growth of hepatocellular carcinoma and reduced tumor microvessel density in nude mice. Ucn 1 administered in tumor-bearing mice inhibited the growth of established tumors in vivo. In addition, in vitro three-dimensional culture assays showed that Ucn 1 inhibited angiogenesis via CRF2 activation. Finally, Ucn 1 inhibited the proliferation, promoted the apoptosis of endothelial cells and down-regulated vascular endothelial growth factor (VEGF) expression in vivo via CRF2. The connection of the CRF system and angiogenesis in HCC should be further studied, because it may lead to new therapeutic approaches for this lethal liver cancer. Supporting a potential clinical significance of these findings, in the study of Simopoulos et al, we described Ucn 1 and CRF receptor expression by malignant cells in primary or metastatic liver carcinoma. These observations need to be confirmed by a larger number of specimens.
Ucn 1 and CRF receptors in liver biopsies have recently been discovered in normal and pathological human hepatic tissue with cirrhosis and primary or metastatic carcinoma,77 as well as in rat KCs.78 These data suggested a receptor-mediated paracrine involvement in local inflammatory phenomena within the liver. Furthermore, an antitumor effect of Ucn in HCC and in tumors growing in rodents has been demonstrated, via activation of CRF2, which inhibited cell growth and angiogenesis,101 whereas a CRF-based apoptosis-regulating mechanism was shown in obstructive jaundice challenged liver, but not under basal conditions (Table 1).76 These findings, although limited, advocate a potential regulatory role of the CRF system in the liver, regarding immunological functions, apoptotic mechanisms as well as oncogenic, antitumor and neoangiogenic processes. Taking into consideration the paramount role of the liver in the homeostasis and survival of the human body, further research addressing functionality and signaling of local receptors under basal and challenged conditions is necessary to consolidate the available knowledge concerning the CRF system impact in liver physiology and pathology and elucidate any clinical dimensions.
1.Guillemin R, Rosenberg B, 1955 Humoral hypothalamic control of anterior pituitary: a study with combined tissue cultures. Endocrinology 57: 599-607.
2.Saffran M, Schally AV, Benfey BG, 1955 Stimulation of the release of corticotropin from the adenohypophysis by a neurohypophysial factor. Endocrinology 57: 439-444.
3.Vale W, Spiess J, Rivier C, Rivier J, 1981 Characterization of a 41-residue ovine hypothalamic peptide that stimulates secretion of corticotropin and beta-endorphin. Science 213: 1394-1397.
4.Chen R, Lewis KA, Perrin MH, Vale WW, 1993 Expression cloning of a human corticotropin releasing-factor receptor. Proc Natl Acad Sci USA 90: 8967-8971.
5.Lovenberg TW, Liaw CW, Grigoriadis DE, et al, 1995 Cloning and characterization of a functionally distinct corticotropin-releasing factor receptor subtype from rat brain. Proc Natl Acad Sci U S A 92: 836-840.
6.Perrin MH, Vale WW, 1999 Corticotropin releasing factor receptors and their ligand family. Ann N Y Acad Sci 885: 312-328.
7.Lewis K, Li C, Perrin MH, et al, 2001 Identification of urocortin III, an additional member of the corticotropin-releasing factor (CRF) family with high affinity for the CRF2 receptor. Proc Natl Acad Sci U S A 98: 7570-7575.
8.Vaughan J, Donaldson C, Bittencourt J, et al, 1995 Urocortin, a mammalian neuropeptide related to fish urotensin I and to corticotropin-releasing factor. Nature 378: 287-292.
9.Reyes TM, Lewis K, Perrin MH, et al, 2001 Urocortin II: a member of the corticotropin-releasing factor (CRF) neuropeptide family that is selectively bound by type 2 CRF receptors. Proc Natl Acad Sci USA 98: 2843-2848.
10.Gulyas J, Rivier C, Perrin M, et al, 1995 Potent, structurally constrained agonists and competitive antagonists of corticotropin-releasing factor. Proc Natl Acad Sci U S A 92: 10575-10579.
11.Rivier J, Gulyas J, Kirby D, et al, 2002 Potent and long-acting corticotropin releasing factor (CRF) receptor 2 selective peptide competitive antagonists. J Med Chem 45: 4737-4747.
12.Rivier J, Gulyas J, Corrigan A, et al, 1998 Astressin analogues (corticotropin-releasing factor antagonists) with extended duration of action in the rat. J Med Chem 41: 5012-5019.
13.Hauger RL, Grigoriadis DE, Dallman MF, Plotsky PM, Vale WW, Dautzenberg FM, 2003 International Union of Pharmacology. XXXVI. Current status of the nomenclature for receptors for corticotropin-releasing factor and their ligands. Pharmacol Rev 55: 21-26.
14.Lovejoy DA, Balment RJ, 1999 Evolution and physiology of the corticotropin-releasing factor (CRF) family of neuropeptides in vertebrates. Gen Comp Endocrinol 115: 1-22.
15.Zhao L, Donaldson CJ, Smith GW, Vale WW, 1998 The structures of the mouse and human urocortin genes (Ucn and UCN). Genomics 50: 23-33.
16.Cepoi D, Sutton S, Arias C, Sawchenko P, Vale WW, 1999 Ovine genomic urocortin: cloning, pharmacologic characterization, and distribution of central mRNA. Brain Res Mol Brain Res 68: 109-118.
17.Bittencourt JC, Vaughan J, Arias C, Rissman RA, Vale WW, Sawchenko PE, 1999 Urocortin expression in rat brain: evidence against a pervasive relationship of urocortin-containing projections with targets bearing type 2 CRF receptors. J Comp Neurol 415: 285-312.
18.Kageyama K, Bradbury MJ, Zhao L, Blount AL, Vale WW, 1999 Urocortin messenger ribonucleic acid: tissue distribution in the rat and regulation in thymus by lipopolysaccharide and glucocorticoids. Endocrinology 140: 5651-5658.
19.Chatzaki E, Charalampopoulos I, Leontidis C, et al, 2003 Urocortin in human gastric mucosa: relationship to inflammatory activity. J Clin Endocrinol Metab 88: 478-483.
20.Hsu SY, Hsueh AJ, 2001 Human stresscopin and stresscopin-related peptide are selective ligands for the type 2 corticotropin-releasing hormone receptor. Nat Med 7: 605-611.
21.Grammatopoulos DK, Chrousos GP, 2002 Functional characteristics of CRH receptors and potential clinical applications of CRH-receptor antagonists. Trends Endocrinol Metab 13: 436-444.
22.Kostich WA, Chen A, Sperle K, Largent BL, 1998 Molecular identification and analysis of a novel human corticotropin-releasing factor (CRF) receptor: the CRF2gamma receptor. Mol Endocrinol 12: 1077-1085.
23.Dautzenberg FM, Hauger RL, 2002 The CRF peptide family and their receptors: yet more partners discovered. Trends Pharmacol Sci 23: 71-77.
24.Grigoriadis DE, 2005 The corticotropin-releasing factor receptor: a novel target for the treatment of depression and anxiety-related disorders. Expert Opin Ther Targets 9: 651-684.
25.Zmijewski MA, Slominski AT, 2010 Emerging role of alternative splicing of CRF1 receptor in CRF signaling. Acta Biochim Pol 57: 1-13.
26.Wu SV, Yuan PQ, Wang L, Peng YL, Chen CY, Tache Y, 2007 Identification and characterization of multiple corticotropin-releasing factor type 2 receptor isoforms in the rat esophagus. Endocrinology 148: 1675-1687.
27.Pisarchik A, Slominski A, 2004 Molecular and functional characterization of novel CRFR1 isoforms from the skin. Eur J Biochem 271: 2821-2830.
28.Slominski A, Pisarchik A, Tobin D, Mazurkiewicz JW, Wortsman J, 2004 Differential expression of a cutaneous corticotropin-releasing hormone system. Endocrinology 145: 941-950.
29.Lovenberg TW, Chalmers DT, Liu C, De Souza EB, 1995 CRF2 alpha and CRF2 beta receptor mRNAs are differentially distributed between the rat central nervous system and peripheral tissues. Endocrinology 136: 4139-4142.
30.Kimura Y, Takahashi K, Totsune K, et al, 2002 Expression of urocortin and corticotropin-releasing factor receptor subtypes in the human heart. J Clin Endocrinol Metab 87: 340-346.
31.Catalano RD, Kyriakou T, Chen J, Easton A, Hillhouse EW, 2003 Regulation of corticotropin-releasing hormone type 2 receptors by multiple promoters and alternative splicing: identification of multiple splice variants. Mol Endocrinol 17: 395-410.
32.Dautzenberg FM, Higelin J, Wille S, Brauns O, 2004 Molecular cloning and functional expression of the mouse CRF2(a) receptor splice variant. Regul Pept 121: 89-97.
33.Smart D, Coppell A, Rossant C, Hall M, McKnight AT, 1999 Characterisation using microphysiometry of CRF receptor pharmacology. Eur J Pharmacol 379: 229-235.
34.Tezval H, Jahn O, Todorovic C, Sasse A, Eckart K, Spiess J, 2004 Cortagine, a specific agonist of corticotropin-releasing factor receptor subtype 1, is anxiogenic and antidepressive in the mouse model. Proc Natl Acad Sci U S A 101: 9468-9473.
35.Valverde R, Seasholtz A, Cortright D, Denver R, 2001 Biochemical characterization and expression analysis of the Xenopus laevis corticotropin-releasing hormone binding protein. Mol Cell Endocrinol 173: 29-40.
36.Stengel A, Taché Y, 2010 Corticotropin-releasing factor signaling and visceral response to stress. Exp Biol Med (Maywood) 235: 1168-1178.
37.Grino M, Chrousos G, Margioris A, 1987 The corticotropin releasing hormone gene is expressed in human placenta. Biochem Biophys Res Commun 148: 1208-1214.
38.Petrusz P, Merchenthaler I, Ordronneau P, Maderdrut J, Vigh S, Schally A, 1984 Corticotropin-releasing factor (CRF)-like immunoreactivity in the gastro-entero-pancreatic endocrine system. Peptides 5 Suppl 1: 71-78.
39.Stephanou A, Jessop D, Knight R, Lightman S, 1990 Corticotrophin-releasing factor-like immunoreactivity and mRNA in human leukocytes. Brain Behav Immun 4: 67-73.
40.Makrigiannakis A, Zoumakis E, Margioris A, Theodoropoulos P, Stournaras C, Gravanis A, 1995 The corticotropin-releasing hormone (CRH) in normal and tumoral epithelial cells of human endometrium. J Clin Endocrinol Metab 80: 185-189.
41.Zoumakis E, Chatzaki E, Charalampopoulos I, et al, 2001 Cycle and age-related changes in corticotropin-releasing hormone levels in human endometrium and ovaries. Gynecol Endocrinol 15: 98-102.
42.Brar B, Stephanou A, Okosi A, et al, 1999 CRH-like peptides protect cardiac myocytes from lethal ischaemic injury. Mol Cell Endocrinol 158: 55-63.
43.Fabbri A, Tinajero J, Dufau M, 1990 Corticotropin-releasing factor is produced by rat Leydig cells and has a major local antireproductive role in the testis. Endocrinology 127: 1541-1543.
44.Mastorakos G, Webster E, Chrousos G, 1993 Corticotropin-releasing hormone and its receptors in the ovary: physiological implications. Ann N Y Acad Sci 687: 20-28.
45.Aird F, Clevenger C, Prystowsky M, Redei E, 1993 Corticotropin-releasing factor mRNA in rat thymus and spleen. Proc Natl Acad Sci U S A 90: 7104-7108.
46.Bruhn T, Engeland W, Anthony E, Gann D, Jackson I, 1987 Corticotropin-releasing factor in the adrenal medulla. Ann N Y Acad Sci 512: 115-128.
47.Dermitzaki E, Tsatsanis C, Minas V, et al, 2007 Corticotropin-releasing factor (CRF) and the urocortins differentially regulate catecholamine secretion in human and rat adrenals, in a CRF receptor type-specific manner. Endocrinology 148: 1524-1538.
48.Muglia L, Jenkins N, DJ G, Copeland N, Majzoub J, 1994 Expression of the mouse corticotropin-releasing hormone gene in vivo and targeted inactivation in embryonic stem cells. J Clin Invest 93: 2066-2072.
49.Bruhn T, Engeland W, Anthony E, Gann D, Jackson I, 1987 Corticotropin-releasing factor in the dog adrenal medulla is secreted in response to hemorrhage. Endocrinology 120: 25-33.
50.Minamino N, Uehara A, Arimura A, 1988 Biological and immunological characterization of corticotropin-releasing activity in the bovine adrenal medulla. Peptides 9: 37-45.
51.Goland R, Wardlaw S, Fortman J, Stark R, 1992 Plasma corticotropin-releasing factor concentrations in the baboon during pregnancy. Endocrinology 131: 1782-1786.
52.Robinson B, Arbiser J, Emanuel R, Majzoub J, 1989 Species-specific placental corticotropin releasing hormone messenger RNA and peptide expression. Mol Cell Endocrinol 62: 337-341.
53.Chatzaki E, Crowe PD, Wang L, Million M, Tache Y, Grigoriadis DE, 2004 CRF receptor type 1 and 2 expression and anatomical distribution in the rat colon. J Neurochem 90: 309-316.
54.Chatzaki E, Lambropoulou M, Constantinidis T, et al, 2006 Corticotropin-releasing factor (CRF) receptor type 2 in the human stomach: protective biological role by inhibition of apoptosis. J Cell Physiol 209: 905-911.
55.Yuan P, Wu S, Elliott J, et al, 2012 Expression of corticotropin releasing factor receptor type 1 (CRF(1)) in the human gastrointestinal tract and upregulation in the colonic mucosa in patients with ulcerative colitis. Peptides 38: 62-69.
56.Kimura T, Amano T, Uehara H, et al, 2007 Urocortin I is present in the enteric nervous system and exerts an excitatory effect via cholinergic and serotonergic pathways in the rat colon. Am J Physiol Gastrointest Liver Physiol 293: G903-910.
57.Harada S, Imaki T, Naruse M, Chikada N, Nakajima K, Demura H, 1999 Urocortin mRNA is expressed in the enteric nervous system of the rat. Neurosci Lett 267: 125-128.
58.Imperatore A, Florio P, Torres P, et al, 2006 Urocortin 2 and urocortin 3 are expressed by the human placenta, deciduas, and fetal membranes. Am J Obstet Gynecol 195: 288-295.
59.Tache Y, Perdue MH, 2004 Role of peripheral CRF signalling pathways in stress-related alterations of gut motility and mucosal function. Neurogastroenterol Motil 16 Suppl 1: 137-142.
60.Tache Y, Bonaz B, 2007 Corticotropin-releasing factor receptors and stress-related alterations of gut motor function. J Clin Invest 117: 33-40.
61.Boorse GC, Denver RJ, 2006 Widespread tissue distribution and diverse functions of corticotropin-releasing factor and related peptides. Gen Comp Endocrinol 146: 9-18.
62.Valdenaire O, Giller T, Breu V, Gottowik J, Kilpatrick G, 1997 A new functional isoform of the human CRF2 receptor for corticotropin-releasing factor. Biochim Biophys Acta 1352: 129-132.
63.Nishikimi T, Miyata A, Horio T, et al, 2000 Urocortin, a member of the corticotropin-releasing factor family, in normal and diseased heart. Am J Physiol Heart Circ Physiol 279: H3031-3039.
64.Yuan PQ, Million M, Wu SV, Rivier J, Tache Y, 2007 Peripheral corticotropin releasing factor (CRF) and a novel CRF1 receptor agonist, stressin1-A activate CRF1 receptor expressing cholinergic and nitrergic myenteric neurons selectively in the colon of conscious rats. Neurogastroenterol Motil 19: 923-936.
65.Porcher C, Juhem A, Peinnequin A, Sinniger V, Bonaz B, 2005 Expression and effects of metabotropic CRF1 and CRF2 receptors in rat small intestine. Am J Physiol Gastrointest Liver Physiol 288: G1091-1103.
66.Chalmers DT, Lovenberg TW, De Souza EB, 1995 Localization of novel corticotropin-releasing factor receptor (CRF2) mRNA expression to specific subcortical nuclei in rat brain: comparison with CRF1 receptor mRNA expression. J Neurosci 15: 6340-6350.
67.Tsatsanis C, Androulidaki A, Dermitzaki E, et al, 2005 Urocortin 1 and Urocortin 2 induce macrophage apoptosis via CRFR2. FEBS Lett 579:4259-4264.
68.Scarabelli TM, Pasini E, Ferrari G, et al, 2004 Warm blood cardioplegic arrest induces mitochondrial-mediated cardiomyocyte apoptosis associated with increased urocortin expression in viable cells. J Thorac Cardiovasc Surg 128: 364-371.
69.Chanalaris A, Lawrence KM, Stephanou A, et al, 2003 Protective effects of the urocortin homologues stresscopin (SCP) and stresscopin-related peptide (SRP) against hypoxia/reoxygenation injury in rat neonatal cardiomyocytes. J Mol Cell Cardiol 35:1295-1305.
70.Venihaki M, Ain K, Dermitzaki E, Gravanis A, Margioris AN, 1998 KAT45, a noradrenergic human pheochromocytoma cell line producing corticotropin-releasing hormone. Endocrinology 139: 713-722.
71.Makrigiannakis A, Margioris AN, Chatzaki E, Zoumakis E, Chrousos GP, Gravanis A, 1999 The decidualizing effect of progesterone may involve direct transcriptional activation of corticotrophin-releasing hormone from human endometrial stromal cells. Mol Hum Reprod 5: 789-796.
72.Paschos K, Kolios G, Chatzaki E, 2009 The corticotropin-releasing factor system in inflammatory bowel disease: prospects for new therapeutic approaches. Drug Discov Today 14: 713-720.
73.Devetzis V, Zarogoulidis P, Kakolyris S, Vargemezis V, Chatzaki E, 2012 The corticotropin releasing factor system in the kidney: perspectives for novel therapeutic intervention in nephrology. Med Res Rev 33: 847-872.
74.Muramatsu Y, Fukushima K, Iino K, et al, 2000 Urocortin and corticotropin-releasing factor receptor expression in the human colonic mucosa. Peptides 21: 1799-1809.
75.Chatzaki E, Murphy BJ, Wang L, et al, 2004 Differential profile of CRF receptor distribution in the rat stomach and duodenum assessed by newly developed CRF receptor antibodies. J Neurochem 88: 1-11.
76.Paschos KA, Charsou C, Constantinidis TC, et al, 2010 Corticotropin-releasing hormone receptors mediate opposing effects in cholestasis-induced liver cell apoptosis. Endocrinology 151: 1704-1712.
77.Simopoulos C, Christodoulou E, Lambropoulou M, et al, 2009 Neuropeptide urocortin 1 and its receptors are expressed in the human liver. Neuroendocrinology 89: 315-326.
78.Charalampopoulos I, Androulidaki A, Minas V, et al, 2006 Neuropeptide urocortin and its receptors are expressed in rat Kupffer cells. Neuroendocrinology 84: 49-57.
79.Dotzler S, Digeronimo R, Yoder B, Siler-Khodr TM, 2004 Distribution of corticotropin releasing hormone in the fetus, newborn, juvenile, and adult baboon. Pediatr Res 55: 120-125.
80.Potter E, Behan D, Fischer W, Linton E, Lowry P, Vale W, 1991 Cloning and characterization of the cDNAs for human and rat corticotropin releasing factor-binding proteins. Nature 349: 423-426.
81.Kasckow JW, Lupien SJ, Behan DP, Welge J, Hauger RJ, 2001 Circulating human corticotropin-releasing factor-binding protein levels following cortisol infusions. Life Sci 69: 133-142.
82.Kemp CF, Woods RJ, Lowry PJ, 1998 The corticotrophin-releasing factor-binding protein: an act of several parts. Peptides 19: 1119-1128.
83.Chatzaki E, Margioris A, Gravanis A, 2002 Expression and regulation of corticotropin-releasing hormone binding protein (CRH-BP) in rat adrenals. J Neurochem 80: 81-90.
84.Shi M, Yan X, Ryan DH, Harris RB, 2000 Identification of urocortin mRNA antisense transcripts in rat tissue. Brain Res Bull 53: 317-324.
85.Park JH, Lee YJ, Na SY, Kim KL, 2000 Genomic organization and tissue-specific expression of rat urocortin. Neurosci Lett 292: 45-48.
86.Yokohama S, Yoneda M, Watanobe H, et al, 2001 Effect of central urocortin on carbon tetrachlorideinduced acute liver injury in rats. Neurosci Lett 313:149-152.
87.Nakade Y, Yoneda M, Yokohama S, et al, 2003 Central injection of astressin inhibits carbon tetrachloride-induced acute liver injury in rats. Eur J Pharmacol 460: 35-38.
88.Agnello D, Bertini R, Sacco S, Meazza C, Villa P, Ghezzi P, 1998 Corticosteroid-independent inhibition of tumor necrosis factor production by the neuropeptide urocortin. Am J Physiol 275: E757-62.
89.Tsatsanis C, Androulidaki A, Dermitzaki E, Gravanis A, Margioris A, 2007 Corticotropin releasing factor receptor 1 (CRF1) and CRF2 agonists exert an anti-inflammatory effect during the early phase of inflammation suppressing LPS-induced TNF-alpha release from macrophages via induction of COX-2 and PGE2. J Cell Physiol 210: 774-783.
90.Tsatsanis C, Androulidaki A, Alissafi T, et al, 2006 Corticotropin-releasing factor and the urocortins induce the expression of TLR4 in macrophages via activation of the transcription factors PU.1 and AP-1. J Immunol 176: 1869-1877.
91.Dermitzaki E, Tsatsanis C, Gravanis A, Margioris A, 2002 Corticotropin-releasing hormone induces Fas ligand production and apoptosis in PC12 cells via activation of p38 mitogenactivated protein kinase. J Biol Chem 277: 12280–12287.
92.Kondo T, Suda T, Fukuyama H, Adachi M, Nagata S, 1997 Essential roles of the Fas ligand in the development of hepatitis. Nat Med 3: 409-413.
93.Strand S, Hofmann W, Grambihler A, et al, 1998 Hepatic failure and liver cell damage in acute Wilson’s disease involve CD95 (APO-1/Fas) mediated apoptosis. Nat Med 4: 588-593.
94.Li Z, Mizuno S, Nakamura T, 2007 Antinecrotic and antiapoptotic effects of hepatocyte growth factor on cholestatic hepatitis in a mouse model of bile-obstructive diseases. Am J Physiol Gastrointest Liver Physiol 292: G639-646.
95.Hauger R, Risbrough V, Brauns O, Dautzenberg F, 2006 Corticotropin releasing factor (CRF) receptor signaling in the central nervous system: new molecular targets. CNS Neurol Disord DrugTargets 5: 453-479.
96.Kaprara A, Pazaitou-Panayiotou K, Kortsaris A, Chatzaki E, 2010 The corticotropin releasing factor system in cancer: expression and pathophysiological implications. Cell Mol Life Sci 67: 1293-1306.
97.Graziani G, Tentori L, Portarena I, et al, 2002 CRH inhibits cell growth of human endometrial adenocarcinoma cells via CRH-receptor 1-mediated activation of cAMP-PKA pathway. Endocrinology 143: 807-813.
98.Carlson KW, Nawy SS, Wei ET, et al, 2001 Inhibition of mouse melanoma cell proliferation by corticotropin-releasing hormone and its analogs. Anticancer Res 21: 1173-1179.
99.Slominski AT, Roloff B, Zbytek B, et al, 2000 Corticotropin releasing hormone and related peptides can act as bioregulatory factors in human keratinocytes. In Vitro Cell Dev Biol Anim 36: 211-216.
100.Graziani G, Tentori L, Muzi A, et al, 2007 Evidence that corticotropin-releasing hormone inhibits cell growth of human breast cancer cells via the activation of CRH-R1 receptor subtype. Mol Cell Endocrinol 264: 44-49.
101.Wang J, Xu Y, Xu Y, et al, 2008 Urocortin’s inhibition of tumor growth and angiogenesis in hepatocellular carcinoma via corticotrophin-releasing factor receptor 2. Cancer Invest 26: 359-368.
102.Nakade Y, Yoneda M, Nakamura K, Makino I, Terano A, 2002 Involvement of endogenous CRF in carbon tetrachloride-induced acute liver injury in rats. Am J Physiol Regul Integr Comp Physiol 282: R1782-1788.
Address for correspondence:
Dr. Ekaterini Chatzaki, Laboratory of Pharmacology,
DUTH, Dragana, Alexandroupolis 68100, Thrace, Greece,
Tel./Fax: +302551030533, e-mail: firstname.lastname@example.org
Received 19-11-2012, Accepted 08-03-2013