Roles of caudal-related homeobox gene Cdx1 in oesophageal epithelial cells in Barrett's epithelium development.

BACKGROUND AND AIMS: The mechanism of transformation to intestinal metaplasia in Barrett's oesophagus has not been clarified. We previously reported that bile acids activate the Cdx2 promoter via nuclear factor kappa B (NF-kappaB) and stimulate production of Cdx2 protein in oesophageal keratinocytes with a resulting production of intestinal type mucin. In addition to Cdx2, Cdx1 may play an important role in the development of Barrett's oesophagus. Therefore, we studied the direct effects of bile acids on the expression of Cdx1 as well as the precise mechanisms of Cdx1 expression in cultured oesophageal squamous epithelial cells. Furthermore, we investigated the relationship between Cdx1 and Cdx2 expression in cultured oesophageal squamous epithelial cells. METHODS: A rat model of Barrett's oesophagus was produced by anastomosing the oesophagus and jejunum. The expression of Cdx1 was investigated by immunohistochemistry, while the response of that expression to bile acids was studied using a Cdx1 promoter luciferase assay. In addition, oesophageal squamous epithelial cells were transfected with a Cdx1 or Cdx2 expression vector, after which their possible transformation to intestinal-type epithelial cells was investigated. RESULTS: In our Barrett's rat model, the metaplastic epithelium and adjoining squamous epithelium strongly expressed Cdx1. Further, the bile acids mixture dose-dependently increased Cdx1 promoter activity and Cdx1 protein in oesophageal epithelial cells. Transfection of the Cdx1 expression vector in cultured oesophageal epithelial cells induced production of Cdx2 protein. CONCLUSION: Bile acid-induced sequential expression of Cdx1 followed by Cdx2 may have an important role in the development of Barrett's epithelium.

Reg I-knockout mice reveal its role in regulation of cell growth that is required in generation and maintenance of the villous structure of small intestine.

Reg I (regenerating gene product I) is a growth factor that plays a central role in the generation and regeneration of the gastric mucosal architecture. On the other hand, mouse Reg I mRNA is expressed at the highest levels in the small intestine among the gastrointestinal tissues. In the current study, with the aim to clarify the role of Reg I protein in the small intestine, the temporal and spatial pattern of Reg I expression and the phenotype of Reg I-knockout mice in the tissue were examined. In the wild-type mice, immunohistochemistry localized Reg I protein expression in absorptive cells located in the lower half of the intestinal villi. Reg I expression was undetectable until embryonic day 13 (E13), when the fetal intestine still lacks villous structure; however, it dramatically increased at E17 along with the formation and maturation of the fetal intestinal villi. In the small intestine of the adult Reg I-knockout mice, less densely packed, round-shaped aberrant morphology of the absorptive cells was observed light microscopically, and electron microscopical examination revealed a strikingly loose connection of these cells to the basement membrane. Antiproliferating cell nuclear antigen staining and anti-Ki67 staining demonstrated the marked decrease in the number of proliferating cells in the small intestinal mucosa of the knockout mice. The cell migration speed visualized by one shot labeling of 5-bromodeoxyuridine was significantly slower in the knockout mice. These phenotypes of Reg I-knockout mice emerged, in accordance with the temporal pattern of Reg I expression described above, from E17. Reg I was considered to be a regulator of cell growth that is required to generate and maintain the villous structure of the small intestine.

Analysis of gastrin receptor gene expression in proliferating cells in the neck zone of gastric fundic glands using laser capture microdissection.

Gastrin stimulates proliferation of progenitor cells in the neck zone of gastric fundic mucosa. However, whether it directly enhances this proliferation through its receptors remains unclear. We investigated the expression of gastrin receptors in neck zone proliferating cells in rat gastric fundic glands using a reverse transcription polymerase chain reaction (RT-PCR) coupled with laser capture microdissection and in situ RT-PCR. Gastrin receptor expression was identified in c-fos-expressing cells located in the neck zone, and results of the RT-PCR analysis argued against contamination by other cells, such as enterochromaffin-like, parietal or D cells. Supporting this finding, gastrin receptor gene expression was identified in the neck zone as well as base glands by in situ RT-PCR. Therefore, it is suggested that proliferating cells in the neck zone are stimulated directly by gastrin via their gastrin receptors.

Can PPAR gamma ligands be used in cancer therapy?

The role of peroxisome-proliferator activated receptor (PPAR)gamma in tumor growth inhibition has been extensively studied during last seven years but still remains debated. Many in vitro and xenograft studies have demonstrated that PPARgamma ligands are anti-tumorigenic due to anti-proliferative, pro-differentiation and anti-angiogenic effects. In animal models, PPARgamma ligands have shown preventive effects against chemical carcinogenesis. On the other hand, evidences are accumulating against the possible use of this ligand activated nuclear receptor in molecular targeting for cancer therapy. The growth inhibitory effects of certain PPARgamma ligands have recently been shown to be independent of PPARgamma-activation. Studies have also come up with results indicating the growth promoting effects of PPARgamma-activation, particularly in certain animal models genetically predisposed to cancer development. Loss-of-function mutations of PPARgamma in tumors and increased susceptibility of PPARgamma heterozygote knockout mice to carcinogenesis suggested a tumor-suppressing role of PPARgamma. However, recent findings do not support PPARgamma as a tumor suppressor gene. Although initial clinical trials with PPARgamma ligand troglitazone reported promising results in liposarcoma and prostate cancers, recent studies failed to show the expected therapeutic values in advanced colorectal and breast cancers. In this review, we have addressed these controversies on potential use of PPARgamma ligands in cancer therapy.

Time-course changes of ECL cell markers in acetic acid-induced gastric ulcers in rats.

BACKGROUND AND AIM: Enterochromaffin-like (ECL) cells are the major source of histamine for the regulation of gastric acid secretion, and also contain histidine decarboxylase (HDC), vesicular monoamine transporter 2 (VMAT2), and chromogranin A (CgA). Although gastric acid secretion is suppressed during ulcer healing, the role of ECL cells in that process is not yet fully understood. In the present study, we investigated the changes in ECL cell number during healing of experimental ulcers in rats. MATERIALS AND METHODS: Seven-week-old male Wistar rats were used. Acetic acid-induced ulcers were caused by an application of 100% acetic acid to the serosal surface of the rat stomachs. At different time points following the induction (12 h-15 days), time-course changes of HDC, VMAT2, and CgA mRNA expression were investigated by Northern blot analysis. The expressions of HDC, VMAT2, and CgA were immunostained on gastric mucosal sections with ulcers. RESULTS: HDC, VMAT2, and CgA mRNA in gastric mucosa each showed an initial marked transient decrease, followed by an increase on day 10 back to the initial value. HDC, VMAT2, and CgA-immunoreactive cells at the ulcer margin were reduced in number on day 3, compared with those in distant areas. On day 10, however, they returned to levels similar to those in distant areas. CONCLUSION: The present study revealed a local down-regulation of HDC, VMAT2, and CgA in ECL cells at the ulcer margin. As a result, we concluded that a suppression of ECL cell activity during ulcer healing may be involved in suppressed gastric acid secretion.

Expression of midkine and receptor-like protein tyrosine phosphatase (RPTP)-beta genes in the rat stomach and the influence of rebamipide.

BACKGROUND: Midkine has been reported to bind to receptor-like protein tyrosine phosphatase (RPTP)-beta and to play important roles in growth and differentiation of various cells. Midkine is expressed in rat stomach during experimental ulcer healing, suggesting that the midkine-RPTP-beta system has some physiological functions in the stomach. Rebamipide is a mucoprotective drug used for the treatment of gastric ulcers. We have tested the hypothesis that the ulcer healing mechanism stimulated by rebamipide is linked physiologically to the gastric midkine-RPTP-beta system. MATERIALS AND METHODS: Seven-week-old-male Wistar rats were used. Midkine and RPTP-beta gene expression in rat stomach was investigated by laser capture microdissection coupled with the reverse transcription-polymerase chain reaction (RT-PCR). The effects of rebamipide on midkine and RPTP-beta expression in rat stomach and the gastric epithelial cell line RGM1 were evaluated by RT-PCR and Northern blot analyses. RESULTS: Midkine and RPTP-beta expression was detected in the gastric mucosal, submucosal and muscle layers. Rebamipide stimulated both midkine and RPTP-beta expression in rat stomach and RGM1 cells. CONCLUSION: Rebamipide may protect the gastric mucosa by regulating midkine and RPTP-beta expression.

Helicobacter pylori infection prevents the occurrence of the tolerance phenomenon of histamine H2 receptor antagonists.

BACKGROUND: The attenuated anti-secretory activity of H2 receptor antagonists (H2RA) during continuous administration is referred to as the tolerance phenomenon. However, it is not clarified whether Helicobacter pylori infection affects the occurrence of tolerance to H2RA. It is also not clarified whether the tolerance phenomenon occurs to a new H2RA, lafutidine. AIM: To investigate the occurrence of the tolerance phenomenon in subjects with and without H. pylori infection during the continuous administration of lafutidine and famotidine. SUBJECTS AND METHODS: Subjects were 20 healthy male volunteers (seven H. pylori positive and 13 H. pylori negative cases). All subjects were examined by ambulatory intragastric pH monitoring five times without medication, on the first and 15th day of the administration of 20 mg b.d. famotidine and 10 mg b.d. lafutidine in a cross-over fashion. RESULTS: The tolerance phenomenon was not observed in H. pylori-positive subjects during the 15-day-long administration of both H2RAs. In contrast, the tolerance phenomenon was observed in H. pylori negative subjects, which has been previously reported. CONCLUSIONS: This study demonstrated that H. pylori infection affects the tolerance phenomenon during continuous administration of H2RAs.

Intragastric distribution of Helicobacter pylori during short-term omeprazole therapy: study using Carnoy's fixation and immunohistochemistry for detection of bacteria.

BACKGROUND: There is controversy about the effect of acid-suppressive therapy on Helicobacter pylori density and the severity of histological gastritis in the corpus. AIM: To evaluate the precise distribution of H. pylori, both on the surface mucus cells and in the surface mucus gel layer, by using Carnoy's fixation and immunostaining for the detection of bacteria. METHODS: A total of 19 peptic ulcer patients with H. pylori infection were studied. All patients received a 6-week course of treatment with omeprazole (20 mg/day). Before and after the therapy, H. pylori density in Carnoy-fixed tissue sections was examined immunohistochemically. The effect of omeprazole therapy on the severity of gastritis was also evaluated. RESULTS: H. pylori density and the grade of gastritis significantly decreased in the antrum after omeprazole therapy. In the corpus, however, there were no significant changes in H. pylori density or the severity of gastritis after omeprazole therapy. CONCLUSION: Carnoy's fixation and immunostaining was found to be useful for the detection of H. pylori in the surface mucus gel layer as well as on the surface mucus cells in biopsy tissue sections. By using this method, H. pylori density decreased in the antrum, but remained unchanged in the corpus after a 6-week course of omeprazole therapy.

Lymphoepithelial cyst of the pancreas.

A case of lymphoepithelial cyst (LEC) of the pancreas is presented. A 48-year-old man complaining of general fatigue was found to have a heterogeneous water-dense mass protruding from the surface of the pancreas on plain computed tomography (CT). Dynamic CT disclosed septa within the mass. Magnetic resonance imaging, (MRI) showed a hypointense mass on T1-weighted imaging, and a hyperintense mass on T2-weighted imaging. MRI with gadolinium enhancement revealed septa within the mass. Endoscopic ultrasonography showed septa and fine echogenic structures within the cystic echoic lesion. Endoscopic retrograde pancreatography showed a normal duct system. Distal pancreatectomy with splenectomy was performed, with a suspected diagnosis of cystic neoplasms of the pancreas. Histopathologic examination disclosed LEC of the pancreas. Our case suggests that LEC should be considered in the differential diagnosis of cystic neoplasms of the pancreas.

Sclerosing cholangitis and systemic lymphadenopathy.

A 48-year-old man was admitted to our hospital with jaundice and systemic lymphadenopathy. Cholangiographic findings and liver histology disclosed the presence of sclerosing cholangitis. The patient also had a marked polyclonal increase in IgG levels. The cholangiographic findings, the systemic lymphadenopathy, and the increase in IgG levels resolved completely after treatment with prednisolone. This case suggests that there is an association between sclerosing cholangitis and immunologic abnormalities, and that corticosteroid treatment is useful for this disorder.

Gastrointestinal stromal tumor with a novel mutation of KIT proto-oncogene.

The majority of human gastrointestinal mesenchymal tumors are gastrointestinal stromal tumors (GISTs). Recent reports have shown the existence of gain-of-function mutations in the juxta-membrane domain of receptor tyrosine kinase (KIT) in GISTs. We present a 77-year-old woman with GIST diagnosed by positive immunostaining of cluster designation (CD) 34 and KIT. This case had a novel mutation at codon 576 located in the juxta-membrane domain of KIT. Our results indicate the importance of mutations in this KIT region and suggest the possibility of the existence of other types of mutations in this region in GISTs.

[A case of giant hepatocellular carcinoma effectively treated with UFT].

A 73-year-old man complaining of general fatigue and abdominal fullness was hospitalized in April 1994. Hepatocellular carcinoma (HCC) measuring 25 x 11 cm was detected in the right liver lobe. The patient received transcatheter artery embolization, and AFP and PIVKA-II levels were decreased thereafter. However, after three months, AFP levels were increased gradually. Therefore, 300 mg of UFT was administered daily. AFP and PIVKA-II levels decreased and the tumor decreased in size. The patient remained in a good state of health for about two years and six months. Our case suggests that UFT is effective for the treatment of HCC.

Bile acids directly augment caudal related homeobox gene Cdx2 expression in oesophageal keratinocytes in Barrett's epithelium.

BACKGROUND AND AIMS: The mechanism of transformation to intestinal metaplasia in Barrett's oesophagus has not been clarified. We investigated the effects of various bile acids on expression of the caudal related homeobox gene Cdx2 in cultured oesophageal squamous epithelial cells. In addition, morphological and histochemical changes in squamous cells to intestinal epithelial cells were studied in response to bile acid induced expression of Cdx2. METHODS: A rat model of Barrett's oesophagus was created by anastomosing the oesophagus and jejunum, and Cdx2 expression was investigated by immunohistochemistry. Also, the response of various bile acids on Cdx2 gene expression was studied in the human colon epithelial cell lines Caco-2 and HT-29, as well as in cultured rat oesophageal squamous epithelial cells using a Cdx2 promoter luciferase assay. In addition, primary cultured oesophageal squamous epithelial cells were transfected with Cdx2 expression vectors and their possible transformation to intestinal-type epithelial cells was investigated. RESULTS: Oesophagojejunal anastomoses formed intestinal goblet cell metaplasia in rat oesophagus specimens and metaplastic epithelia strongly expressed Cdx2. When the effects of 11 types of bile acids on Cdx2 gene expression were examined, only cholic acid (CA) and dehydrocholic acid dose dependently increased Cdx2 promoter activity and Cdx2 protein production in Caco-2 and HT-29 cells, and cultured rat oesophageal keratinocytes. Results from mutation analysis of Cdx2 promoter suggested that two nuclear factor kappaB (NFkappaB) binding sites were responsible for the bile acid induced activation of the Cdx2 promoter. When bile acids were measured in oesophageal refluxate of rats with experimental Barrett's oesophagus, the concentration of CA was found to be consistent with the experimental dose that augmented Cdx2 expression in vitro. Furthermore, transfection of the Cdx2 expression vector in cultured rat oesophageal keratinocytes induced production of intestinal-type mucin, MUC2, in cells that expressed Cdx2. CONCLUSIONS: We found that CA activates Cdx2 promoter via NFkappaB and stimulates production of Cdx2 protein in oesophageal keratinocytes with production of intestinal-type mucin. This may be one of the mechanisms of metaplasia in Barrett's oesophagus.

Site-dependent production of transforming growth factor beta1 in colonic mucosa: its possible role in tumorigenesis of the colon.

Transforming growth factor (TGF) beta1 has an antitumorigenic role in the gastrointestinal tract and may be associated with the development of colon neoplasia. In the present study we investigated whether TGF-beta1 production in mucosa is lower in the distal colon, which is where clinical evidence shows that the incidence of colon neoplasia is higher, and whether TGF-beta1 levels were lower in the mucosa of patients with colon adenoma. Production of colon mucosa TGF-beta1 was investigated by means of a 24-hour organ culture with biopsy specimens taken from different segments of the colon of 58 normal subjects by using an enzyme immunoassay. TGF-beta1 production in colon mucosa from locations near the site of sporadic adenoma was also investigated in 46 patients. TGF-beta1 production gradually increased from the rectum to the ascending colon in a statistically significant manner in both normal (r = 0.77, P < .0001) and adenoma-bearing (r = 0.8, P < .0001) mucosa. When TGF-beta1 production was compared between normal and adenoma-bearing mucosa, levels were lower in the latter, although statistically significant results were seen only in the transverse colon (P < .05). TGF-beta1 production has clear site dependency, being lowest in the rectum and highest in the ascending colon. Furthermore, low levels of TGF-beta1 are associated with the development of adenoma. Our results suggest the possibility that this site dependency is associated with the higher epidemiologic incidence of colon neoplasia in the distal colon.

Primary sclerosing pancreatitis and cholangitis.

CONCLUSION: The clinical course of our patient suggests the association between chronic pancreatitis and primary sclerosing cholangitis (PSC), as well as the usefulness of prednisolone for the treatment of this condition. BACKGROUND: Although alterations in the pancreatic duct have been reported, the association between chronic pancreatitis and PSC remains uncertain. METHODS AND RESULTS: A long-term follow-up case of chronic pancreatitis accompanied by PSC is presented. A 58-yr-old man complaining of epigastric distress was admitted to our hospital in July 1990. Endoscopic retrograde cholangio-pancreatography (ERCP) showed a stricture of the distal common bile duct and a narrowing of the main pancreatic duct (MPD) with mild ectasia of its branches in the head of the pancreas. ERCP taken in June 1992 revealed localized narrowings in both the right and the left main hepatic ducts, and irregularity of the MPD through the entire pancreas. An ERCP taken in June 1996 showed a progression of the narrowings of the bile ducts. The patient was diagnosed as having chronic pancreatitis accompanied by PSC. ERCP revealed a remarkable improvement of the bile ducts after 4 wk of treatment with prednisolone.

Effect of rebamipide on prostaglandin EP4 receptor gene expression in rat gastric mucosa.

Prostaglandin E2 (PGE2) plays an important role in the regulation of gastric mucus secretion. We have previously shown that the prostaglandin EP4 receptor (EP4) gene is abundantly expressed in gastric mucus-producing cells. Furthermore, we have shown that EP4 is present in a rat normal gastric mucosal cell line (RGM1) and that PGE2 increases mucus secretion from these cells via EP4. Rebamipide, an anti-gastric ulcer agent, has been reported to promote gastric PGE2 production and mucus secretion. However, it is unclear whether rebamipide influences mucus secretion by altering expression of the EP4 gene. Therefore, we tested the effect of rebamipide on EP4 gene expression in the gastric mucosa. Seven-week-old Wistar rats received oral rebamipide (100 mg/kg) with and without water-immersion restraint stress (WRS). All rats were killed, and their gastric tissues were used to investigate the expression of mRNA for EP4 and cyclooxygenase types 1 and 2. The thickness of the gastric mucus layer was also measured. The effect of rebamipide on EP4 gene expression and PGE2 production in RGM1 cells was also investigated in vitro. Furthermore, the effect of PGE2 on cyclic adenosine monophosphate (cAMP) production by RGM1 cells with or without rebamipide was studied. Oral rebami-pide significantly increased EP4 gene expression in the gastric antrum but not in the corpus after WRS. Furthermore, it increased surface mucus thickness and suppressed ulcer formation in the gastric mucosa after WRS. In vitro, rebamipide significantly augmented EP4 gene expression in RGM1 cells, and PGE2 significantly increased the cAMP production by RGM1 cells incubated with rebamipide. Rebamipide promotes EP4 gene expression and may consequently increase the gastric mucus secretion via EP4 receptors in the rat antral mucosa.

Influence of Helicobacter pylori infection and cetraxate on gastric mucosal blood flow during healing of endoscopic mucosal resection-induced ulcers.

BACKGROUND AND AIM: Helicobacter pylori (H. pylori) infection is known to affect the gastric microcirculation, and cetraxate is reported to accelerate gastric ulcer healing, possibly by augmenting gastric mucosal blood flow (MBF). The aim of this study is to clarify the effect of H. pylori infection and cetraxate on MBF during gastric ulcer healing. METHODS: Forty-two patients who had undergone endoscopic mucosal resection (EMR) were studied. Mucosal blood flow was measured by the use of a laser Doppler flowmeter in the surrounding mucosa and at the ulcer margin, before, 1 day, 1 week and 4 weeks after EMR. Helicobacter pylori infection was confirmed by the use of bacterial culture and histology. After EMR, patients were randomly assigned to receive 30 mg lansoprazole (u.i.d; L-regimen) or 30 mg lansoprazole (u.i.d.) with 200 mg cetraxate (q.i.d; LC-regimen) for 4 weeks. RESULTS: The MBF ratio (MBF at ulcer margin/MBF in surrounding mucosa) 1 week after EMR was significantly lower than that before or 4 weeks after EMR only in H. pylori-positive patients treated with the L-regimen. No such decrease in MBF was observed after 1 week in H. pylori-positive patients treated with the LC-regimen or in H. pylori-negative patients. CONCLUSION: A transient decrease in MBF was detected at the ulcer margin during healing of EMR-induced ulcers in H. pylori-infected patients. Cetraxate seemed to prevent this decrease in MBF.

Peroxisome proliferator-activated receptor gamma ligand-induced growth inhibition of human hepatocellular carcinoma.

Peroxisome proliferator-activated receptor gamma (PPARgamma) ligands have been implicated in the growth inhibition and differentiation of certain human cancers with diverse tissue origin. In this study, expression of PPARgamma in human hepatocellular carcinoma (HCC) and the effect of PPARgamma ligands on HCC cells were investigated in vitro using Hep G2, HuH-7, KYN-1 and KYN-2 cell lines. All cell lines were found to express functionally active PPARgamma and a marked growth inhibition was induced by thiazolidinedione ligands troglitazone, and pioglitazone as well as with its natural ligand 15-deoxy-Delta(12,14)-prostaglandin J(2). The growth inhibitory effect was associated with a dose-dependent inhibition of DNA synthesis, cell cycle progression and alpha fetoprotein expression.

Expression of peroxisome proliferator-activated receptor (PPAR)gamma in gastric cancer and inhibitory effects of PPARgamma agonists.

Peroxisome proliferator-activated receptor (PPAR) gamma is expressed in human colon cancer, prostate cancer and breast cancer cells, and PPARgamma activation induces growth inhibition in these cells. PPARgamma expression in human gastric cancer cells, however, has not been fully investigated. We report the PPARgamma expression in human gastric cancer, and the effect of PPARgamma ligands on proliferation of gastric carcinoma cell lines. Immunohistochemistry was used to demonstrate the presence of PPARgamma protein in surgically resected specimens from well differentiated, moderately differentiated and poorly differentiated adenocarcinoma. We used reverse transcription-polymerase chain reaction and Northern and Western blot analyses to demonstrate PPARgamma expression in four human gastric cancer cell lines. PPARgamma agonists (troglitazone and 15-deoxy-Delta(12,14)-prostaglandin J2) showed dose-dependent inhibitory effects on the proliferation of the gastric cancer cells, and their effect was augmented by the simultaneous addition of 9- cis retinoic acid, a ligand of RXRalpha. Flow cytometry demonstrated G1 cell cycle arrest and a significant increase of annexin V-positive cells after treatment with troglitazone. These results suggest that induction of apoptosis together with G1 cell cycle arrest may be one of the mechanisms of the antiproliferative effect of PPARgamma activation in human gastric cancer cells.

Activation of prostaglandin E2-receptor EP2 and EP4 pathways induces growth inhibition in human gastric carcinoma cell lines.

The effect of prostaglandin E2 (PGE2) on the proliferation of gastric cancer cells is still unclear. PGE2 receptors are divided into four subtypes - EP1, EP2, EP3, and EP4 - which are coupled to three different intracellular signal-transduction systems. Stimulation of EP2 and EP4 is linked with cyclic adenosine 3', 5'-monophosphate (cAMP)-dependent protein kinase A (PKA). In some human gastric cancer cells, PGE2 has been suggested to have an antiproliferative effect by way of increased cAMP production. Expression of EP2 and EP4 in human gastric carcinoma cells, however, has not been examined. We examined the expression of EP2 and EP4 and the antiproliferative effects of specific EP2 and EP4 agonists on four different human gastric cancer cell lines. Our data clarified that all the cell lines investigated in this study expressed EP2 and EP4 and that the specific agonists of these receptors induced growth inhibition with an accompanying increase in cAMP production. In summary, gastric cancer cells have EP2 and EP4 receptors, and their selective activation is linked with the decreased cell proliferation.