The circulating peptide leptin, which is the product of the ob gene, provides feedback information on the size of fat stores to central Ob receptors that control food intake and body-weight homeostasis. Leptin has so far been reported to be secreted only by adipocytes and the placenta. Here we show that leptin messenger RNA and leptin protein are present in rat gastric epithelium, and that cells in the glands of the gastric fundic mucosa are immunoreactive for leptin. The physiological function of this previously unsuspected source of leptin is unknown. However, both feeding and administration of CCK-8 (the biologically active carboxy-terminal end of cholecystokinin) result in a rapid and large decrease in both leptin cell immunoreactivity and the leptin content of the fundic epithelium, with a concomitant increase in the concentration of leptin in the plasma. These results indicate that gastric leptin may be involved in early CCK-mediated effects activated by food intake, possibly including satiety.

The traditional view on the role of serine proteases in tumor biology has changed with the recent discovery of a family of protease-activated receptors (PARs). In this study we explored the expression and functional role of the thrombin receptor PAR-1 in human colon cancer cells. Reverse transcriptase-polymerase chain reaction analysis showed that PAR-1 mRNAs are present in 11 of 14 human colon cancer cell lines tested but not in normal human colonic epithelial cells. This is in line with the immunolocalization of PAR-1 in human colon tumors and its absence in normal human colonic mucosa. The functional significance of the aberrant expression of PAR-1 in colon cancer cells was then investigated. We found that 1) a prompt increase in intracellular calcium concentration was observed on thrombin (10 nmol/L) or PAR-1 agonist AP1 (100 micro mol/L) challenge of HT29 cells; 2) HT29 quiescent cells treated with thrombin (0.01 to 20 nmol/L) or AP1 (1 to 300 micro mol/L) exhibited dramatic mitogenic responses (3.5-fold increase in cell number). Proliferative effects of thrombin or AP1 were also observed in other colon cancer cell lines expressing PAR-1. This effect was reversed by the MEK inhibitor PD98059 in consonance with the ability of thrombin or AP1 to induce phosphorylation of p42/p44 extracellular-regulated protein kinases. 3) PAR-1 activation by thrombin or AP1 led to a two-fold increase in cell motility of wounded HT29-D4. Our results demonstrate for the first time the aberrant expression of the functional thrombin receptor PAR-1 in colon cancers and its important involvement in cell proliferation and motility. Thrombin should now be considered as a growth factor for human colon cancer.

Resistance to apoptosis is a recurrent theme in colon cancer. We have shown previously that the 7-transmembrane spanning receptor OX1R for orexins promotes robust apoptosis in the human colon cancer cell line HT29 through an entirely novel mechanism involving phosphorylation of tyrosine-based motifs in OX1R. Here, we investigated the status of OX1R in a large series of human colorectal tumors and hepatic metastases. All primary colorectal tumors regardless of their localization and Duke's stages and all hepatic metastases tested expressed OX1R mRNA and/or protein. In sharp contrast, adjacent normal colonocytes or hepatocytes as well as control normal tissues were negative. Next, we showed that nine human colon cancer cell lines established from primary tumors or metastases expressed OX1R mRNA and underwent important apoptosis on orexin-A challenge. Most interestingly, orexin-A also promoted robust apoptosis in cells that are resistant to the most commonly used drug in colon cancer chemotherapy, 5-fluorouracil. When human colon cancer cells were xenografted in nude mice, orexin-A administered at day 0 strongly slowed the tumor growth and even reversed the development of established tumors when administered 7 days after cell inoculation. Orexin-A also acts by promoting tumor apoptosis in vivo because caspase-3 is activated in tumors on orexin treatment of nude mice. These findings support that OX1R is an Achilles heel of colon cancers, even after metastasis or chemoresistance. They suggest that OX1R agonists might be novel candidates for colon cancer therapy. Cancer Res; 71(9);

Background and aim-The circulating peptide leptin produced by fat cells acts on central receptors to control food intake and body weight homeostasis. Contrary to initial reports, leptin expression has also been detected in the human placenta, muscles, and recently, in rat gastric chief cells. Here we investigate the possible presence of leptin and leptin receptor in the human stomach. Methods-Leptin and leptin receptor expression were assessed by immunohistochemistry, reverse transcriptasepolymerase chain reaction (RT-PCR), and western blot analysis on biopsy samples from 24 normal individuals. Fourteen (10 healthy volunteers and four patients with non-ulcer dyspepsia and normal gastric mucosa histology) were analysed for gastric secretions. Plasma and fundic mucosa leptin content was determined by radioimmunoassay. Results-In fundic biopsies from normal individuals, immunoreactive leptin cells were found in the lower half of the fundic glands. mRNA encoding ob protein was detected in the corpus of the human stomach. The amount of fundic leptin was 10.4 (3.7) ng leptin/g mucosa, as determined by radioimmunoassay. Intravenous infusions of pentagastrin or secretin caused an increase in circulating leptin levels and leptin release into the gastric juice. The leptin receptor was present in the basolateral membranes of fundic and antral gastric cells. mRNA encoding Ob-RL was detected in both the corpus and antrum, consistent with a protein of ∼120 kDa detected by immunoblotting. Conclusion-These data provide the first evidence of the presence of leptin and leptin receptor proteins in the human stomach and suggest that gastric epithelial cells may be direct targets for leptin. Therefore, we conclude that leptin may have a physiological role in the human stomach, although much work is required to establish this.

The influences ofmultiple endocrine neoplasia type 1 (MEN 1), hypergastrinaemia, age, and sex on gastric endocrine cell densities were studied in 48 patients with the ZollingerEllison syndrome of either the sporadic type (n=31) or associated with MEN 1 (n= 17). The mean fundic argyrophil cell density was higher in women (p<005). It showed no appreciable difference between young and old women but it declined with age in men. The mean argyrophil cell density, when adjusted for sex, was higher (+48.5%, p=006) in patients with ZollingerEllison syndrome associated with MEN 1 than in those with sporadic type disease. This measurement was not significantly different between the two groups of patients when antisecretory treatments were considered. In patients with sporadic type disease, fundic argyrophil cells showed a normal pattern (16%) or diffuse (71%) or linear (13%) hyperplasia. In patients with MEN 1 diffuse and linear hyperplasia were of the same order (53% and 47%). Furthermore, fundic argyrophil endocrine tumours developed in five of 17 -that is, 29.5% of patients with associated MEN 1 while none was seen in patients with sporadic type disease. These tumours showed an exclusive or prominent enterochromaffin like cell population. Antral gastrin and somatostatin cell densities and fasting serum gastrin concentrations were similar in the two groups of patients with Zollinger-Ellison syndrome. Whatever the underlying mechanism for carcinoidosis, the risk of developing fundic enterochromaffin like cell tumours in Zollinger-Ellison syndrome patients who present with MEN 1 is probably higher than was initially estimated and suggests that regular follow up of these patients is necessary.

Tumour progression to the metastatic phenotype is mainly dependent on tumour cell invasiveness. Cell migration is a crucial step in this process. Here we investigate the effect of hepatocyte growth factor (HGF) on the induction of in vitro invasiveness of poorly aggressive Caco-2 colonic cancer epithelial cells. Invasion assays through a Matrigel barrier were performed. Proteases were assessed by zymography, reverse transcription-polymerase chain reaction and immunoblotting. Caco-2 cells were found to express HGF receptor but not HGF and to secrete several proteases, namely matrix metalloproteinase-1 (MMP-1), MMP-2, possibly MMP-9 and urokinase plasminogen activator (uPA). Exogenous HGF promoted invasiveness of Caco-2 cells through an artificial basement membrane matrix and enhanced their production of proteases. In addition, analyses of media at the end of invasion assays indicated that anti-HGF antibody inhibited protease production in parallel with cell invasion. The involvement of proteases in the HGF-induced invasion process was further investigated using either a synthetic general MMP inhibitor or neutralizing antibodies against MMPs or uPA. All components significantly inhibited HGF-promoted cell invasion. Moreover, specific inhibitors of PKCalpha/beta1 and PI3 kinase also decreased both HGF-promoted cell invasion and protease expression in invasion assay media. Thus, our findings provide evidence that the process of HGF-activated invasiveness of Caco-2 cells involves PI3 kinase and PKC and results from close association of two events, stimulation of cell motile activity and concomitant overproduction of proteases, which permits cell migration through a degraded extracellular matrix.

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A direct participation in maintaining the mucosal defense barrier can be ascribed to RELMbeta in line with a regulatory role in intestinal inflammation.