c-Met signalling: spatio-temporal decisions.

The spatial control of signalling events is critical in determining the outcome of a cellular response. Recent studies on the signal output from the growth factor/receptor HGF/c-Met, demonstrates that the PKC-regulated location of downstream transducers, specifically the MAPkinase ERK1/2, has a profound positive influence on cell migration, despite apparently reducing the steady state level of ERK1/2 activation. The mechanisms involved and the implications for signalling studies are discussed.

Integrin-protein kinase C relationships.

The integrins have an ability to interact with extracellular matrix proteins to confer adhesive and motile properties on cells. The means by which these activities operate and the manner in which they are integrated with cell functions is of particular relevance to many biological processes. In the present paper, the developing understanding of the bi-directional relationship between the protein kinase C family of signal transducers and integrins is discussed.

Antral mucosa expresses functional leptin receptors coupled to STAT-3 signaling, which is involved in the control of gastric secretions in the rat.

BACKGROUND & AIMS: Leptin is a circulating hormone that communicates the peripheral nutritional status to the hypothalamus, which controls food intake, energy expenditure, and body weight. This study characterizes leptin receptors and leptin-sensitive STAT proteins in the antrum and investigates the effects of leptin on gastric secretions. METHODS: The effects of leptin on gastrin messenger RNA (mRNA), plasma gastrin, gastric acid in vivo in the rat, and on somatostatin and gastrin secretions by isolated antral cells were determined in vitro. Leptin receptors were investigated in isolated rat antral cells by reverse transcription-polymerase chain reaction and binding of [(125)I]-leptin studies. The effects of in vivo and in vitro leptin on transduction signal STAT proteins were investigated by immunoblotting antral extracts. RESULTS: Peripheral injection of leptin inhibited in a dose-dependent manner, basal gastric secretion, gastrinemia, and mucosal gastrin mRNA in vivo. mRNAs encoding the long (Ob-Rb) and short (Ob-Ra) receptor forms were detected in rat antral mucosa, as were STAT-1, -3, and -5b immunoreactive proteins. Isolated antral cells specifically bound [(125)I]-leptin, and addition of leptin to these cells inhibited the release of somatostatin and increased the release of gastrin. These effects were associated with an increase in nuclear STAT-3 proteins in vitro and in vivo. CONCLUSIONS: This study provides the first molecular evidence for the coexpression of leptin receptors and STAT-3 in antral mucosa. It provides further evidence for the involvement of leptin in the control of gastric secretions.

HGF upregulates and modifies subcellular distribution of proteins in colon cancer cell enterocytic differentiation.

Hepatocyte growth factor (HGF) and its receptor, c-Met, are involved in cell transformation. To study their role in intestinal cell differentiation, we used Caco-2 colon cancer cells, which differentiate spontaneously into enterocytes during culture. Cells grown continuously in the presence of HGF reached confluence more quickly than control cells. Markers of enterocytic differentiation, such as alkaline phosphatase and sucrase-isomaltase activities, adhesion molecules, and structural proteins such as E-cadherin, villin, and F-actin were upregulated by HGF throughout the 35 days of culture, and actin fibers were reorganized. HGF also stimulated expression and tyrosine phosphorylation of c-Met and Gab-1 as well as protein kinase C (PKC)-alpha expression. PKC-alpha has been shown to be involved in intestinal differentiation. We therefore investigated the possibility that increases in PKC-alpha protein levels were responsible for the HGF-promoted events. We did this by incubating cells with Gö-6976, an inhibitor of PKC-alpha and -beta1, concomitantly with HGF. This inhibitor abolished the HGF-induced increase in villin levels before, but not after, confluence. Thus HGF accelerates Caco-2 cell differentiation and stimulates the metabolic and structural events accompanying this process. These HGF-promoted events may be mediated partly by Gab-1, and the effects of HGF on villin before confluence seem to involve PKC.

Glycine-extended gastrin promotes the invasiveness of human colon cancer cells.

Colorectal cancers express significant amounts of immature glycine-extended gastrin (G-Gly) and G-Gly is able to stimulate cell proliferation in colonic cell lines and mucosa. Here we wished to investigate whether G17-Gly promote the invasiveness of LoVo human colonic cancer cells, a process which requires degradation of extracellular matrix by proteases and concomitant induction of cell migration. We confirmed that LoVo cells express gastrin and gastrin/CCK-B receptor mRNAs. We showed that these cells secrete matrix metalloproteinase (MMP)-1, -2, and -9. The function of MMP being to degrade components of extracellular matrix, they may thus favor cell migration. As compared to controls, G17-Gly (10(-7) to 10(-12) M) significantly enhanced about two to three times the LoVo cell migration through Matrigel, an artificial basement matrix barrier. Moreover, G17-Gly increased and gastrin/CCK-B receptor antagonists decreased MMP secretion in conditioned culture media of LoVo cells. Our findings show that physiological doses of incompletely processed form of gastrin induce the invasiveness of tumor cells in vitro and suggest a novel potential role for this peptide in the metastatic process of colonic cancers in vivo.

Hepatocyte growth factor induces colonic cancer cell invasiveness via enhanced motility and protease overproduction. Evidence for PI3 kinase and PKC involvement.

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.

Transforming growth factor-alpha and epidermal growth factor receptor in colonic mucosa in active and inactive inflammatory bowel disease.

Transforming growth factor-alpha (TGF-alpha) is overexpressed in colonic carcinomas and promotes mucosal wound healing. It may be implicated in chronic inflammatory bowel disease (IBD). We analyzed the expression of TGF-alpha and its receptor, epidermal growth factor receptor (EGF-r), in the colonic mucosa of patients with Crohn's disease (CD) or ulcerative colitis (UC), in active or inactive stages, as compared with controls. Proteins and mRNA were detected in biopsies from the right and left colon and in surgical colonic specimens. Immunoblot analysis revealed TGF-alpha protein as a 29 kDa band. This band was normally expressed in uninvolved colonic mucosa of patients with CD or UC whether in active or inactive stages, but decreased or absent in involved mucosa of active IBD, even when TGF-alpha mRNA and EGF-r protein were detected. In the unaffected mucosa of CD, the intensity of TGF-alpha immunoreactivity was similar to that of controls in the right colon but stronger (P = 0.05) in the left colon. There was no TGF-alpha overexpression in dysplastic regions. In conclusion, in active IBD disease, the decreased TGF-alpha protein amount seems not only related to epithelial cell loss but reflects a down-regulation at least at the protein level. We speculate that TGF-alpha does not play a role within the active stage but may be implicated later in the repair process.

Leptin secretion and leptin receptor in the human stomach.

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 transcriptase-polymerase 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 approximately 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.

Matrix metalloproteinase inhibition prevents colon cancer peritoneal carcinomatosis development and prolongs survival in rats.

Matrix metalloproteinases (MMP) are enzymes responsible for extracellular matrix degradation which play a role in cancer progression and metastatic spreading. We investigated the effects of the MMP inhibitor, batimastat, in vitro on the proliferation and invasiveness of the rat colon cancer cell line DHD/K12, and in vivo on the growth of an aggressive model of peritoneal carcinomatosis producing haemorrhagic ascites and metastases, obtained in the rat by i.p. injection of DHD/K12 cells. MMP production was studied in conditioned culture media, solid tumors and ascitic fluid. In vivo, after injection of tumor cells on day 0, rats received i.p. daily either batimastat (30 mg/kg) or equal volume of vehicle from day 2 until killing on day 43 (series I) or from day 13 until death (series II). The grade of peritoneal carcinomatosis, ascite volume, number and size of liver metastases were evaluated in both series, and survival in series II. MMPs-1, -2 and -9 were identified in culture media, tumors and ascites. In vitro, batimastat did not modify DHD/K12 cell proliferation and slightly reduced cell invasion. In vivo, in series I, batimastat treatment totally prevented peritoneal carcinomatosis and liver metastasis development. In series II, it significantly prolonged survival (P < 0.0002) and reduced peritoneal carcinomatosis (P < 0.001) and hepatic metastases number as compared with controls. However, batimastat-treated rats of the two series had peritoneal inflammation with marked ascites. Nevertheless, inhibition of MMP is a new therapeutic approach which may be promising in treatment of microtumors as in more advanced cancer stages.

[Effects of HGF on the production of matrix metalloproteinases by colonic cancer cells DHD/K12]. / Effets de l'HGF sur la production de métalloprotéinases matricielles par les cellules cancéreuses coliques DHD/K12.

Matrix metalloproteinases (MMPs) and growth factors such as hepatocyte growth factor (HGF) are implicated in tumoral progression of several digestive cancers. The rat DHD/K12 colonic cancer cell line is very invasive in vivo. We showed by RT-PCR and western immunoblotting the presence of HGF receptor, c-Met, in DHD/K12 cells. Then, we detected by zymography and western blots the secretion of MMP-2 and MMP-9 in the conditioned medium of these cells. After 24 or 48 h of culture in medium supplemented with HGF, transforming growth factor-alpha (TGF-alpha) or sodium butyrate, MMP production by DHD/K12 cells was stimulated by HGF and TGF-alpha and inhibited by sodium butyrate. Knowing the capacity of MMPs to degrade the extracellular matrix and thus to favour tumoral invasion, results suggest that HGF is implicated in the aggressive behaviour of DHD/K12 cells since it increased MMPs secretion by these cells.

The stomach is a source of leptin.

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.

Developmental expression and functionality of hepatocyte growth factor and c-Met in human fetal digestive tissues.

BACKGROUND & AIMS: Hepatocyte growth factor (HGF) and its receptor c-Met are presumed to play a morphogenic role during embryogenesis. The possible implication of HGF and c-Met during the digestive system development was approached by investigating their ontogeny, distribution, and functionality in human fetal tissues. METHODS: Thirty fetuses, 7-24 weeks old, were obtained. HGF and c-Met messenger RNAs and proteins were detected in liver, pancreas, esophagus, stomach, and small and large intestine. Tyrosine phosphorylation assays were realized on homogenates and membrane preparations from fetal tissues. RESULTS: The temporal appearance of HGF and c-Met was established between 7 and 8 weeks of gestation in digestive tissues. Immunoblot analysis showed the presence of the c-Met beta-subunit 145-kilodalton band and of the HGF alpha-subunit 70-kilodalton band. c-Met was localized in epithelia, especially in fundic parietal cells, pancreatic and gut endocrine cells, and in muscular layers. HGF immunoreactivity was first detected in epithelia and then in mesenchyme and muscular layers. In young fetal stages, the c-Met immunoprecipitated 145-kilodalton band showed tyrosine phosphorylation after HGF stimulation. CONCLUSIONS: This study provides evidence for HGF and c-Met expression early in all human fetal digestive tissues and implicates HGF-c-Met in the digestive system morphogenesis.

[Expression of hepatocyte growth factor and its receptor, C-Met in human digestive tissues and different gastric and colonic cancer cell lines]. / Expression de I' "hepatocyte growth factor" et de son récepteur, c-Met, dans les tissus digestifs humains et certaines lignées cellulaires cancéreuses gastrique et coliques.

OBJECTIVES AND METHODS: Hepatocyte growth factor (HGF) and its receptor c-Met exert mitogene and motogene activities in digestive tissues. The aim of the study was a) to detect and localize these proteins in adult human digestive mucosae, liver and pancreas, using western immunoblotting and immunohistochemistry with anti-HGF and c-Met antibodies and b) to identify the receptor in three digestive cancer cell lines. RESULTS: HGF and c-Met were detected by the two techniques used in esophagus, fundus, antrum, duodenum, cecum, colon and rectum where they were localized in epithelial and sometimes lamina propria cells. HGF and c-Met were also present in hepatocytes, and c-Met in pancreatic endocrine cells. c-Met was identified in human gastric HGT-1 and rat colon DHD/K12 cancer cells. HGF (40 ng/mL) scattered colonies formed by these cells as well as human T84 colon cancer cells. CONCLUSIONS: Our findings demonstrate the presence of HGF and c-Met in all human digestive tissues and are compatible with the implication of HGF in metastatic processes of digestive cancers.