MET Protein Expression Research Articles

Expression of Met protein and urokinase-type plasminogen activator receptor (uPA-R) in papillary carcinoma of the thyroid.

Met protein encoded by MET oncogene is the high affinity receptor for hepatocyte growth factor (HGF)/scatter factor (SF). HGF/SF has to be cleaved in its heterodimeric form by the urokinase-type plasminogen activator (uPA) to become active as a ligand for Met receptor. The expression of Met protein and of the high affinity receptor for uPA (uPA-R) was investigated in 39 samples of papillary carcinoma using immunohistochemistry. Reactivity for Met protein was present in 33 of 34 tumours, mostly with a diffuse pattern of staining. Reactivity for uPA-R was present in 78 per cent of papillary tumours and exhibited a pattern of staining similar to that of Met protein. Staining for uPA-R was present in 23 of 25 cases (92 per cent) of papillary carcinoma with prominent sclerosis, and in only 1 of 7 cases (14 per cent) without sclerosis. Peritumoural normal thyroid, follicular adenomas, and follicular carcinomas were negative for Met protein and for uPA-R. Hyperfunctioning tall thyroid cells showed weak membrane reactivity for uPA-R and for Met protein. The findings of immunohistochemistry were confirmed at the mRNA level using in situ hybridization, since the signal for uPA-R and Met RNAs was detected in most tumour cells of five cases of papillary carcinoma.

Expression of Met protein and urokinase‐type plasminogen activator receptor (uPA‐R) in papillary carcinoma of the thyroid

Expression of Met protein and urokinase‐type plasminogen activator receptor (uPA‐R) in papillary carcinoma of the thyroid

Interleukin-6, hepatocyte growth factor, and their receptors in biliary epithelial cells during a type I ductular reaction in mice: interactions between the periductal inflammatory and stromal cells and the biliary epithelium.

The interleukin-6 (IL-6)/gp-80 and hepatocyte growth factor (HGF)/met ligand/receptor systems have been shown to stimulate biliary epithelial cell (BEC) DNA synthesis in vitro. The mRNA and protein production of these two in vitro mitogens were mapped in vivo during the first week after bile duct ligation (BDL) when peak BEC DNA synthesis is seen. Changes around the biliary tree were compared with those seen in the peripheral liver using a combination of Northern blotting and a unique biliary tree isolation technique, in which the bile ducts and the surrounding portal stroma and inflammatory cells are separated from the hepatocytes by perfusion digestion. Further localization was performed with in situ hybridization and immunohistochemistry. In the normal liver, there is low-level expression of HGF mRNA by periportal stellate cells, and HGF protein localizes to these cells and to neutrophils; extracellular HGF protein is present in the bile. There is no detectable IL-6 mRNA by Northern analysis or IL-6 protein expression in the normal liver, but both met and IL-6 receptor (IL-6R) mRNA are detectable; met mRNA is expressed strongly in the biliary tree, and met protein is expressed weakly on hepatocytes and strongly on BEC. IL-6R mRNA is weakly expressed in the biliary tree, and IL-6R protein is detectable on hepatocytes, with a periportal-to-perivenular gradient, but not on BEC. During the first 3 days after BDL, HGF mRNA expression is increased in both the biliary tree and in the peripheral liver, and production is localized to stellate cells, periductal neutrophils, and stromal cells, which typically accompany the proliferating ductules. IL-6 mRNA and protein were detected only near the biliary tree after BDL, and not in the peripheral liver, and the production was localized to periductal hematolymphoid cells, which had the morphological appearance of macrophages and/or dendritic cells. There is also a distinct up-regulation of met and gp-80 mRNA and protein in the biliary tree, which is stronger than that seen in the peripheral liver. Met protein expression is increased, and IL-6R(gp-80) protein is induced on the proliferating BEC, consistent with the participation of both the HGF/met and IL-6/gp-80 systems in the early phases of type I ductular reactions. These observations show that periductal hematolymphoid and stromal cells are the source of BEC growth factors, and receptors for these factors are up-regulated on BEC during active ductular proliferation. Complex interactions between the inflammatory, stromal, and BEC results in a dysmorphogenic repair response that eventually leads to cirrhosis.

Differential expression of Met/hepatocyte growth factor receptor in subtypes of non-small cell lung cancers

Hepatocyte growth factor (HGF)/scatter factor (SF) is a multifunctional factor that stimulates epithelial cell motility, invasion and morphogenesis. Its receptor is a transmembrane tyrosine kinase encoded by the Met proto-oncogene. Several studies have suggested a possible role for HGF/Met in tumor development and progression. To investigate the potential roles of Met in human lung cancer biology, we have studied the mRNA and protein expression of Met in normal lung tissue, primary non-small cell lung carcinoma (NSCLC), and NSCLC cell lines. The results indicated a differential pattern of Met expression among various subtypes of NSCLC. The majority of squamous cell carcinoma (SQCC), either in vivo or in vitro, expressed Met mRNA and its protein product at levels much lower than or similar to normal lung tissue or bronchial epithelium. Moreover, SQCC characteristically over-expressed a variant Met mRNA which corresponds to a 5′ partially deleted transcript produced by alternative splicing. In contrast, the expression of Met mRNA and its protein product in adenocarcinoma (ADC) and large cell undifferentiated carcinoma were more heterogeneous. Overexpression was demonstrated in approximately 35% and 20% of these subtypes of NSCLC, respectively. Among ADC, intermediate to high levels of Met immunoreactivity correlated with greater degree of tumor differentiation. Furthermore, an accentuation of Met immunoreactivity was often noted in cancer cells at the advancing edge of tumors. These findings support a role for Met in lung cancer cell invasion and differentiation in vivo, but its expression and functions may be modified by the differentiation phenotype of the tumor cells.

Activated ras and ret oncogenes induce over-expression of c-met (hepatocyte growth factor receptor) in human thyroid epithelial cells.

Hepatocyte Growth Factor (HGF) receptor, encoded by the protooncogene c-met, is overexpressed in many human tumours, including those of thyroid epithelium. The absence in most cases of any primary structural abnormality of the met gene suggests that overexpression is secondary to mutation of other gene(s). To test this hypothesis we investigated the effect on met expression of two activated oncogenes known to play a major role in thyroid oncogenesis, ras and ret. To minimize the possibility of unknown co-operating events, we introduced these genes directly into normal human thyrocytes in primary culture using amphotropic retroviral vectors and assessed met expression as early as possible in the resulting epithelial colonies. Double immunofluorescence revealed expression of met protein, strictly localized to cells expressing the mutant ras and ret vectors, expression in background normal cells being barely detectable. In contrast, colonies induced to proliferate at a comparable rate by a vector expressing SV40 T showed no increase in met expression. To permit quantitation by Western blotting we also extended these findings to a thyroid cell line (R18) containing a zinc-inducible mutant ras gene. Induction of the oncogene led to a fourfold increase in met protein expression. We conclude that overexpression of met is induced by activation of the ras or ret signalling pathway and not simply by deregulation of the cell cycle per se. The data suggest that the proliferative advantage conferred by these oncogenes may be in part due to the resulting sensitization of tumour epithelium to paracrine HGF secreted by stromal cells.

Expression of Met protein in thyroid tumours.

Met protein is a transmembrane 190 kD heterodimer with tyrosine kinase activity, encoded by c-MET oncogene. It serves as a high affinity receptor for hepatocyte growth factor (HGF)/scatter factor (SF), a cytokine which stimulates cell proliferation, motility, and invasion. Expression of Met protein was investigated in 116 thyroid tumours using an anti-Met mouse monoclonal antibody (DQ-13) active on paraffin-embedded material. Reactivity for DQ-13 was observed in 77 per cent of papillary carcinomas, in 70 per cent of Hürthle cell tumours, and rarely in other tumours. The staining was either uniformly present throughout the tumour or limited to nests of infiltrating tumour cells. In some Hürthle cell tumours, prominent accumulation of the protein was observed in the Golgi area. Reactivity for Met protein was decreased or absent in poorly differentiated tumours and was not influenced by tumour size, presence of lymph node metastases, or age of the patient. Immunostaining for Ki-67 revealed that cytoplasmic accumulation of Met protein was not associated with enhanced proliferation of tumour cells. Overexpression of Met protein in thyroid papillary carcinoma may result in increased motility of tumour cells, which in turn may account for intraglandular multifocal dissemination and early lymph node metastasis.

Expression and phosphorylation of rat c-met/hepatocyte growth factor receptor during rat liver regeneration

Hepatocyte growth factor receptor is identified as a heterodimeric tyrosine kinase encoded by the c-met gene. This study was designed to determine how the c-met/hepatocyte growth factor receptor participates in the intracellular events involved in rat liver regeneration induced by administration of carbon tetrachloride.Expressin of the rat c-met mRNA increased, peaking 24 h after carbon tetrachloride administration almost in parallel with MET protein expression. Histochemical studies demonstrated that expression of the rat c-met was enhanced in cells surrounding the damaged areas, and also that the distribution of cells expressing MET was almost in accordance with that of cells expressing proliferating cells nuclear antigen. The MET protein underwent intense tyrosine phosphorylation peaking at 12 h after carbon tetrachloride administration, and prior to DNA synthesis. Phospholipase Cy and phosphatidylinositol 3-kinase, intracellular signal transducing molecules containing Src homology 2 domain, were associated with the MET protien following tyrosine phosphorylation in vivo.These observations suggest that expression and tyrosin phosphorylation of MET protein associated with signal transducing molecules may provide a mechanism whereby hepatocyte growth factor exerts its action on hepatocyte growth during rat liver regeneration induced by carbon tetrachloride administration