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C-terminal truncated forms of Met, the hepatocyte growth factor receptor
M Prat1, T Crepaldi, L Gandino
1Department of Biomedical Sciences and Oncology, University of Torino School of Medicine, Italy.
Abstract:
The MET proto-oncogene encodes a transmembrane tyrosine kinase of 190 kDa (p190MET), which has recently been identified as the receptor for hepatocyte growth factor/scatter factor. p190MET is a heterodimer composed of two disulfide-linked chains of 50 kDa (p50 alpha) and 145 kDa (p145 beta). We have produced four different monoclonal antibodies that are specific for the extracellular domain of the Met receptor. These antibodies immunoprecipitate with p190MET two additional Met proteins of 140 and 130 kDa. The first protein (p140MET) is membrane bound and is composed of an alpha chain (p50 alpha) and an 85-kDa C-terminal truncated beta chain (p85 beta). The second protein (p130MET) is released in the culture supernatant and consists of an alpha chain (p50 alpha) and a 75-kDa C-terminal truncated beta chain (p75 beta). Both truncated forms lack the tyrosine kinase domain. p140MET and p130MET are consistently detected in vivo, together with p190MET, in different cell lines or their culture supernatants. p140MET is preferentially localized at the cell surface, where it is present in roughly half the amount of p190MET. The two C-terminal truncated forms of the Met receptor are also found in stable transfectants expressing the full-length MET cDNA, thus showing that they originate from posttranslational proteolysis. This process is regulated by protein kinase C activation. Together, these data suggest that the production of the C-terminal truncated Met forms may have a physiological role in modulating the Met receptor function.
Insights
Researchers identified truncated forms of the MET receptor tyrosine kinase (p140MET and p130MET) generated by posttranslational proteolysis. These forms, regulated by protein kinase C, may modulate MET receptor function.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- The MET proto-oncogene encodes the p190MET receptor tyrosine kinase, a heterodimer crucial for cell signaling.
- Hepatocyte growth factor/scatter factor (HGF/SF) binds to the Met receptor.
- Understanding Met receptor processing is vital for cancer research.
Purpose of the Study:
- To characterize novel truncated forms of the Met receptor.
- To investigate the origin and regulation of these truncated Met proteins.
- To explore the potential physiological role of truncated Met forms.
Main Methods:
- Production of monoclonal antibodies specific to the Met receptor's extracellular domain.
- Immunoprecipitation assays to identify Met protein variants.
- Detection of Met proteins in cell lines and culture supernatants in vivo.
- Analysis of stable transfectants expressing full-length MET cDNA.
Main Results:
- Identified two C-terminal truncated Met proteins: membrane-bound p140MET (p50 alpha/p85 beta) and secreted p130MET (p50 alpha/p75 beta).
- Both truncated forms lack the tyrosine kinase domain and are detected alongside full-length p190MET.
- Truncated Met forms originate from posttranslational proteolysis, regulated by protein kinase C activation.
- p140MET is found at the cell surface, approximately half the amount of p190MET.
Conclusions:
- The Met receptor undergoes posttranslational proteolysis to generate functional truncated forms.
- Protein kinase C activation regulates the production of truncated Met proteins.
- These truncated Met forms (p140MET and p130MET) likely play a physiological role in modulating Met receptor signaling.