title: Oncogenic activation of the Met receptor tyrosine kinase fusion protein, Tpr-Met, involves exclusion from the endocytic degradative pathway.
abstract: Multiple mechanisms of dysregulation of receptor tyrosine kinases (RTKs) are observed in human cancers. In addition to gain-of-function, loss of negative regulation also contributes to oncogenic activation of RTKs. Negative regulation of many RTKs involves their internalization and degradation in the lysosome, a process regulated through ubiquitination. RTK oncoproteins activated following chromosomal translocation, are no longer transmembrane proteins, and are predicted to escape lysosomal degradation. To test this, we used the Tpr-Met oncogene, generated following chromosomal translocation of the hepatocyte growth factor receptor (Met). Unlike Met, Tpr-Met is localized in the cytoplasm and also lacks the binding site for Cbl ubiquitin ligases. We determined whether subcellular localization of Tpr-Met, and/or loss of its Cbl-binding site, is important for oncogenic activity. Presence of a Cbl-binding site and ubiquitination of cytosolic Tpr-Met oncoproteins does not alter their transforming activity. In contrast, plasma membrane targeting allows Tpr-Met to enter the endocytic pathway, and Tpr-Met transforming activity as well as protein stability are decreased in a Cbl-dependent manner. We show that transformation by Tpr-Met is in part dependent on its ability to escape normal downregulatory mechanisms. This provides a paradigm for many RTK oncoproteins activated following chromosomal translocation.
authors.affiliation: Molecular Oncology Group, McGill University Health Centre, Montreal, Quebec, Canada.
authors.forename: H H L
authors.initials: HH
authors.lastname: Mak
authors.forename: P
authors.initials: P
authors.lastname: Peschard
authors.forename: T
authors.initials: T
authors.lastname: Lin
authors.forename: M A
authors.initials: MA
authors.lastname: Naujokas
authors.forename: D
authors.initials: D
authors.lastname: Zuo
authors.forename: M
authors.initials: M
authors.lastname: Park
mesh_terms: D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D019556:COS Cells; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002522:Chlorocebus aethiops; D017931:DNA Primers; D004705:Endocytosis; D006801:Humans; D051379:Mice; D008856:Microscopy, Fluorescence; D050490:Oncogene Protein tpr-met / Q000378:metabolism*; D009857:Oncogenes; D013347:Subcellular Fractions / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D017931:DNA Primers; D050490:Oncogene Protein tpr-met; D025801:Ubiquitin