Oncogenic activation of the Met receptor tyrosine kinase fusion protein, Tpr-Met, involves exclusion from the endocytic degradative pathway

Oncogene. 2007 Nov 8;26(51):7213-21. doi: 10.1038/sj.onc.1210522. Epub 2007 May 28.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Base Sequence
  • Binding Sites
  • COS Cells
  • Cell Line
  • Cell Membrane / metabolism
  • Chlorocebus aethiops
  • DNA Primers
  • Endocytosis*
  • Humans
  • Mice
  • Microscopy, Fluorescence
  • Oncogene Protein tpr-met / metabolism*
  • Oncogenes*
  • Subcellular Fractions / metabolism
  • Ubiquitin / metabolism

Substances

  • DNA Primers
  • Oncogene Protein tpr-met
  • Ubiquitin