C-Met oncogenic mutants sustain signals in the endosome and are protected against downregulation


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Carine Joffre, Stephanie Kermorgant

Institute of Cancer and Cancer Research UK Clinical Centre, Bart's and The London School of Medicine and Dentistry, London, UK

Abstract

C-Met oncogenic mutants sustain signals in the endosome and are protected against downregulation

Background

C-Met, the tyrosine kinase receptor of hepatocyte growth factor (HGF), influences behaviour of several cancer types by controlling growth, survival and metastasis. Various c-Met activating mutations have been detected in solid tumours where they have been proposed to play a role in modulating tumour metastasis. However their mechanisms of action have remained undetermined. From recent literature concerning Wild Type c-Met and other receptors, it is evident that receptor localisation dynamics, due to endocytosis/trafficking, have a significant influence on their signalling and, consequently, on cell function.

Aim

The aim of this study was to evaluate whether endocytosis/trafficking of c-Met mutants could play a role in cell transformation. The model used was mouse fibroblastic NIH3T3 cells stably transfected with c-Met Wild Type or with three distinct c-Met mutants reported in human cancers.

Results

The mutants were found to be highly phosphorylated and were highly tumourigenic in xenograft experiments as compared to the Wild Type. Using confocal microscopy and quantitative biochemical assays we provide evidence that activating point mutations in the c-Met kinase domain trigger an accumulation of phosphorylated c-Met in endosomal compartments. This is due to important modifications in mutated c-Met trafficking: 1) increased endocytosis; 2) sorting default from endosomal compartments leading to a decreased downregulation. Consequences are sustained signalling, remodelling of the actin cytoskeleton, increased cell migration and survival. Blocking endocytosis by pharmacological and RNA interference approaches reduces the signalling and concomitantly reduces cell transformation.

Conclusion

This study demonstrates that oncogenic c-Met mutations detected in tumour samples trigger a persistent signalling due to deregulated trafficking and downregulation.