Met receptor-induced Grb2 or Shc signals both promote transformation of intestinal epithelial cells, albeit they are required for distinct oncogenic functions.
BACKGROUND
Deregulation of receptor tyrosine kinases (RTK) contributes to the initiation and progression of intestinal-derived epithelial cancers, including colorectal cancer (CRC). However, the roles of the proximal signaling molecules engaged by RTKs in different oncogenic functions of CRC remain unclear.


METHODS
Herein, the functional impact of expressing variant forms of the oncogenic Met receptor (Tpr-Met) that selectively recruit the adaptor proteins Grb2 or Shc was investigated in a model derived from normal intestinal epithelial cells (IEC-6). An RNA interference (RNAi) approach was used to define the requirement of Grb2 or Shc in Tpr-Met-transformed IEC-6 cells. Since Grb2 and Shc couple RTKs to the activation of the Ras/MEK/Erk and PI3K/Akt pathways, Erk and Akt phosphorylation/activation states were monitored in transformed IEC-6 cells, and a pharmacological approach was employed to provide insights into the roles of these pathways in oncogenic processes evoked by activated Met, and downstream of Grb2 and Shc.


RESULTS
We show, for the first time, that constitutive activation of either Grb2 or Shc signals in IEC-6 cells, promotes morphological transformation associated with down-regulation of E-cadherin, as well as increased cell growth, loss of growth contact inhibition, anchorage-independent growth, and resistance to serum deprivation and anoikis. Oncogenic activation of Met was revealed to induce morphological transformation, E-cadherin down-regulation, and protection against anoikis by mechanisms dependent on Grb2, while Shc was shown to be partly required for enhanced cell growth. The coupling of activated Met to the Ras/MEK/Erk and PI3K/Akt pathways, and the sustained engagement of Grb2 or Shc in IECs, was shown to trigger negative feedback, limiting the extent of activation of these pathways. Nonetheless, morphological alterations and E-cadherin down-regulation induced by the oncogenic Tpr-Met, and by Grb2 or Shc signals, were blocked by MEK, but not PI3K, inhibitors while the enhanced growth and resistance to anoikis induced by Tpr-Met were nearly abolished by co-treatment with both inhibitors.


CONCLUSIONS
Overall, these results identify Grb2 and Shc as central signaling effectors of Met-driven progression of intestinal epithelial-derived cancers. Notably, they suggest that Grb2 may represent a promising target for the design of novel CRC therapies.
Véronique
V
Pomerleau
Mélissa
M
Landry
Jimmy
J
Bernier
Pierre H
PH
Vachon
Department of Anatomy and Cell Biology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3201, rue Jean-Mignault, Sherbrooke, Quebec J1E 4K8, Canada. caroline.saucier@usherbrooke.ca.
Caroline
C
Saucier
D015820:Cadherins / Q000378:metabolism; D002460:Cell Line; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology / Q000628:therapy; D004847:Epithelial Cells / Q000378:metabolism; D051380:GRB2 Adaptor Protein / Q000096:biosynthesis* / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000473:pathology; D019859:Proto-Oncogene Proteins c-met / Q000235:genetics / Q000378:metabolism*; D055765:Shc Signaling Adaptor Proteins / Q000096:biosynthesis* / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics
D015820:Cadherins; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; D055765:Shc Signaling Adaptor Proteins; C491743:MET protein, human; D019859:Proto-Oncogene Proteins c-met