Le cancer colorectal (CCR) demeure l'une des principales causes de décès par cancer dans le monde. Récemment, une nouvelle immunothérapie basée sur le ciblage du récepteur à activité tyrosine kinase (RTK) EGFR via l'anticorps cetuximab a montré une amélioration significative de la survie des patients atteints de CCR métastatique (CCRm). Cependant, une grande partie de ces patients présente une résistance qui est associée à la présence de mutations gains de fonction dans la voie de signalisation Ras. Dans ce contexte, l'identification de cibles thérapeutiques Ras-indépendantes pourrait avoir un intérêt particulier. Une analyse pharmacologique effectuée au laboratoire démontre que le nilotinib, un inhibiteur de la TK oncogénique BCR-ABL utilisée en clinique pour le traitement des leucémies myéloïdes chroniques, affecte également les propriétés invasives et métastatiques de cellules de CCR. Nous avons identifié la cible majoritaire de cet inhibiteur dans cette réponse tumorale : il s'agit de DDR1, un récepteur au collagène ayant une activité TK intrinsèque. Mon travail de thèse a mis en évidence que DDR1 est fréquemment et fortement activé dans les métastases de patients atteints de CCR. J'ai ensuite analysé la signalisation DDR1-dépendante dans ces cellules tumorales par phosphoprotéomique quantitative. Cette analyse montre la nature Ras-indépendante de cette signalisation et révèle la protéine de signalisation BCR comme un nouveau substrat essentiel de DDR1 pour induire l'invasion cellulaire. Enfin, je montre que l'inhibition de DDR1 par le nilotinib améliore la réponse au cetuximab y compris pour les cellules tumorales ayant une mutation oncogénique de K-Ras ou B-Raf. En conclusion, ces résultats suggèrent que le ciblage de DDR1 par le nilotinib pourrait avoir un intérêt thérapeutique dans le traitement des CCRm. / Colorectal cancer (CRC) is one of the leading causes of cancer-related death in the Western world. Cancer that metastasizes to distant sites is usually not curable, although chemotherapy can extend survival. Recently, a novel immunotherapy approach based on targeting the EGFR tyrosine kinase (TK) via the antibody cetuximab was shown to significantly improve the survival of patients with metastatic CRC (mCRC). However, only patients with wild-type KRAS may hope to gain from EGFR inhibition. The majority of patients expresses oncogenic K-Ras alleles and thus have hyperactive Ras cascade operating independently from EGFR. Therefore, there is an urgent need for discovery of a new Ras-independent target that regulates tumor cell invasion and metastasis in mCRC. A pharmacological approach in the lab revealed that the small inhibitor of the leukemic TK BCR-Abl also inhibits invasive and metastatic abilities of CRC cells. This effect was also observed in cells expressing deregulated KRAS signalling. We next identified the receptor for collagen and atypical TK DDR1 as that the main target of nilotinib in these cells. Accordingly, DDR1 was found frequently and strongly activated in metastatic nodules of CRC patients. I also characterized DDR1 signalling by quantitative phosphoproteomic. This analysis revealed the Ras-independent nature of DDR1 signalling but also the Rho GTPase regulator BCR as an essential DDR1 substrate that leads to cell invasion. Finally, I demonstrate that nilotinib potentiates cetuximab response in CRC cells expressing oncogenic K-Ras signaling. Overall, these results suggest that the targeting of DDR1 by nilotinib may be of therapeutic value in mCRC.

Thrombocytes are important players in hemostasis. There is still much to be explored regarding the molecular basis of the thrombocyte function. In our previous microarray analysis data, we found IFT122 (an intraflagellar transport protein known to be involved in cilia formation) transcripts in zebrafish thrombocytes. Given recent discoveries of non-ciliary roles for IFTs, we examined the possibility that IFT122 affects thrombocyte function. We studied the role of IFT122 in thrombocyte function. We also found that IFT122 plays a central role in thrombocyte activation initiated by the agonists ADP, collagen, PAR-1 peptide and epinephrine. Although the receptors for ADP, PAR-1 peptide and epinephrine are present in the zebrafish genome, the collagen receptor GPVI was missing. In this study, we identified G6fL as a collagen receptor in zebrafish thrombocytes. Furthermore, IFT knockdown results in reduction in Wnt signaling. The Wnt signaling has been shown to be involved in megakaryocyte proliferation and proplatelets production. Therefore, defects in IFT could lead to thrombocytopenia. Splenectomy is performed in humans to treat such conditions. Therefore, in this study we developed a survival surgery protocol for splenectomy. We have shown that number of thrombocytes and their microparticles increase following splenectomy in zebrafish. Thus overall the studies on thrombocyte function in zebrafish could enhance fundamental knowledge on hemostasis and may provide future target candidates for therapies.