Sylvain Delaunay

Elp3 links tRNA modification to IRES-dependent translation of LEF1 to sustain metastasis in breast cancer

Delaunay et al. reveal the role of U34 tRNA-modifying enzymes in the regulation of specific mRNA translation to support cell invasion and metastasis.

Elp3 drives Wnt-dependent tumor initiation and regeneration in the intestine

Tumor initiation in the intestine can rapidly occur from Lgr5+ crypt columnar stem cells. Dclk1 is a marker of differentiated Tuft cells and, when coexpressed with Lgr5, also marks intestinal cancer stem cells. Here, we show that Elp3, the catalytic subunit of the Elongator complex, is required for Wnt-driven intestinal tumor initiation and radiation-induced regeneration by maintaining a subpool of Lgr5+/Dclk1+/Sox9+ cells. Elp3 deficiency dramatically delayed tumor appearance in Apc-mutated intestinal epithelia and greatly prolonged mice survival without affecting the normal epithelium. Specific ablation of Elp3 in Lgr5+ cells resulted in marked reduction of polyp formation upon Apc inactivation, in part due to a decreased number of Lgr5+/Dclk1+/Sox9+ cells. Mechanistically, Elp3 is induced by Wnt signaling and promotes Sox9 translation, which is needed to maintain the subpool of Lgr5+/Dclk1+ cancer stem cells. Consequently, Elp3 or Sox9 depletion led to similar defects in Dclk1+ cancer stem cells in ex vivo organoids. Finally, Elp3 deficiency strongly impaired radiation-induced intestinal regeneration, in part because of decreased Sox9 protein levels. Together, our data demonstrate the crucial role of Elp3 in maintaining a subpopulation of Lgr5-derived and Sox9-expressing cells needed to trigger Wnt-driven tumor initiation in the intestine.

tRNA modification: is cancer having a wobble?

Translational control of protein synthesis supports tumor development and progression to metastasis. Wobble tRNA modifications are required during translation elongation and sustain proteome homeostasis. Recent work has highlighted the surprising upregulation of the wobble uridine 34 (U34) tRNA cascade in cancer, which underlies the specific requirement for this pathway in tumor development.

Codon-specific translation reprogramming promotes resistance to targeted therapy

Reprogramming of mRNA translation has a key role in cancer development and drug resistance1. However, the molecular mechanisms that are involved in this process remain poorly understood. Wobble tRNA modifications are required for specific codon decoding during translation2,3. Here we show, in humans, that the enzymes that catalyse modifications of wobble uridine 34 (U34) tRNA (U34 enzymes) are key players of the protein synthesis rewiring that is induced by the transformation driven by the BRAFV600E oncogene and by resistance to targeted therapy in melanoma. We show that BRAFV600E-expressing melanoma cells are dependent on U34 enzymes for survival, and that concurrent inhibition of MAPK signalling and ELP3 or CTU1 and/or CTU2 synergizes to kill melanoma cells. Activation of the PI3K signalling pathway, one of the most common mechanisms of acquired resistance to MAPK therapeutic agents, markedly increases the expression of U34 enzymes. Mechanistically, U34 enzymes promote glycolysis in melanoma cells through the direct, codon-dependent, regulation of the translation of HIF1A mRNA and the maintenance of high levels of HIF1α protein. Therefore, the acquired resistance to anti-BRAF therapy is associated with high levels of U34 enzymes and HIF1α. Together, these results demonstrate that U34 enzymes promote the survival and resistance to therapy of melanoma cells by regulating specific mRNA translation.Enzymes that catalyse modifications of wobble uridine 34 tRNA are essential for the survival of melanoma cells that rely on HIF1α-dependent metabolism through codon-dependent regulation of the translation of HIF1A mRNA.

The Endosomal Protein CEMIP Links WNT Signaling to MEK1–ERK1/2 Activation in Selumetinib-Resistant Intestinal Organoids

MAPK signaling pathways are constitutively active in colon cancer and also promote acquired resistance to MEK1 inhibition. Here, we demonstrate that BRAFV600E -mutated colorectal cancers acquire resistance to MEK1 inhibition by inducing expression of the scaffold protein CEMIP through a β-catenin- and FRA-1-dependent pathway. CEMIP was found in endosomes and bound MEK1 to sustain ERK1/2 activation in MEK1 inhibitor-resistant BRAFV600E-mutated colorectal cancers. The CEMIP-dependent pathway maintained c-Myc protein levels through ERK1/2 and provided metabolic advantage in resistant cells, potentially by sustaining amino acids synthesis. CEMIP silencing circumvented resistance to MEK1 inhibition, partly, through a decrease of both ERK1/2 signaling and c-Myc. Together, our data identify a cross-talk between Wnt and MAPK signaling cascades, which involves CEMIP. Activation of this pathway promotes survival by potentially regulating levels of specific amino acids via a Myc-associated cascade. Targeting this node may provide a promising avenue for treatment of colon cancers that have acquired resistance to targeted therapies.Significance: MEK1 inhibitor-resistant colorectal cancer relies on the scaffold and endosomal protein CEMIP to maintain ERK1/2 signaling and Myc-driven transcription. Cancer Res; 78(16); 4533-48. ©2018 AACR.

Correction: Elp3 drives Wnt-dependent tumor initiation and regeneration in the intestine

Correction: Elp3 drives Wnt-dependent tumor initiation and regeneration in the intestine Aurélie Ladang, Francesca Rapino, Lukas C. Heukamp, Lars Tharun, Kateryna Shostak, Damien Hermand, Sylvain Delaunay, Iva Klevernic, Zheshen Jiang, Nicolas Jacques, Diane Jamart, Valérie Migeot, Alexandra Florin, Serkan Göktuna, Brigitte Malgrange, Owen J. Sansom, Laurent Nguyen, Reinhard Büttner, Pierre Close, and Alain Chariot Vol. 212, No. 12, November 16, 2015. Pages 2057–2075.