B-Raf inhibitors induce epithelial differentiation in BRAF-mutant colorectal cancer cells.
BRAF mutations are associated with aggressive, less-differentiated and therapy-resistant colorectal carcinoma. However, the underlying mechanisms for these correlations remain unknown. To understand how oncogenic B-Raf contributes to carcinogenesis, in particular to aspects other than cellular proliferation and survival, we generated three isogenic human colorectal carcinoma cell line models in which we can dynamically modulate the expression of the B-Raf(V600E) oncoprotein. Doxycyclin-inducible knockdown of endogenous B-Raf(V600E) decreases cellular motility and invasion in conventional and three-dimensional (3D) culture, whereas it promotes cell-cell contacts and induces various hallmarks of differentiated epithelia. Importantly, all these effects are recapitulated by B-Raf (PLX4720, vemurafenib, and dabrafenib) or MEK inhibitors (trametinib). Surprisingly, loss of B-Raf(V600E) in HT29 xenografts does not only stall tumor growth, but also induces glandular structures with marked expression of CDX2, a tumor-suppressor and master transcription factor of intestinal differentiation. By performing the first transcriptome profiles of PLX4720-treated 3D cultures of HT29 and Colo-205 cells, we identify several upregulated genes linked to epithelial differentiation and effector functions, such as claudin-1, a Cdx-2 target gene encoding a critical tight junction component. Thereby, we provide a mechanism for the clinically observed correlation between mutant BRAF and the loss of Cdx-2 and claudin-1. PLX4720 also suppressed several metastasis-associated transcripts that have not been implicated as targets, effectors or potential biomarkers of oncogenic B-Raf signaling so far. Together, we identify a novel facet of clinically applied B-Raf or MEK inhibitors by showing that they promote cellular adhesion and differentiation of colorectal carcinoma cells.
Signal Transduction in Tumour Development and Drug Resistance Group, Institute of Molecular Medicine and Cell Research (IMMZ), Albert-Ludwigs-University (ALU), Freiburg, Germany. Faculty of Biology, ALU, Freiburg, Germany.
Ricarda
R
Herr
Signal Transduction in Tumour Development and Drug Resistance Group, Institute of Molecular Medicine and Cell Research (IMMZ), Albert-Ludwigs-University (ALU), Freiburg, Germany. Faculty of Biology, ALU, Freiburg, Germany. Spemann Graduate School of Biology and Medicine (SGBM), ALU, Freiburg, Germany.
Martin
M
Köhler
Department of Hematology and Oncology, University Medical Center, ALU, Freiburg, Germany.
Hana
H
Andrlová
Signal Transduction in Tumour Development and Drug Resistance Group, Institute of Molecular Medicine and Cell Research (IMMZ), Albert-Ludwigs-University (ALU), Freiburg, Germany. Faculty of Biology, ALU, Freiburg, Germany.
Florian
F
Weinberg
Institute of Cell Biology and Immunology, University of Stuttgart, Stuttgart, Germany.
Yvonne
Y
Möller
Signal Transduction in Tumour Development and Drug Resistance Group, Institute of Molecular Medicine and Cell Research (IMMZ), Albert-Ludwigs-University (ALU), Freiburg, Germany. Faculty of Biology, ALU, Freiburg, Germany. Spemann Graduate School of Biology and Medicine (SGBM), ALU, Freiburg, Germany.
Sebastian
S
Halbach
Department of Pathology, University Medical Center, ALU, Freiburg, Germany.
Lisa
L
Lutz
Faculty of Biology, ALU, Freiburg, Germany. Department of Hematology and Oncology, University Medical Center, ALU, Freiburg, Germany.
Justin
J
Mastroianni
Systems Biology of the Cellular Microenvironment Group, IMMZ, ALU, Freiburg, Germany.
Martin
M
Klose
Department of Pathology, University Medical Center, ALU, Freiburg, Germany.
Nicola
N
Bittermann
Systems Biology of the Cellular Microenvironment Group, IMMZ, ALU, Freiburg, Germany.
Silke
S
Kowar
Department of Hematology and Oncology, University Medical Center, ALU, Freiburg, Germany. Centre for Biological Signalling Studies BIOSS, ALU Freiburg.
Robert
R
Zeiser
Institute of Cell Biology and Immunology, University of Stuttgart, Stuttgart, Germany.
Monilola A
MA
Olayioye
Department of Pathology, University Medical Center, ALU, Freiburg, Germany. Centre for Biological Signalling Studies BIOSS, ALU Freiburg. German Cancer Consortium (DKTK), Freiburg, Germany. German Cancer Research Center (DKFZ), Heidelberg, Germany.
Silke
S
Lassmann
Systems Biology of the Cellular Microenvironment Group, IMMZ, ALU, Freiburg, Germany. German Cancer Consortium (DKTK), Freiburg, Germany. German Cancer Research Center (DKFZ), Heidelberg, Germany.
Hauke
H
Busch
Systems Biology of the Cellular Microenvironment Group, IMMZ, ALU, Freiburg, Germany. German Cancer Consortium (DKTK), Freiburg, Germany. German Cancer Research Center (DKFZ), Heidelberg, Germany.
Melanie
M
Boerries
Signal Transduction in Tumour Development and Drug Resistance Group, Institute of Molecular Medicine and Cell Research (IMMZ), Albert-Ludwigs-University (ALU), Freiburg, Germany. Centre for Biological Signalling Studies BIOSS, ALU Freiburg. tilman.brummer@zbsa.de.
Tilman
T
Brummer
D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics; D055785:Gene Knockdown Techniques; D019073:HT29 Cells; D006801:Humans; D051379:Mice; D016513:Mice, SCID; D008822:Mice, Transgenic; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D048493:Proto-Oncogene Proteins B-raf / Q000037:antagonists & inhibitors* / Q000235:genetics; D011897:Random Allocation; D015398:Signal Transduction; D023041:Xenograft Model Antitumor Assays
D047428:Protein Kinase Inhibitors; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf