B-Raf inhibitors induce epithelial differentiation in BRAF-mutant colorectal cancer cells.

Abstract

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.

• Authors: Ricarda Herr, Martin Köhler, Hana Andrlová, Florian Weinberg, Yvonne Möller, Sebastian Halbach, Lisa Lutz, Justin Mastroianni, Martin Klose, Nicola Bittermann, Silke Kowar, Robert Zeiser, Monilola A Olayioye, Silke Lassmann, Hauke Busch, Melanie Boerries, Tilman Brummer
• Journal: Cancer research (Cancer Res) Vol. 75 Issue 1 Pg. 216-29 (Jan 01 2015) ISSN: 1538-7445 [Electronic] United States
• PMID: 25381152 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: ©2014 American Association for Cancer Research.

Chemical References

• Protein Kinase Inhibitors
• BRAF protein, human
• Proto-Oncogene Proteins B-raf

Topics

• Animals
• Cell Differentiation (drug effects)
• Cell Proliferation (drug effects)
• Colorectal Neoplasms (drug therapy, enzymology, genetics)
• Gene Knockdown Techniques
• HT29 Cells
• Humans
• Mice
• Mice, SCID
• Mice, Transgenic
• Phosphorylation
• Protein Kinase Inhibitors (pharmacology)
• Proto-Oncogene Proteins B-raf (antagonists & inhibitors, genetics)
• Random Allocation
• Signal Transduction
• Xenograft Model Antitumor Assays