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Identification of recurrent SMO and BRAF mutations in ameloblastomas

A Corrigendum to this article was published on 30 December 2014

This article has been updated


Here we report the discovery of oncogenic mutations in the Hedgehog and mitogen-activated protein kinase (MAPK) pathways in over 80% of ameloblastomas, locally destructive odontogenic tumors of the jaw, by genomic analysis of archival material. Mutations in SMO (encoding Smoothened, SMO) are common in ameloblastomas of the maxilla, whereas BRAF mutations are predominant in tumors of the mandible. We show that a frequently occurring SMO alteration encoding p.Leu412Phe is an activating mutation and that its effect on Hedgehog-pathway activity can be inhibited by arsenic trioxide (ATO), an anti-leukemia drug approved by the US Food and Drug Administration (FDA) that is currently in clinical trials for its Hedgehog-inhibitory activity. In a similar manner, ameloblastoma cells harboring an activating BRAF mutation encoding p.Val600Glu are sensitive to the BRAF inhibitor vemurafenib. Our findings establish a new paradigm for the diagnostic classification and treatment of ameloblastomas.

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Figure 1: Mutation frequency, distribution and relationship with pathological features.
Figure 2: SMO Leu412Phe activity and inhibition.
Figure 3: SMO Leu412Phe enhances ameloblast-lineage cell proliferation.
Figure 4: An ameloblastoma cell line harboring BRAF p.Val600Glu is sensitive to the BRAF inhibitor vemurafenib.

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  • 12 November 2014

    In the version of this article initially published, the introductory paragraph mistakenly stated that ameloblasts were "cells in the tooth roots of the upper (maxilla) and lower (mandible) jaw responsible for depositing enamel during tooth development (odontogenesis)." The correct location for human ameloblasts is in the developing tooth. Ameloblasts are the normal cell type that ameloblastoma cells resemble and are responsible for forming the enamel covering on tooth crowns. The error has been corrected in the HTML and PDF versions of the article.


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We would like to thank E. Epstein for assistance. We would like to thank C. Millward, H. Kaplan and M. Labusch for histology and pathology support. We are also grateful to H. Harada (Iwate Medical University) for sharing the AM-1 cell line.

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Authors and Affiliations



R.T.S., A.C.M., J.R.P. and R.B.W. designed the study and wrote the manuscript. A.C.M., B.R.M., J.R.P. and R.B.W. designed the figures. R.T.S., X.G., J.R.P. and R.B.W. analyzed raw sequence data. J.B. and J.R.P. performed mutation validation (PCR and Sanger sequencing). B.R.M., L.N., J.B., J.R.P. and P.A.B. designed and implemented functional studies. C.D.J., J.I.O. and J.L.Z. performed targeted sequencing (TruSeq). K.A.K., K.Q. and R.J.P. performed transcriptome sequencing. S.V. performed immunohistochemistry. T.N., B.P.R. and M.L.T. provided cases for evaluation. T.S. and S.K. provided key cell line reagents.

Corresponding authors

Correspondence to Philip A Beachy, Jonathan R Pollack or Robert B West.

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The authors declare no competing financial interests.

Integrated supplementary information

Supplementary Figure 1 Representative Sanger tracings for mutations.

(a) Tracing for representative SMO mutation encoding L412F in ameloblastoma and matched normal tissue. (b) Tracing for representative BRAF mutation encoding V600E in ameloblastoma and matched normal tissue.

Supplementary Figure 2 Expression of BRAF V600E protein.

The four cases evaluated with BRAF mutations encoding V600E show diffuse cytoplasmic staining of the epithelial component with antibody to BRAF V600E. (a) Rare, patchy staining is observed. (b–d) Darker staining, and greater cell density, is seen at the leading edge of the epithelial cell component, adjacent to the stroma. The stroma is completely negative. No staining was seen in 15 cases without the mutation encoding V600E (data not shown).

Supplementary Figure 3 Suppression of activity of SMO mutants by Ptch1 overexpression.

Relative GLI-dependent luciferase assays in ShhN-stimulated Smo–/– MEFs expressing wild-type SMO, SMO L412F, SMO W535L or GFP control, with or without engineered overexpression of Ptch1, show significant suppression of the activity of the SMO mutants by Ptch1. Each data point is based on three independent transfections (three biological replicates); error bars, s.d. Results presented for each experiment are representative of multiple independent trials.

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Supplementary Figures 1–3 and Supplementary Table 2 (PDF 1443 kb)

Supplementary Table 1

Clinical features and mutation status of cases. (XLSX 15 kb)

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Sweeney, R., McClary, A., Myers, B. et al. Identification of recurrent SMO and BRAF mutations in ameloblastomas. Nat Genet 46, 722–725 (2014).

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