BRAF V600E and previously unidentified KRAS G12C mutations in odontogenic tumors may affect MAPK activation differently depending on tumor type

Abstract

Although several types of odontogenic tumors share the same mutations in MAPK pathway genes, their effects on MAPK activation remain unclarified. This study aimed to evaluate the associations between these mutations and ERK phosphorylation in ameloblastoma and mixed odontogenic tumors (MOTs) and to analyze the expression pattern of phosphorylated ERK (p‐ERK) for determining the involvement of MAPK activation in the development and progression of odontogenic tumors. Forty‐three odontogenic tumors consisting of 18 ameloblastomas and 25 MOTs were analyzed for BRAF, KRAS, and NRAS mutations by Sanger sequencing. The expressions of BRAFV600E protein and p‐ERK were detected by immunohistochemistry. The associations between mutation status and p‐ERK expression were statistically analyzed. The effect of BRAFV600E inhibition on MAPK activation was investigated in ameloblastoma cells. In benign MOTs, BRAFV600E mutations were neither expressed at the protein level nor associated with p‐ERK expression. In contrast, BRAFV600E‐mutant ameloblastic fibrosarcoma showed co‐expression of BRAF V600E protein and p‐ERK, especially in the sarcomatous component. In ameloblastoma, p‐ERK was predominantly expressed in the tumor periphery showing a significant correlation with BRAFV600E mutations, and in vitro BRAFV600E inhibition decreased ERK phosphorylation. KRASG12C mutations, previously unidentified in odontogenic tumors, were detected in one case each of benign MOT and ameloblastoma; only the latter was high‐p‐ERK. In conclusion, unlike in benign MOTs, BRAFV600E and KRASG12C mutations lead to MAPK activation in ameloblastoma, suggesting their role as therapeutic targets. p‐ERK intratumoral heterogeneity indicates that MAPK pathway activation may be associated with sarcomatous proliferation of ameloblastic fibrosarcoma and infiltrative behavior of ameloblastoma.

Association of MDM2 Overexpression in Ameloblastomas with MDM2 Amplification and BRAFV600E Expression

“…Those findings support the suggestion that MAPK activation through BRAF V600E mutation may be the main cause of MDM2 overexpression in BRAF V600E -positive tumors. As for BRAF V600E -negative cases that overexpress MDM2, it should be noticed that MAPKactivating mutations other than BRAF V600E have been identified in ameloblastomas [16], and in some ameloblastomas the TGF-β pathway may be activated [71]. Further evaluation of MDM2 overexpression/MAPK activation association could show its possible utility as a marker of MAPK activation.…”

“…Ameloblastomas commonly show the activating mutation V600E in the v-Raf murine sarcoma viral oncogene homologue B (BRAF V600E ) located on chromosome 7q34; BRAF is a key member of the mitogen-activated protein kinase (MAPK) signaling pathway, which plays a crucial role in cell growth and proliferation [10][11][12][13][14][15][16][17]. This finding prompted the clinical trial of BRAF inhibitors (BRAFi) as a targeted therapy in this tumor.…”

Differential expression of PEA3 in odontogenic cysts and tumors

“…Further research is necessary to confirm our results. With regard to AFs, previous studies displayed BRAF V600E mutation in AFs ranging from 40% to 100% 17–19 . BRAF V600E mutation is a missense mutation in change at a residue 600 that substitutes glutamine (E) for valine (V) resulting in aberrant activation of downstream targets of MAPK pathway 14 .…”

“…With regard to AFs, previous studies displayed BRAF V600E mutation in AFs ranging from 40% to 100%. [17][18][19] BRAF V600E mutation is a missense mutation in change at a residue 600 that substitutes glutamine (E) for valine (V) resulting in aberrant activation of downstream targets of MAPK pathway. 14 Our results showing a small proportion (20%) of high PEA3 expression in AFs seems to contradict previous studies [17][18][19] and may indicate uncertain behavior of AFs.…”

“…[17][18][19] BRAF V600E mutation is a missense mutation in change at a residue 600 that substitutes glutamine (E) for valine (V) resulting in aberrant activation of downstream targets of MAPK pathway. 14 Our results showing a small proportion (20%) of high PEA3 expression in AFs seems to contradict previous studies [17][18][19] and may indicate uncertain behavior of AFs. AFs usually appear as a slowly growing mass detected due to disturbances of tooth eruption, though a few AFs were extensive and presented local recurrences.…”