Ultra‐frequent HRAS p.Q61R somatic mutation in canine acanthomatous ameloblastoma reveals pathogenic similarities with human ameloblastoma

Abstract

Ameloblastoma is a locally aggressive odontogenic tumour that occurs in humans and dogs. Most ameloblastomas (AM) in humans harbour mutually‐exclusive driving mutations in BRAF, HRAS, KRAS, NRAS or FGFR2 that activate MAPK signalling, and in SMO that activates Hedgehog signalling. The remarkable clinical and histological similarities between canine acanthomatous ameloblastoma (CAA) and AM suggest they may harbour similar driving mutations. In this study, aimed at characterizing the mutational status of SMO, BRAF, HRAS, KRAS, NRAS and FGFR2 in CAA, we used RNA sequencing, Sanger sequencing and restriction fragment length polymorphism assays to demonstrate that 94% of CAA (n = 16) harbour a somatic HRAS p.Q61R mutation. The similarities in MAPK‐activating mutational profiles between CAA and AM implicate conserved molecular mechanisms of tumorigenesis, thus, qualifying the dog as a potentially useful model of disease. Given the relevance of RAS mutations in the pathogenesis of odontogenic tumours and other types of cancer, the results of this study are of comparative, translational, and veterinary value.

Comparative transcriptional profiling of canine acanthomatous ameloblastoma and homology with human ameloblastoma

“…The predicted activation of the PI3K-AKT pathway also coincides with this trend given that aberrant RAS signaling frequently underlies dysregulation of this pathway 35 , 36 . The finding that RAS signaling contributes to CAA is consistent with its mutational landscape, which includes highly recurrent HRAS p.Q61R somatic mutations 5 , 16 . Given that HRAS p.Q61R is one of several mutations that can constitutively activate RAS 36 , 37 , the results of the present and previous studies 13 , 16 suggest that this hotspot mutation acts as a driver in CAA.…”

“…An additional 12 samples were used to complement RNA-seq data validation assays including reverse transcriptase quantitative PCR (qPCR) and immunohistochemistry (IHC) assays. The mutational profile of 28 of the 37 samples had previously been reported using a candidate gene approach 16 . Briefly, results showed that 15 of the 16 (93.8%) analyzed CAA samples harbored HRAS p.Q61R somatic mutations, 2 of the 8 (25%) analyzed COSCC analyzed harbored BRAF p.V600E somatic mutations, and 1 of the 8 (12.5%) analyzed COSCC samples harbored an HRAS p.Q61L somatic mutation.…”

“…Recent discoveries by us and others reveal mutually exclusive RAS-RAF-MAPK pathway activating mutations suggesting conserved molecular mechanisms in AM and CAA 15 , 16 . The MAPK pathway, which regulates cell survival, is of major interest given that it is a widely used target for several different tumors expressing driving mutations 17 , 18 .…”

“…Since CAA has clinical, histomorphological, tumor biological, and mutational similarities to AM 16 , 22 , and compared to existing laboratory animal models, domestic dogs develop spontaneous tumors that recapitulate the environmental, genetic, immunological, metabolic, pharmacological, and clinical complexities of human oncogenesis 23 – 25 , CAA represents a suitable pre-clinical model to test novel therapies for AM. Moreover, the high incidence of CAA compared to AM provides a readily available patient population, while simultaneously offering client-owned dogs an opportunity to benefit from rational and potentially more effective, less detrimental interventions.…”

Case Report: Amyloid-Producing Odontogenic Tumor With Pulmonary Metastasis in a Spinone Italiano—Proof of Malignant Potential

“…New evidence on oncogenesis of canine ameloblastoma supports that ameloblastoma in dogs develops similarly to its human counterpart via mutations in the MAPK pathway ( 13 ). Thus, given the similar biologic oncogenetics between canine and human ameloblastomas, this tumor most likely also carries a small metastatic potential within the canine population.…”