Activating Mutations in PTPN11 and KRAS in Canine Histiocytic Sarcomas

Abstract

While the genetic contributions to the predisposition of Bernese mountain dogs (BMDs) to histiocytic sarcoma (HS) remains unclear, some insights into key genetic drivers have been gained. Our group recently reported a mutation in the PTPN11 gene (E76K). We have now identified a second missense mutation in PTPN11 (G503V), and a mutation in KRAS (Q61H) present in HS cell lines. These mutations are associated with malignancies in humans, and known to be gain-of-function mutations that result in activation of the mitogen-activated protein kinase (MAPK) pathway. The goal of the present study was to evaluate the prevalence of these mutations in a large sample of HS cases from BMDs and golden retrievers, and in lymphoma cases, from a cohort of BMDs. Mutations in PTPN11 were present in HS in 41/96 (43%) BMDs, and in 3/13 (23%) golden retrievers. PTPN11 mutations E76K and G503V did not coexist in the same neoplasm. The KRAS mutation was much less frequent, with a prevalence of 3.1% (3/96). We did not identify either PTPN11 nor KRAS mutations in any of the lymphoma samples. These results point out the potential relevance of PTPN11 and KRAS mutations as activators of the oncogenic MAPK pathway for canine HS, particularly in BMDs.

Keywords: Bernese mountain dog; KRAS; PTPN11; histiocytic sarcoma; somatic mutation.

Figure 1

Sites of PTPN11 mutations. (A) Schematic representation of PTPN11 gene product with corresponding functional domains of SHP-2, indicating the locations of E76K and G503V mutations, with the predicted amino acid changes. Top bar is a schematic representation of the genomic structure with numbered exons (dark blue), and the lower bar depicts the functional domains. (B) Alignment of SHP-2 protein sequences from histiocytic sarcoma (HS) cell lines (BD, OD and PJ), normal canine dendritic cells (DCs), and reference sequences from relevant species (Dog, Human and Mouse). Missense mutations identified in canine HS, highlighted in pink (E76K) and green (G503V), are located within the highly conserved regions shown in yellow. Protein sequences were aligned using Clustal Omega software [31].

Figure 2

Age distribution in years of cases of histiocytic sarcoma (HS) from Bernese mountain dogs (BMDs) and golden retrievers. Blue horizontal lines represent the median age value.

Figure 3

Frequency of tumor PTPN11 mutation status based on breed, and disease type.