Identification of JAK2 mutations in canine primary polycythemia

Primary polycythemia in dogs is classified as a myeloproliferative syndrome with a chronic progressive course and unspecific symptoms. Diagnosis is based on exclusion criteria. In humans, the presence of an acquired recurrent mutation within the JAK2 gene has recently been identified in 90% of the patients with polycythemia vera. This mutation (V617F) is located in the pseudokinase domain of JAK2, leading to constitutive activation of the kinase responsible for the polycythemia. Detection of the mutation has now become a major diagnostic tool in humans for polycythemia vera diagnosis. As the canine JAK2 gene shares strong homology with its human counterpart, we looked for the presence of JAK2 mutations in dogs with an elevated hematocrit.

Direct sequencing of the JAK2 exon 14 was performed on DNA extracted from the peripheral blood of five dogs suspected of primary polycythemia. Mutant subclones were expressed in interleukin-3-dependent BaF3 cells and tested for cytokine independency.

One dog presented with a three-base change in codons 617 and 618 of JAK2 giving rise to V617F and C618L mutations. By polymerase chain reaction product subcloning, we demonstrated the coexistence of the wild-type sequence and a triple mutant sequence, while DNA from buccal swab contained the wild-type sequence only. Transfection of BaF3 cells with the triple mutant cDNA, but not with the wild-type complementary DNA, resulted in cytokine-independent growth and constitutive signal transducer and activation of transcription 5 phosphorylation.

Identical mutations of the JAK2 gene occur in humans and dogs, giving rise to a constitutively active JAK2 kinase, suggesting a common mechanism for human and canine diseases. Thus, common diagnostic tools and therapeutic approaches may be relevant.