CD44 in canine leukemia: Analysis of mRNA and protein expression in peripheral blood

Hyaluronan receptor CD44 mediates interaction between cells and extracellular matrix. The expression of standard form and its variants is dysregulated in human leukemias and is associated with metastasis and prognosis. The aim of this work is the evaluation of CD44 mRNA and protein expression in canine leukemia. Peripheral blood from 20 acute leukemias (AL) (10 acute lymphoblastic, 6 acute myeloid and 4 acute undifferentiated leukemias), 21 chronic lymphocytic leukemias (CLL) and thirteen healthy dogs were collected. The mRNA expression of all CD44 variants presenting exons 1-5 and/or 16-20 (CD44_ex1-5 and CD44_ex16-20) and CD44 protein were determined by real-time RT-PCR and flow cytometry, using the mean fluorescent index (MFI), respectively. CD44 MFI was significantly higher in leukemic samples compared to controls and a higher expression was found in AL in respect with CLL. No significant differences were found when considering different phenotypic subtypes of AL and CLL. CD44_ex1-5 mRNA expression was significantly higher in AL compared to controls, whereas there was no difference in CLL compared to controls and AL. CD44_es16-20 showed the same trend, but without differences among groups. The high CD44 expression found in canine leukemias could be considered a step toward the definition of their molecular features.