Clinical relevance of WNT10B / WNT10BIVS1 allele variant expression and its potential in Acute Myeloid Leukemia risk assessment

Acute myeloid leukemia (AML) develops as the consequence of a series of genetic changes in a hematopoietic precursor cell, that alter normal hematopoietic growth and differentiation, resulting in an accumulation of large numbers of abnormal, immature myeloid cells in the bone marrow and peripheral blood. The deceivingly homogeneous, undifferentiated morphology of the leukemic blasts is now known to mask a heterogeneous collection of cells that recapitulate the hierarchy of precursor cells that characterize the normal process of blood-cell differentiation. Leukemia-initiating cell (LIC) properties occur in a self-renewing non-hematopoietic stem cell progenitor cell population, preceded by the expansion of a pre-leukemic long-term hematopoietic stem cell (LT-HSC). The WNT/β-catenin pathway has been show to play a critical role in the regulation of cell proliferation, differentiation, and apoptosis of different malignant entities. Previous results obtained by our research team provided direct evidence that the WNT/β-catenin signaling is diffusely activated in the AC133+ AML population, with a specific transcriptional signature involving over-expression of the WNT pathway agonists and down-modulation of the major antagonists. Appling the new in situ technique on AML bone marrow sections, we confirmed a dramatic increase of WNT10B expression and protein release within the microenvironment in the large majority of sample. Conversely, the activation of WNT signaling, marked by expression of the dephosphorylated β-catenin, was restricted only to a smaller subpopulation of AC133bright cells. Focusing our attention on the major locus associated to the regenerative function, in the actual study we performed a 5’-RACE analysis on WNT10B mRNA, evidencing the presence of a non-physiological transcript variant named WNT10BIVS1, retaining 77 nucleotide of IVS1 and lacking exon1. In order to provide accurate quantification of mRNA levels of WNT10B and the related WNT10BIVS1 transcript variant and to analyze the clinical relevance of their expression, we carried out the gene expression analysis by Droplet DigitalTM PCR on mononucleated cells derived from 125 AML patients. Analyzing patients according to specific genetic or risk profiles, we demonstrated that canonical WNT10B mRNA was highly expressed in all de novo AML patients here examined, representing the gene with the highest expression in leukemic patients among all the genes actually known. Furthermore, non-physiological WNT10BIVS1 variant was highly expressed in all non-favorable risk de novo AML, whereas it has non-detectable levels in core-binding factor AML, acute promyelocytic leukemia, and therapy-related disease. The results presented here provided a compelling evidence that regeneration-associated WNT signaling exceeds the homeostatic range in the majority of human AML cases. These newly discovered genetic abnormalities WNT10B / WNT10BIVS1 seem to be associated with clinical, morphologic, and phenotypic features that allow identification of specific leukemic entity. Finally, we presented distinct molecular signatures capable of distinguish with extremely high accuracy de novo AML patients from both favorable-risk and therapy-related patients, using a non-time consuming and inexpensive test. These findings, if confirmed in a larger population of patients, may help in refine diagnostic or prognostic criteria for previously described neoplasms, and to introduce newly recognized disease entities possibly characterized by distinct causative pathogenic mechanisms.