WNT receptors profile expression in mature blood cells and immature leukemic cells: RYK emerges as a hallmark receptor of acute leukemia.

BACKGROUND: Wnt signaling induces a plethora of intracellular responses that dictate normal or abnormal cellular behavior. Abnormal WNT signaling has been related to the development of leukemogenic processes. In this regard, it is important to know the expression profile of WNT receptors in normal and malignant cells, in order to understand the WNT mechanisms that control the cell behavior. This work aimed to determine the WNT receptors expression profile in normal and leukemia cells. METHODS: Expression of WNT receptors was determined by flow cytometry using leukemia-derived cell lines, peripheral blood cells, and blood marrow samples from healthy volunteers and acute leukemia patients. RESULTS: Despite the heterogenic WNT receptors expression in mature normal blood cells and in immature tumorigenic cells, the RYK receptor was found highly express in leukemia cells, but not in normal cells. RYK expression was found mainly in cells positive to immature markers like CD33, CD13, CD7, and CD117. CONCLUSIONS: Our data show differences in FZD receptors expression between T and B leukemic cells, but both cell types and also myeloblast-derived cells express high levels of RYK. The association of RYK expression with immature markers indicates its possible use as a diagnostic marker or therapeutic target.

Restoration of WNT4 inhibits cell growth in leukemia-derived cell lines.

BACKGROUND: WNT signaling pathways are significantly altered during cancer development. Vertebrates possess two classes of WNT signaling pathways: the "canonical" WNT/ß-catenin signaling pathway, and the "non-canonical" pathways including WNT/Ca²âº and WNT/Planar cell polarity [PCP] signaling. WNT4 influences hematopoietic progenitor cell expansion and survival; however, WNT4 function in cancer development and the resulting implications for oncogenesis are poorly understood.The aim of this study was twofold: first, to determine the expression of WNT4 in mature peripheral blood cells and diverse leukemia-derived cells including cell lines from hematopoietic neoplasms and cells from patients with leukemia; second, to identify the effect of this ligand on the proliferation and apoptosis of the blast-derived cell lines BJAB, Jurkat, CEM, K562, and HL60. METHODS: We determined WNT4 expression by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) in peripheral blood mononuclear cells (PBMCs) and T- and B-lymphocytes from healthy individuals, as well as from five leukemia-derived cell lines and blasts derived from patients with leukemia. To analyze the effect of WNT4 on cell proliferation, PBMCs and cell lines were exposed to a commercially available WNT4 recombinant human protein. Furthermore, WNT4 expression was restored in BJAB cells using an inducible lentiviral expression system. Cell viability and proliferation were measured by the addition of WST-1 to cell cultures and counting cells; in addition, the progression of the cell cycle and the amount of apoptosis were analyzed in the absence or presence of WNT4. Finally, the expression of WNT-pathway target genes was measured by qRT-PCR. RESULTS: WNT4 expression was severely reduced in leukemia-derived cell lines and blasts derived from patients with leukemia. The exposure of cell lines to WNT4 recombinant protein significantly inhibited cell proliferation; inducing WNT4 expression in BJAB cells corroborated this observation. Interestingly, restoration of WNT4 expression in BJAB cells increased the accumulation of cells in G1 phase, and did not induce activation of canonical WNT/ß-catenin target genes. CONCLUSIONS: Our findings suggest that the WNT4 ligand plays a role in regulating the cell growth of leukemia-derived cells by arresting cells in the G1 cell cycle phase in an FZD6-independent manner, possibly through antagonizing the canonical WNT/ß-catenin signaling pathway.