WNT signaling genes in human hematopoietic cells

Wnt proteins are highly conserved secreted glycoproteins that bind tightly to the extracellular matrix and act as short-range signaling molecules. We have identified and cloned three members of this gene family from primary human fetal bone marrow stromal cells (Wnt-5A, Wnt-2B, Wnt-108). We have previously shown bioactivity of the three Wnt genes on purified CD34+ bone marrow cells (CD34+BM) in an in vitro coculture system. To further characterize the role of Wnt genes in hematopoiesis we have evaluated the expression of genes within the Wnt signaling pathway in hematopoietic cells. Wnt signaling in animal development has revealed a common theme including cell-surface receptors, signal cascade from cell surface to cell nucleus, and activation of specific transcription factors. Members of the frizzled (Fz) gene family are proteins with seven transmembrane domains and a cystein-rich extracellular domain that act as cell surface receptors for Wnt proteins. A family of frizzled-related proteins (FRP) that contain an extracellular cystein-rich domain but lack the transmembrane domains are believed to prevent Wnt protein binding to cell-surface receptors. Members of the disheveled family of proteins (Dsh) are cytoplasmic proteins that act in the Wnt signal transduction pathway by inhibiting zeste-white 3 (Zw3) leading to accumulation of armadillo/-catenin (Arm). Arm/-catenin binds to members of the TcfLEF-1 family of HMG box transcription factors, leading to translocation to the nucleus and activation of target gene expression. We pursued a strategy using RT-PCR, RNase protection, and Northern blot analysis to evaluate the expression of Wnt signaling genes in stromal cells and CD34+ hematopoietic progenitors. This analysis has identified the expression of genes at each level of Wnt signaling in hematopoietic cells including 6 members of the Fz gene family, 2 members of the FRP gene family, 2 members of the Dsh family, a human homolog of Zw3 (GSK-3), β-catenin, and 2 members of the Tcf-LEF-1 family. This data is consistant with Wnt signaling in hematopoietic cells using the common signaling pathways, but does not rule out other signaling mechanisms.