How do they do Wnt they do?: regulation of transcription by the Wnt/β-catenin pathway

The intersection of genetic and chemical genomic screens identifies GSK-3α as a target in human acute myeloid leukemia

Acute myeloid leukemia (AML) is the most common form of acute leukemia in adults. Long-term survival of patients with AML has changed little over the past decade, necessitating the identification and validation of new AML targets. Integration of genomic approaches with small-molecule and genetically based high-throughput screening holds the promise of improved discovery of candidate targets for cancer therapy. Here, we identified a role for glycogen synthase kinase 3α (GSK-3α) in AML by performing 2 independent small-molecule library screens and an shRNA screen for perturbations that induced a differentiation expression signature in AML cells. GSK-3 is a serine-threonine kinase involved in diverse cellular processes, including differentiation, signal transduction, cell cycle regulation, and proliferation. We demonstrated that specific loss of GSK-3α induced differentiation in AML by multiple measurements, including induction of gene expression signatures, morphological changes, and cell surface markers consistent with myeloid maturation. GSK-3α-specific suppression also led to impaired growth and proliferation in vitro, induction of apoptosis, loss of colony formation in methylcellulose, and anti-AML activity in vivo. Although the role of GSK-3β has been well studied in cancer development, these studies support a role for GSK-3α in AML.

WNTing embryonic stem cells

Embryonic stem cells (ESCs) - undifferentiated cells originating from preimplantation stage embryos - have prolonged self-renewal capacity and are pluripotent. Activation of the canonical Wnt pathway is implicated in maintenance of and exit from the pluripotent state. Recent findings demonstrate that the essential mediator of canonical Wnt signaling, β-catenin, is dispensable for ESC maintenance; however, its activation inhibits differentiation through derepression of T cell factor 3 (Tcf3)-bound genes. Wnt agonists are useful in deriving ESCs from recalcitrant mouse strains and the rat and in nuclear reprogramming of somatic stem cells. We discuss recent advances in our understanding of the role of canonical Wnt signaling in the regulation of ESC self-renewal and how its manipulation can improve pluripotent ESC derivation and maintenance.

Maintaining embryonic stem cell pluripotency with Wnt signaling

Wnt signaling pathways control lineage specification in vertebrate embryos and regulate pluripotency in embryonic stem (ES) cells, but how the balance between progenitor self-renewal and differentiation is achieved during axis specification and tissue patterning remains highly controversial. The context- and stage-specific effects of the different Wnt pathways produce complex and sometimes opposite outcomes that help to generate embryonic cell diversity. Although the results of recent studies of the Wnt/β-catenin pathway in ES cells appear to be surprising and controversial, they converge on the same conserved mechanism that leads to the inactivation of TCF3-mediated repression.