Wnt signaling: physiology and pathology

Signaling by the Wnt family of secreted glycoproteins has been demonstrated to be essential both in normal embryonic development and in the pathogenesis of a variety of diseases, including cancer. This signaling pathway is exquisitely regulated by a large and complex array of proteins, which act as agonists or antagonists of signal transduction, modulating the Wnt signal extracellularly, in the cytoplasm and in the nucleus. Here, we will briefly review the canonical Wnt signaling pathway and consider molecular defects in Wnt signaling components known to promote uncontrolled cell growth following induction of Wnt signaling. We will also focus on two recently identified factors in this pathway, that seem to act as Wnt signaling antagonists, one functioning in the cytoplasm called Disabled-2 and the other in the nucleus named Chibby.