WIF-1: ProductsWIF-1 (Wnt Inhibitory Factor 1) is a secreted protein that binds to Wnt proteins and inhibits their activity. In situ hybridization analysis in Xenopus laevis and zebrafish indicate that the message is highly expressed in presomitic mesoderm, the notochord, anterior regions of the brain, branchial arches, nasal placodes, and otic vescicles. WIF-1 inhibits secondary axis induction by Wnts and promotes secondary axis induction by Chordin in Xenopus embryos. In vitro, WIF-1 binds to Drosophila Wingless and Xenopus Wnt8 proteins. WIF-1 is implicated as an early event tumor suppressor in cancers of the prostate, breast, lung, and bladder, while in other cancer types, such as colon adenocarcinoma, WIF-1 facilitates tumorigenesis. WIF-1 is also expressed in mammalian retina and may play a role in photoreceptor development. The protein is synthesized as a 379 amino acid (aa) molecule that contains a signal sequence, a 150 aa WIF domain, 5 EGF-like repeats, and a hydrophilic domain at the carboxy terminus.