The regulators of G protein signaling (RGS) domain of Axin, a negative regulator of the Wnt signaling pathway, made a complex with full-length adenomatous polyposis coli (APC) in COS, 293, and L cells but not with truncated APC in SW480 or DLD-1 cells. The RGS domain directly interacted with the region containing the 20-amino acid repeats but not with that containing the 15-amino acid repeats of APC, although both regions are known to bind to ␤-catenin. In the region containing seven 20-amino acid repeats, the region containing the latter five repeats bound to the RGS domain of Axin. Axin and ␤-catenin simultaneously interacted with APC. Furthermore, Axin stimulated the degradation of ␤-catenin in COS cells. Taken together with our recent observations that Axin directly interacts with glycogen synthase kinase-3␤ (GSK-3␤) and ␤-catenin and that it promotes GSK-3␤-dependent phosphorylation of ␤-catenin, these results suggest that Axin, APC, GSK-3␤, and ␤-catenin make a tetrameric complex, resulting in the regulation of the stabilization of ␤-catenin.Axin, which is a product of the mouse Fused locus, has been identified as a negative regulator of the Wnt signaling pathway (1). Fused is a mutation that causes dominant skeletal and neurological defects and recessive lethal embryonic defects including neuroectodermal abnormalities (2-4). Because dorsal injection of wild type Axin in Xenopus embryos blocks axis formation and coinjection of Axin inhibits Wnt8-, Dsh-, and kinase-negative GSK-3␤ 1 -induced axis duplication (1), Axin could exert its effects on axis formation by inhibiting the Wnt signaling pathway. However, the molecular mechanism by which Axin regulates axis formation has not been shown. We have recently identified rat Axin (rAxin) as a GSK-3␤-interacting protein (5). rAxin is phosphorylated by GSK-3␤, directly binds to not only GSK-3␤ but also ␤-catenin, and promotes GSK-3␤-dependent phosphorylation of ␤-catenin (5). Because the phosphorylation of ␤-catenin by GSK-3␤ is essential for the down-regulation of ␤-catenin (6, 7), our results suggest that rAxin may induce the degradation of ␤-catenin. These actions of rAxin are consistent with the observation that Axin inhibits dorsal axis formation in Xenopus embryos, because the accumulation of ␤-catenin induces the axis duplication (8).It has been shown that besides the phosphorylation by GSK-3␤, the down-regulation of ␤-catenin requires APC, which is a tumor suppressor linked to FAP and to the initiation of sporadic human colorectal cancer (9). The middle portion of APC contains three successive 15-amino acid (aa) repeats followed by seven related but distinct 20-aa repeats. Both types of repeats are able to bind independently to ␤-catenin (10 -12). In FAP and colorectal cancers, most patients carry APC mutations that result in the expression of truncated proteins (9). Almost all mutant proteins lack the C-terminal half including most of the 20-aa repeats but retain the 15-aa repeats. Colorectal carcinoma cells with mutant APC contain large amounts of monom...

No abstract

␤-Catenin is efficiently phosphorylated by glycogen synthase kinase-3␤ in the Axin complex in the cytoplasm, resulting in the down-regulation. In response to Wnt, ␤-catenin is stabilized and translocated into the nucleus where it stimulates gene expression through Tcf/Lef. Here we report a novel protein, designated Duplin (for axis duplication inhibitor), which negatively regulates the function of ␤-catenin in the nucleus. Duplin was located in the nucleus. Duplin bound directly to the Armadillo repeats of ␤-catenin, thereby inhibiting the binding of Tcf to ␤-catenin. It did not affect the stability of ␤-catenin but inhibited Wnt-or ␤-catenin-dependent Tcf activation. Furthermore, expression of Duplin in Xenopus embryos inhibited the axis formation and ␤-catenin-dependent axis duplication, and prevented the ␤-catenin's ability to rescue ventralizing phenotypes induced by ultraviolet light irradiation. Thus, Duplin is a nuclear protein that inhibits ␤-catenin signaling.

No abstract

Characteristics of patients with type 2 diabetes in Mexico: results from a large populationbased nationwide survey.

These results suggest that neuropeptides play an important role in the regulation of RPE cell growth.

When performing intracarotid injection of carboplatin, we must be aware of its potentially blinding ocular toxicity. It is recommended that further studies and investigations are undertaken in the effort to minimize such severe side effects.

No abstract