The stability of the Wnt pathway transcription factor beta-catenin is tightly regulated by the multi-subunit destruction complex. Deregulated Wnt pathway activity has been implicated in many cancers, making this pathway an attractive target for anticancer therapies. However, the development of targeted Wnt pathway inhibitors has been hampered by the limited number of pathway components that are amenable to small molecule inhibition. Here, we used a chemical genetic screen to identify a small molecule, XAV939, which selectively inhibits beta-catenin-mediated transcription. XAV939 stimulates beta-catenin degradation by stabilizing axin, the concentration-limiting component of the destruction complex. Using a quantitative chemical proteomic approach, we discovered that XAV939 stabilizes axin by inhibiting the poly-ADP-ribosylating enzymes tankyrase 1 and tankyrase 2. Both tankyrase isoforms interact with a highly conserved domain of axin and stimulate its degradation through the ubiquitin-proteasome pathway. Thus, our study provides new mechanistic insights into the regulation of axin protein homeostasis and presents new avenues for targeted Wnt pathway therapies.

In yeast, the TREX complex contains the THO transcription elongation complex, which functions in direct cotranscriptional recruitment of the mRNA export proteins Sub2 and Yra1 to nascent transcripts. Here we report the identification of the human THO complex and show that it associates with spliced mRNA, but not with unspliced pre-mRNA in vitro. Transcription is not required for this recruitment. We also show that the human THO complex colocalizes with splicing factors in nuclear speckle domains in vivo. Considering that splicing occurs cotranscriptionally in humans, our data indicate that recruitment of the human TREX complex to spliced mRNA is not directly coupled to transcription, but is instead coupled to transcription indirectly through splicing.

Pre-mRNAs undergo splicing to remove introns, and the spliced mRNA is exported to the cytoplasm for translation. Here we investigated the mechanism for recruitment of the conserved mRNA export machinery (TREX complex) to mRNA. We show that the human TREX complex is recruited to a region near the 5' end of mRNA, with the TREX component Aly bound closest to the 5' cap. Both TREX recruitment and mRNA export require the cap, and these roles for the cap are splicing dependent. CBP80, which is bound to the cap, associates efficiently with TREX, and Aly mediates this interaction. Together, these data indicate that the CBP80-Aly interaction results in recruitment of TREX to the 5' end of mRNA, where it functions in mRNA export. As a consequence, the mRNA would be exported in a 5' to 3' direction through the nuclear pore, as observed in early electron micrographs of giant Balbiani ring mRNPs.

Samoans are a unique founder population with a high prevalence of obesity1–3, making them well suited for identifying new genetic contributors to obesity4. We conducted a genome-wide association study (GWAS) in 3,072 Samoans, discovered a variant, rs12513649, strongly associated with body mass index (BMI) (P = 5.3 × 10−14), and replicated the association in 2,102 additional Samoans (P = 1.2 × 10−9). Targeted sequencing identified a strongly associated missense variant, rs373863828 (p.Arg457Gln), in CREBRF (meta P = 1.4 × 10−20). Although this variant is extremely rare in other populations, it is common in Samoans (frequency of 0.259), with an effect size much larger than that of any other known common BMI risk variant (1.36–1.45 kg/m2 per copy of the risk-associated allele). In comparison to wild-type CREBRF, the Arg457Gln variant when overexpressed selectively decreased energy use and increased fat storage in an adipocyte cell model. These data, in combination with evidence of positive selection of the allele encoding p.Arg457Gln, support a ‘thrifty’ variant hypothesis as a factor in human obesity.

Germ-line mutations of the tumor suppressor APC are implicated in attenuated adenomatous polyposis coli (AAPC), a variant of familial adenomatous polyposis (FAP). AAPC is recognized by the occurrence of <100 colonic adenomas and a later onset of colorectal cancer (age >40 years). The aim of this study was to assess genotype-phenotype correlations in AAPC families. By protein-truncation test (PTT) assay, the entire coding region of the APC gene was screened in affected individuals from 11 AAPC kindreds, and their phenotypic differences were examined. Five novel germ-line APC mutations were identified in seven kindreds. Mutations were located in three different regions of the APC gene: (1) at the 5' end spanning exons 4 and 5, (2) within exon 9, and (3) at the 3' distal end of the gene. Variability in the number of colorectal adenomas was most apparent in individuals with mutations in region 1, and upper-gastrointestinal manifestations were more severe in them. In individuals with mutations in either region 2 or region 3, the average number of adenomas tended to be lower than those in individuals with mutations in region 1, although age at diagnosis was similar. In all AAPC kindreds, a predominance of right-sided colorectal adenomas and rectal polyp sparing was observed. No desmoid tumors were found in these kindreds. Our data suggest that, in AAPC families, the location of the APC mutation may partially predict specific phenotypic expression. This should help in the design of tailored clinical-management protocols in this subset of FAP patients.