Achaete-scute like 2 (ascl2) is a target of Wnt signalling and is upregulated in intestinal neoplasia

Abstract

Achaete-scute like (ASCL)2 is a basic helix-loop-helix transcription factor essential for the maintenance of proliferating trophoblasts during placental development. Using oligonucleotide microarrays we identified ascl2 as a gene significantly upregulated in colorectal adenocarcinomas (n ¼ 36 cancers, n ¼ 16 normals; 15-fold, Po0.0001). This finding was confirmed by quantitative reverse transcriptase (RT)-PCR on large intestinal cancers (n ¼ 29 cancers, n ¼ 16 normals; 10-fold, Po0.0001).In situ hybridization for ascl2 demonstrated expression at the base of small and large intestinal crypts (n ¼ 304), but in no other normal tissues excepting placenta. By in situ hybridization, 52-71% of colorectal adenomas (n ¼ 187), 50-73% of large (n ¼ 327) and 33-64% of small intestinal adenocarcinomas (n ¼ 124) were positive for ascl2 expression. Upregulation of murine ascl2 was also observed using oligonucleotide microarrays, quantitative RT-PCR and in situ hybridization on apc min/ þ and apc 1638N/ þ smad4 À/ þ tumours. Tumour cell lines stably transfected with LEF1 DN or APC2, or transiently transfected with short-interfering RNA (siRNA) against b-catenin showed a significant downregulation of ascl2. Colocalization of ascl2 with nuclear b-catenin was observed in 73 small intestinal adenocarcinomas (P ¼ 0.0008) and apc min/ þ tumours. Preliminary in vitro data suggest ascl2 may promote progression through the G2/M cell cycle checkpoint. In summary, ascl2 is a putative regulator of proliferation that is overexpressed in intestinal neoplasia.

The Soluble Wnt Receptor Frizzled8CRD-hFc Inhibits the Growth of Teratocarcinomas In vivo

“…Immunohistochemistry for h-catenin was done on tumor xenograft tissue, skin and intestine harvested at the termination of efficacy studies. Tissues were formalin-fixed, paraffin-embedded, and serial sections were subjected to antigen retrieval (Dako Target Retrieval), following which h-catenin was detected with a monoclonal antibody (clone 14; BD PharMingen) as previously described (33). The sections were counterstained with hematoxylin (Vector Lab) and mounted using Histomount (Zymed).…”

Brg1 is required for stem cell maintenance in the murine intestinal epithelium in a tissue-specific manner

“…2C). Since Lgr5 and Ascl2 have been found to be Wnt target genes [25,26], it may be argued that their reduced expression levels upon Brg1 loss are merely a result of attenuated Wnt signaling rather than an indicator of stem cell depletion. In order to overcome this limitation, we examined expression levels of Olfm4, a Wntindependent stem cell marker [27].…”

Myc heterozygosity attenuates the phenotypes of APC deficiency in the small intestine

“…Of the genes downregulated, Ascl2 was reduced back to wild-type levels. Recent studies have shown that Ascl2 is a Wnt target gene and overexpression of this alone is sufficient to cause increased intestinal enterocyte proliferation and crypt size (Jubb et al, 2006;van der Flier et al, 2009). This reduction of Ascl2, in conjunction with reduction of Cyclin D2, provides a ready mechanism for reduced crypt proliferation and size in c-Myc heterozygotes.…”