Tumor escape in a Wnt1-dependent mouse breast cancer model is enabled by p19^Arf/p53 pathway lesions but not p16^Ink4a loss
J. Clin. Invest. Michael T. Debies, et al. 118:51 doi:10.1172/JCI33320 [Go to this article.]

Figure 1
Mechanisms of mammary tumor relapse in MTB/TWNT mice. (A) Mammary expression of putative Wnt pathway target genes. Northern hybridization analyses are shown. Mammary gland RNA came from 5-week-old virgin female MTB/TWNT mice that were either Dox naive (Off Dox) or treated with Dox for 96 hours (On Dox). Tumor RNA came from clonally related outgrowths derived from a Dox-dependent MTB/TWNT tumor that was explanted onto the flanks of Dox-treated host mice. Paired flank explants were harvested during ongoing Dox treatment or after timed Dox withdrawal. (B) Tumor gene expression patterns. Northern hybridization analysis was performed on RNA samples from primary and relapsed MTB/TWNT mammary tumors. Three relapsed DITs expressed Wnt1 transgene in an inducer-independent manner (lanes marked T), and 3 expressed aberrant transcripts encoding activated β-catenin variants (β). (C) Molecular genetic analysis of the Ctnnb1 (β-catenin) gene. Segments of transcripts encoding the regulatory domain of β-catenin were amplified from tumor-derived RNA via RT-PCR and subjected to DNA sequencing. The coding region of mouse β-catenin is shown schematically, with arrows indicating the primers used for RT-PCR placed relative to their approximate annealing sites along the open reading frame. The blowup depicts critical aa residues encoded within exon 3; known hot spots for cancer-associated aa substitutions are in b. Asterisks denote the residue affected by the S33Y mutation identified in 2 DITs. The upper chromatograms show detection of only the wild-type β-catenin allele in an antecedent primary tumor but additional detection of the S33Y allele in a descendant recurrent tumor. The lower panels depict RT-PCR–based detection of an aberrantly spliced β-catenin transcript lacking exon 3 within a relapsed tumor (R) and not within the antecedent primary tumor (P). (D) Tumor histology. Photomicrographs of H&E-stained sections derived from representative primary-relapse tumor pairs. The mode of tumor escape identified for each relapse is indicated. Scale bar: 50 μm.