Cell Cycle and Senescence Cooperativity of E-cadherin and Smad4 Loss to Promote Diffuse-Type Gastric Adenocarcinoma and Metastasis

Loss of E-cadherin (CDH1), Smad4, and p53 has been shown to play an integral role in gastric, intestinal, and breast cancer formation. Compound conditional knockoutmice for Smad4, p53, and E-cadherin were generated to define and compare the roles of these genes in gastric, intestinal, and breast cancer development by crossing with Pdx-1-Cre, Villin-Cre, and MMTV-Cre transgenic mice. Interestingly, gastric adenocarcinoma was significantly more frequent in Pdx-1-Cre;Smad4F/F;Trp53F/F;Cdh1F/þ mice than in Pdx-1-Cre;Smad4F/F;Trp53F/F;Cdh1þ/þ mice, demonstrating that Cdh1 heterozygosity accelerates the development and progression of gastric adenocarcinoma, in combination with loss of Smad4 and p53. Pdx-1-Cre;Smad4F/F;Trp53F/F;Cdh1F/þ mice developed gastric adenocarcinomas without E-cadherin expression. However, intestinal andmammary adenocarcinomas with the same genetic background retained E-cadherin expression and were phenotypically similar to mice with both wild-typeCdh1 alleles. Lung metastases were identified in Pdx-1-Cre;Smad4F/F;Trp53F/F;Cdh1F/þmice, but not in the other genotypes. Nuclear b-catenin accumulation was identified at the invasive tumor front of gastric adenocarcinomas arising in Pdx-1-Cre;Smad4F/F;Trp53F/F;Cdh1F/þ mice. This phenotype was less prominent in mice with intact E-cadherin or Smad4, indicating that the inhibition ofb-catenin signaling by E-cadherin or Smad4 downregulates signaling pathways involved in metastases in Pdx-1-Cre;Smad4F/F;Trp53F/F;Cdh1F/þ mice. Knockdownofb-catenin significantly inhibited themigratory activity ofPdx-1-Cre;Smad4F/F;Trp53F/F;Cdh1F/þ cell lines. Thus, loss of E-cadherin and Smad4 cooperates with p53 loss to promote the development and metastatic progression of gastric adenocarcinomas, with similarities to human gastric adenocarcinoma. Implications: This study demonstrates that inhibition of b-catenin is a converging node for the antimetastatic signaling pathways driven by E-cadherin and Smad4 in Pdx-1-Cre;Smad4F/F;Trp53F/F;Cdh1F/þ mice, providing novel insights into mechanisms for gastric cancer metastasis. Mol Cancer Res; 12(8); 1–12. 2014 AACR.