<i>miR-34a</i> and <i>miR-34b/c</i> Suppress Intestinal Tumorigenesis.

Abstract

The p53-inducible <i>miR-34a</i> and <i>miR-34b/c</i> genes are frequently silenced in colorectal cancer. To address the <i>in vivo</i> relevance of <i>miR-34a/b/c</i> function for suppression of intestinal tumor formation, we generated <i>Apc</i>^Min/+ mice with deletions of the <i>miR-34a</i> and/or <i>miR-34b/c</i> genes separately or in combination. Combined deletion of <i>miR-34a/b/c</i> increased the number of intestinal stem cells as well as Paneth and Goblet cells, resulting in enlarged intestinal crypts. <i>miR-34a/b/c</i>-deficient <i>Apc</i>^Min/+ mice displayed an increased tumor burden and grade and decreased survival. <i>miR-34a/b/c</i>-deficient adenomas showed elevated proliferation and decreased apoptosis and displayed pronounced bacterial infiltration, which may be due to an observed decrease in infiltrating immune cells and downregulation of barrier proteins. mRNA induction in <i>miR-34a/b/c</i>-deficient tumors was enriched for miR-34a/b/c seed-matching sites and for mRNAs encoding proteins related to epithelial-mesenchymal transition, stemness, and Wnt signaling. Accordingly, cells explanted from <i>miR-34a/b/c</i>-deficient adenomas formed tumor organoids at an increased rate. Several upregulated miR-34 targets displayed elevated expression in primary human colorectal cancers that was associated with lymph-node metastases (<i>INHBB, AXL, FGFR1,</i> and <i>PDFGRB</i>) and upregulation of <i>INHBB</i> and <i>AXL</i> in primary colorectal cancer was associated with poor patient survival. In conclusion, our results show that <i>miR-34a/b/c</i> suppress tumor formation caused by loss of <i>Apc</i> and control intestinal stem cell and secretory cell homeostasis by downregulation of multiple target mRNAs. <i>Cancer Res; 77(10); 2746-58. ©2017 AACR</i>.