Monoallelic silencing and haploinsufficiency in early murine intestinal neoplasms.

Abstract

Studies of tumors from human familial adenomatous polyposis, sporadic colon cancer, and mouse and rat models of intestinal cancer indicate that the majority of early adenomas develop through loss of normal function of the Adenomatous polyposis coli (APC) gene. In murine models of familial adenomatous polyposis, specifically the multiple intestinal neoplasia mouse (Min) and the polyposis in the rat colon (Pirc) rat, most adenomas have lost their WT copy of the Apc gene through loss of heterozygosity by homologous somatic recombination. We report that large colonic adenomas in the Pirc rat have no detectable copy number losses or gains in genomic material and that most tumors lose heterozygosity only on the short arm of chromosome 18. Examination of early mouse and rat tumors indicates that a substantial subset of tumors shows maintenance of heterozygosity of Apc in genomic DNA, apparently violating Knudson's two-hit hypothesis. Sequencing of the Apc gene in a sampling of rat tumors failed to find secondary mutations in the majority of tumors that maintained heterozygosity of Apc in genomic DNA. Using quantitative allele-specific assays of Apc cDNA, we discovered two neoplastic pathways. One class of tumors maintains heterozygosity of Apc(Min/+) or Apc(Pirc/+) RNA expression and may involve haploinsufficiency for Apc function. Another class of tumors exhibits highly biased monoallelic expression of the mutant Apc allele, providing evidence for a stochastic or random process of monoallelic epigenetic silencing of the tumor suppressor gene Apc.

• Authors: James M Amos-Landgraf, Amy A Irving, Cory Hartman, Anthony Hunter, Brianna Laube, Xiaodi Chen, Linda Clipson, Michael A Newton, William F Dove
• Journal: Proceedings of the National Academy of Sciences of the United States of America (Proc Natl Acad Sci U S A) Vol. 109 Issue 6 Pg. 2060-5 (Feb 07 2012) ISSN: 1091-6490 [Electronic] United States
• PMID: 22308460 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• DNA, Complementary
• RNA, Messenger

Topics

• Alleles
• Alternative Splicing (genetics)
• Animals
• Base Sequence
• DNA, Complementary (genetics)
• Epigenesis, Genetic
• Gene Dosage (genetics)
• Gene Expression Regulation, Neoplastic
• Gene Silencing
• Genes, APC
• Genetic Loci (genetics)
• Genome (genetics)
• Haploinsufficiency (genetics)
• Heterozygote
• Humans
• Immunohistochemistry
• Intestinal Neoplasms (genetics, pathology)
• Mice
• Mice, Inbred C57BL
• Models, Genetic
• Molecular Sequence Data
• Mutation (genetics)
• RNA, Messenger (genetics, metabolism)
• Rats
• Reproducibility of Results
• Reverse Transcriptase Polymerase Chain Reaction