ABSTRACT
Flap endonuclease 1 (Fen1) and exonuclease 1 (Exo1) have sequence homology and similar nuclease capabilities. Both function in multiple pathways of DNA metabolism, but appear to have distinct in vivo nucleic acid substrates, and therefore distinct metabolic roles. When combined with Apc(1638N), Fen1 promotes tumor progression. Because of functional similarity to Fen1, and because Exo1 is involved in DNA mismatch repair (MMR) by interaction with Msh2 and Mlh1, genes that cause hereditary nonpolyposis colorectal cancer (HNPCC), we investigated the possibility that Exo1 might also act as a modifier to Apc(1638N). We present evidence that mice with combined mutations in Apc(1638N) and Exo1 and Apc(1638N), Exo1 and Fen1 genes show moderate increased tumor incidence and multiplicity in comparison to Apc(1638N) siblings, implying a low penetrance role for Exo1 in early gastrointestinal (GI) tumorigenesis. Despite a decrease in median survival (10 months) in Apc(1638N) Exo1 mice, their tumors do not progress any more rapidly than those of Apc(1638N). Instead these animals die from infections that are the result of impaired immune response. Apc(1638N) Exo1 Fen1 mice survive longer (18 months), and therefore appear relatively immune competent. They die of invasive GI tumors that display microsatellite instability (MSI). Our results show that Exo1 has a modest tumor suppressor function.
Subject(s)
Adenomatous Polyposis Coli Protein/genetics , Adenomatous Polyposis Coli Protein/metabolism , Exodeoxyribonucleases/deficiency , Flap Endonucleases/deficiency , Genes, APC , Neoplasms/genetics , Neoplasms/pathology , Animals , Asparagine/genetics , Asparagine/metabolism , Disease Progression , Exodeoxyribonucleases/genetics , Exodeoxyribonucleases/metabolism , Flap Endonucleases/genetics , Flap Endonucleases/metabolism , Mice , Mice, Transgenic , Mutation/genetics , Neoplasms/metabolism , Survival RateABSTRACT
We explored the role of hypocretins in human narcolepsy through histopathology of six narcolepsy brains and mutation screening of Hcrt, Hcrtr1 and Hcrtr2 in 74 patients of various human leukocyte antigen and family history status. One Hcrt mutation, impairing peptide trafficking and processing, was found in a single case with early onset narcolepsy. In situ hybridization of the perifornical area and peptide radioimmunoassays indicated global loss of hypocretins, without gliosis or signs of inflammation in all human cases examined. Although hypocretin loci do not contribute significantly to genetic predisposition, most cases of human narcolepsy are associated with a deficient hypocretin system.
Subject(s)
Brain Chemistry/genetics , Carrier Proteins , Intracellular Signaling Peptides and Proteins , Mutation , Narcolepsy/genetics , Neuropeptides/genetics , Receptors, Neuropeptide/genetics , Adult , Age of Onset , Aged , Aged, 80 and over , Cerebral Cortex/chemistry , Female , Genetic Testing , Humans , Hypothalamus/chemistry , Hypothalamus/cytology , Male , Middle Aged , Molecular Sequence Data , Neuropeptides/analysis , Neurotransmitter Agents/genetics , Orexin Receptors , Orexins , Pons/chemistry , Protein Processing, Post-Translational , Receptors, G-Protein-Coupled , Tissue Distribution , White PeopleABSTRACT
Repair of mismatches in DNA in mammalian cells is mediated by a complex of proteins that are members of two highly conserved families of genes referred to as MutS and MutL homologues. Germline mutations in several members of these families, MSH2, MSH6, MLH1, and PMS2, but not MSH3, are responsible for hereditary non-polyposis colorectal cancer. To examine the role of MSH3, we generated a mouse with a null mutation in this gene. Cells from Msh3-/- mice are defective in repair of insertion/ deletion mismatches but can repair base-base mismatches. Msh3-/- mice develop tumors at a late age. When the Msh3-/- and Msh6-/- mutations are combined, the tumor predisposition phenotype is indistinguishable from Msh2-/- or Mlh1-/- mice. These results suggest that MSH3 cooperates with MSH6 in tumor suppression.
