ABSTRACT
The E3 ubiquitin ligase Mule is often overexpressed in human colorectal cancers, but its role in gut tumorigenesis is unknown. Here, we show in vivo that Mule controls murine intestinal stem and progenitor cell proliferation by modulating Wnt signaling via c-Myc. Mule also regulates protein levels of the receptor tyrosine kinase EphB3 by targeting it for proteasomal and lysosomal degradation. In the intestine, EphB/ephrinB interactions position cells along the crypt-villus axis and compartmentalize incipient colorectal tumors. Our study thus unveils an important new avenue by which Mule acts as an intestinal tumor suppressor by regulation of the intestinal stem cell niche.
Subject(s)
Ephrin-B3/metabolism , Intestines/cytology , Lysosomes/metabolism , Proteasome Endopeptidase Complex/metabolism , Proteolysis , Stem Cell Niche , Ubiquitin-Protein Ligases/metabolism , Wnt Signaling Pathway , Adenomatous Polyposis Coli/pathology , Alleles , Animals , Carcinogenesis/metabolism , Carcinogenesis/pathology , Cell Proliferation , Colonic Neoplasms/genetics , Colonic Neoplasms/pathology , Endocytosis , HEK293 Cells , Humans , Mice, Knockout , Models, Biological , Mutation/genetics , Paneth Cells/pathology , Proto-Oncogene Proteins c-myc/metabolism , Tumor Suppressor Proteins , Ubiquitin/metabolism , Ubiquitin-Protein Ligases/deficiencyABSTRACT
The influx of leukocytes (eosinophils, lymphocytes, and monocytes) into the airways and their production of proinflammatory cytokines contribute to the severity of allergic asthma. We describe here the synthesis and pharmacological evaluation of a series of triazinylphenylalkylthiazolecarboxylic acid esters that were designed to act as lung-specific antedrugs and inhibitors of the production of interleukin (IL)-5, a primary eosinophil-activating and proinflammatory cytokine. Closer examination of the hydroxypropyl ester, 15, indicated its high metabolic stability (t(1/2) > 240 min) in human lung S9 fraction but rapid conversion (t(1/2) = 15 min) into the pharmacologically inactive carboxylic acid by human liver preparations. In stimulated human whole blood cultures, 15 reduced not only the production of IL-5 (IC(50) = 78 nM) but also the biosynthesis of the monocyte chemotactic proteins MCP-1 (IC(50) = 220 nM), MCP-2 (IC(50) = 580 nM), and MCP-3 (IC(50) = 80 nM). In vivo, intratracheal administration of 15 (6 mg/animal) to allergic sheep, either before (-4 h) or after (+1.5 h) the pulmonary allergen challenge, completely abrogated the late-phase airway response and reduced the bronchial hyperreactivity to inhaled carbachol.
