title: AP-1B-mediated protein sorting regulates polarity and proliferation of intestinal epithelial cells in mice.
abstract: OBJECTIVE
  In epithelial cells, protein sorting mechanisms regulate localization of plasma membrane proteins that generate and maintain cell polarity. The clathrin-adaptor protein (AP) complex AP-1B is expressed specifically in polarized epithelial cells, where it regulates basolateral sorting of membrane proteins. However, little is known about its physiological significance.
  
  
  METHODS
  We analyzed the intestinal epithelia of mice deficient in Ap1m2 (Ap1m2(-/-) mice), which encodes the AP-1B μ1B subunit, and compared it with 129/B6/CD1 littermates (controls). Notch signaling was inhibited by intraperitoneal injection of dibenzazepine, and β-catenin signaling was inhibited by injection of IWR1. Intestinal tissue samples were collected and analyzed by immunofluorescence analysis.
  
  
  RESULTS
  Ap1m2(-/-) mice developed intestinal epithelial cell hyperplasia. The polarity of intestinal epithelial cells was disrupted, as indicated by the appearance of ectopic microvilli-like structures on the lateral plasma membrane and mislocalization of basolateral membrane proteins, including the low-density lipoprotein receptor and E-cadherin. The E-cadherin-β-catenin complex therefore was disrupted at the adherens junction, resulting in nuclear translocation of β-catenin. This resulted in up-regulation of genes regulated by β-catenin/transcription factor 4 (Tcf4) complex, and increased the proliferation of intestinal epithelial cells.
  
  
  CONCLUSIONS
  AP-1B is required for protein sorting and polarization of intestinal cells in mice. Loss of AP-1B in the intestinal epithelia results in mislocalization of E-cadherin, activation of β-catenin/Tcf4 complex, proliferation, and hyperplasia.
authors.affiliation: The University of Tokyo, Tokyo, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Hase
authors.forename: Fubito
authors.initials: F
authors.lastname: Nakatsu
authors.forename: Masumi
authors.initials: M
authors.lastname: Ohmae
authors.forename: Kazushi
authors.initials: K
authors.lastname: Sugihara
authors.forename: Noriko
authors.initials: N
authors.lastname: Shioda
authors.forename: Daisuke
authors.initials: D
authors.lastname: Takahashi
authors.forename: Yuuki
authors.initials: Y
authors.lastname: Obata
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Furusawa
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Fujimura
authors.forename: Taisuke
authors.initials: T
authors.lastname: Yamashita
authors.forename: Shinji
authors.initials: S
authors.lastname: Fukuda
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Okamoto
authors.forename: Masahide
authors.initials: M
authors.lastname: Asano
authors.forename: Shigenobu
authors.initials: S
authors.lastname: Yonemura
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ohno
mesh_terms: D033961:Adaptor Protein Complex 1 / Q000172:deficiency* / Q000502:physiology; D033983:Adaptor Protein Complex mu Subunits / Q000172:deficiency* / Q000502:physiology; D000818:Animals; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / Q000378:metabolism; D015415:Biomarkers / Q000378:metabolism; D015820:Cadherins / Q000378:metabolism; D016764:Cell Polarity; D049109:Cell Proliferation; D004847:Epithelial Cells / Q000378:metabolism* / Q000473:pathology / Q000502:physiology; D005260:Female; D005455:Fluorescent Antibody Technique; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D007421:Intestine, Small / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D008297:Male; D051379:Mice; D057507:Mice, 129 Strain; D018345:Mice, Knockout; D000073940:Transcription Factor 4; D051176:beta Catenin / Q000378:metabolism
chemical_list: D033961:Adaptor Protein Complex 1; D033983:Adaptor Protein Complex mu Subunits; C438884:Ap1m2 protein, mouse; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D015415:Biomarkers; C495267:CTNNB1 protein, mouse; D015820:Cadherins; C090743:Tcf4 protein, mouse; D000073940:Transcription Factor 4; D051176:beta Catenin
keywords: AJ; AP; Apical and Basolateral; BMP; BrdU; Gene Regulation; LDLR; MDCK; Madin–Darby canine kidney; TGF; TGN; Tight Junction; ZO-1; adaptor protein; adherens junction; bone morphogenic protein; bromodeoxyuridine; low-density lipoprotein receptor; trans-Golgi network; transforming growth factor; zonula occludens-1