title: Myosin VI mediates the movement of NHE3 down the microvillus in intestinal epithelial cells.
abstract: The intestinal brush border Na(+)/H(+) exchanger NHE3 is tightly regulated through changes in its endocytosis and exocytosis. Myosin VI, a minus-end-directed actin motor, has been implicated in endocytosis at the inter-microvillar cleft and during vesicle remodeling in the terminal web. Here, we asked whether myosin VI also regulates NHE3 movement down the microvillus. The basal NHE3 activity and its surface amount, determined by fluorometry of the ratiometric pH indicator BCECF and biotinylation assays, respectively, were increased in myosin-VI-knockdown (KD) Caco-2/Bbe cells. Carbachol (CCH) and forskolin (FSK) stimulated NHE3 endocytosis in control but not in myosin VI KD cells. Importantly, immunoelectron microscopy results showed that NHE3 was preferentially localized in the basal half of control microvilli but in the distal half in myosin VI KD cells. Treatment with dynasore duplicated some aspects of myosin VI KD: it increased basal surface NHE3 activity and prevented FSK-induced NHE3 endocytosis. However, NHE3 had an intermediate distribution along the microvillus (between that in myosin VI KD and untreated cells) in dynasore-treated cells. We conclude that myosin VI is required for basal and stimulated endocytosis of NHE3 in intestinal cells, and suggest that myosin VI also moves NHE3 down the microvillus.
authors.affiliation: Department of Medicine, Division of Gastroenterology and Hepatology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
authors.forename: Tiane
authors.initials: T
authors.lastname: Chen
authors.affiliation: Department of Medicine, Division of Gastroenterology and Hepatology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
authors.forename: Ann
authors.initials: A
authors.lastname: Hubbard
authors.affiliation: Department of Medicine, Division of Gastroenterology and Hepatology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
authors.forename: Rakhilya
authors.initials: R
authors.lastname: Murtazina
authors.affiliation: Department of Medicine, Division of Gastroenterology and Hepatology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA Department of Gastroenterology, University of California, School of Medicine, San Francisco, CA 94143, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Price
authors.affiliation: Department of Medicine, Division of Gastroenterology and Hepatology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
authors.forename: Jianbo
authors.initials: J
authors.lastname: Yang
authors.affiliation: Department of Medicine, Division of Gastroenterology and Hepatology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
authors.forename: Boyoung
authors.initials: B
authors.lastname: Cha
authors.affiliation: Department of Medicine, Division of Gastroenterology and Hepatology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
authors.forename: Rafiquel
authors.initials: R
authors.lastname: Sarker
authors.affiliation: Department of Medicine, Division of Gastroenterology and Hepatology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA Departments of Medicine and Physiology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA mdonowit@jhmi.edu.
authors.forename: Mark
authors.initials: M
authors.lastname: Donowitz
mesh_terms: D000818:Animals; D002217:Carbachol / Q000378:metabolism; D002460:Cell Line; D004705:Endocytosis; D004847:Epithelial Cells / Q000378:metabolism*; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000166:cytology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008871:Microvilli / Q000235:genetics / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*
chemical_list: C000613385:SLC9A3 protein, human; C000613386:Slc9a3 protein, mouse; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; C089785:myosin VI; D002217:Carbachol; D018995:Myosin Heavy Chains
keywords: Brush border; Endocytosis; Myosin VI; Na+ absorption; Na+/H+ exchanger; Trafficking