title: Molecular cloning and characterization of an aquaporin cDNA from salivary, lacrimal, and respiratory tissues.
abstract: The Aquaporin family of water channels plays a fundamental role in transmembrane water movements in numerous plant and animal tissues. Since the molecular pathway by which water is secreted by salivary glands is unknown, a cDNA was isolated from rat submandibular gland by homology cloning. Similar to other Aquaporins, the salivary cDNA encodes a 265-residue polypeptide with six putative transmembrane domains separated by five connecting loops (A-E); the NH2- and COOH-terminal halves of the polypeptide are sequence-related, and each contains the motif Asn-Pro-Ala. A mercurial-inhibition site is present in extracellular loop E, and cytoplasmic loop D contains a cAMP-protein kinase phosphorylation consensus. In vitro translation yielded a 27-kDa polypeptide, and expression of the cRNA in Xenopus oocytes conferred a 20-fold increase in osmotic water permeability (Pf) which was reversibly inhibited by 1 mM HgCl2. Northern analysis demonstrated a 1.6-kilobase mRNA in submandibular, parotid, and sublingual salivary glands, lacrimal gland, eye, trachea, and lung. In situ hybridization revealed a strong hybridization over the corneal epithelium in eye and over the secretory lobules in salivary glands. These studies have identified a new mammalian member of the Aquaporin water channel family (gene symbol AQP5) which is implicated in the generation of saliva, tears, and pulmonary secretions.
authors.affiliation: Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
authors.forename: S
authors.initials: S
authors.lastname: Raina
authors.forename: G M
authors.initials: GM
authors.lastname: Preston
authors.forename: W B
authors.initials: WB
authors.lastname: Guggino
authors.forename: P
authors.initials: P
authors.lastname: Agre
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D051398:Aquaporin 1; D020346:Aquaporins; D001483:Base Sequence; D015152:Blotting, Northern; D003001:Cloning, Molecular; D017931:DNA Primers; D018076:DNA, Complementary / Q000032:analysis / Q000096:biosynthesis; D005260:Female; D007473:Ion Channels / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism; D007668:Kidney / Q000378:metabolism; D007765:Lacrimal Apparatus / Q000378:metabolism*; D007908:Lens, Crystalline / Q000378:metabolism; D008168:Lung / Q000378:metabolism*; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology; D009928:Organ Specificity; D014176:Protein Biosynthesis; D017433:Protein Structure, Secondary; D018075:RNA, Complementary / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis / Q000302:isolation & purification; D051381:Rats; D015183:Restriction Mapping; D012469:Salivary Glands / Q000378:metabolism; D013363:Submandibular Gland / Q000378:metabolism*; D014132:Trachea / Q000378:metabolism*; D014981:Xenopus
chemical_list: C496022:Aqp1 protein, rat; D020346:Aquaporins; D017931:DNA Primers; D018076:DNA, Complementary; D007473:Ion Channels; D018075:RNA, Complementary; D012333:RNA, Messenger; D051398:Aquaporin 1