Molecular Cloning and Characterization of an Aquaporin cDNA from Salivary, Lacrimal, and Respiratory Tissues

doi:10.1074/jbc.270.4.1908

Molecular Cloning and Characterization of an Aquaporin cDNA from Salivary, Lacrimal, and Respiratory Tissues (*)

From the Departments of Biological Chemistry, Medicine, and Physiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205

^¶ To whom correspondence and reprint requests should be addressed:
Dept. of Biological Chemistry, The Johns Hopkins University School of Medicine, 725 N. Wolfe St., Baltimore, MD 21205
. Fax: 410-955-3149.

↵^§ Present address: Dept. of Embryology, Carnegie Institution of Washington, 115 W. University Parkway, Baltimore, MD 21210.

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 (P) 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.

Footnotes

↵* This work was supported in part by National Institutes of Health Grants HL33991 and HL48268 (to P. A.) and DK32753 (to W. B. G.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank_(TM)/EMBL Data Bank with accession number(s) U16245[GenBank].
↵¹ The abbreviations used are:

bp

base pair(s)

kb

kilobase(s)

P

coefficient of osmotic water permeability.
- Received September 8, 1994.
- Revision received October 24, 1994.