title: Analysis of the Proteolytic Processing of ABCA3: Identification of Cleavage Site and Involved Proteases.
abstract: BACKGROUND
  ABCA3 is a lipid transporter in the limiting membrane of lamellar bodies in alveolar type II cells. Mutations in the ABCA3 gene cause respiratory distress syndrome in new-borns and childhood interstitial lung disease. ABCA3 is N-terminally cleaved by an as yet unknown protease, a process believed to regulate ABCA3 activity.
  
  
  METHODS
  The exact site where ABCA3 is cleaved was localized using mass spectrometry (MS). Proteases involved in ABCA3 processing were identified using small molecule inhibitors and siRNA mediated gene knockdown. Results were verified by in vitro digestion of a synthetic peptide substrate mimicking ABCA3's cleavage region, followed by MS analysis.
  
  
  RESULTS
  We found that cleavage of ABCA3 occurs after Lys174 which is located in the proteins' first luminal loop. Inhibition of cathepsin L and, to a lesser extent, cathepsin B resulted in attenuation of ABCA3 cleavage. Both enzymes showed activity against the ABCA3 peptide in vitro with cathepsin L being more active.
  
  
  CONCLUSIONS
  We show here that, like some other proteins of the lysosomal membrane, ABCA3 is a substrate of cathepsin L. Therefore, cathepsin L may represent a potential target to therapeutically influence ABCA3 activity in ABCA3-associated lung disease.
authors.affiliation: German Centre for Lung Research, Dr. von Hauner Children's Hospital, Ludwig-Maximilians University, 80337, Munich, Germany.
authors.forename: Nicole
authors.initials: N
authors.lastname: Hofmann
authors.affiliation: Proteomics facility, University of Konstanz, 78547, Konstanz, Germany.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Galetskiy
authors.affiliation: German Centre for Lung Research, Dr. von Hauner Children's Hospital, Ludwig-Maximilians University, 80337, Munich, Germany.
authors.forename: Daniela
authors.initials: D
authors.lastname: Rauch
authors.affiliation: German Centre for Lung Research, Dr. von Hauner Children's Hospital, Ludwig-Maximilians University, 80337, Munich, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Wittmann
authors.affiliation: Proteomics facility, University of Konstanz, 78547, Konstanz, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Marquardt
authors.affiliation: German Centre for Lung Research, Dr. von Hauner Children's Hospital, Ludwig-Maximilians University, 80337, Munich, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Griese
authors.affiliation: German Centre for Lung Research, Dr. von Hauner Children's Hospital, Ludwig-Maximilians University, 80337, Munich, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Zarbock
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000378:metabolism*; D000595:Amino Acid Sequence; D002401:Cathepsin B / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D056668:Cathepsin L / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D010447:Peptide Hydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010455:Peptides / Q000032:analysis; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D053719:Tandem Mass Spectrometry
chemical_list: C441524:ABCA3 protein, human; D018528:ATP-Binding Cassette Transporters; D010455:Peptides; D034741:RNA, Small Interfering; D010447:Peptide Hydrolases; D002401:Cathepsin B; D056668:Cathepsin L