title: Involvement of cathepsin H in the processing of the hydrophobic surfactant-associated protein C in type II pneumocytes.
abstract: Surfactant protein C (SP-C) is synthesized by type II pneumocytes as a 21-kD propeptide (proSP-C) which is proteolytically processed to a 4.2-kD dipalmitoylated protein. To characterize the processing of proSP-C and the role of the cysteine protease cathepsin H, we studied the localization of proSP-C and cathepsin H in human as well as proSP-C in rat lungs, the enzymatic cathepsin H activity in isolated rat lamellar bodies, and the cleavage of human proSP-C by purified cathepsin H. Using antisera directed against the N-terminal E(11)-R(23) (NPROSP-C(11-23)), the C-terminal G(162)-G(174) domain (CPROSP-C(162-174)) of proSP-C, and against cathepsin H, immunogold labeling identified all three in electron-dense multivesicular bodies, but only NPROSP-C(11-23) and cathepsin H in composite as well as lamellar bodies of type II pneumocytes. Immuno double-labeling further distinguished electron-dense vesicles containing cathepsin H or electron light vesicles/multivesicular bodies containing proSP-C. Isolated lamellar bodies contained enzymatically active cathepsin H, a 6-kD proSP-C processing intermediate detected only by NPROSP-C(11-23), and mature SP-C. Using enzyme activities comparable to those in isolated lamellar bodies, purified cathepsin H generated a partially N-terminal processed proSP-C intermediate in vitro. In conclusion, our results indicate that after the fusion of electron-dense vesicles containing cathepsin H and electron-light vesicles or multivesicular bodies containing proSP-C, cathepsin H is involved in the first N-terminal processing step of proSP-C in electron-dense multivesicular bodies of type II pneumocytes.
authors.affiliation: Division of Electron Microscopy, Department of Anatomy, University of Göttingen, Germany. Frank.E.Brasch@ruhr-uni-bochum.de
authors.forename: Frank
authors.initials: F
authors.lastname: Brasch
authors.forename: Anja
authors.initials: A
authors.lastname: Ten Brinke
authors.forename: Georg
authors.initials: G
authors.lastname: Johnen
authors.forename: Matthias
authors.initials: M
authors.lastname: Ochs
authors.forename: Nadine
authors.initials: N
authors.lastname: Kapp
authors.forename: Klaus M
authors.initials: KM
authors.lastname: Müller
authors.forename: Michael F
authors.initials: MF
authors.lastname: Beers
authors.forename: Heinz
authors.initials: H
authors.lastname: Fehrenbach
authors.forename: Joachim
authors.initials: J
authors.lastname: Richter
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Batenburg
authors.forename: Frank
authors.initials: F
authors.lastname: Bühling
mesh_terms: D000818:Animals; D001483:Base Sequence; D056655:Cathepsin H; D002403:Cathepsins / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D017931:DNA Primers; D006801:Humans; D008168:Lung / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008854:Microscopy, Electron / Q000379:methods; D011499:Protein Processing, Post-Translational; D011510:Proteolipids / Q000378:metabolism*; D011663:Pulmonary Surfactants / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: D017931:DNA Primers; D011510:Proteolipids; D011663:Pulmonary Surfactants; D011994:Recombinant Proteins; D002403:Cathepsins; D003546:Cysteine Endopeptidases; C534126:CTSH protein, human; D056655:Cathepsin H; C534128:Ctsh protein, rat