Involvement of cathepsin H in the processing of the hydrophobic surfactant-associated protein C in type II pneumocytes.
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.
Brasch
Frank
F
Division of Electron Microscopy, Department of Anatomy, University of Göttingen, Germany. Frank.E.Brasch@ruhr-uni-bochum.de
Ten Brinke
Anja
A
Johnen
Georg
G
Ochs
Matthias
M
Kapp
Nadine
N
Müller
Klaus M
KM
Beers
Michael F
MF
Fehrenbach
Heinz
H
Richter
Joachim
J
Batenburg
Joseph J
JJ
Bühling
Frank
F
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
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