Surfactant protein B in type II pneumocytes and intra-alveolar surfactant forms of human lungs.
Surfactant protein B (SP-B) is synthesized by type II pneumocytes as a proprotein (proSP-B) that is proteolytically processed to an 8-kD protein. In human type II pneumocytes, we identified not only proSP-B, processing intermediates of proSP-B, and mature SP-B, but also fragments of the N-terminal propeptide. By means of immunoelectron microscopy, proSP-B and processing intermediates were localized in the endoplasmic reticulum, Golgi vesicles, and few multivesicular bodies in type II pneumocytes in human lungs. A colocalization of fragments of the N-terminal propeptide and mature SP-B was found in multivesicular, composite, and some lamellar bodies. Mature SP-B was localized over the projection core of lamellar bodies and core-like structures in tubular myelin figures. In line with immunoelectron microscopy and Western blot analysis of human type II pneumocytes, a fragment of the N-terminal propeptide was also detected in isolated rat lamellar bodies. In conclusion, our data indicate that the processing of proSP-B occurs between the Golgi complex and multivesicular bodies and provide evidence that a fragment of the N-terminal propeptide and mature SP-B are transported together to the lamellar bodies. In human lungs, mature SP-B is involved in the structural organization of lamellar bodies and tubular myelin by the formation of core particles.
Brasch
Frank
F
Department of Anatomy, University of Göttingen, Göttingen, Germany. Frank.E.Brasch@ruhr-uni-bochum.de
Johnen
Georg
G
Winn-Brasch
Alexandra
A
Guttentag
Susan H
SH
Schmiedl
Andreas
A
Kapp
Nadine
N
Suzuki
Yasuhiro
Y
Müller
Klaus M
KM
Richter
Joachim
J
Hawgood
Samuel
S
Ochs
Matthias
M
D000328:Adult; D000818:Animals; D001992:Bronchoalveolar Lavage Fluid; D002478:Cells, Cultured; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008168:Lung / Q000166:cytology* / Q000378:metabolism*; D008297:Male; D016253:Microscopy, Immunoelectron / Q000379:methods; D009186:Myelin Sheath / Q000648:ultrastructure; D011498:Protein Precursors / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D011510:Proteolipids / Q000378:metabolism; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure; D037662:Pulmonary Surfactant-Associated Protein A / Q000276:immunology / Q000378:metabolism; D037701:Pulmonary Surfactant-Associated Protein B / Q000276:immunology / Q000378:metabolism*; D011663:Pulmonary Surfactants / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013347:Subcellular Fractions
D011498:Protein Precursors; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037701:Pulmonary Surfactant-Associated Protein B; D011663:Pulmonary Surfactants; C105511:surfactant protein B propeptide