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Surfactant protein B in type II pneumocytes and intra-alveolar surfactant forms of human lungs.

Brasch F, Johnen G, Winn-Brasch A, Guttentag SH, Schmiedl A, Kapp N, Suzuki Y, Müller KM, Richter J, Hawgood S, Ochs M
Am J Respir Cell Mol Biol. 2004 30 (4): 449-58

PMID: 12972403 · DOI:10.1165/rcmb.2003-0262OC

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.

MeSH Terms (21)

Adult Animals Bronchoalveolar Lavage Fluid Cells, Cultured Golgi Apparatus Humans In Vitro Techniques Lung Male Microscopy, Immunoelectron Myelin Sheath Protein Precursors Protein Processing, Post-Translational Proteolipids Pulmonary Alveoli Pulmonary Surfactant-Associated Protein A Pulmonary Surfactant-Associated Protein B Pulmonary Surfactants Rats Rats, Wistar Subcellular Fractions

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