Surfactant protein B processing in human fetal lung.
Surfactant protein B (SP-B8), an 8-kDa hydrophobic protein essential for surfactant and normal lung function, is produced from the intracellular processing of preproSP-B. To characterize SP-B processing in human type 2 cells, we used human fetal lung in explant culture and polyclonal antibodies to human SP-B8 (Phe201-Met279) and to specific epitopes within the NH2- and COOH-terminal propeptide domains (Ser145-Leu160, Gln186-Gln200, and Gly284-Ser304). Western blot analysis revealed a novel intermediate at approximately 9 kDa, representing mature SP-B8, with a residual NH2-terminal peptide of approximately 10 amino acids. Pulse-chase studies showed a precursor-product relationship between the 9- and 8-kDa forms. During differentiation of type 2 cells in explant culture, the rate of proSP-B conversion to 25-kDa intermediate remained constant, whereas the rate of 25-kDa intermediate conversion to SP-B8 increased, resulting in a net increase in tissue SP-B8. Dexamethasone did not affect the rate of proSP-B processing but markedly enhanced the rate of SP-B8 accumulation. We conclude that NH2-terminal propeptide cleavage of proSP-B is a multistep process and that more distal processing events are rate limiting and both developmentally and hormonally regulated.
Guttentag
S H
SH
Division of Neonatology, Department of Pediatrics, Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA.
Beers
M F
MF
Bieler
B M
BM
Ballard
P L
PL
D000595:Amino Acid Sequence; D000906:Antibodies; D000939:Epitopes / Q000032:analysis; D005260:Female; D005333:Fetus; D005865:Gestational Age; D006801:Humans; D008168:Lung / Q000196:embryology* / Q000378:metabolism; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011498:Protein Precursors / Q000737:chemistry / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D021382:Protein Sorting Signals / Q000378:metabolism; D011510:Proteolipids / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D011663:Pulmonary Surfactants / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics
D000906:Antibodies; D000939:Epitopes; D011498:Protein Precursors; D021382:Protein Sorting Signals; D011510:Proteolipids; D011663:Pulmonary Surfactants