期刊
AMERICAN JOURNAL OF RESPIRATORY CELL AND MOLECULAR BIOLOGY
卷 28, 期 1, 页码 69-79出版社
AMER THORACIC SOC
DOI: 10.1165/rcmb.2002-0111OC
关键词
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资金
- NHLBI NIH HHS [HL59959, P50 HL56401, HL 19737] Funding Source: Medline
- NATIONAL HEART, LUNG, AND BLOOD INSTITUTE [R56HL059959, P01HL019737, R01HL059959, P50HL056401] Funding Source: NIH RePORTER
Surfactant protein (SP)-B is essential for lamellar body genesis and for the final steps in proSP-C post-translational processing. The mature SP-B protein is derived from multistep processing of the primary translation product proSP-B; however, the enzymes required for these events are currently unknown. Recent ultrastructural colocalization studies have suggested that the cysteine protease Cathepsin H may be involved in proSP-B processing. Using models of isolated human type 2 cells in culture, we describe the effects of cysteine protease inhibition by E-64 on SP-B processing and type 2 cell differentiation. Pulse-chase labeling and Western immunoblotting studies showed that the final step of SP-B processing, specifically cleavage of SP-B-9 to SP-B., was significantly inhibited by E-64, resulting in delayed accumulation of SP-B-8 without adverse effects on SP-A or glyceraldehyde phosphate dehydrogenase expression. E-64 treatment during type 2 cell differentiation mimicked features of inherited SP-B deficiency in humans and mice, specifically disrupted lamellar body genesis, and aberrant processing of proSP-C. Reverse transcriptase-polymerase chain reaction and Western immunoblotting studies showed that Cathepsin H is induced during in vitro differentiation of type 2 cells and localizes with SP-B in multivesicular bodies, composite bodies, and lamellar bodies by immunoelectron microscopy. Furthermore, Cathepsin H activity was specifically inhibited in a dose-dependent fashion by E-64. Our data show that a cysteine protease is involved in SP-B processing, lamellar body genesis, and SP-C processing, and suggest that Cathepsin H is the most likely candidate protease.
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