Secretion of unprocessed human surfactant protein B in milk of transgenic mice |
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Authors: | Yarus Sinai Greenberg Norman M. Wei Yongli Whitsett Jeffrey A. Weaver Timothy E. Rosen Jeffrey M. |
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Affiliation: | (1) Department of Cell Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030-3498, USA;(2) Scott Department of Urology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030- 3498, USA;(3) Division of Neonatology and Pulmonary Biology, University of Cincinnati College of Medicine and Children's Hospital Medical Center, Cincinnati, Ohio 45267-0541, USA |
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Abstract: | Because of the apparent clinical importance of human pulmonary surfactant B (SP-B), the expression of SP-B was directed to the mammary gland of transgenic mice using previously characterized rat whey acidic protein (WAP) regulatory sequences. rWAP/SP-B mRNA was expressed specifically in the mammary gland, and ranged from 1 to 5% of the endogenous WAP mRNA levels. SP-B was detected immunologically in both tissue and milk. The transgene product had an apparent molecular weight of 40--45 kDa, corresponding to the predicted size of the SP-B proprotein. Incubation of an SP-B-enriched fraction of milk with cathepsin D in vitro produced 20--25 kDa species, consistent with cleavage of the amino terminal domain by cathepsin D. This was confirmed using antibodies specific to the carboxy-terminal domain of SP-B. However, the appearance of only the SP-B proprotein in milk suggests that cathepsin D is not involved in the in vivo processing of SP-B. The SP-B proprotein can be expressed in milk of transgenic mice without any observed effects on mammary gland morphology or lactation |
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Keywords: | WAP SP-B transgenic mouse pulmonary surfactant |
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