title: Secretion of unprocessed human surfactant protein B in milk of transgenic mice.
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 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.
authors.affiliation: Department of Cell Biology, Baylor College of Medicine, Houston, TX 77030-3498, USA.
authors.forename: S
authors.initials: S
authors.lastname: Yarus
authors.forename: N M
authors.initials: NM
authors.lastname: Greenberg
authors.forename: Y
authors.initials: Y
authors.lastname: Wei
authors.forename: J A
authors.initials: JA
authors.lastname: Whitsett
authors.forename: T E
authors.initials: TE
authors.lastname: Weaver
authors.forename: J M
authors.initials: JM
authors.lastname: Rosen
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002402:Cathepsin D / Q000494:pharmacology; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D007150:Immunohistochemistry; D007774:Lactation; D008321:Mammary Glands, Animal / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008892:Milk / Q000378:metabolism; D008894:Milk Proteins / Q000235:genetics; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D011663:Pulmonary Surfactants / Q000235:genetics* / Q000276:immunology / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D011994:Recombinant Proteins / Q000276:immunology / Q000378:metabolism*; D019076:Transgenes
chemical_list: D008894:Milk Proteins; D011663:Pulmonary Surfactants; D012333:RNA, Messenger; D011994:Recombinant Proteins; C024471:whey acidic proteins; D002402:Cathepsin D