Primary translation products of pulmonary surfactant protein D.
Surfactant protein D (SP-D) is a collagenous, surfactant-associated, carbohydrate-binding protein that is synthesized by alveolar type II epithelial cells. To further characterize SP-D, we isolated RNA from adult rat lungs and rat type II cells and translated mRNAs in vitro. [35S]methionine-labeled translation products were precipitated with antibodies to rat SP-D, resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and visualized by fluorography. Immune precipitates of translation reactions for rat lung or rat type II cells demonstrated a single collagenous polypeptide (39.3 kDa) that was smaller than surfactant-associated SP-D (43 kDa, reduced) but larger than the mature secreted form of rat SP-A. This component was not identified in translation reactions of rat liver, gut, brain, mammary gland, or rat L2 cell RNA. There was a fivefold enrichment of SP-D mRNA in freshly isolated type II cells relative to lung; however, the levels of translatable SP-D mRNA decreased rapidly during the first 24 h of cell culture. The SP-D translation product migrated faster than the major cellular form of SP-D but approximately 1 kDa slower than cellular SP-D synthesized in the presence of 2,2'-dipyridyl plus tunicamycin. Translation in the presence of canine pancreatic microsomes gave a single glycosylated, endoglycosidase F-sensitive form (40.6 kDa) and demonstrated cleavage of a small signal peptide. These results indicate that SP-D is a secretory product of differentiated type II epithelial cells and that SP-D is secreted in a mature form that does not undergo further proteolytic processing in vivo.
Crouch
E
E
Department of Pathology, Jewish Hospital, Washington University Medical Center, St. Louis, Missouri.
Rust
K
K
Persson
A
A
Mariencheck
W
W
Moxley
M
M
Longmore
W
W
D000818:Animals; D002474:Cell-Free System; D004285:Dogs; D004848:Epithelium / Q000378:metabolism; D006023:Glycoproteins / Q000096:biosynthesis / Q000235:genetics*; D008297:Male; D008715:Methionine / Q000378:metabolism; D008861:Microsomes / Q000378:metabolism; D010179:Pancreas / Q000378:metabolism; D011061:Poly A / Q000235:genetics / Q000302:isolation & purification; D014176:Protein Biosynthesis; D011499:Protein Processing, Post-Translational; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism*; D037663:Pulmonary Surfactant-Associated Protein D; D011663:Pulmonary Surfactants / Q000096:biosynthesis / Q000235:genetics*; D012313:RNA / Q000302:isolation & purification; D012333:RNA, Messenger / Q000235:genetics / Q000302:isolation & purification; D051381:Rats; D011919:Rats, Inbred Strains; D012156:Reticulocytes / Q000378:metabolism
D006023:Glycoproteins; D037663:Pulmonary Surfactant-Associated Protein D; D011663:Pulmonary Surfactants; D012333:RNA, Messenger; D011061:Poly A; D012313:RNA; D008715:Methionine