Synthesis and secretion of apolipoprotein A-I by chick skin.
Chick skin slices were incubated with [35S]methionine and labeled apoA-I was immunoprecipitated from incubation medium and tissue homogenate. ApoA-I accounted for approximately 13 and 2.5% of radioactive medium and cell proteins, respectively. After ultracentrifugation of the medium, 55% of labeled apoA-I was found as a constituent of lipoproteins (d less than 1.210 g/ml) and 45% in a lipid-poor form (1.210-1.260 g/ml). To ascertain whether this large proportion of lipid-poor apoA-I was due to a dissociation of this peptide from medium lipoproteins during ultracentrifugation, labeled incubation medium was applied to an anti-chick apoA-I immunoaffinity column. The material bound to the column was analyzed by nondenaturing polyacrylamide gradient gel electrophoresis and found to contain three subpopulations of lipoproteins with a particle size of 12, 11, and 9 nm, respectively. The radioactivity of these subpopulations accounted for 82% of total radioactive medium apoA-I. ApoA-I was localized by immunohistochemistry in the viable cells of the epidermis and in the stratum corneum. Rat skin slices were found to synthesize and secrete apoE but no apoA-I. ApoA-I and apoE secreted by chick and rat skin, respectively, may play a role in the secretion of lipids from the differentiating keratinocytes and thus contribute to the formation of the hydrophobic barrier of the skin.
Tarugi
P
P
Istituto di Patologia Generale, Università di Modena, Italy.
Albertazzi
L
L
Nicolini
S
S
Ottaviani
E
E
Calandra
S
S
D000818:Animals; D016632:Apolipoprotein A-I; D001054:Apolipoproteins A / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D001057:Apolipoproteins E / Q000096:biosynthesis / Q000378:metabolism; D015152:Blotting, Northern; D002645:Chickens; D002846:Chromatography, Affinity; D004591:Electrophoresis, Polyacrylamide Gel; D007150:Immunohistochemistry; D008297:Male; D009693:Nucleic Acid Hybridization; D012313:RNA / Q000032:analysis; D051381:Rats; D011919:Rats, Inbred Strains; D012867:Skin / Q000378:metabolism*
D016632:Apolipoprotein A-I; D001054:Apolipoproteins A; D001057:Apolipoproteins E; D012313:RNA