Defective secretion of albumin encoded by exon-skipped mRNA found in aged analbuminemic rat liver.
Remarkable increases in the amount of exon H-skipped (delta H), exons G and H-skipped (delta GH), and exons H and I-skipped (delta HI) mRNAs of rat albumin have been found in the livers of aged or mutagen-treated analbuminemic rats (Kaneko, T., H. Shima, H. Esumi, M. Ochiai, S. Nagase, T. Sugimura, M. Nagao: Proc. Natl. Acad. Sci. USA 98, 2707-2711 (1991)), in association with increases in numbers of immunohistochemically albumin-positive hepatocytes and the accumulation of albumin(s) in the cells. To determine which type of mRNA is responsible for the accumulation of albumin(s), expression vector systems for intact mRNA and three kinds of exon-skipped albumin mRNAs were constructed and transfected into COS-1 and HepG2 cells. Transient expression and secretion of albumins were examined in these cells. delta HI albumin and intact albumin were efficiently expressed by both types of transfected cells. The delta HI albumin expressed had a similar molecular weight to the major albumin isolated from the microsome fraction of the liver of aged analbuminemic rats, as judged by SDS-PAGE. The rate of secretion of delta HI albumin was very low in both types of transfected cells, whereas those of delta H and delta GH albumins were normal. Immunocytochemical analyses of the transfected COS-1 cells with antiserum against rat albumin showed that the distribution of intact albumin had a compact Golgi-like pattern, whereas that of delta HI albumin had a diffuse endoplasmic reticulum-like pattern. These distribution patterns were similar to those in aged analbuminemic rat hepatocytes.(ABSTRACT TRUNCATED AT 250 WORDS)
Sugiyama
K
K
Biochemistry Division, National Cancer Center Research Institute, Tokyo, Japan.
Sugimura
T
T
Esumi
H
H
D000375:Aging / Q000235:genetics / Q000502:physiology*; D000818:Animals; D001483:Base Sequence; D020126:Brefeldin A; D006528:Carcinoma, Hepatocellular; D002451:Cell Compartmentation; D002460:Cell Line; D002522:Chlorocebus aethiops; D003517:Cyclopentanes / Q000494:pharmacology; D018076:DNA, Complementary / Q000235:genetics; D005091:Exons; D006801:Humans; D008099:Liver / Q000378:metabolism*; D008113:Liver Neoplasms; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000235:genetics*; D051381:Rats; D017207:Rats, Sprague-Dawley / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012709:Serum Albumin / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D014407:Tumor Cells, Cultured
D003517:Cyclopentanes; D018076:DNA, Complementary; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D012709:Serum Albumin; D020126:Brefeldin A