Regulation of fibrinogen assembly. Transfection of Hep G2 cells with B beta cDNA specifically enhances synthesis of the three component chains of fibrinogen.
Previous studies indicated that synthesis of B beta chain may be a rate-limiting factor in the production of human fibrinogen since Hep G2 cells contain surplus pools of A alpha and gamma but not of B beta chains, and fibrinogen assembly commences by the addition of preformed A alpha and gamma chains to nascent B beta chains attached to polysomes. To test whether B beta chain synthesis is rate limiting Hep G2 cells were transfected with B beta cDNA, and its effect on fibrinogen synthesis and secretion was measured. Two sets of stable B beta cDNA-transfected Hep G2 cells were prepared, and both cell lines synthesized 3-fold more B beta chains than control cells. The B beta-transfected cells also synthesized and secreted increased amounts of fibrinogen. Transfection with B beta cDNA not only increased the synthesis of B beta chain but also increased the rate of synthesis of the other two component chains of fibrinogen and maintained surplus intracellular pools of A alpha and gamma chains. Transfection with B beta cDNA did not affect the synthesis of albumin, transferrin, or anti-chymotrypsin and had a small inhibitory effect on the synthesis of C-reactive protein. Taken together these studies demonstrate that increased B beta chain synthesis specifically causes increased production of the other two component chains of fibrinogen and that unequal and surplus amounts of A alpha and gamma chains are maintained intracellularly.
Roy
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Lindsley F. Kimball Research Institute, New York Blood Center, New York 10021.
Mukhopadhyay
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Redman
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D015152:Blotting, Northern; D002097:C-Reactive Protein / Q000096:biosynthesis; D002294:Carcinoma, Squamous Cell; D002460:Cell Line; D004247:DNA / Q000235:genetics*; D005340:Fibrinogen / Q000096:biosynthesis / Q000235:genetics*; D005786:Gene Expression Regulation; D005822:Genetic Vectors; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D008715:Methionine / Q000378:metabolism; D010957:Plasmids; D012333:RNA, Messenger / Q000235:genetics; D015183:Restriction Mapping; D012709:Serum Albumin / Q000096:biosynthesis; D014162:Transfection
D046911:Macromolecular Substances; D012333:RNA, Messenger; D012709:Serum Albumin; D005340:Fibrinogen; D002097:C-Reactive Protein; D004247:DNA; D008715:Methionine