Biosynthesis of human acute-phase serum amyloid A protein (A-SAA) in vitro: the roles of mRNA accumulation, poly(A) tail shortening and translational efficiency.
Human 'acute-phase' serum amyloid A protein (A-SAA) is a major acute-phase reactant (APR) and an apolipoprotein of high density lipoprotein 3 (HDL3). We have examined several parameters of A-SAA biosynthesis in PLC/PRF/5 hepatoma cells in response to monocyte conditioned medium (MoCM) and dual treatment with interleukin-1 beta and interleukin-6 (IL-1 beta + IL-6). Treatment of PLC/PRF/5 cells with MoCM or IL-1 beta + IL-6 caused a dramatic and rapid increase in A-SAA mRNA and protein synthesis; A-SAA mRNA was first detectable at 3 h, with peak levels reached by 24 h. A-SAA mRNA accumulation is accompanied by a gradual and homogeneous decrease in the length of the A-SAA poly(A) tail; the poly(A) tail shortening does not apparently affect the intrinsic stability of A-SAA mRNA. Analysis of RNA isolated from the ribonucleoprotein, monosome and polysome fractions of cytokine-treated PLC/PRF/5 cells showed that most A-SAA mRNA was associated with small polyribosomes, regardless of time post-stimulus, suggesting that the translational efficiency of A-SAA mRNA is constant throughout cytokine-driven induction. Moreover, the transit time of A-SAA protein out of the cell is also constant throughout the time course of induction. These data provide evidence of a paradox with regard to the transcriptional upregulation of A-SAA by IL-1 beta + IL-6 and the relative synthesis of A-SAA protein and suggest a role for post-transcriptional control of A-SAA biosynthesis during the acute phase.
Steel
D M
DM
Department of Genetics, Trinity College, University of Dublin, Ireland.
Rogers
J T
JT
DeBeer
M C
MC
DeBeer
F C
FC
Whitehead
A S
AS
D001483:Base Sequence; D015152:Blotting, Northern; D006528:Carcinoma, Hepatocellular; D017077:Culture Media, Conditioned; D003609:Dactinomycin / Q000494:pharmacology; D004355:Drug Stability; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology; D015850:Interleukin-6 / Q000494:pharmacology; D007700:Kinetics; D008113:Liver Neoplasms; D008969:Molecular Sequence Data; D009000:Monocytes / Q000378:metabolism; D011061:Poly A / Q000378:metabolism*; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism*; D000685:Serum Amyloid A Protein / Q000096:biosynthesis* / Q000235:genetics*; D014407:Tumor Cells, Cultured
D017077:Culture Media, Conditioned; D007375:Interleukin-1; D015850:Interleukin-6; D012333:RNA, Messenger; D000685:Serum Amyloid A Protein; D003609:Dactinomycin; D011061:Poly A