amanitins and Inflammation

The regulation of the synthesis of plasma proteins in rat liver during the acute phase response was studied by measuring gene transcription activities in a cell-free nuclear transcription system. The transcription activities for the genes of major acute phase alpha 1-protein, the beta-chain of fibrinogen, transferrin, alpha 1-acid glycoprotein, and alpha 2-macroglobulin increased, reaching a maximum level between 18 and 36 h after inducing an acute inflammation. The transcription activities for the genes of alpha 2u-globulin, albumin, and transthyretin (formerly called prealbumin) decreased, reaching a minimum level after 12 to 24 h. The extent of the relative changes in transcription activities was similar to that of the relative changes in mRNA levels for major acute phase alpha 1-protein, the beta-chain of fibrinogen, transferrin, alpha 2u-globulin, albumin, and transthyretin. This is consistent with the assumption that the principal mechanism of the regulation of the synthesis of these proteins operates at the level of transcription. In contrast, the relative changes in transcription activities for alpha 1-acid glycoprotein and alpha 2-macroglobulin were far smaller than the changes of their mRNA levels, suggesting that, in addition to transcriptional changes, other mechanism(s) are involved in the regulation of the synthesis of these proteins.

Topics: alpha-Macroglobulins; Amanitins; Animals; Blood Proteins; C-Reactive Protein; Fibrinogen; Inflammation; Liver; Male; Nucleic Acid Hybridization; Orosomucoid; Rats; Rats, Inbred BUF; RNA, Messenger; Time Factors; Transcription, Genetic; Transferrin; Uridine Monophosphate; Uridine Triphosphate

Serum amyloid A (SAA) is a plasma apolipoprotein produced by the liver in response to inflammatory stimuli. The murine SAA gene family is made up of three genes, SAA1, SAA2, and SAA3, plus a pseudogene. The SAA1 and SAA2 genes are highly homologous while the SAA3 gene has diverged substantially from the other two genes. Using small fragments from the cloned genes, we have analyzed the expression of each gene in the SAA family. Within 12 h after endotoxin administration, total liver SAA mRNA increases by 2000-fold, reaching approximately 20,000 transcripts/cell. Each gene accounts for approximately one-third of total SAA mRNA transcripts at this time. The increase is specific, since the levels of the mRNAs encoding albumin and apolipoprotein A-I in liver decrease 2-fold by 24 h. This correlates with a 2-fold decrease of the serum concentrations of these two proteins as well as their in vitro protein synthesis in primary hepatocytes. SAA1+2 mRNAs maintain their maximum levels until 36 h after lipopolysaccharide administration, while SAA3 mRNA is degraded to 20% its maximal level. As assayed by in vitro transcription in isolated hepatocyte nuclei, total SAA gene transcription increases at least 300-fold during the inflammatory response. The transcription rates of the individual SAA genes are similar during the initial stages of this response, reaching peak levels at 3 h. A comparison of the rates of SAA gene transcription and SAA mRNA accumulation suggests that SAA mRNA levels are regulated during the acute phase response by increased transcription and mRNA stabilization.

Topics: Albumins; Amanitins; Amyloid; Animals; Apolipoprotein A-I; Apolipoproteins A; Endonucleases; Gene Expression Regulation; Heparin; Inflammation; Lipopolysaccharides; Mice; Nucleic Acid Hybridization; RNA, Messenger; Sarcosine; Serum Amyloid A Protein; Single-Strand Specific DNA and RNA Endonucleases; Transcription, Genetic

Nuclei isolated from livers of turpentine-treated rats show an increased RNA synthesis, reaching a maximum at 10 h after treatment. The stimulation affects both alpha-amanitin-resistant and alpha-amanitin-sensitive activities, suggesting that pre-ribosomal and pre-messenger RNA formation are activated at the same time and to the same extent. The amount of ribosomal RNA, which is still normal 10 h after treatment, increases significantly at 24 h, but the increase is limited to the bound ribosomes, in keeping with the fact that the acute phase reactants are export proteins. These ribosomes, however, are not more active per se and the stimulation of protein synthesis in cell-free preparations depends essentially on an increased activity of soluble factors located in the cytosol. In living cells these soluble factors co-operate with an increased amount of some specific mRNAs and an expanded population of membrane-bound polyribosomes, thus leading to the increased protein synthesis peculiar to the liver of turpentine-treated rats.

Topics: Amanitins; Animals; Cell Nucleus; Cell-Free System; Cytosol; Inflammation; Leucine; Liver; Male; Polyribosomes; Protein Biosynthesis; Rats; Rats, Inbred Strains; RNA; Time Factors; Turpentine