Molecular cloning of human genes for serum amyloid A

Three human DNA fragments hybridizing to a mouse cDNA plasmid for the acute phase protein amyloid A have been isolated from the human lambda Charon 4A phage library. Two of these recombinants, GSAA1 (12.8 kb insert) and GSAA2 (15.9 kb insert), share an apparently identical internal region of 9.7 kb while the third, GSAA3 (15.95-kb insert) shows different restriction enzyme fragments. Hybridization studies localize the coding region to single HindIII fragments and suggest that all coding information is present in these recombinants; these fragments have been subcloned into pBR322 and mapped for further study.

Regulation of synthesis of amyloid A-related protein

The concentration of serum amyloid A polypeptide (SAAL) increases greatly during the acute phase responses to infection or inflammation. We find that SAAL synthesis comprises 2.5% of murine hepatic protein synthesis after lipopolysaccharide (LPS) administration, but much less in normal liver. SAAL messenger RNA (mRNA) in liver increases at least 500-fold above the normal level. A recombinant plasmid homologous to SAAL mRNA has been isolated, as has most of the mouse genome DNA encoding the plasmid's nucleotide sequence. This gene is transcribed into RNA much more frequently after LPS administration than it is in normal liver. In a number of other mammalian genes, cytosine methylation is inversely related to the rate of transcription. Methylation of CCGG sequences in hepatic DNA homologous to the recombinant plasmid has been examined. Little or no change is found after LPS administration. This suggests that other factors are responsible for the increase in SAAL mRNA in the acute phase response.

Induction of hepatic synthesis of serum amyloid A protein and actin

Major changes in the mRNA population of murine liver occur after administration of bacterial lipopolysaccharide, an agent that causes increases in the concentrations of acute-phase serum proteins. The mRNA for one of these, serum amyloid A, is increased at least 500-fold compared to the normal level. It becomes one of the most abundant hepatic mRNAs, and serum amyloid A synthesis comprises about 2.5% of total hepatic protein synthesis in the acute-phase response. Its synthesis is tissue-specific in that amyloid A mRNA was not detected in the kidney, an important site of amyloid fibril accumulation. The protein synthesized in largest amount by acute-phase liver tissue in culture is cytoplasmic actin. Its relative rate of synthesis is increased about 5-fold compared to the normal tissue; that of serum albumin is decreased to about one-third of its normal rate. The concentration of mRNA for serum albumin is decreased by a similar amount. Starting with induced liver RNA, we have constructed a recombinant plasmid containing most of the DNA sequence encoding the serum amyloid A polypeptide.