Human Serum Amyloid a Three Hepatic Mrnas and the Corresponding Proteins in One Person Barbara Kluve-Beckerman, Francis E
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Human Serum Amyloid A Three Hepatic mRNAs and the Corresponding Proteins in One Person Barbara Kluve-Beckerman, Francis E. Dwulet, and Merrill D. Benson Departments ofMedical Genetics, Medicine, and Biochemistry, Indiana University School ofMedicine, Indianapolis, Indiana 46223; Rheumatology Section, Richard L. Roudebush Veterans Administration Medical Center, Indianapolis, Indiana 46202 Abstract could explain the relatively low incidence of amyloidosis seen in American patients with chronic inflammatory diseases. Serum amyloid A protein (SAA) is a major acute-phase protein Amyloid fibrils which form the deposits in reactive amy- in humans and most other mammals. In addition, it is the loidosis are composed primarily of amyloid A protein (AA),' a serum precursor of the major protein constituent of reactive degradation product ofthe acute-phase protein serum amyloid amyloid fibrils. Sequence analyses have identified a number of A (SAA). It is commonly hypothesized that increased synthesis polymorphic forms of human SAA and amyloid A protein of SAA during inflammatory conditions contributes to the (AA), but the question of the number of genes encoding SAA in development of amyloidosis. High blood concentrations of the human has not been addressed. In addition, there are in- SAA, however, are seen in most patients with infection and sufficient data to predict whether one form of SAA predisposes inflammation without resultant amyloid deposition. Thus it to amyloid fibril formation. In the present study three separate appears that additional factors such as metabolic variations, SAA proteins have been isolated from the plasma of one indi- protein processing, and structural gene polymorphisms may vidual and completely sequenced. While two of the SAA forms influence the likelihood for developing this disease. (SAA2a and SAA2,6) differ from each other only at position An important role for SAA structure in amyloid fibril for- 71, they differ from the most abundant form (SAA1) at seven mation has been suggested by the finding that two major forms and eight other positions, respectively. Nucleotide sequencing of SAA are present in the mouse, but only one form is incorpo- of cDNAs from a liver library of this individual identified all rated into amyloid deposits (1). Because humans represent an three mRNAs coding for these proteins and proved that: (a) the exceedingly complex population relative to inbred mouse often-reported absence of arginine at the amino terminus of strains, more human SAA and AA molecules will have to be SAA proteins must result from proteolytic processing of the structurally characterized to evaluate the possibility of selec- protein; (b) the polymorphism involving histidine and arginine tive deposition. To investigate the importance of the primary at position 71 is present at the DNA level and therefore is not structure of SAA proteins in amyloidogenesis, we have studied due to an event at the translational level; (c) there are at least the forms of this protein in one individual at both the DNA two genes coding for human SAA. Comparison of these data to and protein levels. published sequences of SAA and AA proteins may help in identifying genetically determined forms of SAA which pre- Methods dispose to reactive amyloid fibril formation. Cloning and sequence determination ofSAA cDNAs. Liver tissue was obtained at the time of organ donation from patient COL, a man who Introduction had suffered accidental traumatic injury. Poly A' RNA isolated from this liver served as the template for the synthesis of cDNA. The cDNA Reactive amyloidosis is a fatal condition characterized by ex- was ligated into the PstI site of pBR322 which, in turn, was used to tracellular protein deposition in patients with chronic inflam- transform Escherichia coli HB1O1 cells. The exact procedures used to matory diseases. It also develops in a high percentage of indi- construct and the conditions used to screen this library have been viduals with familial Mediterranean fever, an autosomal re- described (2). The size ofthe cDNA inserts was determined and restric- cessive disease most in and tion analysis carried out using recombinant plasmid DNA prepared prevalent Sephardic Jews, Arabs, according to the rapid alkaline lysis method (3). For sequence analysis, Turks. While a genetic pattern of amyloidosis has not been recombinant plasmid DNA was generated on a larger scale (4) and noted among patients with chronic diseases, its frequent asso- further purified by ultracentrifugation through ethidium bromide-ce- ciation with familial Mediterranean fever suggests that genetic sium chloride gradients. factors may be involved in its pathogenesis. Such factor(s) The nucleotide sequences of SAAl and SAA2a cDNAs were de- termined by the chemical degradation procedure (5). The strategy used to sequence SAA2a cDNA has been described (2). To sequence SAA I This study was presented in part at the American Rheumatism Associ- cDNA, pSAAI was first cleaved within the cDNA by NcoI and the ation Annual Meeting, Washington, DC (1987. Arthritis Rheum. overlapping 5'-ends radiolabeled using [y-32P]ATP and T4 polynu- 30:S1 5). cleotide kinase. Secondary digestions were then performed with PvuI Dr. Dwulet is now with Boehringer-Mannhein, Indianapolis, IN. and HhaI which cut the vector at sites relatively close to each end ofthe Address reprint requests to Dr. Kluve-Beckerman, Rheumatology cDNA. The resulting two radiolabeled fragments, which together Section, Room A772, Richard L. Roudebush VA Medical Center contained all the cDNA and a small portion of pBR322, were purified (583/11 lRh), 1481 West 10th St., Indianapolis, IN 46202. by polyacrylamide gel electrophoresis and sequenced from the NcoI Receivedfor publication 25 January 1988 and in revisedform 27 ends. June 1988. The Journal of Clinical Investigation, Inc. 1. Abbreviations used in this paper: AA, amyloid A protein; SAA, Volume 82, November 1988, 1670-1675 serum amyloid A. 1670 B. Kluve-Beckerman, F. E. Dwulet, and M. D. Benson Sequence determination ofSAA2f cDNA was accomplished by the pSAAI pSAA2at pSAA2B chain termination method (6) using Ml 3mp l 8 and Ml 3mp1 9 vectors (7). Initially SAA2fl cDNA was excised from pBR322 by digestion with p P+N P P+N P P+N PstI and purified by PAGE. The isolated insert was digested with Sau3A and the resulting fragments ligated to BamHI/PstI- or BamHI- digested replicative form M13. The infection of E. coli JMI01 cells E. with recombinant Ml 3 was carried out using competent coli DH5 4362 - cells as a transient host (8). Southern blot analysis. 18 ug of DNA extracted from COL liver tissue (9) was digested with HindIII. The resulting fragments were separated by electrophoresis through a 1% agarose gel in Tris-borate- EDTA buffer and transferred to nitrocellulose. Hybridization was car- 575 - ried out at 650C in 6X SSC (IX = 0.15 M NaCl, 0.015 M sodium citrate, pH 7.0), 2X Denhardt's solution (50X = 1% Ficoll, 1% poly- vinylpyrrolidone, 1% bovine serum albumin), 100 jsg of salmon sperm DNA per ml, 50 mM sodium phosphate, pH 7.0, 1 mM EDTA, and 313 - 0.2% sodium dodecyl sulfate as previously described (10). SAA2a cDNA served as the probe and was radiolabeled with 32P by nick translation. Final washing was at 650C in 0.2X SSC, 0.2% sodium 270 - dodecyl sulfate. SAA protein purification and sequence determination. Blood was obtained from patient COL at the time of organ donation. Radioim- munodiffusion assays indicated that the level of SAA in the plasma was significantly elevated. Purification of SAA from plasma was accom- plished using the protocol developed by Dwulet et al. (11), which consisted of ultracentrifugation through potassium bromide density gradients, Sepharose CL6B chromatography, and reverse-phase high performance liquid chromatography (HPLC) using a Synchropak RP-P, C- 18, column. SAA-containing fractions were identified by im- munoreactivity with anti-AA protein antiserum. Digestion of purified SAA with trypsin, purification of tryptic peptides, and determination of peptide sequences and amino acid compositions were performed as previously described (1 1). Results with and Selection and sequence determination of three distinct SAA Figure 1. Digestion of pSAA 1, pSAA2a, and pSAA2fl PstI PstI NcoI. Recombinant DNA was ei- cDNA plus plasmid (1 gg) digested clones. Three distinct SAA cDNA clones, designated ther with PstI (F) or with PstI, followed by NcoI (P + N). After di- pSAA 1, pSAA2a, and pSAA2fl, were isolated from the cDNA gestion, the DNA was subjected to electrophoresis through a 5% library constructed using poly A' RNA extracted from a single polyacrylamide gel in Tris-borate-EDTA buffer at 200 V. DNA was liver. The cloning and sequence determination of pSAA2a stained with ethidium bromide and visualized under ultraviolet light. (previously referred to as pSAA82) has been described (2). The Numbers at the left are fragment sizes in base pairs. The band at cDNA inserts of the three clones were readily distinguished 4362 base pairs represents pBR322. from each other by the particular cleavage pattern which re- sulted from digestion with PstI and NcoI (Fig. 1). SAA 1 cDNA was cleaved internally by PstI as evidenced by its excision from acid differences occur in the first or second positions of codons pBR322 as two fragments; the larger of the two fragments was 52, 57, 60, 68, 84, and 90. Single-base substitutions also are in turn cut by NcoI. SAA2a cDNA, excised as an intact frag- present in codons 54 and 78, but because the heterogeneity is ment of - 575 base pairs, was not cut internally by PstI; how- in the third position, both codons specify the same amino acid. ever, it was cleaved by NcoI. SAA2$ cDNA was not cut by The third position cytosine of codon 54 in SAA1 cDNA is either enzyme. noteworthy, however, since it is within the recognition se- The nucleotide sequences determined for SAA1, SAA2a, quence of PstI. Additional heterogeneity is seen in codon 69, and SAA2,B cDNAs confirm that they encode SAA and show where all three bases of SAA1 cDNA differ from those of that all three extend from a 5'-untranslated region through a SAA2a and SAA2$ cDNAs.