Comparison of the nucleic acid sequence of anglerfish and mammalian insulin mRNA's from cloned cDNA's.

Anglerfish (Lophius americanus) insulin complementary DNA was cloned in bacterial plasmids, and its sequence was determined. Fish insulin messenger RNA is larger (1.5 times) than the messenger RNA encoding mammalian (rat and human) insulin, in part because of a larger C peptide (an additional six amino acids or 18 nucleotides in length) but mainly because of increases in the 5' and 3' untranslated regions. Comparison of the fish, rat, and human insulin messenger RNA (from the complementary DNA) reveals that, in addition to the regions coding for the A and B peptides, sequence conservation is limited to a segment within the 5' untranslated region which may be involved in ribosomal binding, two small segments of the signal peptide, and two stretches of sequence in the 3' untranslated region.

The 3-D structure of HIV-1 proteinase and the design of antiviral agents for the treatment of AIDS.

A proteinase is essential for replication of HIV. Cloning and chemical synthesis have provided a sufficient supply of HIV-1 proteinase for the determination of its three-dimensional structure. Analogies between the structures of HIV-1 proteinase and the mammalian enzyme renin, which is involved in the control of blood pressure, have given important clues concerning the design of specific inhibitors that have antiviral activity.

Persistent cytoplasmic location of a DNA polymerase beta in sea urchins during development.

A subcellular localization study of a low molecular weight DNA polymerase beta indicates that this enzyme, as well as a high molecular weight DNA polymerase alpha, is found in large quantities in the cytoplasm of Strongylocentrotus purpuratus eggs. The two enzyme activities are distinguished by DEAE-sievorptive chromatography and by their differential activities with activated DNA and oligo(dT)10 . poly(dA)200 primer-templates. Using an enucleation procedure, it is concluded that an extremely low proportion if any, of both polymerases is present in the egg nucleus. At blastula stage, a period of rapid cell proliferation, similar studies of DNA polymerase subcellular localization using two different methods of nuclear isolation indicate that the DNA polymerase beta remains largely cytoplasmic while the alpha enzyme is found to be predominantly nuclear. Since the results for the alpha enzyme agree with previous reports (Loeb, L.A. (1969) J. Biol. Chem. 244, 1672) and since one method of nuclear isolation, using hypotonic solutions, enables us to recover both DNA polymerase alpha and beta activities in isolated mouse L-cell nuclei, the enzyme quantitation of isolated sea urchin nuclei is considered accurate. Thus, although there is a translocation of the polymerase alpha from a cytoplasmic to nuclear site during early embryonic development, such a massive relocalization of the polymerase beta does not occur.

Insulin delivery with plasmid DNA.

Success in controlling hyperglycemia in type I diabetics will require a restoration of basal insulin. To this end, three plasmid DNAs (pDNA) encoding preproinsulin were compared for constitutive expression and processing to insulin in nonendocrine cells in vitro. The pDNAs were designed to express rat proinsulin I (VR-3501), rat proinsulin I with the B10 aspartic acid point mutation (VR-3502), and a derivative of VR-3502 with a furin cleavage site added at the B-chain and C-peptide junction (VR-3503). Cells transfected with VR-3501 or VR-3502 were able to secrete only proinsulin, whereas transfection with VR-3503 yielded 30-70% mature insulin, which could be increased to >99% by cotransfection with a furin expression plasmid (VR-3505). The insulin produced was biologically active. The bilateral injection of 100 microg of VR-3502 plasmid into the tibialis anterior muscles of mice on two consecutive days yielded, on average, several hundred picograms of heterologous proinsulin per milliliter of serum. In BALB/c mice, serum proinsulin peaked 7-14 days postinjection and declined to preinjection levels by days 21-28. In athymic nude mice, serum proinsulin was sustained for at least 6 weeks. The therapeutic efficacy of delivering insulin via muscle injection of pDNA was evaluated in athymic nude mice made diabetic with the beta cell toxin streptozotocin (STZ). All animals given control DNA died within 1 week of receiving STZ while 40% of the mice coinjected with plasmids VR-3503 and VR-3505 lived through the duration of the 4-week experiment. Muscles of the surviving animals contained 17-100 ng of immune-reactive insulin (IRI), 86-94% of which was mature insulin. The results suggest that heterologous insulin made in muscle increased the survival rate. We propose that insulin plasmid expression in skeletal muscle may be a valid approach to basal insulin delivery. The feasibility of plasmid DNA-based delivery of basal insulin was investigated. An expression system consisting of pDNAs encoding a selectively mutated rat preproinsulin and mouse furin was developed and characterized in vitro and in vivo. When injected with preproinsulin pDNA, the mouse tibialis anterior muscle expressed and released proinsulin into serum at levels comparable to normal basal insulin in rodents. These heterologous proinsulin levels were sustained for several weeks in immune-compromised nondiabetic mice. Mouse muscle coinjected with a pDNA encoding the endopeptidase furin and a pDNA encoding a pre-proinsulin modified to contain two furin cleavage sites produced fully processed insulin. This muscle-made insulin appears to have contributed to the survival of mice treated with a highly diabetogenic dose of streptozotocin, a beta cell toxin. The results demonstrate that skeletal muscle is able to express and deliver therapeutic insulin from plasmid DNA.

Computer graphics modelling of human renin. Specificity, catalytic activity and intron-exon junctions.

A model has been constructed using computer graphics for human renin based on the sequence derived from that of the gene and the 3-dimensional structure defined at high resolution for other homologous aspartic proteinases. Human renin can adopt a 3-dimensional structure close to that of other aspartic proteinases, in which amino acids corresponding to intron-exon junctions in the gene are at surface regions in the 3-dimensional structure. As expected, the essential catalytic residues are retained and the nearby residue 304 is alanine as in the mouse sequence, supporting the idea that Asp 304 of other aspartic proteinases may contribute to the low pH of their optimal activity. There are interesting differences at subsite S3' which may contribute to the specificity of human renin. Certain residues at the surface of the enzyme adjacent to the active site cleft are unique to renins and may play a role in recognition and binding of angiotensinogen.

A low molecular weight DNA polymerase beta in the sea urchin Strongylocentrotus purpurantus. Partial purification, properties, and changes in development.

A low molecular weight DNA polymerase which sediments at 3.3 S on sucrose gradients has been purified from total cell homogenates of rapidly dividing embryos of the sea urchin Strongylocentrotus purpuratus. In the presence of 2 mM N-ethylmaleimide, it is the major polymerase activity in whole cell homogenates when assayed with an oligo(dT)10.poly(dA)200 template; a template which it uses about 200 times more efficiently than activated DNA. The requirement for N-ethylmaleimide exists only in crude cell fractions where it acts to inhibit a template digesting nuclease activity. The polymerase is highly stable if maintained in the presence of 20% glycerol, is completely dependent on added template, and shows no end addition activity. The physical and enzymatic properties of this enzyme clearly distinguish it from the DNA polymerase previously described by Loeb (Loeb, L. A. (1969) J. Biol. Chem. 244, 1672-1681) which sediments as a high moeluclar weight (5.6 to 6.6 S) enzyme and prefers the activated DNA template. In addition, these two DNA polymerase enzymes show distinctive chromatographic properties using DEAE-cellulose and phosphocellulose columns as well as their sensitivity to N-ethylmaleimide. The properties of the low molecular weight polymerase indicate close similarity to the beta-polymerase isolated from mammalian cells. These low molecular weight enzymes are both sensitive to phosphate salt and able to utilize the artificial ribohomopolymer template oligo(dT)10.poly(rA)200. A quantitative analysis of the low molecular weight DNA polymerase during early embryonic development indicates that the activity of this enzyme increases at least 2-fold immediately following fertilization and again during early blastula stage (hatching). Such quantitative changes in a beta enzyme activity are in contrast to findings with the alpha-polymerase which remains constant during early development.

Different secretory pathways of renin from mouse cells transfected with the human renin gene.

Mammalian cells in culture, transfected with human renin gene, can provide a useful tool for studying renin biosynthesis and secretion. We transfected fibroblast cells (mouse L929 and Chinese hamster ovary cells) and pituitary tumor cells (mouse AtT-20) with the human renin gene and a selectable plasmid (pSV2Neo). Transfected fibroblasts synthesize prorenin only. Prorenin is secreted by fibroblasts constitutively and the secretion is not influenced by 8-bromo-cAMP. On the other hand, transfected AtT-20 cells synthesized both prorenin and mature active renin. Transfected AtT-20 cells release prorenin by constitutive secretion but mature renin is secreted by a regulated mechanism since the secretion of the former is not influenced by 8-bromo-cAMP but the release of the latter is significantly stimulated. Our studies demonstrate that human renin may be secreted by at least two cellular pathways: prorenin by a constitutive pathway and mature renin by a regulated pathway. These transfected cells may provide useful models for studies of human renin synthesis, processing, and secretion.

Human renin gene: structure and sequence analysis.

The complete protein precursor of human kidney renin has been determined from the sequence of cloned genomic DNA. The gene spans 12 kilobases of DNA and is interrupted by eight intervening sequences. The nine regions (exons) encoding the protein were mapped with a mouse renin cDNA probe, synthetic oligonucleotide probes, and by hybridization of genomic restriction fragments to a 1600-nucleotide human kidney mRNA. The predicted 403-amino acid preprorenin consists of mature renin and a 66-residue amino-terminal prepropeptide. The DNA sequence 5' to the first exon indicates the location of a transcriptional promoter (T-A-T-A-A-A) for a mRNA encoding preprorenin. An additional transcriptional promoter site is located within the first intron, which, if used, would express a shortened nonsecreted prorenin. The structure of the human renin gene is similar to that of human pepsinogen, a closely related aspartyl protease enzyme. This observation suggests that renin and pepsinogen have a common evolutionary origin.

Long-term expression of erythropoietin in the systemic circulation of mice after intramuscular injection of a plasmid DNA vector.

Erythropoietin (Epo)-responsive anemia is a common and debilitating complication of chronic renal failure and human immunodeficiency virus infection. Current therapy for this condition involves repeated intravenous or subcutaneous injections of recombinant Epo. In this report, we describe the development of a novel muscle-based gene transfer approach that produces long-term expression of physiologically significant levels of Epo in the systemic circulation of mice. We have constructed a plasmid expression vector, pVRmEpo, that contains the murine Epo cDNA under the transcriptional control of the cytomegalovirus immediate early (CMV-IE) promoter, the CMV-IE 5' untranslated region, and intron A. A single intramuscular (i.m.) injection of as little as 10 micrograms of this plasmid into immunocompetent adult mice produced physiologically significant elevations in serum Epo levels and increased hematocrits from preinjection levels of 48 +/- 0.4% to levels of 64 +/- 3.3% 45 days after injection. Hematocrits in these animals remained elevated at greater than 60% for at least 90 days after a single i.m. injection of 10 micrograms of pVRmEpo. We observed a dose-response relationship between the amount of plasmid DNA injected and subsequent elevations in hematocrits. Mice injected once with 300 micrograms of pVRmEpo displayed 5-fold increased serum Epo levels and elevated hematocrits of 79 +/- 3.3% at 45 days after injection. The i.m. injected plasmid DNA remained localized to the site of injection as assayed by the PCR. We conclude that i.m. injection of plasmid DNA represents a viable nonviral gene transfer method for the treatment of acquired and inherited serum protein deficiencies.

Crystallizable HIV-1 protease derived from expression of the viral pol gene in Escherichia coli.

A plasmid vector was used to express the HIV-1 pol open reading frame under the regulation of the bacterial trp promoter in Escherichia coli. This expression system has been used as a source of recombinant viral protease. The self-processed active enzyme was recovered from a soluble fraction of a bacterial cell lysate and purified by a procedure involving four steps of chromatography. The protocol yielded 0.3 mg of protease for each liter of bacterial culture. The protease formed tetragonal bipyramidal crystals which have been used in high-resolution X-ray diffraction studies.