Angeline Douvas

Negative regulation of Scl-70/topoisomerase I by zinc and an endogenous macromolecule

Scl-70/topoisomerase I (topo I), a target of autoantibodies in the human disorder scleroderma, may be linked to collagen overproduction. We report that physiologic concentrations of zinc (greater than or equal to 80 microM) potently inactivate human and rat topo I in the presence of a 125-fold molar excess of MgCl2. We also describe a highly acidic nuclear molecule which competitively inhibits topo I. 89kD complexes of topo I and inhibitor can be separated from active 70kD monomers by glycerol density gradient centrifugation. The complexes have a 20-fold higher Km for DNA than monomers. Dissociation by dilution results in a 50-fold increase in rat liver and a 47-fold increase in human fibroblast specific activity. Zinc inhibition is non-competitive, and independent of the endogenous inhibitor. Our studies suggest that the majority of topo I is normally maintained in an inactive state by physiologic inhibitors, and loss of negative regulation may have pathogenetic consequences.

Caprine arthritis-encephalitis virus-infected goats can generate human immunodeficiency virus-gp120 cross-reactive antibodies

Lentiviruses display surprisingly disparate clinical manifestations in their specific hosts, share complex genetic structures, and exhibit extensive diversity, particularly in their envelope genes. The envelope protein, gp135, of caprine arthritis-encephalitis virus (CAEV) has minimal primary sequence homology to gp120, the envelope protein of human immunodeficiency virus (HIV). Nevertheless, they bear certain similarities in that they both possess five variable regions, both are heavily glycosylated, and both share short sequence motifs. We establish a further relationship and demonstrate that some goats, infected with CAEV, possess gp135-specific antibodies which cross-react with gp120 from several HIV strains, provided the protein is expressed in insect cells. We show that, although the cross-reactivity of these immunoglobulins depends on the level of glycosylation, nevertheless, some antibodies recognize the protein epitopes on gp120, at least some of which are linear in character. Further characterization of this unexpected cross-reaction will define its potential therapeutic utility.