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Author(s): Matthew Stremlau [1]; Christopher M. Owens [1]; Michel J. Perron [1]; Michael Kiessling [1]; Patrick Autissier [2]; Joseph Sodroski (corresponding author) [1, 3] Host cell barriers to the early [...]

Research has been conducted on the plasminogen activator inhibitor-1. The results of the fluorescence and rapid kinetic studies of the inhibition by plasminogen activator inhibitor-1 of its physiological target proteinases are presented.

The 43 kDa protein involved in the regulation of fibrinolysis is plasminogen activator inhibitor-1 (PAI-1). PAI-1 is the principal inhibitor of tissue-type plasminogen activator (t-PA), trapping the proteinase as an acyl-enzyme covalent complex (~ 105 kDa).

Interactions within the conserved sorption breach region play a direct role in the critical step of the serpin reaction in which the acyl-enzyme intermediate must first be exposed to hydrolyzing water and aqueous deacylation. The initial loop insertion is restricted with a raise in the kinetic barrier on substitution of the tryptophan residue.

Reovirus replication and assembly are thought to occur within cytoplasmic inclusion bodies, which we call viral factories. A strain-dependent difference in the morphology of these structures reflects more effective microtubule association by the mu2 core proteins of some viral strains, which form filamentous factories, than by those of others, which form globular factories. For this report, we identified and characterized another strain-dependent attribute of the factories, namely, the extent to which they colocalized with conjugated ubiquitin (cUb). Among 16 laboratory strains and field isolates, the extent of factory costaining for cUb paralleled factory morphology, with globular strains exhibiting higher levels by far. In reassortant viruses, factory costaining for cUb mapped primarily to the mu2-encoding M1 genome segment, although contributions by the lambda3- and lambda2-encoding L1 and L2 genome segments were also evident. Immunoprecipitations revealed that cells infected with globular strains contained higher levels of ubiquitinated mu2 (Ub-mu2). In M1-transfected cells, cUb commonly colocalized with aggregates formed by mu2 from globular strains but not with microtubules coated by mu2 from filamentous strains, and immunoprecipitations revealed that mu2 from globular strains displayed higher levels of Ub-mu2. Allelic changes at mu2 residue 208 determined these differences. Nocodazole treatment of cells infected with filamentous strains resulted in globular factories that still showed low levels of costaining for cUb, indicating that higher levels of costaining were not a direct result of decreased microtubule association. The factories of globular strains, or their mu2 proteins expressed in transfected cells, were furthermore shown to gain microtubule association and to lose colocalization with cUb when cells were grown at reduced temperature. From the sum of these findings, we propose that mu2 from globular strains is more prone to temperature-dependent misfolding and as a result displays increased aggregation, increased levels of Ub-mu2, and decreased association with microtubules. Because so few of the viral strains formed factories that were regularly associated with ubiquitinated proteins, we conclude that reovirus factories are generally distinct from cellular aggresomes.