Effects of Intracellular Redox Status on Cellular Regulation and Viral Infection

Cell activation by changes of cell redox state is in many instances related to oxidative modifications of the transcription factors. In particular, we investigated the effects of redox state on the DNA binding capacity of the zinc-finger transcription factor Spl. H2O2, diamide or dialysis under nonreducing conditions completely abolished the ability of Sp1 to bind to its consensus DNA sequence. This inhibition was quantitatively reversed by reduced glutathione (GSH), dithiotreitol (DTT) or β-mercaptoethanol (β-ME), but not by ascorbate. Using the thiol alkylating agents N-ethylmaleimide (NEM) and iodacetamide we showed that Spl contains SH groups that are necessary for DNA binding. We suggest that the NEM-reactive SH groups confer redox-susceptibility to the Spl molecule and are most likely located within the zinc finger domain. On the other hand, virus infection may be adversely affected by thiol reagents, since formation and stability of S-S bridges is often essential to proteins involved in virus binding and infectivity. In particular, we have investigated the effects of exogenous glutathione on Sendai virus replication, a virus-host cell system in which virus replication is associated with a marked decrease in total glutathione content. Addition of reduced glutathione inhibited the production of Sendai virus in AGMK cells. The effect was dose-dependent, associated with an increase of the intracellular glutathione level, while it did not affect cellular metabolism. The antiviral effect of glutathione was accompanied by decrease and inactivation of the hemagglutinin-neuraminidase (HN) Sendai virus glycoprotein, which normally assembles into oligomers via formation of disulfide bonds. Reductive cleavage of the S-S bridges by GSH may, at least in part, be responsible for the lower amount of HN detected in virus produced by AGMK cells.