Requirements for the different cysteines in the chemotactic and desensitizing activity of human thioredoxin.

Thioredoxin (Trx) is a protein disulfide oxidoreductase that can be secreted and act as a chemoattractant for leukocytes. Like chemokines, it causes desensitization of monocytes against its chemotactic activity and that of monocyte chemoattractant protein-1 (MCP-1). To investigate the role of the redox properties of Trx, and particularly of some of its five cysteines, in its chemotactic and desensitizing action, we tested different mutants, including Trx80, a truncated form, and various mutants lacking specific cysteines: Trx C62S/C73S and the redox-inactive mutant Trx C32S/C35S. Of the mutants, only Trx80 maintained the chemotactic activity of wild-type Trx toward both monocytes and polymorphonuclear neutrophils, all of them desensitized monocytes against wild-type Trx or MCP-1, but not chemotactic peptide formyl-methionyl-leucil peptide. These data indicate that different redox-active cysteines are important for Trx chemotactic action, whereas its desensitizing action does not have these requirements, suggesting a redox-independent mechanism.