Mapping the phenotypic repertoire of the cytoplasmic 2-Cys peroxiredoxin - thioredoxin system. 1. Understanding commonalities and differences among cell types.

Abstract

The system (PTTRS) formed by typical 2-Cys peroxiredoxins (Prx), thioredoxin (Trx), Trx reductase (TrxR), and sulfiredoxin (Srx) is central in antioxidant protection and redox signaling in the cytoplasm of eukaryotic cells. Understanding how the PTTRS integrates these functions requires tracing phenotypes to molecular properties, which is non-trivial. Here we analyze this problem based on a model that captures the PTTRS conserved features. We have mapped the conditions that generate each distinct response to H2O2 supply rates ({nu}sup), and estimated the parameters for thirteen human cell types and for Saccharomyces cerevisiae. The resulting composition-to-phenotype map yielded the following experimentally testable predictions. The PTTRS permits many distinct responses including ultra-sensitivity and hysteresis. However, nearly all tumor cell lines showed a similar response characterized by limited Trx-S- depletion and a substantial but self-limited gradual accumulation of hyperoxidized Prx at high{nu} sup. This similarity ensues from strong correlations between the TrxR, Srx and Prx activities over cell lines, which contribute to maintain the Prx-SS reduction capacity in slight excess over the maximal steady state Prx-SS production. In turn, in erythrocytes, hepatocytes and HepG2 cells high{nu} sup depletes Trx-S- and oxidizes Prx mainly to Prx-SS. In all nucleated human cells the Prx-SS reduction capacity defined a threshold separating two different regimes. At sub-threshold{nu} sup cytoplasmic H2O2 is determined by Prx, nM-range and spatially localized, whereas at supra-threshold{nu} sup it is determined by much less active alternative sinks and M-range throughout the cytoplasm. The yeast shows a distinct response where the Prx Tsa1 accumulates in sulfenate form at high{nu} sup. This is mainly due to an exceptional stability of Tsa1s sulfenate.\n\nThe implications of these findings for thiol redox regulation and cell physiology are discussed. All estimates were thoroughly documented and provided, together with analytical approximations for system properties, as a resource for quantitative redox biology.\n\nAbbreviationsASK1, apoptosis signal-regulating kinase 1; Cat, catalase; GSH, glutathione; GPx1, glutathione peroxidase 1; Grx, glutaredoxin; KEAP1, Kelch-like ECH-associated protein 1; NRF2, nuclear factor erythroid 2-related factor 2; Prx, typical 2-Cys peroxiredoxin; PTTRS, peroxiredoxin / thioredoxin / thioredoxin reductase system; Srx, sulfiredoxin; Trx, thioredoxin; TrxR, thioredoxin reductase.