Interactions of GMP with Human Glrx3 and with Saccharomyces cerevisiae Grx3 and Grx4 Converge in the Regulation of the Gcn2 Pathway

Abstract

The human monothiol glutaredoxin Glrx3 (PICOT) is ubiquitously distributed in cytoplasm and nuclei in mammalian cells. Its overexpression has been associated to the development of several types of tumors whereas its deficiency might cause retardation in embryogenesis. Its exact biological role has not been well resolved, although a function as chaperone distributing iron/sulphur clusters is currently accepted. Yeast humanization and the use of a mouse library has allowed us to find a new partner for PICOT: the human GMP synthase (hGMPs), both proteins carry out collaborative functions regarding down-regulation of the S. cerevisiae Gcn2 pathway, in conditions of nutritional stress. Glrx3/hGMPs interact through conserved residues which bridge iron/sulphur clusters and glutathione. This mechanism is also conserved in budding yeast whose proteins Grx3/Grx4 along with GUA1 (S. cerevisiae GMPs) also downregulate ISR pathway. Heterologous expression of Glrx3/hGMPs efficiently complements Grx3/Grx4. Moreover, heterologous expression of Glrx3 efficiently complements the novel participation in chronological life span that has been characterized for both Grx3 and Grx4. Our results underscore that the family Glrx3/Grx3/Grx4 present an evolutive and functional conservation in signaling events, partly related to GMPs function, that contribute to cell life extension. IMPORTANCE Saccharomyces cerevisiae is an optimal eukaryotic microbial model to study biological processes in superior organisms, despite the divergence in evolution. The molecular function of yeast glutaredoxins Grx3 and Grx4 has an enormous interest since both proteins are required to maintain a correct iron homeostasis and an efficient response to oxidative stress. The human orthologous Glrx3 (PICOT) is involved in a number of human diseases including cancer. Our research expanded its utility to human cells. Yeast has allowed the characterization of GMP synthase as a new interacting partner for Glrx3 and also for yeast Grx3 and Grx4, the complex monothiol glutaredoxins/GMPs participates in the down regulation of the activity of Gcn2 stress pathway. This mechanism is conserved in yeast and humans. Here we also show that this family of glutaredoxins, Grx3/Grx4/Glrx3 also shares a function related to life extension.