Adenosine Triphosphate (ATP) Is a Candidate Signaling Molecule in the Mitochondria-to-Nucleus Retrograde Response Pathway

Feng Zhang,Janet Thornton,Tammy Pracheil,Zhengchang Liu

doi:10.3390/genes4010086

Abstract

Intracellular communication from the mitochondria to the nucleus is achieved via the retrograde response. In budding yeast, the retrograde response, also known as the RTG pathway, is regulated positively by Rtg1, Rtg2, Rtg3 and Grr1 and negatively by Mks1, Lst8 and two 14-3-3 proteins, Bmh1/2. Activation of retrograde signaling leads to activation of Rtg1/3, two basic helix-loop-helix leucine zipper transcription factors. Rtg1/3 activation requires Rtg2, a cytoplasmic protein with an N-terminal adenosine triphosphate (ATP) binding domain belonging to the actin/Hsp70/sugar kinase superfamily. The critical regulatory step of the retrograde response is the interaction between Rtg2 and Mks1. Rtg2 binds to and inactivates Mks1, allowing for activation of Rtg1/3 and the RTG pathway. When the pathway is inactive, Mks1 has dissociated from Rtg2 and bound to Bmh1/2, preventing activation of Rtg1/3. What signals association or disassociation of Mks1 and Rtg2 is unknown. Here, we show that ATP at physiological concentrations dissociates Mks1 from Rtg2 in a highly cooperative fashion. We report that ATP-mediated dissociation of Mks1 from Rtg2 is conserved in two other fungal species, K. lactis and K. waltii. Activation of Rtg1/3 upregulates expression of genes encoding enzymes catalyzing the first three reactions of the Krebs cycle, which is coupled to ATP synthesis through oxidative phosphorylation. Therefore, we propose that the retrograde response is an ATP homeostasis pathway coupling ATP production with ATP-mediated repression of the retrograde response by releasing Mks1 from Rtg2.

Highlights

MLWRFKRQGULD SURGXFH WKH PDMRULW\ RI FHOOV¶ DGHQRVLQH WULSKRVSKDWH $73 WR EH XVHG DV 3energy currency in eukaryotic cells
We find that adenosine triphosphate (ATP) has an all-or-none effect on releasing Mks1 from Rtg2 in three different fungal species
We report that Rtg2 and Mks1 homologs from two other fungal species, K. lactis and K. waltii, are able to complement rtg2' and mks1' mutations in S. cerevisiae, respectively

Summary

Introduction

MLWRFKRQGULD SURGXFH WKH PDMRULW\ RI FHOOV¶ DGHQRVLQH WULSKRVSKDWH $73 WR EH XVHG DV 3energy currency in eukaryotic cells. Due to the versatility of mitochondrial functions, it's critically important for cells to monitor the functional state of mitochondria and adjust nuclear gene expression to achieve functional homeostasis of mitochondrial activity This is achieved via the coordination of mitochondria-to-nucleus signaling pathways, known as the retrograde response [5,6]. The integrity of the ATP binding domain of Rtg is important for its interaction with Mks1 [28]. Transcriptional regulation of the Krebs cycle genes, CIT1, ACO1, IDH1 and IDH2, switches from the Hap complex to the Rtg1/3 complex in cells with respiratory deficiencies [18]. With the exception of Grr, all of these factors are negative regulators of the RTG pathway Among these proteins, Mks is a key regulatory component [6]. We further show that ATP-dependent regulation of this interaction is evolutionarily conserved

Experimental Section

Yeast Transformation and ȕ-Galactosidase Activity Assays

Results and Discussion

Conclusions