Opi1-mediated transcriptional modulation orchestrates genotoxic stress response in budding yeast

Abstract

Inositol is a six-carbon sugar that functions as a precursor for signaling molecules such as phosphoinositides and inositol polyphosphates, which are involved in the regulation of important biological processes such as energy metabolism, environmental stress response, phosphate signaling, among others. Given its role in a myriad of signaling pathways, regulation of inositol synthesis is essential for cellular homeostasis. In budding yeast, transcription of genes involved in inositol metabolism is regulated by the transcriptional repressor Opi1, which repress transcription of genes containing cis-acting inositol-sensitive upstream activation sequences (UASINO). Upon genotoxic stress, cells activate the DNA Damage Response (DDR) to coordinate DNA repair and cell cycle progression. It has been proposed that inositol containing molecules might act as modulators of the DDR, but evidences are still scarce. Herein, we report thatopi1cells fail to downregulate the inositol phosphate pathway leading to sensitivity to genotoxins and replication defects. Moreover, cells lacking Opi1 show decreased gamma-H2A levels which might indicate that Opi1 contributes to the activation of the DDR kinases Mec1/Tel1 (ATR/ATM in mammals). Importantly, we show that deletion of the inositol pyrophosphate kinase Kcs1 (IP6K1/2/3 in mammals), which leads to inhibition of inositol pyrophosphate synthesis, rescues the MMS sensitivity and replication defects ofopi1cells. Further, overexpression of Kcs1 recapitulates the MMS sensitivity of cells lacking Opi1. Therefore, we propose that cells must downregulate inositol pyrophosphate synthesis during replication stress in order to trigger an effective DNA Damage Response.

Kcs1 and Vip1: The Key Enzymes behind Inositol Pyrophosphate Signaling in Saccharomyces cerevisiae

“…The study's line of reasoning was validated by a genetic rescue experiment, wherein the deletion of KCS1 in an opi1∆ knockout strain successfully mitigated the MMS sensitivity that typically manifests in the absence of Opi1. This outcome implies a contrasting function for Opi1 and PP-IPs in the modulation of Ino2-Ino4 action [47].…”

“…The focal point of this argument is Opi1, studied for its potential to mediate genotoxic stress. A recent study [47] revealed that in opi1∆, the expression of INO1, involved in the synthesis of inositol phospholipids and inositol polyphosphates, exhibited a significant increase upon exposure to the genotoxic agent methyl methane sulfonate (MMS). This induction of INO1 expression is attributed to the activation mediated by Ino2-Ino4 [48], transcriptional activators whose levels surge in the absence of Opi1.…”