Ksp1-dependent phosphorylation of eIF4G modulates post-transcriptional regulation of specific mRNAs under glucose deprivation conditions

Abstract

Post-transcriptional regulation is an important mechanism for modulating gene expression and is performed by numerous mRNA-binding proteins. To understand the mechanisms underlying post-transcriptional regulation, we investigated the phosphorylation status of 32 mRNA-binding proteins under glucose deprivation conditions in Saccharomyces cerevisiae. We identified 17 glucose-sensitive phosphoproteins and signal pathways implicated in their phosphorylation. Notably, phosphorylation of the eukaryotic translation initiation factor 4G (eIF4G) was regulated by both the Snf1/AMPK pathway and the target of rapamycin complex 1 (TORC1) pathway. The serine/threonine protein kinase Ksp1 has previously been suggested to be a downstream effector of TORC1, but its detailed function has rarely been discussed. We identified that Snf1/AMPK and TORC1 signalings converge on Ksp1, which phosphorylates eIF4G under glucose deprivation conditions. Ksp1-dependent phosphorylation of eIF4G regulates the degradation of specific mRNAs (e.g. glycolytic mRNAs and ribosomal protein mRNAs) under glucose deprivation conditions likely through the recruitment of Dhh1. Taken together, our results suggest that Ksp1 functions as a novel modulator of post-transcriptional regulation in yeast.

Translational regulation in response to stress in Saccharomyces cerevisiae

“…Slf1 appears to play a substantial role in translational response under these conditions: ~40% of proteins found to be upregulated following hydrogen peroxide treatment are encoded by Slf1 targets (Kershaw, Costello, Castelli, et al, ). Conversely, both yeast LARPs move from the cytoplasm to P bodies (Mitchell et al, ) and become hyperphosphorylated, along with a number of other RBPs, during glucose starvation (Chang & Huh, ).…”

Control of Translation at the Initiation Phase During Glucose Starvation in Yeast

“…Phosphorylation of eIF4G may affect cap attachment by the reduced formation of eIF4F complex, and thus, regulate translation in yeast during glucose starvation response, as was determined by assessing phosphorylation status of multiple mRNA-binding proteins [58]. Thirty-two RBPs in yeast strains of BY4741 background were individually C-terminally tagged with the Tandem Affinity Purification (TAP) tag and the strains were subjected to glucose deprivation.…”

“…The phosphorylation status of the tagged proteins was analyzed by a mobility shift assay comparing results for standard and Phos-tag SDS-PAGE, which slows down the mobility of phosphorylated variants. Seventeen out of thirty-two mRNA-binding proteins showed changes in phosphorylation status (electrophoretic mobility) under glucose deprivation conditions; thirteen were hyperphosphorylated and four hypophosphorylated [58]. Three major signaling pathways regulated during glucose starvation, the PKA (Protein Kinase A), Snf1p/AMPK (Sucrose Non-Fermenting / Adenosine Monophosphate-activated Protein Kinase) and TORC1, were studied for possible involvement.…”

“…Bcy1Δ mutants showed a lack of phosphorylation change under glucose starvation stress for Pat1p, Puf3p and Puf4p (otherwise hypophosphorylated in stress) and Pab1p and Eap1p (otherwise hyperphosphorylated in stress). In snf1Δ mutants, starvation-induced hyperphosphorylation of Bre5p, Eap1p, Nab6p, Pab1p, Pub1p, Sbp1p, Slf1p, eIF4G1/Tif4631p and eIF4G2/Tif4632p, and hypophosphorylation of Ksp1p, were abolished [58]. Phosphorylation of eIF4G1 (Tif4631p) and eIF4G2 (Tif4632p) decreased, whereas phosphorylation of Ksp1p increased under cycloheximide treatment, suggesting regulation by TORC1, which is known to be hyperactivated by the drug [237].…”

The Eukaryotic Translation Initiation Factor 4F Complex Restricts Rotavirus Infection via Regulating the Expression of IRF1 and IRF7

“…The eIF4E recognizes and binds to the 7-methylguanosine (m7G) cap located at the 5′-UTRs of mRNA to mediate the mRNA recruitment on ribosomes, thus initiating the translation together with other initiation factors [17]. As a scaffold protein, eIF4G plays a central role in translation initiation by assembling eIF4E and eIF4A to further form the eIF4F complex [18]. The programmed cell death protein 4 (PDCD4) is a translation suppressor of mRNAs by interacting with eIF4A to suppress its helicase activity [19].…”