@article {2205, title = {Methylated PP2A stabilizes Gcn4 to enable a methionine-induced anabolic program.}, journal = {J Biol Chem}, volume = {295}, year = {2020}, month = {2020 Dec 25}, pages = {18390-18405}, abstract = {

Methionine, through S-adenosylmethionine, activates a multifaceted growth program in which ribosome biogenesis, carbon metabolism, and amino acid and nucleotide biosynthesis are induced. This growth program requires the activity of the Gcn4 transcription factor (called ATF4 in mammals), which facilitates the supply of metabolic precursors that are essential for anabolism. However, how Gcn4 itself is regulated in the presence of methionine is unknown. Here, we discover that Gcn4 protein levels are increased by methionine, despite conditions of high cell growth and translation (in which the roles of Gcn4 are not well-studied). We demonstrate that this mechanism of Gcn4 induction is independent of transcription, as well as the conventional Gcn2/eIF2α-mediated increased translation of Gcn4. Instead, when methionine is abundant, Gcn4 phosphorylation is decreased, which reduces its ubiquitination and therefore degradation. Gcn4 is dephosphorylated by the protein phosphatase 2A (PP2A); our data show that when methionine is abundant, the conserved methyltransferase Ppm1 methylates and alters the activity of the catalytic subunit of PP2A, shifting the balance of Gcn4 toward a dephosphorylated, stable state. The absence of Ppm1 or the loss of the PP2A methylation destabilizes Gcn4 even when methionine is abundant, leading to collapse of the Gcn4-dependent anabolic program. These findings reveal a novel, methionine-dependent signaling and regulatory axis. Here methionine directs the conserved methyltransferase Ppm1 via its target phosphatase PP2A to selectively stabilize Gcn4. Through this, cells conditionally modify a major phosphatase to stabilize a metabolic master regulator and drive anabolism.

}, issn = {1083-351X}, doi = {10.1074/jbc.RA120.014248}, author = {Walvekar, Adhish S and Kadamur, Ganesh and Sreedharan, Sreesa and Gupta, Ritu and Srinivasan, Rajalakshmi and Laxman, Sunil} } @article {2144, title = {Methylated PP2A stabilizes Gcn4 to enable a methionine-induced anabolic program.}, journal = {J Biol Chem}, year = {2020}, month = {2020 Oct 29}, abstract = {

Methionine, through S-adenosylmethionine, activates a multifaceted growth program in which ribosome biogenesis, carbon metabolism, amino acid and nucleotide biosynthesis are induced. This growth program requires the activity of the Gcn4 transcription factor (called ATF4 in mammals), which facilitates the supply of metabolic precursors that are essential for anabolism. However, how Gcn4 itself is regulated in the presence of methionine is unknown. Here, we discover that Gcn4 protein levels are increased by methionine, despite conditions of high cell growth and translation (where the roles of Gcn4 are not well studied). We demonstrate that this mechanism of Gcn4 induction is independent of transcription, as well as the conventional Gcn2/eIF2α-mediated increased translation of Gcn4. Instead, when methionine is abundant, Gcn4 phosphorylation is decreased, which reduces its ubiquitination and therefore degradation. Gcn4 is dephosphorylated by the protein phosphatase PP2A; our data show that when methionine is abundant, the conserved methyltransferase Ppm1 methylates and alters the activity of the catalytic subunit of PP2A, shifting the balance of Gcn4 towards a dephosphorylated, stable state. The absence of Ppm1 or the loss of the PP2A methylation destabilizes Gcn4 even when methionine is abundant, leading to collapse of the Gcn4-dependent anabolic program. These findings reveal a novel, methionine-dependent signaling and regulatory axis. Here methionine directs a conserved methyltransferase Ppm1, via its target phosphatase PP2A, to selectively stabilize Gcn4. Through this, cells conditionally modify a major phosphatase to stabilize a metabolic master-regulator and drive anabolism.

}, issn = {1083-351X}, doi = {10.1074/jbc.RA120.014248}, author = {Walvekar, Adhish S and Kadamur, Ganesh and Sreedharan, Sreesa and Gupta, Ritu and Srinivasan, Rajalakshmi and Laxman, Sunil} } @article {1988, title = {Methionine at the Heart of Anabolism and Signaling: Perspectives From Budding Yeast.}, journal = {Front Microbiol}, volume = {10}, year = {2019}, month = {2019}, pages = {2624}, abstract = {

Studies using a fungal model, , have been instrumental in advancing our understanding of sulfur metabolism in eukaryotes. Sulfur metabolites, particularly methionine and its derivatives, induce anabolic programs in yeast, and drive various processes integral to metabolism (one-carbon metabolism, nucleotide synthesis, and redox balance). Thereby, methionine also connects these processes with autophagy and epigenetic regulation. The direct involvement of methionine-derived metabolites in diverse chemistries such as transsulfuration and methylation reactions comes from the elegant positioning and safe handling of sulfur through these molecules. In this mini-review, we highlight studies from yeast that reveal how this amino acid holds a unique position in both metabolism and cell signaling, and illustrate cell fate decisions that methionine governs. We further discuss the interconnections between sulfur and NADPH metabolism, and highlight critical nodes around methionine metabolism that are promising for antifungal drug development.

}, issn = {1664-302X}, doi = {10.3389/fmicb.2019.02624}, author = {Walvekar, Adhish S and Laxman, Sunil} } @article {1596, title = {Methionine coordinates a hierarchically organized anabolic program enabling proliferation.}, journal = {Mol Biol Cell}, year = {2018}, month = {2018 Oct 24}, pages = {mbcE18080515}, abstract = {

Methionine availability during overall amino acid limitation metabolically reprograms cells to support proliferation, the underlying basis for which remains unclear. Here, we construct the organization of this methionine mediated anabolic program, using yeast. Combining comparative transcriptome analysis, biochemical and metabolic flux based approaches, we discover that methionine rewires overall metabolic outputs by increasing the activity of a key regulatory node. This comprises of: the pentose phosphate pathway (PPP) coupled with reductive biosynthesis, the glutamate dehydrogenase (GDH) dependent synthesis of glutamate/glutamine, and pyridoxal-5-phosphate (PLP) dependent transamination capacity. This PPP-GDH-PLP node provides the required cofactors and/or substrates for subsequent rate-limiting reactions in the synthesis of amino acids, and therefore nucleotides. These rate-limiting steps in amino acid biosynthesis are also induced in a methionine-dependent manner. This thereby results in a biochemical cascade establishing a hierarchically organized anabolic program. For this methionine mediated anabolic program to be sustained, cells co-opt a "starvation stress response" regulator, Gcn4p. Collectively, our data suggest a hierarchical metabolic framework explaining how methionine mediates an anabolic switch.

}, issn = {1939-4586}, doi = {10.1091/mbc.E18-08-0515}, author = {Walvekar, Adhish S and Srinivasan, Rajalakshmi and Gupta, Ritu and Laxman, Sunil} }