In response to environmental cues, cells coordinate a balance between anabolic and catabolic pathways. In eukaryotes, growth factors promote anabolic processes and stimulate cell growth, proliferation, and survival through activation of the phosphoinositide 3-kinase (PI3K)-Akt pathway. Akt-mediated phosphorylation of glycogen synthase kinase-3β (GSK-3β) inhibits its enzymatic activity, thereby stimulating glycogen synthesis. We show that GSK-3β itself inhibits Akt by controlling the mammalian target of rapamycin complex 2 (mTORC2), a key activating kinase for Akt. We found that during cellular stress, GSK-3β phosphorylated the mTORC2 component rictor at serine-1235, a modification that interfered with the binding of Akt to mTORC2. The inhibitory effect of GSK-3β on mTORC2-Akt signaling and cell proliferation was eliminated by blocking phosphorylation of rictor at serine-1235. Thus, in response to cellular stress, GSK-3β restrains mTORC2-Akt signaling by specifically phosphorylating rictor, thereby balancing the activities of GSK-3β and Akt, two opposing players in glucose metabolism.

Growth factor signaling coupled to activation of the phosphatidylinositol-3-OH kinase (PI3K)/Akt pathway plays a crucial role in the regulation of cell proliferation and survival. The key regulatory kinase of Akt has been identified as mammalian target of rapamycin complex 2 (mTORC2), which functions as the PI3K-dependent Ser-473 kinase of Akt. This kinase complex is assembled by mTOR and its essential components rictor, Sin1 and mLST8. The recent genetic screening study in Caenorhabditis elegans has linked a specific point mutation of rictor to an elevated storage of fatty acids that resembles the rictor deficiency phenotype. In our study, we show that in mammalian cells the analogous single rictor point mutation (G934E) prevents the binding of rictor to Sin1 and the assembly of mTORC2, but this mutation does not interfere with the binding of the rictor-interacting protein Protor. A substitution of the rictor Gly-934 residue to a charged amino acid prevents formation of the rictor/Sin1 heterodimer. The cells expressing the rictor G934E mutant remain deficient in the mTORC2 signaling, as detected by the reduced phosphorylation of Akt on Ser-473 and a low cell proliferation rate. Thus, although a full length of rictor is required to interact with its binding partner Sin1, a single amino acid of rictor Gly-934 controls its interaction with Sin1 and assembly of mTORC2.

The H3.3 histone variant has been a subject of increasing interest in the field of chromatin studies due to its two distinguishing features. First, its incorporation into chromatin is replication independent unlike the replication-coupled deposition of its canonical counterparts H3.1/2. Second, H3.3 has been consistently associated with an active state of chromatin. In accordance, this histone variant should be expected to be causally involved in the regulation of gene expression, or more generally, its incorporation should have downstream consequences for the structure and function of chromatin. This, however, leads to an apparent paradox: In cells that slowly replicate in the organism, H3.3 will accumulate with time, opening the way to aberrant effects on heterochromatin. Here, we review the indications that H3.3 is expected both to be incorporated in the heterochromatin of slowly replicating cells and to retain its functional downstream effects. Implications for organismal aging are discussed.

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Starvation is a complex adaptive response to insufficiency of nutrients that has been known to implicate a number of stress networks, and modulate pathogenicity and antibiotic resistance in bacteria. However, naturally occurring abrupt elimination of nutrients and prolonged periods of their complete absence, e.g. when bacteria are placed in natural or artificial water reservoirs, are qualitatively different from in-culture late stationary phase energy source diminution. Despite the obvious importance of proteomic investigation of bacteria exposed to nutrient deficiency, no comprehensive study on the subject has been published. In order to address the said shortage of knowledge, we decided to quantitatively look into the proteome-level alterations elicited by the complete lack of nutrients that constitute a viable source of carbon, i.e. carbon starvation, in the Escherichia coli HT115-derived SLE1 strain cells using the combination of label-free and SILAC-based proteomics. As a result, we obtained protein ratios for 1,757 and 1,241 protein groups for each technique respectively, 2D-annotated the quantifiable proteins present in both datasets, identified over-and underrepresented Gene Ontology terms, and isolated protein groups ≥2-fold up-and downregulated in response to carbon starvation (44 and 36 protein groups respectively). We observed upregulation of proteins implicated in various stress-related networks, most notably those that constitute the Gene Ontology term 'Biological adhesion', as well as various terms related to stress. Additionally, we identified several uncharacterized proteins, and our report is the first to ascribe them to a stress-induced proteome. Our data are available via ProteomeXchange with identifier ABSTRACT Starvation is a complex adaptive response to insufficiency of nutrients that has been known to implicate a number of stress networks, and modulate pathogenicity and antibiotic resistance in bacteria. However, naturally occurring abrupt elimination of nutrients and prolonged periods of their complete absence, e.g. when bacteria are placed in natural or artificial water reservoirs, are qualitatively different from in-culture late stationary phase energy source diminution. Despite the obvious importance of proteomic investigation of bacteria exposed to nutrient deficiency, no comprehensive study on the subject has been published. In order to address the said shortage of knowledge, we decided to quantitatively look into the proteome-level alterations elicited by the complete lack of nutrients that constitute a viable source of carbon, i.e. carbon starvation, in the Escherichia coli HT115-derived SLE1 strain cells using the combination of label-free and SILAC-based proteomics. As a result, we obtained protein ratios for 1,757 and 1,241 protein groups for each technique respectively, 2D-annotated the quantifiable proteins present in both datasets, identified over-and underrepresented Gene Ontology terms, and isolated protein groups ≥2-fold up-and downregulated in response to carbon starvati...

Starvation is a complex adaptive response to insufficiency of nutrients that has been known to implicate a number of stress networks, and modulate pathogenicity and antibiotic resistance in bacteria. However, naturally occurring abrupt elimination of nutrients and prolonged periods of their complete absence, e.g. when bacteria are placed in natural or artificial water reservoirs, are qualitatively different from in-culture late stationary phase energy source diminution. Despite the obvious importance of proteomic investigation of bacteria exposed to nutrient deficiency, no comprehensive study on the subject has been published. In order to address the said shortage of knowledge, we decided to quantitatively look into the proteome-level alterations elicited by the complete lack of nutrients that constitute a viable source of carbon, i.e. carbon starvation, in the Escherichia coli HT115-derived SLE1 strain cells using the combination of label-free and SILAC-based proteomics. As a result, we obtained protein ratios for 1,757 and 1,241 protein groups for each technique respectively, 2D-annotated the quantifiable proteins present in both datasets, identified over- and underrepresented Gene Ontology terms, and isolated protein groups ≥2-fold up- and downregulated in response to carbon starvation (44 and 36 protein groups respectively). We observed upregulation of proteins implicated in various stress-related networks, most notably those that constitute the Gene Ontology term 'Biological adhesion', as well as various terms related to stress. Additionally, we identified several uncharacterized proteins, and our report is the first to ascribe them to a stress-induced proteome. Our data are available via ProteomeXchange with identifier PXD003255 and DOI:10.6019/PXD003255.

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