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Phosphoinositides (PI) are important signaling molecules in the nucleus that influence gene expression. However, if and how nuclear PI directly affects the transcriptional machinery is not known. We report that the lipid kinase PIP4K2B regulates nuclear PI5P and the expression of myogenic genes during myoblast differentiation. A targeted screen for PI interactors identified the PHD finger of TAF3, a TATA box binding protein-associated factor with important roles in transcription regulation, pluripotency, and differentiation. We show that the PI interaction site is distinct from the known H3K4me3 binding region of TAF3 and that PI binding modulates association of TAF3 with H3K4me3 in vitro and with chromatin in vivo. Analysis of TAF3 mutants indicates that TAF3 transduces PIP4K2B-mediated alterations in PI into changes in specific gene transcription. Our study reveals TAF3 as a direct target of nuclear PI and further illustrates the importance of basal transcription components as signal transducers.

The deacetylation and repression of the activity of forkhead transcription factor - Foxo3a and other mammalian forkhead factors by the mammalian SIR2 ortholog SIRT1 is reported. The speculation over the down regulation of the two classes of damage - responsive mammalian factors, favoring longer life - span under specific environmental conditions is presented.

Oxidative stress initiates signaling pathways, which protect from stress-induced cellular damage, initiate apoptosis, or drive cells into senescence or into tumorigenesis. Oxidative stress regulates the activity of the cell survival factor PKB, through the regulation of PtdIns(3,4,5)P3 synthesis. Whether oxidative stress regulates other phosphoinositides to control PKB activation is not clear. Here we show that PtdIns5P is a redox-regulated second messenger. In response to hydrogen peroxide (H2O2), we measured an increase in PtdIns5P in cells derived from human osteosarcoma, U2OS (5-fold); breast tumors, MDA-MB-468 (2-fold); and fibrosarcoma, HT1080 (3-fold); and in p53-null murine embryonic fibroblasts (8-fold). In U2OS cells, the increase in H2O2-dependent PtdIns5P did not require mTOR, PDK1, PKB, ERK, and p38 signaling or PIKfyve, a lipid kinase that increases PtdIns5P in response to osmotic and oncogenic signaling. A reduction in H2O2-induced PtdIns5P levels by the overexpression of PIP4K revealed its role in PKB activation. Suppression of H2O2-induced PtdIns5P generation reduced PKB activation and, surprisingly, reduced cell sensitivity to growth inhibition by H2O2. These data suggest that inhibition of PIP4K signaling might be useful as a novel strategy to increase the susceptibility of tumor cells to therapeutics that function through increased oxidative stress. [ABSTRACT FROM AUTHOR]

Phosphatidylinositol (PtdIns) and its phosphorylated derivatives represent less than 5% of total membrane phospholipids in cells. Despite their low abundance, they form a dynamic signaling system that is regulated in response to a variety of extra- and intracellular cues. Protein domains including PH, FYVE, ENTH, PHOX, PHD fingers, and lysine-/arginine-rich patches can bind to specific phosphoinositide isomers, which, in turn, can induce changes in the subcellular localization, posttranslational modification, protein interaction partners, or activity of the protein containing such a domain. Phosphoinositides and the enzymes that synthesize them are found in many different subcellular compartments including the nuclear matrix, heterochromatin, and sites of active RNA splicing, suggesting that phosphoinositides may regulate specific functions within the nuclear compartment. The existence of distinct subcellular pools has led to the challenging task of the quantitation of temporal and spatial changes in phosphoinositides. We report methods to measure the mass levels of three different phosphoinositides within the nuclear compartment.