The phosphoinositide (PI) 3-kinase family (original) (raw)

Class IA phosphoinositide 3-kinases are obligate p85-p110 heterodimers

Proceedings of the National Academy of Sciences, 2007

Class IA phosphoinositide 3-kinases (PI3Ks) signal downstream of tyrosine kinases and Ras and control a wide variety of biological responses. In mammals, these heterodimeric PI3Ks consist of a p110 catalytic subunit (p110␣, p110␤, or p110␦) bound to any of five distinct regulatory subunits (p85␣, p85␤, p55␥, p55␣, and p50␣, collectively referred to as ''p85s''). The relative expression levels of p85 and p110 have been invoked to explain key features of PI3K signaling. For example, free (i.e., non-p110-bound) p85␣ has been proposed to negatively regulate PI3K signaling by competition with p85/p110 for recruitment to phosphotyrosine docking sites. Using affinity and ion exchange chromatography and quantitative mass spectrometry, we demonstrate that the p85 and p110 subunits are present in equimolar amounts in mammalian cell lines and tissues. No evidence for free p85 or p110 subunits could be obtained. Cell lines contain 10,000 -15,000 p85/p110 complexes per cell, with p110␤ and p110␦ being the most prevalent catalytic subunits in nonleukocytes and leukocytes, respectively. These results argue against a role of free p85 in PI3K signaling and provide insights into the nonredundant functions of the different class IA PI3K isoforms.

Mammalian phosphoinositide kinases and phosphatases

Progress in Lipid Research, 2009

Phosphoinositides are lipids that are present in the cytoplasmic leaflet of a cell's plasma and internal membranes and play pivotal roles in the regulation of a wide variety of cellular processes. Phosphoinositides are molecularly diverse due to variable phosphorylation of the hydroxyl groups of their inositol rings. The rapid and reversible configuration of the seven known phosphoinositide species is controlled by a battery of phosphoinositide kinases and phosphoinositide phosphatases, which are thus critical for phosphoinositide isomer-specific localization and functions. Significantly, a given phosphoinositide generated by different isozymes of these phosphoinositide kinases and phosphatases can have different biological effects. In mammals, close to 50 genes encode the phosphoinositide kinases and phosphoinositide phosphatases that regulate phosphoinositide metabolism and thus allow cells to respond rapidly and effectively to ever-changing environmental cues. Understanding the distinct and overlapping functions of these phosphoinositide-metabolizing enzymes is important for our knowledge of both normal human physiology and the growing list of human diseases whose etiologies involve these proteins. This review summarizes the structural and biological properties of all the known mammalian phosphoinositide kinases and phosphoinositide phosphatases, as well as their associations with human disorders. phosphatase and tensin homologue deleted on chromosome 10; PTPMT1, protein tyrosine phosphatase localized to the mitochondrion-1; PX, phox; RANKL, receptor activator of nuclear factor-jB ligand; RhoGDI, guanine nucleotide dissociation inhibitor of Rho; ROCK, Rho kinase; ROS, reactive oxygen species; S6K, S6 kinase; Sac, suppressor of actin; SAM, sterile a motif; SBF1, SET binding factor 1; SCF, stem cell factor; SDF1, stromal cell-derived factor-1; SET, Suvar3-9 Enhancer-of-zeste Trithorax; SH2, Src homology 2; SHIP, SH2-containing inositol phosphatase; SID, SET-interacting domain; SKICH, SKIP carboxyl homology; SKIP, skeletal muscle-and kidney-enriched inositol polyphosphate phosphatase

Signaling by Distinct Classes of Phosphoinositide 3-Kinases

Experimental Cell Research, 1999

Many signaling pathways converge on and regulate phosphoinositide 3-kinase (PI3K) enzymes whose inositol lipid products are key mediators of intracellular signaling. Different PI3K isoforms generate specific lipids that bind to FYVE and pleckstrin homology (PH) domains in a variety of proteins, affecting their localization, conformation, and activities. Here we review the activation mechanisms of the different types of PI3Ks and their downstream actions, with focus on the PI3Ks that are acutely triggered by extracellular stimulation.

Cloning of a novel, ubiquitously expressed human phosphatidylinositol 3-kinase and identification of its binding site on p85

Molecular and cellular biology, 1993

Phosphatidylinositol 3-kinase (PI 3-kinase) has been implicated as a participant in signaling pathways regulating cell growth by virtue of its activation in response to various mitogenic stimuli. Here we describe the cloning of a novel and ubiquitously expressed human PI 3-kinase. The 4.8-kb cDNA encodes a putative translation product of 1,070 amino acids which is 42% identical to bovine PI 3-kinase and 28% identical to Vps34, a Saccharomyces cerevisiae PI 3-kinase involved in vacuolar protein sorting. Human PI 3-kinase is also similar to Tor2, a yeast protein required for cell cycle progression. Northern (RNA) analysis demonstrated expression of human PI 3-kinase in all tissues and cell lines tested. Protein synthesized from an epitope-tagged cDNA had intrinsic PI 3-kinase activity and associated with the adaptor 85-kDa subunit of PI 3-kinase (p85) in intact cells, as did endogenous human PI 3-kinase. Coprecipitation assays showed that a 187-amino-acid domain between the two src ho...

Phosphoinositide 3-kinase is activated by phosphopeptides that bind to the SH2 domains of the 85-kDa subunit

Journal of Biological Chemistry, 1993

Tyrosine-phosphorylated peptides based on the regions of polyoma virus middle t antigen and the platelet-derived growth factor receptor that bind phosphoinositide 3-kinase are shown to activate this enzyme 2-3-fold in vitro. The concentrations of the peptides required to activate the enzyme are at least 10-1000fold higher than the dissociation constants of these peptides for the individual SH2 domains of the 85-kDa subunit (KO < 100 nM). Doubly phosphorylated peptides are more effective than singly phosphorylated peptides. The results suggest that a fraction of the cellular phosphoinositide 3-kinase has SH2 domains with relatively low affinity for phosphopeptides and that binding of phosphopeptides to these enzymes causes activation. Thus, SH2 domains may be involved not only in recruiting the enzyme but also in regulating activity. Phosphoinositide (PtdIns)' 3-kinase is the critical enzyme in a recently discovered intracellular signaling pathway that is activated by a wide range of growth factors, oncoproteins, and nonmitogenic stimuli (1). PtdIns 3-kinase was discovered because of its association with the oncogene products pp60""" and middle T. pp60"'"" complex (2-5). Studies of polyoma virus middle t antigen (mT) mutants indicate that m T must associate with both pp60"" (or a close relative of pp60""") and with PtdIns 3-kinase to transform cells (2, 4-12). The association of m T with ~~6 0 "~" results in activation of the protein-tyrosine kinase activity of pp6OC-" and the phosphorylation of m T (11, 13). The lipid products of PtdIns 3-kinase are elevated in cells transformed by mT, indicating a correlation between the association of this enzyme with m T and increased activity in intact cells (14,15). Similarly, PtdIns 3-kinase directly associates with and is activated by a variety * This work was supported by National Institutes of Health Grants GM 41890 and GM 36624 (to L.