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Biomedical subjects

M D Waterfield

Publications and source records attributed to M D Waterfield.

At least 91 records · Page 5Linked to original sources
PubMed1994

A comparison of demethoxyviridin and wortmannin as inhibitors of phosphatidylinositol 3-kinase.

The mammalian Ptdlns 3-kinase is shown to be inhibited by low nanomolar concentrations of demethoxyviridin, an antifungal agent structurally related to wortmannin. The inhibitory potency of both compounds could be observed in purified Ptdlns 3-kinase whether or not the regulatory subunit (p85 alpha) was present, suggesting that the inhibitors bind to the catalytic subunit (p110) of the Ptdlns 3-kinase. These inhibitors also show similar potency against the intrinsic p85-phosphorylating activity of the p110-kinase. However, the structurally related Ptdlns 3-kinase from Saccharomyces cerevisiae (Vps34p) is not inhibited by either compound. Both inhibitors target the mammalian Ptdlns 3-kinase in vitro and in vivo, implying that these compounds should be useful in suppressing Ptdlns 3-kinase in mammalian systems. The inhibitors did not affect the mammalian Ptdlns 4-kinase, but they are able to inhibit a membrane-associated Ptdlns 4-kinase from Schizosaccharomyces pombe.

Androstadienes↗
PubMed1994

Characterization of a phosphatidylinositol-specific phosphoinositide 3-kinase from mammalian cells.

BACKGROUND: As phosphoinositides can serve as signalling molecules within cells, the enzymes responsible for their synthesis and cleavage are likely to be involved in the transduction of signals from the cell surface through the cytoplasm. The precise role of the phosphoinositide 3-kinase that has been cloned from mammalian cells is not known, but it has been implicated in receptor-stimulated mitogenesis, glucose uptake and membrane ruffling. The enzyme can use phosphatidylinositol (PtdIns), PtdIns 4-phosphate and PtdIns (4,5)-bisphosphate as substrates in vitro, but it seems to phosphorylate PtdIns (4,5)-bisphosphate preferentially in vivo. The VPS34 gene product of yeast, by contrast, is a phosphoinositide 3-kinase homologue implicated in vacuolar protein sorting that apparently utilizes only PtdIns as a substrate. The significance of this difference in lipid-substrate preference and its relationship to the functions of the two phosphoinositide kinases is unknown. RESULTS: We have characterized a distinct PtdIns-specific phosphoinositide 3-kinase activity in mammalian cells. Unlike the previously identified, broad-specificity mammalian phosphoinositide kinase, this enzyme is resistant to the drug wortmannin and uses only PtdIns as a substrate in vitro; it therefore has the capacity to generate PtdIns 3-phosphate specifically. The newly characterized enzyme, which was purified by chromatography from cytosol, has biochemical and pharmacological characteristics distinct from those of the broad-specificity enzyme. CONCLUSIONS: The enzyme we have characterized may serve to generate PtdIns 3-phosphate for fundamentally different roles in the cell from those of PtdIns (3,4)-bisphosphate and/or PtdIns (3,4,5)-trisphosphate. Furthermore, the functions of the VSP34 gene product, which may not be relevant to the broad-specificity mammalian phosphoinositide 3-kinase, may be related to those of the enzyme we describe.

Amino Acid Sequence↗
PubMed1994

PI 3-kinase: structural and functional analysis of intersubunit interactions.

Phosphatidylinositol (PI) 3-kinase has an 85 kDa subunit (p85 alpha) which mediates its association with activated protein tyrosine kinase receptors through SH2 domains, and an 110 kDa subunit (p110) which has intrinsic catalytic activity. Here p85 alpha and a related protein p85 beta are shown to form stable complexes with recombinant p110 in vivo and in vitro. Using a panel of glutathione S-transferase (GST) fusion proteins of the inter-SH2 region of p85, 104 amino acids were found to bind directly the p110 protein, while deletion mutants within this region further defined the binding site to a sequence of 35 amino acids. Transient expression of the mutant p85 alpha protein in mouse L cells showed it was unable to bind PI 3-kinase activity in vivo. Mapping of the complementary site of interaction on the p110 protein defined 88 amino acids in the N-terminal region of p110 which mediate the binding of this subunit to either the p85 alpha or the p85 beta proteins. The inter-SH2 region of p85 is predicted to be an independently folded module of a coiled-coil of two long anti-parallel alpha-helices. The predicted structure of p85 suggests a basis for the intersubunit interaction and the relevance of this interaction with respect to the regulation of the PI 3-kinase complex is discussed.

Amino Acid Sequence↗
PubMed1994

Mammalian phosphatidylinositol 3'-kinase induces a lethal phenotype on expression in Schizosaccharomyces pombe; comparison with the VPS34 gene product.

The 110-kDa catalytic subunit of the phosphatidylinositol 3'-kinase (p110) is shown to be expressed in Schizosaccharomyces pombe as a functional protein, as judged by the accumulation of 3'-phosphorylated lipids in vivo and the extraction of 3'-kinase activity in vitro. On expression of p110, the cells fail to grow and lose viability. In contrast, while the Saccharomyces cerevisiae protein Vps34p can be expressed in S. pombe as a functional, extractable, phosphatidylinositol 3-kinase, expression of this protein fails to increase substantially 3'-phosphorylated lipids in vivo and does not induce a phenotype equivalent to that induced by p110. The results indicate that (over-)-accumulation of 3'-phosphorylated inositol lipids in S. pombe causes loss of viability.

Cell Division↗
PubMed1994

Molecular cloning, cDNA sequence, and chromosomal localization of the human phosphatidylinositol 3-kinase p110 alpha (PIK3CA) gene.

Phosphatidylinositol (PI) 3-kinase is a heterodimeric enzyme comprising a 110-kDa catalytic subunit and an 85-kDa regulatory subunit that binds to tyrosine phosphopeptide sites linked directly or indirectly to receptors serving diverse signal functions. Knowledge of the structure and function of PI 3-kinase was greatly advanced by the purification, cDNA cloning, and subsequent expression of the bovine enzyme. Here the cloning of the cDNA for the human p110 alpha subunit of PI 3-kinase (PIK3CA), encoding a protein 99% identical to the bovine p110, and of its gene in YAC is described. The chromosomal localization of the gene for PIK3CA is shown to be at 3q21-qter as determined using somatic cell hybrids. In situ hybridization performed using Alu-PCR from the YAC DNA located the gene in 3q26.3.

Animals↗
PubMed1993

Association of the p85 regulatory subunit of phosphatidylinositol 3-kinase with an essential erythropoietin receptor subdomain.

Using an active, HAI epitope-tagged form of the murine erythropoietin (EPO) receptor and via direct coimmunoprecipitation, the p85 regulatory subunit of phosphatidyl inositol-3 kinase (p85/PI3-K) is shown to associate with the EPO receptor in transfected FDC-P1 cell lines. Coimmunoprecipitation of p85 with epitope-tagged EPO receptors was observed initially in FDC-HER cells labeled metabolically with [32P]orthophosphate, and association of these factors was confirmed by Western analyses of receptor immunoprecipitates using p85 antiserum. Interestingly, this association occurred in the absence of ligand, and exposure of FDC-HER cells to EPO did not detectably affect levels of receptor-associated p85 or overall levels of p85 phosphorylation. However, EPO was observed to stimulated the rapid formation of phosphatidylinositol 32P-phosphate in FDC-HER and FDC-ER cells. Through baculovirus-mediated expression of epitope-tagged EPO receptor forms in SF9 cells, domains for p85 association were mapped. Analyses of receptor forms with cytosolic truncations and deletions delineated a candidate subdomain for p85 binding to an essential extended box-2 region (P329-E374; including a putative motif for SH2 binding, Y343LVL). These findings extend a mechanistic alignment between the EPO receptor and protein tyrosine kinase-encoding receptors that likewise activate PI3-K, and expand the importance of further defining pathways to PI3-K activation.

Amino Acid Sequence↗
PubMed1993

Purification of multiple forms of glial growth factor.

Glial growth factors (GGFs) were purified from bovine pituitaries using an in vitro rat Schwann cell mitogenesis assay. In addition to an approximately 34-kDa species termed GGF-I, similar in molecular mass to a previously identified molecule (Lemke, G. E., and Brockes, J. P. (1984) J. Neuroscience 4, 75-83), two species named GGF-II and GGF-III were characterized with apparent molecular masses of approximately 59 and approximately 45 kDa, respectively. Highly purified preparations of all species share a similar dose-dependent stimulation of Schwann cell DNA synthesis at nanomolar concentrations. Forskolin synergizes with all three GGFs, shifting their dose dependence 3-8-fold into the sub-nanomolar range. The GGFs, which contain N-linked carbohydrate groups not essential for their in vitro mitogenic effects, are three distinct members of a novel family of glial cell mitogens.

Animals↗
PubMed1993

Structure and function of phosphatidylinositol 3-kinase: a potential second messenger system involved in growth control.

Ligand stimulation of growth factor receptors with intrinsic protein-tyrosine kinase activity initiates the assembly of multienzyme signalling complexes. This is mediated by binding of proteins with src homology 2 (SH2) domains to receptor autophosphorylation sites. Among the proteins involved in complex formation is phosphatidylinositol (PI) 3-kinase, a heterodimeric enzyme composed of 85 kDa and 110 kDa subunits, which binds to receptor (and non-receptor) phosphotyrosine residues through the two SH2 domains in the p85 subunit. p85 acts as an adaptor protein and possibly a regulator of the p110 catalytic subunit that phosphorylates phosphoinositides at the D-3 position of the inositol ring. p85 subunit is composed of several distinct functional domains: one SH3 and two SH2 domains, a p110 binding site and a region with homology to BCR. Expression of these domains in E. coli as GST-fusion proteins has allowed definition by nuclear magnetic resonance (NMR) of three-dimensional structures for the SH2 and SH3 domains. The relationship of structure to function for these domains is discussed. The p110 catalytic domain has a region of homology with vps34p of Saccharomyces cerevisiae, a protein involved in protein sorting to the yeast vacuole. Possible clues to the function of PI 3-kinase derived from this and other observations are presented.

Amino Acid Sequence↗
PubMed1993

Divergent regulation of phosphatidylinositol 3-kinase P85 alpha and P85 beta isoforms upon T cell activation.

Phosphatidylinositol (PtdIns) 3-kinase is composed of a catalytic p110 subunit and a regulatory p85 subunit. A synthetic phosphopeptide corresponding to the kinase insert of the human PDGF beta subunit receptor and monoclonal antibodies raised against the two described p85 isoforms, p85 alpha and p85 beta were used to isolate PtdIns 3-kinase from human T lymphocytes. We demonstrate that T cells express both p85 alpha and p85 beta proteins. Both isoforms tightly associate with a p110 protein and with PtdIns 3-kinase activity in T cells. Upon triggering of the T cell antigen receptor (TCR)/CD3 complex or activation of protein kinase C (PKC) the p110 protein complexed to p85 alpha becomes rapidly phosphorylated exclusively on serine residues. p85 alpha does not appear to undergo a change in its basal serine phosphorylation during T cell activation. In contrast, stimulation of the TCR/CD3 complex or PKC, results in a marked and rapid increase in phosphorylation of p85 beta on threonine residues. These data show that PtdIns 3-kinase can be a substrate for serine/threonine kinases in T cells. The differential phosphorylation of p85 alpha and p85 beta reveals the potential for divergent regulation and function of these two PtdIns 3-kinase isoforms during T cell activation.

Animals↗
PubMed1993

Solution structure and ligand-binding site of the SH3 domain of the p85 alpha subunit of phosphatidylinositol 3-kinase.

SH3 domains are found in proteins associated with receptor tyrosine kinase signal transduction complexes. The solution structure of the SH3 domain of the 85 kd regulatory subunit of phosphatidylinositol 3-kinase is shown to be a compact beta barrel consisting of five beta strands arranged in two beta sheets of three and two strands. The structure is similar to that of chicken brain alpha spectrin but represents a distinct class of SH3 domain, with an insertion between the second and third beta strands that may influence binding specificity. 1H chemical shift changes induced by complex formation with a synthetic peptide derived from the SH3-binding protein dynamin, together with amino acid sequence comparisons, suggest that the ligand-binding site consists of a hydrophobic surface flanked by two charged loops.

Amino Acid Sequence↗
PubMed1993

A biosensor approach to probe the structure and function of the p85 alpha subunit of the phosphatidylinositol 3-kinase complex.

Phosphatidylinositol 3-kinase, which generates putative novel second messenger phospholipids, is a heterodimer composed of regulatory adaptor 85-kDa and catalytic 110-kDa subunits. The p85 alpha subunit contains a NH2-terminal src homology (SH) 3 domain, a region with homology to the product of the breakpoint cluster region (bcr) gene, and a COOH-terminal portion of the molecule which contains two SH2 domains, separated by a spacer region. In this study a panel of monoclonal antibodies (mAb) was raised against recombinant bovine p85 alpha to probe its multidomain structure in relation to function. These mAbs were characterized using a BIAcore biosensor instrument. Epitopes for nine mAbs were mapped in relation to the domain structure of p85 alpha using recombinant protein fragments expressed in bacteria. These mAbs were then used to map the sites on p85 alpha which are involved in growth factor receptor binding. Two interesting classes of functional mAbs were identified. First, mAb U14, whose epitope lies within the NH2-terminal SH2 domain of p85 alpha, blocked the interaction of p85 alpha with activated protein-tyrosine kinase receptors. Second, real-time binding experiments using phospholipid-containing vesicles showed that p85 alpha by itself could specifically bind certain phospholipids. Two mAbs (U9 and U15) with epitopes located in the inter-SH2 spacer region blocked the binding of lipids to this site. The relevance of these observations to understanding the relationship of structure to function of p85 and the phosphatidylinositol 3-kinase are discussed.

Amino Acid Sequence↗
PubMed1993

Phosphatidylinositol 3-kinase encoded by yeast VPS34 gene essential for protein sorting.

The VPS34 gene product (Vps34p) is required for protein sorting to the lysosome-like vacuole of the yeast Saccharomyces cerevisiae. Vps34p shares significant sequence similarity with the catalytic subunit of bovine phosphatidylinositol (PI) 3-kinase [the 110-kilodalton (p110) subunit of PI 3-kinase], which is known to interact with activated cell surface receptor tyrosine kinases. Yeast strains deleted for the VPS34 gene or carrying vps34 point mutations lacked detectable PI 3-kinase activity and exhibited severe defects in vacuolar protein sorting. Overexpression of Vps34p resulted in an increase in PI 3-kinase activity, and this activity was specifically precipitated with antisera to Vps34p. VPS34 encodes a yeast PI 3-kinase, and this enzyme appears to regulate intracellular protein trafficking decisions.

Amino Acid Sequence↗
PubMed1993

Characterization of the bovine brain cytosolic phosphatidylinositol 3-kinase complex.

Receptor-linked phosphatidylinositol (PtdIns) 3-kinase may generate a second-messenger signal. Here a large-scale purification of the bovine brain enzyme, based on methods developed by Morgan, Smith and Parker [(1990) Eur. J. Biochem. 191, 761-767] and Fry, Panayotou, Dhand, Ruiz-Larrea, Gout, Nguyen, Courtneidge and Waterfield [(1992) Biochem. J. 288, 383-393] is described. The purified enzyme is shown to be a heterodimer of 85 kDa and 110 kDa protein subunits (p85 and p110). Labelling with 5'-p-fluorosulphonylbenzoyladenosine shows that p110 contains an ATP-binding site and confers catalytic activity to the complex. The purified complex is known to be highly phosphorylated on both p85 alpha and p110 subunits, and dephosphorylation generates a deactivated complex, indicating that phosphorylation is an important covalent modification of the complex and may modulate PtdIns 3-kinase activity.

Adenosine↗
PubMed1993

The assembly of signalling complexes by receptor tyrosine kinases.

Cell proliferation in response to growth factors is mediated by specific high affinity receptors. Ligand-binding by receptors of the protein tyrosine kinase family results in the stimulation of several intracellular signal transduction pathways. Key signalling enzymes are recruited to the plasma membrane through the formation of stable complexes with activated receptors. These interactions are mediated by the conserved, non-catalytic SH2 domains present in the signalling molecules, which bind with high affinity and specificity to tyrosine-phosphorylated sequences on the receptors. The assembly of enzyme complexes is emerging as a major mechanism of signal transduction and may regulate the pleiotropic effects of growth factors.

Models, Biological↗
PubMed1993

Activation of Src family kinases by colony stimulating factor-1, and their association with its receptor.

The receptor for the macrophage colony stimulating factor-1 (CSF-1R) is a transmembrane glycoprotein with intrinsic tyrosine kinase activity. CSF-1 stimulation promotes the growth of cells of the macrophage lineage and of fibroblasts engineered to express CSF-1R. We show that CSF-1 stimulation resulted in activation of three Src family kinases, Src, Fyn and Yes. Concomitant with their activation, all three Src family kinases were found to associate with the ligand-activated CSF-1 receptor. These interactions were also demonstrated in SF9 insect cells co-infected with viruses encoding the CSF-1 receptor and Fyn, and the isolated SH2 domain of Fyn was capable of binding the CSF-1R in vitro. Analysis of mutant CSF-1Rs revealed that the 'kinase insert' (KI) domain of CSF-1R was not required for interactions with Src family kinases, but that mutation of one of the receptor autophosphorylation sites, Tyr809, reduced both their binding and enzymatic activation. Because fibroblasts expressing this receptor mutant are unable to form colonies in semi-solid medium or to grow in chemically defined medium in the presence of CSF-1, the Src family kinases may play a physiological role in the mitogenic response to CSF-1.

3T3 Cells↗
PubMed1993

Interactions between SH2 domains and tyrosine-phosphorylated platelet-derived growth factor beta-receptor sequences: analysis of kinetic parameters by a novel biosensor-based approach.

The interaction between SH2 domains and phosphotyrosine-containing sequences was examined by real-time measurements of kinetic parameters. The SH2 domains of the p85 subunit of the phosphatidylinositol 3-kinase as well as of other signaling molecules were expressed in bacteria as glutathione S-transferase fusion proteins. Phosphotyrosine-containing peptides, corresponding to two autophosphorylation sites on the human platelet-derived growth factor beta-receptor that are responsible for phosphatidylinositol 3-kinase binding, were synthesized and used as capturing molecules, immobilized on a biosensor surface. The association and dissociation rate constants for binding to both sites were determined for intact p85 and the recombinant SH2 domains. High association rates were found to be coupled to very fast dissociation rates for all interactions studied. A binding specificity was observed for the two SH2 domains of p85, with the N-terminal SH2 binding with high affinity to the Tyr-751 site but not to the Tyr-740 site, and the C-terminal SH2 interacting strongly with both sites. This approach should be generally applicable to the study of the specificity inherent in the assembly of signaling complexes by activated protein-tyrosine kinase receptors.

Amino Acid Sequence↗