Matrix adhesion and Ras transformation both activate a phosphoinositide 3-OH kinase and protein kinase B/Akt cellular survival pathway.

Upon detachment from the extracellular matrix, epithelial cells enter into programmed cell death, a phenomenon known as anoikis, ensuring that they are unable to survive in an inappropriate location. Activated ras oncogenes protect cells from this form of apoptosis. The nature of the survival signals activated by integrin engagement and usurped by oncogenic Ras are unknown: here we show that in both cases phosphoinositide 3-OH kinase (PI 3-kinase), but not Raf, mediates this protection, acting through protein kinase B/Akt (PKB/Akt).

Role of phosphoinositide 3-OH kinase in cell transformation and control of the actin cytoskeleton by Ras.

The pathways by which mammalian Ras proteins induce cortical actin rearrangement and cause cellular transformation are investigated using partial loss of function mutants of Ras and activated and inhibitory forms of various postulated target enzymes for Ras. Efficient transformation by Ras requires activation of other direct effectors in addition to the MAP kinase kinase kinase Raf and is inhibited by inactivation of the PI 3-kinase pathway. Actin rearrangement correlates with the ability of Ras mutants to activate PI 3-kinase.

P110delta, a novel phosphoinositide 3-kinase in leukocytes.

Phosphoinositide 3-kinases (PI3Ks) are a family of lipid kinases that have been implicated in signal transduction through tyrosine kinase- and heterotrimeric G-protein-linked receptors. We report herein the cloning and characterization of p110delta, a novel class I PI3K. Like p110alpha and p110beta, other class I PI3Ks, p110delta displays a broad phosphoinositide lipid substrate specificity and interacts with SH2/SH3 domain-containing p85 adaptor proteins and with GTP-bound Ras.

Cell cycle: routine role for Ras.

The Ras proteins are key mediators of the early cellular response to mitogens; the way in which they influence the later events in the cell cycle is beginning to fall into place.

Suppression of c-Myc-induced apoptosis by Ras signalling through PI(3)K and PKB.

The viability of vertebrate cells depends on survival factors which activate signal transduction pathways that suppress apoptosis. Defects in anti-apoptotic signalling pathways are implicated in many pathologies including cancer, in which apoptosis induced by deregulated oncogenes must be forestalled for a tumour to become established. Phosphatidylinositol-3-kinase (PI(3)K) is involved in the intracellular signal transduction of many receptors and has been implicated in the transduction of survival signals in neuronal cells.

R-Ras can activate the phosphoinositide 3-kinase but not the MAP kinase arm of the Ras effector pathways.

Background: The small GTPase R-Ras displays a less potent transforming activity than the closely related Ras oncogene products. Although R-Ras has been reported to interact with c-Raf1 and Ral-GDS in vitro, the pathways by which it exerts its effects on cellular proliferation are not known.

Results: Both Ras and R-Ras interact with phosphoinositide (PI) 3-kinase in vitro, and induce elevation of the levels of PI 3-kinase lipid products in intact cells.

Critical role for the tyrosine kinase Syk in signalling through the high affinity IgE receptor of mast cells.

Activation of the high affinity IgE receptor (Fc epsilon RI) of mast cells, a member of the antigen receptor family, leads to the release of allergic mediators, a critical event in the onset of immediate hypersensitivity. Stimulation of Fc epsilon RI results in the rapid association and activation of the Syk tyrosine kinase. Using Syk-deficient mast cells we show that they fail to degranulate, synthesize leukotrienes and secrete cytokines when stimulated through Fc epsilon RI, conclusively demonstrating an essential role for Syk in Fc epsilon RI signalling.

Networks of interaction of p120cbl and p130cas with Crk and Grb2 adaptor proteins.

P120cbl, the product of the c-cbl proto-oncogene, has previously been shown to become tyrosine phosphorylated following EGF stimulation of cells, and to bind constitutively to the SH3 domain of the adaptor protein Grb2. Here we show that another adaptor protein, Crk, binds through its SH2 domain to tyrosine phosphorylated p120cbl. In addition, Crk becomes phosphorylated on tyrosine and serine following EGF treatment of PC12 and other cell lines.

Activation of phosphoinositide 3-kinase by interaction with Ras and by point mutation.

We have reported previously that Ras interacts with the catalytic subunit of phosphoinositide 3-kinase (PI 3-kinase) in a GTP-dependent manner. The affinity of the interaction of Ras-GTP with p85alpha/p110alpha is shown here to be approximately 150 nM. The site of interaction on the p110alpha and beta isoforms of PI 3-kinase lies between amino acid residues 133 and 314.

Interactions of Cbl with two adapter proteins, Grb2 and Crk, upon T cell activation.

Several recent studies have demonstrated that Grb2, composed entirely of SH2 and SH3 domains, serves as an adaptor protein in tyrosine kinase signaling pathways. Cb1, the protein product of c-cbl proto-oncogene, has been reported to be phosphorylated on tyrosine residues upon T cell receptor (TCR) engagement. Here we show that in unstimulated Jurkat cells Cbl is co-immunoprecipitated with monoclonal antibody against Grb2.

Phosphatidylinositol 3' kinase: one of the effectors of Ras.

Ras proteins are proto-oncogene products that are critical components of signalling pathways leading from cell surface receptors to control of cellular proliferation, morphology and differentiation. the ability of Ras to activate the MAP kinase pathway through interaction with the serine/threonine kinase Raf is now well established. However, recent work has shown that Ras can also interact directly with the catalytic subunit of phosphatidylinositol 3' kinase and is involved in control of the lipid kinase in intact cells.

Control of ras activation.

Ras proteins are active when bound to GTP and inactive when bound to GDP: the activation state of Ras proteins is regulated by two families of proteins. GTPase activating proteins (p120GAP, neurofibromin and GAP1) are negative regulators that stimulate hydrolysis of bound GTP to GDP, and guanine nucleotide exchange factors (Sos and Ras-GRF) are positive regulators that stimulate the exchange of GDP bound to Ras for fresh GTP from the cytosol. Ras is activated in response to a wide variety of extracellular stimuli.

Downregulation of the Ras activation pathway by MAP kinase phosphorylation of Sos.

Formation of a complex of the nucleotide exchange factor Sos, the SH2 and SH3 containing adaptor protein Grb2/Sem-5 and tyrosine phosphorylated EGF receptor and Shc has been implicated in the activation of Ras by epidermal growth factor (EGF) in fibroblasts: related mechanisms for activation of Ras operate in other cell types. An increase in the apparent molecular weight of Sos has been reported to occur after several minutes of receptor stimulation due to phosphorylation by mitogen-activated protein (MAP) kinases. We report here that treatment of human peripheral blood T lymphoblasts with phorbol esters causes a similar shift in mobility of Sos.

The Grb2 binding domain of mSos1 is not required for downstream signal transduction.

Cellular Ras proteins are activated primarily by specific guanine-nucleotide releasing factors such as the Son of Sevenless (Sos) proteins. This activation event is thought to occur in response to plasma membrane localization of a complex containing Sos and a small adapter protein Grb2. We have isolated a dominant mutant allele of mSos1 which transforms Rat1 cells, yet is no longer able to bind Grb2.

Role of Shc in the activation of Ras in response to epidermal growth factor and nerve growth factor.

Treatment of the rat pheochromocytoma cell line PC12 with nerve growth factor (NGF) or epidermal growth factor (EGF) is known to result in activation of Ras. In response to EGF treatment, complexes form between Sos, Grb2 and tyrosine phosphorylated Shc and/or EGF receptor. In response to NGF treatment, complexes form between Sos, Grb2 and tyrosine phosphorylated Shc.

Tyr-716 in the platelet-derived growth factor beta-receptor kinase insert is involved in GRB2 binding and Ras activation.

Ligand stimulation of the platelet-derived growth factor (PDGF) beta-receptor leads to activation of its intrinsic tyrosine kinase and autophosphorylation of the intracellular part of the receptor. The autophosphorylated tyrosine residues mediate interactions with downstream signal transduction molecules and thereby initiate different signalling pathways. A pathway leading to activation of the GTP-binding protein Ras involves the adaptor molecule GRB2.

The activation of phosphatidylinositol 3-kinase by Ras.

Background: Activation of the mammalian phosphatidylinositol 3-kinase complex can play a critical role in transducing growth factor responses. The lipid kinase complex, which is made up of p85 alpha and p110 alpha regulatory and catalytic subunits, becomes associated with a number of activated receptor protein tyrosine kinases, but the mechanism of its activation has not yet been defined. Recent evidence indicates that Ras can bind to the p85 alpha/p110 alpha complex.

Phosphatidylinositol-3-OH kinase as a direct target of Ras.

Ras (p21ras) interacts directly with the catalytic subunit of phosphatidylinositol-3-OH kinase in a GTP-dependent manner through the Ras effector site. In vivo, dominant negative Ras mutant N17 inhibits growth factor induced production of 3' phosphorylated phosphoinositides in PC12 cells, and transfection of Ras, but not Raf, into COS cells results in a large elevation in the level of these lipids. Therefore Ras can probably regulate phosphatidylinositol-3-OH kinase, providing a point of divergence in signalling pathways downstream of Ras.

SH3 domains of the adapter molecule Grb2 complex with two proteins in T cells: the guanine nucleotide exchange protein Sos and a 75-kDa protein that is a substrate for T cell antigen receptor-activated tyrosine kinases.

In T lymphocytes activated via the T cell antigen receptor (TCR), the SH2- and SH3-containing adapter molecule Grb2 forms a complex with the Ras guanine nucleotide exchange protein Sos and tyrosine phospho-proteins. The interaction of Sos with Grb2 is mediated via the Grb2 SH3 domains. In this study, it is shown that a 75-kDa protein is also complexed with the Grb2 SH3 domains in T cells, but not in Rat-1 fibroblasts.