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

Abstract

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. A point mutation in this region, K227E, blocks the GTP‐dependent interaction of PI 3‐kinase p110alpha with Ras in vitro and the ability of Ras to activate PI 3‐kinase in intact cells. In addition, this mutation elevates the basal activity of PI 3‐kinase in intact cells, suggesting a direct influence of the Ras binding site on the catalytic activity of PI 3‐kinase. Using an in vitro reconstitution assay, it is shown that the interaction of Ras‐GTP, but not Ras‐GDP, with PI 3‐kinase leads to an increase in its enzymatic activity. This stimulation is synergistic with the effect of tyrosine phosphopeptide binding to p85, particularly at suboptimal peptide concentrations. These data show that PI 3‐kinase is regulated by a number of mechanisms, and that Ras contributes to the activation of this lipid kinase synergistically with tyrosine kinases.

A specific function for phosphatidylinositol 3-kinase α (p85α-p110α) in cell survival and for phosphatidylinositol 3-kinase β (p85α-p110β) in de novo DNA synthesis of human colon carcinoma cells

“…In favour with this hypothesis, high PI3K activity associated with Ras and phosphotyrosine containing proteins was observed both in transformed cell lines and primary tumours (not shown). Both mechanisms lead to an increase in intrinsic enzymatic activity (Backer et al, 1992;Rodriguez-Viciana et al, 1996) and therefore may take part of the observed PI3K deregulation. Previous reports attributed a function for PI3Ks in cell division, survival, cell dedi erentiation (Phillips et al, 1998), migration and tumour invasion (Kobayashi et al, 1999;Shaw et al, 1997).…”

“…Association of Ras occurs via a conserved sequence in p110 N-terminus (RodriguezViciana et al, 1996). While such a sequence is also present in p110b to some extent (Rodriguez-Viciana et al, 1996), convincing data for an association between PI3Kb and Ras for cell survival is still missing. A speci®c function for PI3Ka in cell survival could come from a preferential association with Ras.…”

PTEN tumour suppressor is linked to the cell cycle control through the retinoblastoma protein

“…Therefore, this PI-3K activation could also account for the observed rescue. However, since activated Ha-ras can also bind and activate PI-3K (Rodriguez-Viciana et al, 1996) and is unable to overcome the PTEN-induced inhibition (Figure 5), this suggests that the Rac-1 or Cdc42-dependent activation of PI-3K is not the main mechanism responsible for the observed e ect. The activation of PI-3K triggers multiple signals characteristic of growth factor action, leading to cell cycle entry (Klippel et al, 1998).…”

Endocytosis and vesicular trafficking of immune complexes and activation of phospholipase D by the human high-affinity IgG receptor requires distinct phosphoinositide 3-kinase activities

“…PI 3-kinases have been shown to regulate the activity of the Ras-related low-molecular-mass GTPases Rab5 and Rab7, which have been shown to have roles in endocytosis and transport from early to late endocytic compartments [37,38]. In addition some isoforms of PI 3-kinase have binding sites for Ras-related GTPases [39], and Rab, Ras, Rho, Arf and other related low-molecular-mass GTPases have previously been shown to activate PLD isoforms [40][41][42][43][44]. It has also been suggested that there may be a role for isoforms of protein kinase C (PKC) in endocytosis and membrane trafficking [45].…”