Distinct Phosphatidylinositol 3-Kinase Lipid Products Accumulate upon Oxidative and Osmotic Stress and Lead to Different Cellular Responses

Abstract

Signaling by phosphatidylinositol (PI) 3-kinases is mediated by 3-phosphoinositides, which bind to Pleckstrin homology (PH) domains that are present in a wide spectrum of proteins. PH domains can be classified into three groups based on their different lipid binding specificities. Distinct 3-phosphoinositides can accumulate upon PI 3-kinase activation in cells in response to different stimuli and mediate specific cellular responses. In Swiss 3T3 mouse fibroblasts, oxidative stress induced by 1 mM H 2 O 2 caused almost exclusive accumulation of phosphatidylinositol 3,4-bisphosphate (PtdIns(3,4)P 2 ), whereas osmotic stress increased both phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P 3 ) and PtdIns-(3,4)P 2 levels. The increase in PtdIns(3,4)P 2 levels, caused by oxidative stress, correlated with the activation of protein kinase B, which has a promiscuous PH domain that binds both PtdIns(3,4,5)P 3 and PtdIns(3,4)P 2 . p70 S6 kinase, another signaling component downstream of PI 3-kinase, however, was not activated by this oxidative stress-induced increase in PtdIns(3,4)P 2 levels. Increased PtdIns(3,4,5)P 3 and PtdIns(3,4)P 2 levels in response to osmotic stress did not correlate with protein kinase B activation, because of concomitant activation of an inhibitory pathway, but p70 S6 kinase was activated by osmotic stress. These results demonstrate that PtdIns(3,4)P 2 can accumulate independently of PtdIns(3,4,5)P 3 and exerts a pattern of cellular responses that is distinct from that induced by accumulation of PtdIns(3,4,5)P 3 .The significance of PI 1 3-kinases in the regulation of a wide spectrum of cellular signaling events has been well established (1, 2). Based on structural features and substrate specificity, three classes of catalytic subunits of PI 3-kinases have so far been recognized (2, 3). The Type I class, members of which phosphorylate PtdIns, PtdIns4P, and PtdIns(4,5)P 2 in vitro but utilize PtdIns(4,5)P 2 as the likely substrate in vivo, is subdivided into Type I a and Type 1 b . Type I a PI 3-kinases interact with adaptor proteins containing SH2 domains that bind phosphotyrosine residues, linking this class to tyrosine kinase signaling cascades. Type 1 b PI 3-kinases are stimulated by Gprotein ␤␥ subunits and do not interact with SH2 domain containing adaptor proteins but with p101, a novel adaptor protein that has no homology with known proteins. Type II PI 3-kinases phosphorylate PtdIns and PtdIns4P in vitro (and not PtdIns(4,5)P 2 ) and contain a C2 domain, implicated in lipid binding. Type III PI 3-kinases only phosphorylate PtdIns and are thought to be constitutively active. They can be recruited and regulated by their adaptor, a dual specificity protein kinase, with which they form heterodimers.The principle enzymatic activity of PI 3-kinases involves the phosphorylation of phosphoinositides on the 3-position of the inositol ring, resulting in the formation of 3-phosphoinositides, which can either directly interact with appropriate modules of specific target proteins or first under...

The Major Target of the Endogenously Generated Reactive Oxygen Species in Response to Insulin Stimulation Is Phosphatase and Tensin Homolog and Not Phosphoinositide-3 Kinase (PI-3 Kinase) in the PI-3 Kinase/Akt Pathway

“…However, it is not clear how widely this can be applied across a variety of tyrosine phosphorylation-dependent signaling pathways. The examination of PI-3 kinase activity has demonstrated that the increase of PI-3 kinase activity in both SK-N-SH and SK-N-BE(2) cells is much lower in response to exogenous H 2 O 2 (Ͻ2-fold) than insulin (Ͼ7-fold) as noted in a previous report (Van der Kaay et al, 1999). This result suggests that exogenous oxidant is less effective than insulin stimulation in the activation of PI-3 kinase.…”

Identification of pleckstrin-homology-domain-containing proteins with novel phosphoinositide-binding specificities

“…However, the finding that agonists, such as hydrogen peroxide [30], and crosslinking of platelet-integrin receptors [31] elevate PtdIns(3,4)P # , without increasing PtdIns(3,4,5)P $ , suggest that PtdIns(3,4)P # may be able to regulate physiological processes distinct from those controlled by PtdIns(3,4,5)P $ . TAPP1 and TAPP2 ( Figure 3) are the first proteins to be identified that interact with PtdIns(3,4)P # specifically, and may therefore be key mediators of cellular responses that are regulated specifically by this second messenger.…”

The Type Iα Inositol Polyphosphate 4-Phosphatase Generates and Terminates Phosphoinositide 3-Kinase Signals on Endosomes and the Plasma Membrane

“…PtdIns(3,4)P 2 functions as a signaling molecule in growth factor-stimulated pathways and also is generated independently of PtdIns(3,4,5)P 3 in response to oxidative stress (Van der Kaay et al, 1999). The major metabolic pathway for PtdIns(3,4)P 2 synthesis in growth factor-stimulated cells is via 5-phosphatase hydrolysis of PtdIns(3,4,5)P 3 .…”

“…4,4,5)P 3 ] is a transient plasma membrane (PM) signal, rapidly hydrolyzed to phosphatidylinositol-(3,4)-bisphosphate [PtdIns(3,4)P 2 ] by the inositol polyphosphate 5-phosphatases (5-phosphatases) (Stephens et al, 1993;Mitchell et al, 2002). PtdIns(3,4)P 2 is a more sustained signal lasting for up to 60 min, stimulated by B-cell activation, oxidative stress, or irreversible platelet aggregation (Banfic et al, 1998;Van der Kaay et al, 1999;Marshall et al, 2002).…”