Phosphoinositide 3-Kinase Regulates Phospholipase Cγ-mediated Calcium Signaling

Abstract

It has been demonstrated that the lipid products of the phosphoinositide 3-kinase (PI3K) can associate with the Src homology 2 (SH2) domains of specific signaling molecules and modify their actions. In the current experiments, phosphatidylinositol 3,4,5-trisphosphate (PtdIns-3,4,5-P 3 ) was found to bind to the C-terminal SH2 domain of phospholipase C␥ (PLC␥) with an apparent K d of 2.4 M and to displace the C-terminal SH2 domain from the activated platelet-derived growth factor receptor (PDGFR). To investigate the in vivo relevance of this observation, intracellular inositol trisphosphate (IP 3 ) generation and calcium release were examined in HepG2 cells expressing a series of PDGFR mutants that activate PLC␥ with or without receptor association with PI3K. Coactivation of PLC␥ and PI3K resulted in an ϳ40% increase in both intracellular IP 3 generation and intracellular calcium release as compared with selective activation of PLC␥. Similarly, the addition of wortmannin or LY294002 to cells expressing the wild-type PDGFR inhibited the release of intracellular calcium. Thus, generation of PtdIns-3,4,5-P 3 by receptor-associated PI3K causes an increase in IP 3 production and intracellular calcium release, potentially via enhanced PtdIns-4,5-P 2 substrate availability due to PtdIns-3,4,5-P 3 -mediated recruitment of PLC␥ to the lipid bilayer.Activation of the receptor-associated phosphoinositide 3-kinase (PI3K) 1 has been shown to cause mitogenesis and enhanced cell motility, although the exact mechanism by which PI3K mediates cell signaling during these events has been difficult to elucidate (1-3). The lipid products of PI3K have now been found to activate certain calcium-independent protein kinases C and to bind to a subset of Src homology 2 (SH2) domains (4, 5). In addition, PtdIns-3,4-P 2 and/or PtdIns-3,4,5-P 3 has been found to bind to and/or stimulate several pleckstrin homology (PH) domain-containing proteins, including the Akt/PKB serine/threonine protein kinase (6, 7), the PDK serine/threonine protein kinase (8), and the Grp1 exchange factor for Arf1 (9). Falasca et al. (10) have demonstrated that the PH domain of phospholipase C␥ will bind to PtdIns-3,4,5-P 3 , targeting PLC␥ to the membrane.Recently, Bae et al. (11) have found that the addition of PtdIns-3,4,5-P 3 can enhance phospholipase C␥-mediated PtdIns-4,5-P 2 hydrolysis in vitro and that overexpression of a constitutively active form of the p110 catalytic subunit of PI3K increases intracellular IP 3 levels, raising the possibility that PtdIns-3,4,5-P 3 may regulate calcium signaling as well. This possibility is supported by the observation that wortmannin, an inhibitor of the catalytic site of PI3K, as well as several related enzymes, diminishes the intracellular calcium transient seen in adrenal glomerulosa cells, neutrophils, and rat leukemia cells following stimulation (12-15).To determine whether phospholipase C␥ might interact with the lipid products of PI3K in a manner capable of modifying ligand-dependent IP 3 generation and calcium sign...

Novel pathway in Bcr-Abl signal transduction involves Akt-independent, PLC-γ1-driven activation of mTOR/p70S6-kinase pathway

“…Recruitment of PLC-g1 to the membrane by PI 3,4,5 P 3 (PIP3), produced by the action of PI3Ks, has been shown to have a function in PLC-g activation (Falasca et al, 1998;Rameh et al, 1998;Maffucci and Falasca, 2007). In agreement with the literature, we detected PI3K activation in BCR-ABL-positive K562 cells (Supplementary Figure 2, right).…”

Calcium Mobilization Evoked by Hepatocellular Swelling Is Linked to Activation of Phospholipase Cγ

“…PI 3-kinase is required for volume recovery after hepatocellular swelling (27), but it is uncertain whether it is involved in swelling-mediated PLC␥ activation. Specifically, activation of PLC␥ by PI 3-kinase appears to be independent of tyrosine phosphorylation (26); yet tyrosine phosphorylation of PLC␥ was seen in the present study. Thus, regulators of PLC␥ other than PI 3-kinase warrant consideration.…”

The mechanism of phospholipase C-γ1 regulation

“…The influence of PIP 3 on the PLC-γ1 activity has been looked at more closely. In these reports, the investigators suggested that PIP 3 recognized the C-terminal SH2 domain of PLC-γ1 in vitro (Bae et al, 1998;Rameh et al, 1998). Moreover, they demonstrated that inhibition of the PI-3K activity using a specific inhibitor could attenuate PLC-γ1 activation (Bae et al, 1998;Rameh et al, 1998).…”

“…The N-terminal SH2 domain of PLC-γ1 is known to play a major role in the association with the activated growth factor receptor, while the C-terminal SH2 domain is considered to play a minor role (Chattopadyay et al, 1999;Poulin et al, 2000). However, recently, it has been reported that the C-terminal SH2 domain of PLC-γ1 is involved in interactions with synaptojanin (Ahn et al, 1998), the actin-cytoskeleton (Pei et al, 1996), PIP 3 (Bae et al, 1998;Rameh et al, 1998) and FAK (Zhang et al, 1999). These observations suggest that the two SH2 domains of PLC-γ1 are dissimilar and may mediate the recognition of specific phosphorylation sites.…”