PI3K/Akt signaling requires spatial compartmentalization in plasma membrane microdomains

Department of Pharmacology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 08/2011; 108(35):14509-14. DOI: 10.1073/pnas.1019386108
Source: PubMed


Spatial compartmentalization of signaling pathway components generally defines the specificity and enhances the efficiency of signal transduction. The phosphatidylinositol 3-kinase (PI3K)/Akt pathway is known to be compartmentalized within plasma membrane microdomains; however, the underlying mechanisms and functional impact of this compartmentalization are not well understood. Here, we show that phosphoinositide-dependent kinase 1 is activated in membrane rafts in response to growth factors, whereas the negative regulator of the pathway, phosphatase and tensin homolog deleted on chromosome 10 (PTEN), is primarily localized in nonraft regions. Alteration of this compartmentalization, either by genetic targeting or ceramide-induced recruitment of PTEN to rafts, abolishes the activity of the entire pathway. These findings reveal critical steps in raft-mediated PI3K/Akt activation and demonstrate the essential role of membrane microdomain compartmentalization in enabling PI3K/Akt signaling. They further suggest that dysregulation of this compartmentalization may underlie pathological complications such as insulin resistance.

Full-text preview

Available from:
  • Source
    • "PI3K activates PKC f (Le Good et al., 1998) and PKC f inhibition using a specific blocker or siRNA against PKC f reversed the increase in K Ca 1.1 levels in the gastric SMCs of CerS2-null mice, suggesting that PI3K activation plays a critical role in K Ca 1.1 upregulation. PI3K activation by phosphorylation might be caused by a change in lipid rafts, which are associated with several signal transduction molecules including Src family kinases and small G proteins (Yoshizaki et al., 2008) and act as important regulators of PI3K (Gao et al., 2011). In addition, K Ca 1.1 is localized to caveolae (Brainard et al., 2005), a subset of lipid rafts, and has a caveolin-binding motif (Suzuki et al., 2013). "
    [Show abstract] [Hide abstract]
    ABSTRACT: KC a 1.1 regulates smooth muscle contractility by modulating membrane potential, and age-associated changes in KC a 1.1 expression may contribute to the development of motility disorders of the gastrointestinal tract. Sphingolipids (SLs) are important structural components of cellular membranes whose altered composition may affect KC a 1.1 expression. Thus, in this study, we examined whether altered SL composition due to aging may affect the contractility of gastric smooth muscle (GSM). We studied changes in ceramide synthases (CerS) and SL levels in the GSM of mice of varying ages and compared them with those in young CerS2-null mice. The levels of C16- and C18-ceramides, sphinganine, sphingosine, and sphingosine 1-phosphate were increased, and levels of C22, C24:1 and C24 ceramides were decreased in the GSM of both aged wild-type and young CerS2-null mice. The altered SL composition upregulated KC a 1.1 and increased KC a 1.1 currents, while no change was observed in KC a 1.1 channel activity. The upregulation of KC a 1.1 impaired intracellular Ca(2+) mobilization and decreased phosphorylated myosin light chain levels, causing GSM contractile dysfunction. Additionally, phosphoinositide 3-kinase, protein kinase Cζ , c-Jun N-terminal kinases, and nuclear factor kappa-B were found to be involved in KC a 1.1 upregulation. Our findings suggest that age-associated changes in SL composition or CerS2 ablation upregulate KC a 1.1 via the phosphoinositide 3-kinase/protein kinase Cζ /c-Jun N-terminal kinases/nuclear factor kappa-B-mediated pathway and impair Ca(2+) mobilization, which thereby induces the contractile dysfunction of GSM. CerS2-null mice exhibited similar effects to aged wild-type mice; therefore, CerS2-null mouse models may be utilized for investigating the pathogenesis of aging-associated motility disorders. © 2015 The Authors. Aging Cell published by the Anatomical Society and John Wiley & Sons Ltd.
    Full-text · Article · Aug 2015 · Aging cell
  • Source
    • "Thus, stimulation by different growth factors may result in different mechanisms of Akt activation at membrane microdomains. Gao et al. (2011) further investigated the regulatory mechanisms of the compartmentalized activities of PI3 K/ Akt at membrane microdomains (Gao et al. 2011). This study investigated at which membrane microdomains the Akt-related signaling molecules are localized to regulate the spatiotemporal activation of Akt. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Cells recognize and process various extracellular signals via transmembrane receptors and membrane-associated signaling molecules. Therefore, the precise regulation of these signaling events at the plasma membrane, which occur spatiotemporally, is necessary for proper cellular functions such as cell proliferation, migration, and survival. The plasma membrane may contain dynamic microdomains called lipid rafts, which are suggested to be crucial for the regulation of efficient and specific signaling pathways. However, because of the limitation in methodologies, the specific molecular mechanisms underlying dynamic signaling events at lipid rafts are largely unknown. This review discusses the traditional biochemical methods for the visualization of lipid rafts and the related signaling events at these microdomains. In addition, the review reports on fluorescence resonance energy transfer (FRET)-based molecular biosensors with lipid rafts targeting sequences as a powerful tool for live-cell imaging of spatiotemporal signaling events at lipid rafts. In particular, examples of dynamic lipid rafts signaling mechanisms visualized by FRET-based biosensors in live cells are covered in the last section.
    Full-text · Article · May 2015 · Journal of the Korean Society for Applied Biological Chemistry
  • Source
    • "This protocol was adapted from [51], [52]. Briefly, confluent transfected HeLa cells were washed with ice-cold PBS, scraped, collected in 1 mL of lysis buffer (10 mM Tris, pH 7.4, 150 mM NaCl, 5 mM EDTA, 2 mM PMSF, 20 µg/ml leupeptin, and 20 µg/ml aprotinin, 1% Triton X100) and left on ice for 1 h. "
    [Show abstract] [Hide abstract]
    ABSTRACT: We developed genetically-encoded fluorescent sensors based on Förster Resonance Energy Transfer to monitor phosphatidic acid (PA) fluctuations in the plasma membrane using Spo20 as PA-binding motif. Basal PA levels and phospholipase D activity varied in different cell types. In addition, stimuli that activate PA phosphatases, leading to lower PA levels, increased lamellipodia and filopodia formation. Lower PA levels were observed in the leading edge than in the trailing edge of migrating HeLa cells. In MSC80 and OLN93 cells, which are stable cell lines derived from Schwann cells and oligodendrocytes, respectively, a higher ratio of diacylglycerol to PA levels was demonstrated in the membrane processes involved in myelination, compared to the cell body. We propose that the PA sensors reported here are valuable tools to unveil the role of PA in a variety of intracellular signaling pathways.
    Full-text · Article · Jul 2014 · PLoS ONE
Show more