Article

Phosphorylation of inositol 1,4,5-trisphosphate receptors by protein kinase B/Akt inhibits Ca2+ release and apoptosis.

Laboratories of Molecular Signaling and Protein Technologies, The Babraham Institute, Cambridge CB2 3AT, United Kingdom.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 03/2008; 105(7):2427-32. DOI: 10.1073/pnas.0711324105
Source: PubMed

ABSTRACT Imbalance of signals that control cell survival and death results in pathologies, including cancer and neurodegeneration. Two pathways that are integral to setting the balance between cell survival and cell death are controlled by lipid-activated protein kinase B (PKB)/Akt and Ca(2+). PKB elicits its effects through the phosphorylation and inactivation of proapoptotic factors. Ca(2+) stimulates many prodeath pathways, among which is mitochondrial permeability transition. We identified Ca(2+) release through inositol 1,4,5-trisphosphate receptor (InsP(3)R) intracellular channels as a prosurvival target of PKB. We demonstrated that in response to survival signals, PKB interacts with and phosphorylates InsP(3)Rs, significantly reducing their Ca(2+) release activity. Moreover, phosphorylation of InsP(3)Rs by PKB reduced cellular sensitivity to apoptotic stimuli through a mechanism that involved diminished Ca(2+) flux from the endoplasmic reticulum to the mitochondria. In glioblastoma cells that exhibit hyperactive PKB, the same prosurvival effect of PKB on InsP(3)R was found to be responsible for the insensitivity of these cells to apoptotic stimuli. We propose that PKB-mediated abolition of InsP(3)-induced Ca(2+) release may afford tumor cells a survival advantage.

0 Bookmarks
 · 
76 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Cell-death and -survival decisions are critically controlled by intracellular Ca2 + homeostasis and dynamics at the level of the endoplasmic reticulum (ER). Inositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs) play a pivotal role in these processes by mediating Ca2 + flux from the ER into the cytosol and mitochondria. Hence, it is clear that many pro-survival and pro-death signaling pathways and proteins affect Ca2 + signaling by directly targeting IP3R channels, which can happen in an IP3R-isoform-dependent manner. In this review, we will focus on how the different IP3R isoforms (IP3R1, IP3R2 and IP3R3) control cell death and survival. First, we will present an overview of the isoform-specific regulation of IP3Rs by cellular factors like IP3, Ca2 +, Ca2 +-binding proteins, adenosine triphosphate (ATP), thiol modification, phosphorylation and interacting proteins, and of IP3R-isoform specific expression patterns. Second, we will discuss the role of the ER as a Ca2 + store in cell death and survival and how IP3Rs and pro-survival/pro-death proteins can modulate the basal ER Ca2 + leak. Third, we will review the regulation of the Ca2 +-flux properties of the IP3R isoforms by the ER-resident and by the cytoplasmic proteins involved in cell death and survival as well as by redox regulation. Hence, we aim to highlight the specific roles of the various IP3R isoforms in cell-death and -survival signaling. This article is part of a Special Issue entitled: Calcium Signaling In Health and Disease.
    Biochimica et Biophysica Acta (BBA) - Molecular Cell Research 01/2014; · 4.81 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: VDAC1, an outer mitochondrial membrane (OMM) protein, is crucial for regulating mitochondrial metabolic and energetic functions and acts as a convergence point for various cell survival and death signals. VDAC1 is also a key player in apoptosis, involved in cytochrome c release and interactions with anti-apoptotic proteins. Recently, we demonstrated that various pro-apoptotic agents induce VDAC1 oligomerization and proposed that a channel formed by VDAC1 oligomers mediates cytochrome c release. As VDAC1 transports Ca(2+) across the OMM and because Ca(2+) has been implicated in apoptosis induction, we addressed the relationship between cytosolic Ca(2+) levels ([Ca2+]i), VDAC1 oligomerization and apoptosis induction. We demonstrate that different apoptosis inducers elevate cytosolic Ca(2+) and induce VDAC1 over-expression. Direct elevation of [Ca(2+)]i by the Ca(2+)-mobilizing agents A23187, ionomycin and thapsigargin also resulted in VDAC1 over-expression, VDAC1 oligomerization and apoptosis. In contrast, decreasing [Ca(2+)]i using the cell-permeable Ca(2+)-chelating reagent BAPTA-AM inhibited VDAC1 over-expression, VDAC1 oligomerization and apoptosis. Correlation between the increase in VDAC1 levels and oligomerization, [Ca(2+)]i levels and apoptosis induction, as induced by H2O2 or As2O3, was also obtained. On the other hand, cells transfected to overexpress VDAC1 presented Ca(2+)-independent VDAC1 oligomerization, cytochrome c release and apoptosis, suggesting that [Ca(2+)]i elevation is not pre-requisite for apoptosis induction when VDAC1 is over-expressed. The results suggest that Ca(2+) promotes VDAC1 over-expression by an as yet unknown signaling pathway, leading to VDAC1 oligomerization, ultimately resulting in apoptosis. These findings provide new insight into the mechanism of action of existing anti-cancer drugs involving induction of VDAC1 over-expression as a mechanism for inducing apoptosis. This article is part of a Special Issue entitled: Calcium Signaling In Health and Disease.
    Biochimica et Biophysica Acta 04/2014; · 4.66 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Anti-apoptotic Bcl-2 contributes to cancer formation and progression by promoting the survival of altered cells. Hence, it is a prime target for novel specific anti-cancer therapeutics. In addition to its canonical anti-apoptotic role, Bcl-2 has an inhibitory effect on cell-cycle progression. Bcl-2 acts at two different intracellular compartments, the mitochondria and the endoplasmic reticulum (ER). At the mitochondria, Bcl-2 via its hydrophobic cleft scaffolds the Bcl-2-homology (BH) domain 3 (BH3) of pro-apoptotic Bcl-2-family members. Small molecules (like BH3 mimetics) can disrupt this interaction, resulting in apoptotic cell death in cancer cells. At the ER, Bcl-2 modulates Ca(2+) signaling, thereby promoting proliferation while increasing resistance to apoptosis. Bcl-2 at the ER acts via its N-terminal BH4 domain, which directly binds and inhibits the inositol 1,4,5-trisphosphate receptor (IP3R), the main intracellular Ca(2+)-release channel. Tools targeting the BH4 domain of Bcl-2 reverse Bcl-2's inhibitory action on IP3Rs and trigger pro-apoptotic Ca(2+) signaling in cancer B-cells, including chronic lymphocytic leukemia (CLL) cells and diffuse large B-cell lymphoma (DLBCL) cells. The sensitivity of DLBCL cells to BH4-domain targeting tools strongly correlated with the expression levels of the IP3R2 channel, the IP3R isoform with the highest affinity for IP3. Interestingly, bio-informatic analysis of a database of primary CLL patient cells also revealed a transcriptional upregulation of IP3R2. Finally, this review proposes a model, in which cancer cell survival depends on Bcl-2 at the mitochondria and/or the ER. This dependence likely will have an impact on their responses to BH3-mimetic drugs and BH4-domain targeting tools. This article is part of a Special Issue entitled: Calcium Signaling In Health and Disease.
    Biochimica et Biophysica Acta 04/2014; · 4.66 Impact Factor

Full-text (2 Sources)

View
14 Downloads
Available from
Jun 2, 2014