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.

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    Frontiers in oncology. 01/2014; 4:276.
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    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
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    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

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