Nuclear but Not Cytosolic Phosphoinositide 3-Kinase Beta Has an Essential Function in Cell Survival

Department of Immunology and Oncology, Centro Nacional de Biotecnología/CSIC, Darwin 3, Campus de Cantoblanco, Madrid E-28049, Spain.
Molecular and Cellular Biology (Impact Factor: 5.04). 03/2011; 31(10):2122-33. DOI: 10.1128/MCB.01313-10
Source: PubMed

ABSTRACT Class I(A) phosphoinositide 3-kinases (PI3Ks) are heterodimeric enzymes composed of a p85 regulatory and a p110 catalytic subunit that induce the formation of 3-polyphosphoinositides, which mediate cell survival, division, and migration. There are two ubiquitous PI3K isoforms p110α and p110β that have nonredundant functions in embryonic development and cell division. However, whereas p110α concentrates in the cytoplasm, p110β localizes to the nucleus and modulates nuclear processes such as DNA replication and repair. At present, the structural features that determine p110β nuclear localization remain unknown. We describe here that association with the p85β regulatory subunit controls p110β nuclear localization. We identified a nuclear localization signal (NLS) in p110β C2 domain that mediates its nuclear entry, as well as a nuclear export sequence (NES) in p85β. Deletion of p110β induced apoptosis, and complementation with the cytoplasmic C2-NLS p110β mutant was unable to restore cell survival. These studies show that p110β NLS and p85β NES regulate p85β/p110β nuclear localization, supporting the idea that nuclear, but not cytoplasmic, p110β controls cell survival.

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Available from: Vicente Pérez-García, Mar 06, 2014
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    • "However, measurement of PIP 3 levels revealed that BYL719 did not fully suppress PIP 3 levels in PIK3CA mutant cells, especially after 24 hr, and combined inhibition of p110a and p110b resulted in stronger reduction of PIP 3 levels than BYL719 alone (Figure 4C). Because p110b has been shown to induce phosphorylation of nuclear AKT (Kumar et al., 2011), we determined if inhibition of p110b affected AKT signaling specifically in the nucleus, which may have been missed in assessments of AKT phosphorylation in whole cell lysates (Figure 4B). However, in the PIK3CA mutant cell line MCF7, p110b did not control AKT phosphorylation in either the cytoplasm or the nucleus (Figure S4A). "
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    ABSTRACT: BYL719, which selectively inhibits the alpha isoform of the phosphatidylinositol 3-kinase (PI3K) catalytic subunit (p110a), is currently in clinical trials for the treatment of solid tumors, especially luminal breast cancers with PIK3CA mutations and/or HER2 amplification. This study reveals that, even among these sensitive cancers, the initial efficacy of p110α inhibition is mitigated by rapid re-accumulation of the PI3K product PIP3 produced by the p110β isoform. Importantly, the reactivation of PI3K mediated by p110β does not invariably restore AKT phosphorylation, demonstrating the limitations of using phospho-AKT as a surrogate to measure PI3K activation. Consistently, we show that the addition of the p110β inhibitor to BYL719 prevents the PIP3 rebound and induces greater antitumor efficacy in HER2-amplified and PIK3CA mutant cancers. Copyright © 2015 Elsevier Inc. All rights reserved.
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    • "Recombinant and endogenous p85a yielded a similar pattern, although the exogenous protein was expressed at higher levels (Fig. 1A). In contrast, p85b localized in the nucleus, as reported (Kumar et al., 2011), as well as in the first confocal zsection in contact with the matrix, where endogenous and recombinant p85b showed similar dotted staining patterns (Fig. 1A). Preincubation of cells with the p85b Ab plus its antigenic peptide eliminated most of the p85b signal, indicating Ab signal specificity (Fig. 1A). "
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    Biology Open 09/2014; 3(10). DOI:10.1242/bio.20148185 · 2.42 Impact Factor
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    • "ing in cell signaling ( class I , II ) or membrane trafficking ( class II , III ) . Although not yet widely addressed , members of different PI3K classes can act at successive steps in shared pathways and processes ( Dou et al . , 2010 ; Lu et al . , 2012 ) . There are also emerging descriptions of PI3K localization and / or roles in the nucleus ( Kumar et al . , 2011 ) ."
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    ABSTRACT: The phosphoinositide 3-kinase (PI3K) family is important to nearly all aspects of cell and tissue biology and central to human cancer, diabetes and aging. PI3Ks are spatially regulated and multifunctional, and together, act at nearly all membranes in the cell to regulate a wide range of signaling, membrane trafficking and metabolic processes. There is a broadening recognition of the importance of distinct roles for each of the three different PI3K classes (I, II and III), as well as for the different isoforms within each class. Ongoing issues include the need for a better understanding of the in vivo complexity of PI3K regulation and cellular functions. This Cell Science at a Glance article and the accompanying poster summarize the biochemical activities, cellular roles and functional requirements for the three classes of PI3Ks. In doing so, we aim to provide an overview of the parallels, the key differences and crucial interplays between the regulation and roles of the three PI3K classes.
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