PHLPP: A Phosphatase that Directly Dephosphorylates Akt, Promotes Apoptosis, and Suppresses Tumor Growth

Gao, Tianyan; Furnari, Frank B.; Newton, Alexandra C.

doi:10.1016/j.molcel.2005.03.008

Cited by 809 publications

(984 citation statements)

References 37 publications

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“…The presence of an acidic residue allows the atypical PKCs to constitutively associate with PDK1 (Balendran et al, 2000). In addition, this acidic residue should render the atypical PKCs resistant to the protein phosphatase PHLPP, which inactivates Akt by dephosphorylating its hydrophobic motif (Gao et al, 2005).…”

Section: Discussionmentioning

confidence: 99%

Repression of cancer cell senescence by PKCι

et al. 2011

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Section: Discussionmentioning

confidence: 99%

Repression of cancer cell senescence by PKCι

et al. 2011

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“…The PHLPP2 is a member of this family. 2,3 To date four PHLPP substrates, Akt, PKC, Mst1 and S6K1, have been identified, all kinases involved in cell survival or apoptosis. [4][5][6][7] Dephosphorylation inactivates Akt, S6K1 and PKC, and subsequently cell survival signaling, whereas dephosphorylation of Mst1 activates its apoptotic function.…”

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confidence: 99%

Transcription factor C/EBP-β induces tumor-suppressor phosphatase PHLPP2 through repression of the miR-17–92 cluster in differentiating AML cells

et al. 2016

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PHLPP2, a member of the PH-domain leucine-rich repeat protein phosphatase (PHLPP) family, which targets oncogenic kinases, has been actively investigated as a tumor suppressor in solid tumors. Little is known, however, regarding its regulation in hematological malignancies. We observed that PHLPP2 protein expression, but not its mRNA, was suppressed in late differentiation stage acute myeloid leukemia (AML) subtypes. MicroRNAs (miR or miRNAs) from the miR-17-92 cluster, oncomir-1, were shown to inhibit PHLPP2 expression and these miRNAs were highly expressed in AML cells that lacked PHLPP2 protein.Studies showed that miR-17-92 cluster regulation was, surprisingly, independent of transcription factors c-MYC and E2F in these cells; instead all-trans-retinoic acid (ATRA), a drug used for terminally differentiating AML subtypes, markedly suppressed miR-17-92 expression and increased PHLPP2 protein levels and phosphatase activity. Finally, we demonstrate that the effect of ATRA on miR-17-92 expression is mediated through its target, transcription factor C/EBPβ, which interacts with the intronic promoter of the miR-17-92 gene to inhibit transactivation of the cluster. These studies reveal a novel mechanism for upregulation of the phosphatase activity of PHLPP2 through C/EBPβ-mediated repression of the miR-17-92 cluster in terminally differentiating myeloid cells. Phosphatases are pivotal components of intracellular signaling cascades, controlling essential processes like metabolism, apoptosis, proliferation and differentiation. 1 The PH-domain leucine-rich repeat protein phosphatase (PHLPP) family serine-threonine phosphatases are emerging as central factors in cell survival and death regulation. The PHLPP2 is a member of this family. 2,3 To date four PHLPP substrates, Akt, PKC, Mst1 and S6K1, have been identified, all kinases involved in cell survival or apoptosis. 4-7 Dephosphorylation inactivates Akt, S6K1 and PKC, and subsequently cell survival signaling, whereas dephosphorylation of Mst1 activates its apoptotic function.PHLPP protein expression and activity is suppressed through various mechanisms in cancers. Although most studies on PHLPP2 have focused on genetic alterations in solid tumors, 8 PHLPP2 protein expression in small cell lung and colorectal cancers is also restricted through translational suppression 9 and post-transcriptional control by microRNAs (miR or miRNAs), miR-205 and miR-224. 10,11 The PHLPP2 3' untranslated region (3'UTR) harbors complementary binding sites for a subset of miRNAs belonging to the miRNA-17-92 cluster. 12 This cluster comprises six miRNAs on chromosome 13, transcribed as a single polycistronic unit. 13,14 Also known as oncomir-1, the cluster enhances cell proliferation or inhibits apoptosis by suppressing targets such as Bim, E2F1 and PTEN and is markedly overexpressed in human cancers. [15][16][17][18][19][20][21] Reduced levels of PHLPP2 in chemoresistant miR-17-92 overexpressing mantle cell lymphomas had suggested that the phosphatase could be a target of oncomir-1. 12 Kno...

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“…12 Because correct regulation of AKT is of paramount importance, multiple mechanisms have evolved to terminate or limit its activation. Those mechanisms involve AKT dephosphorylation by a variety of phosphatases [13][14][15][16][17] or its degradation by E3 ligases. 18,19 We describe here the identification of HPIP as a MDM2 substrate.…”

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confidence: 99%

MDM2 restrains estrogen-mediated AKT activation by promoting TBK1-dependent HPIP degradation

et al. 2014

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Restoration of p53 tumor suppressor function through inhibition of its interaction and/or enzymatic activity of its E3 ligase, MDM2, is a promising therapeutic approach to treat cancer. However, because the MDM2 targetome extends beyond p53, MDM2 inhibition may also cause unwanted activation of oncogenic pathways. Accordingly, we identified the microtubuleassociated HPIP, a positive regulator of oncogenic AKT signaling, as a novel MDM2 substrate. MDM2-dependent HPIP degradation occurs in breast cancer cells on its phosphorylation by the estrogen-activated kinase TBK1. Importantly, decreasing Mdm2 gene dosage in mouse mammary epithelial cells potentiates estrogen-dependent AKT activation owing to HPIP stabilization. In addition, we identified HPIP as a novel p53 transcriptional target, and pharmacological inhibition of MDM2 causes p53-dependent increase in HPIP transcription and also prevents HPIP degradation by turning off TBK1 activity. Our data indicate that p53 reactivation through MDM2 inhibition may result in ectopic AKT oncogenic activity by maintaining HPIP protein levels. Cell Death and Differentiation (2014) 21, 811-824; doi:10.1038/cdd.2014.2; published online 31 January 2014Restoration of p53 tumor suppressor function in cancer cells expressing wild-type (WT) p53 is a promising therapeutic approach. 1 Reactivation of p53 activity can be achieved by small molecular inhibitors that disrupt the interaction between p53 and its main E3 ligase MDM2. As a result, targeted cells undergo cell cycle arrest and apoptosis through p53 stabilization. 2 A potential drawback associated with this approach is that, besides p53, MDM2 targets other substrates for degradation. 3 In this context, accumulative evidence show that MDM2 promotes the degradation of FOXO3a, a tumor-suppressing transcription factor as well as the apoptosome activator CAS and the ubiquitin E3 ligase HUWE1. 4,5 Although it is currently unclear whether MDM2 targets positive regulators of oncogenic pathways, an exhaustive characterization of MDM2 substrates will help to anticipate undesired side effects of MDM2 inhibitors used in cancer therapy.Oncogenic pathways include AKT-dependent signaling cascades. Indeed, AKT promotes cell proliferation, survival, migration and angiogenesis by targeting numerous substrates ranging from anti-apoptotic transcription factors to regulators of protein synthesis. 6,7 Mutations or altered expressions of various AKT-activating signaling molecules have been described in human malignancies, thereby defining AKT as a hallmark of tumor development and progression. 8,9 AKT activation by estrogens requires the microtubule-binding protein hematopoietic PBX-interaction protein (HPIP). 10 Initially identified as a corepressor of pre-B-cell leukemia homeobox protein 1 (PBX1), 11 HPIP assembles a signaling complex that connects the p85 subunit of PI3K and ERa to microtubules in order to properly activate AKT. 10 Likewise, HPIP also promotes the growth and differentiation of hematopoietic cells through AKT. 12 Because correct reg...

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PHLPP: A Phosphatase that Directly Dephosphorylates Akt, Promotes Apoptosis, and Suppresses Tumor Growth

Cited by 809 publications

References 37 publications

Repression of cancer cell senescence by PKCι

Repression of cancer cell senescence by PKCι

Transcription factor C/EBP-β induces tumor-suppressor phosphatase PHLPP2 through repression of the miR-17–92 cluster in differentiating AML cells

MDM2 restrains estrogen-mediated AKT activation by promoting TBK1-dependent HPIP degradation

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