Mitogen-activated Protein Kinase Extracellular Signal-regulated Kinase 2 Phosphorylates and Promotes Pin1 Protein-dependent Promyelocytic Leukemia Protein Turnover

Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4935, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 12/2011; 286(52):44403-11. DOI: 10.1074/jbc.M111.289512
Source: PubMed


The promyelocytic leukemia (PML) protein is a tumor suppressor that has an important role in several cellular processes, including apoptosis, viral infection, DNA damage repair, cell cycle regulation, and senescence. PML is an essential component of sub-nuclear structures called PML nuclear bodies (NBs). Our laboratory has previously demonstrated that the peptidyl-prolyl cis-trans isomerase, Pin1, binds and targets PML for degradation in a phosphorylation-dependent manner. To further elucidate the mechanisms underlying Pin1-mediated PML degradation, we aimed to identify one or more factors that promote PML phosphorylation. Here we show that treatment with U0126, an inhibitor of the ERK2 upstream kinases MEK1/2, leads to an increase in PML protein accumulation and an inhibition of the interaction between Pin1 and PML in MDA-MB-231 breast cancer cells. Consistent with this observation, phosphorylated ERK2 partially co-localized with PML NBs. Although U0126 up-regulated exogenous wild-type PML levels, it did not have an effect on the steady-state level of a mutant form of PML that is defective in binding Pin1. In addition, exogenous wild-type, but not Pin1 binding-defective PML protein expression levels were decreased by overexpression of ERK2. In contrast, knockdown of ERK2 by siRNA resulted in an increase in PML protein levels and an increase in the formation of PML NBs. Using phospho-specific antibodies, we identified Ser-403 and Ser-505 as the ERK2 targets that promote Pin1-mediated PML degradation. Finally, we demonstrated that EGF induced activation of ERK and interaction between PML and phosphorylated ERK resulting in a decrease in PML protein levels. Taken together, our results support a model in which Pin1 promotes PML degradation in an ERK2-dependent manner.

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    • "Another example of this sequential PML preconditioning occurs with the extracellular signal regulated kinase 2 (ERK2), which is able to localize to the PML-NBs in breast cancer cells (MDA-MB-231), phosphorylate PML at two sites (S403 and S505), resulting in the recruitment of Pin1, and subsequent proteasomal degradation of PML by yet to be identified E3 ligase (Lim et al., 2011). Addition of hydrogen peroxide was capable of attenuating the association between PML and Pin1 to maintain PML levels. "
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    ABSTRACT: The tumor suppressor function of the promyelocytic leukemia (PML) protein was first identified as a result of its dysregulation in acute promyelocytic leukemia, however, its importance is now emerging far beyond hematological neoplasms, to an extensive range of malignancies, including solid tumors. In response to stress signals, PML coordinates the regulation of numerous proteins, which activate fundamental cellular processes that suppress tumorigenesis. Importantly, PML itself is the subject of specific post-translational modifications, including ubiquitination, phosphorylation, acetylation, and SUMOylation, which in turn control PML activity and stability and ultimately dictate cellular fate. Improved understanding of the regulation of this key tumor suppressor is uncovering potential opportunities for therapeutic intervention. Targeting the key negative regulators of PML in cancer cells such as casein kinase 2, big MAP kinase 1, and E6-associated protein, with specific inhibitors that are becoming available, provides unique and exciting avenues for restoring tumor suppression through the induction of apoptosis and senescence. These approaches could be combined with DNA damaging drugs and cytokines that are known to activate PML. Depending on the cellular context, reactivation or enhancement of tumor suppressive PML functions, or targeted elimination of aberrantly functioning PML, may provide clinical benefit.
    Frontiers in Oncology 05/2013; 3:124. DOI:10.3389/fonc.2013.00124
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    • "Instead, deregulated ubiquitination appears to be the common mechanism accounting for PML loss in cancer. Several mechanisms have been reported to be involved in PML ubiquitination (Fanelli et al., 2004; Scaglioni et al., 2006; Lallemand-Breitenbach et al., 2008; Louria-Hayon et al., 2009; Reineke et al., 2010; Lim et al., 2011; Yuan et al., 2011; Chen et al., 2012; Rabellino et al., 2012; Wolyniec et al., 2012). We will review their biological significance in tumorigenesis and in viral infection. "
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    ABSTRACT: The promyelocytic leukemia tumor suppressor gene (PML) critically regulates several cellular functions that oppose tumorigenesis such as oncogene-induced senescence, apoptosis, the response to DNA damage and to viral infections. PML deficiency occurs commonly in a broad spectrum of human cancers through mechanisms that involve its aberrant ubiquitination and degradation. Furthermore, several viruses encode viral proteins that promote viral replication through degradation of PML. These observations suggest that restoration of PML should lead to potent antitumor effects or antiviral responses. In this review we will summarize the mechanisms involved in PML degradation with the intent to highlight novel therapeutic strategies to trigger PML restoration.
    Frontiers in Oncology 03/2013; 3:60. DOI:10.3389/fonc.2013.00060
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    • "Docking of Pin1 to PML then leads to destabilization of PML. Basal PML phosphorylation at Ser403 and Ser505 is detectable in unstimulated cells and can also be further induced by EGF stimulation (Lim et al., 2011), implying that this mechanism regulates PML levels under steady-state and inducible conditions. The phosphorylation site at Ser403 can be also mediated by BMK1/ERK5 (big MAP kinase). "
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    ABSTRACT: Post-translational modifications (PTMs) regulate multiple biological functions of the promyelocytic leukemia (PML) protein and also the fission, disassembly, and rebuilding of PML nuclear bodies (PML-NBs) during the cell cycle. Pathway-specific PML modification patterns ensure proper signal output from PML-NBs that suit the specific functional requirements. Here we comprehensively review the signaling pathways and enzymes that modify PML and also the oncogenic PML-RARα fusion protein. Many PTMs occur in a hierarchical and timely organized fashion. Phosphorylation or acetylation constitutes typical starting points for many PML modifying events, while degradative ubiquitination is an irreversible end point of the modification cascade. As this hierarchical organization of PTMs frequently turns phosphorylation events as primordial events, kinases or phosphatases regulating PML phosphorylation may be interesting drug targets to manipulate the downstream modifications and thus the stability and function of PML or PML-RARα.
    Frontiers in Oncology 12/2012; 2:204. DOI:10.3389/fonc.2012.00204
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