Biomedical subjects

Robin J Dickinson

Publications and source records attributed to Robin J Dickinson.

7 recordsLinked to original sources

PubMed2006

Diverse physiological functions for dual-specificity MAP kinase phosphatases.

A structurally distinct subfamily of ten dual-specificity (Thr/Tyr) protein phosphatases is responsible for the regulated dephosphorylation and inactivation of mitogen-activated protein kinase (MAPK) family members in mammals. These MAPK phosphatases (MKPs) interact specifically with their substrates through a modular kinase-interaction motif (KIM) located within the N-terminal non-catalytic domain of the protein. In addition, MAPK binding is often accompanied by enzymatic activation of the C-terminal catalytic domain, thus ensuring specificity of action. Despite our knowledge of the biochemical and structural basis for the catalytic mechanism of the MKPs, we know much less about their regulation and physiological functions in mammalian cells and tissues. However, recent studies employing a range of model systems have begun to reveal essential non-redundant roles for the MKPs in determining the outcome of MAPK signalling in a variety of physiological contexts. These include development, immune system function, metabolic homeostasis and the regulation of cellular stress responses. Interestingly, these functions may reflect both restricted subcellular MKP activity and changes in the levels of signalling through multiple MAPK pathways.

Animals↗

PubMed2006

Hippi is essential for node cilia assembly and Sonic hedgehog signaling.

Hippi functions as an adapter protein that mediates pro-apoptotic signaling from poly-glutamine-expanded huntingtin, an established cause of Huntington disease, to the extrinsic cell death pathway. To explore other functions of Hippi we generated Hippi knock-out mice. This deletion causes randomization of the embryo turning process and heart looping, which are hallmarks of defective left-right (LR) axis patterning. We report that motile monocilia normally present at the surface of the embryonic node, and proposed to initiate the break in LR symmetry, are absent on Hippi-/- embryos. Furthermore, defects in central nervous system development are observed. The Sonic hedgehog (Shh) pathway is downregulated in the neural tube in the absence of Hippi, which results in failure to establish ventral neural cell fate. Together, these findings demonstrate a dual role for Hippi in cilia assembly and Shh signaling during development, in addition to its proposed role in apoptosis signal transduction in the adult brain under pathogenically stressful conditions.

Adaptor Proteins, Signal Transducing↗

PubMed2005

The dual-specificity protein phosphatase DUSP9/MKP-4 is essential for placental function but is not required for normal embryonic development.

To elucidate the physiological role(s) of DUSP9 (dual-specificity phosphatase 9), also known as MKP-4 (mitogen-activated protein kinase [MAPK] phosphatase 4), the gene was deleted in mice. Crossing male chimeras with wild-type females resulted in heterozygous (DUSP9(+/-)) females. However, when these animals were crossed with wild-type (DUSP9(+/y)) males none of the progeny carried the targeted DUSP9 allele, indicating that both female heterozygous and male null (DUSP9(-/y)) animals die in utero. The DUSP9 gene is on the X chromosome, and this pattern of embryonic lethality is consistent with the selective inactivation of the paternal X chromosome in the extraembryonic tissues of the mouse, suggesting that DUSP9/MKP4 performs an essential function during placental development. Examination of embryos between 8 and 10.5 days postcoitum confirmed that lethality was due to a failure of labyrinth development, and this correlates exactly with the normal expression pattern of DUSP9/MKP-4 in the trophoblast giant cells and labyrinth of the placenta. Finally, when the placental defect was rescued, male null (DUSP9(-/y)) embryos developed to term, appeared normal, and were fertile. Our results indicate that DUSP9/MKP-4 is essential for placental organogenesis but is otherwise dispensable for mammalian embryonic development and highlights the critical role of dual-specificity MAPK phosphatases in the regulation of developmental outcomes in vertebrates.

Alleles↗

PubMed2004

Both nuclear-cytoplasmic shuttling of the dual specificity phosphatase MKP-3 and its ability to anchor MAP kinase in the cytoplasm are mediated by a conserved nuclear export signal.

MAP kinase phosphatase (MKP)-3 is a cytoplasmic dual specificity protein phosphatase that specifically binds to and inactivates the ERK1/2 MAP kinases in mammalian cells. However, the molecular basis of the cytoplasmic localization of MKP-3 or its physiological significance is unknown. We have used MKP-3-green fluorescent protein fusions in conjunction with leptomycin B to show that the cytoplasmic localization of MKP-3 is mediated by a chromosome region maintenance-1 (CRM1)-dependent nuclear export pathway. Furthermore, the nuclear translocation of MKP-3 seen in the presence of leptomycin B is mediated by an active process, indicating that MKP-3 shuttles between the nucleus and cytoplasm. The amino-terminal noncatalytic domain of MKP-3 is both necessary and sufficient for nuclear export of the phosphatase and contains a single functional leucine-rich nuclear export signal (NES). Even though this domain of the protein also mediates the binding of MKP-3 to MAP kinase, we show that mutations of the kinase interaction motif which abrogate ERK2 binding do not affect MKP-3 localization. Conversely, mutation of the NES does not affect either the binding or phosphatase activity of MKP-3 toward ERK2, indicating that the kinase interaction motif and NES function independently. Finally, we demonstrate that the ability of MKP-3 to cause the cytoplasmic retention of ERK2 requires both a functional kinase interaction motif and NES. We conclude that in addition to its established function in the regulated dephosphorylation and inactivation of MAP kinase, MKP-3 may also play a role in determining the subcellular localization of its substrate. Our results reinforce the idea that regulatory proteins such as MKP-3 may play a key role in the spatio-temporal regulation of MAP kinase activity.

3T3 Cells↗

PubMed2003

Negative feedback regulation of FGF signaling levels by Pyst1/MKP3 in chick embryos.

BACKGROUND: The importance of endogenous antagonists in intracellular signal transduction pathways is becoming increasingly recognized. There is evidence in cultured mammalian cells that Pyst1/MKP3, a dual specificity protein phosphatase, specifically binds to and inactivates ERK1/2 mitogen-activated protein kinases (MAPKs). High-level Pyst1/Mkp3 expression has recently been found at many sites of known FGF signaling in mouse embryos, but the significance of this association and its function are not known. RESULTS: We have cloned chicken Pyst1/Mkp3 and show that high-level expression in neural plate correlates with active MAPK. We show that FGF signaling regulates Pyst1 expression in developing neural plate and limb bud by ablating and/or transplanting tissue sources of FGFs and by applying FGF protein or a specific FGFR inhibitor (SU5402). We further show by applying a specific MAP kinase kinase inhibitor (PD184352) that Pyst1 expression is regulated via the MAPK cascade. Overexpression of Pyst1 in chick embryos reduces levels of activated MAPK in neural plate and alters its morphology and retards limb bud outgrowth. CONCLUSIONS: Pyst1 is an inducible antagonist of FGF signaling in embryos and acts in a negative feedback loop to regulate the activity of MAPK. Our results demonstrate both the importance of MAPK signaling in neural induction and limb bud outgrowth and the critical role played by dual specificity MAP kinase phosphatases in regulating developmental outcomes in vertebrates.

Animals↗

PubMed2002

Characterization of a murine gene encoding a developmentally regulated cytoplasmic dual-specificity mitogen-activated protein kinase phosphatase.

Mitogen-activated protein kinases (MAPKs) play a vital role in cellular growth control, but far less is known about these signalling pathways in the context of embryonic development. Duration and magnitude of MAPK activation are crucial factors in cell fate decisions, and reflect a balance between the activities of upstream activators and specific MAPK phosphatases (MKPs). Here, we report the isolation and characterization of the murine Pyst3 gene, which encodes a cytosolic dual-specificity MKP. This enzyme selectively interacts with, and is catalytically activated by, the 'classical' extracellular signal-regulated kinases (ERKs) 1 and 2 and, to a lesser extent, the stress-activated MAPK p38alpha. These properties define the ability of this enzyme to dephosphorylate and inactivate ERK1/2 and p38alpha, but not JNK (c-Jun N-terminal kinase) in vivo. When expressed in mammalian cells, the Pyst3 protein is predominantly cytoplasmic. Furthermore, leptomycin B causes a complete redistribution of the protein to the nucleus, implicating a CRM (chromosomal region maintenance)1/exportin 1-dependent nuclear export signal in determining the subcellular localization of this enzyme. Finally, whole-mount in situ hybridization studies in mouse embryos reveal that the Pyst3 gene is expressed specifically in the placenta, developing liver and in migratory muscle cells. Our results suggest that this enzyme may have a critical role in regulating the activity of MAPK signalling during early development and organogenesis.

Amino Acid Sequence↗

PubMed2002

Expression of the ERK-specific MAP kinase phosphatase PYST1/MKP3 in mouse embryos during morphogenesis and early organogenesis.

Mitogen-activated-protein kinase (MAP kinase) cascades are effector mechanisms for many growth factor signals implicated in developmental processes, including appendage outgrowth and organogenesis. The cascade culminates in extracellular-signal-regulated MAP kinase (ERK), which enters the nucleus. ERK activity reflects the competing actions of upstream activator kinases and inhibitory MAP kinase phosphatases. We have studied embryonic expression of the dual-specificity MAP kinase phosphatase PYST1/MKP3, which is a specific and potent regulator of the ERK class of MAP kinases. We found dynamic patterns of mPyst1 messenger RNA in important signalling centres associated with cell proliferation and patterning in developing mouse embryos, including presegmental paraxial mesoderm, limb bud and branchial arch mesenchyme, midbrain/hindbrain isthmus, and nasal, dental, hair, and mammary placodes. Most of these have been characterised as sites of FGF/FGFR signalling.

Animals↗