Biomedical subjects

Lingfei Hou

Publications and source records attributed to Lingfei Hou.

11 recordsLinked to original sources

PubMed2006

Dynamic translational and proteasomal regulation of fragile X mental retardation protein controls mGluR-dependent long-term depression.

Genetic deletion of fragile X mental retardation protein (FMRP) has been shown to enhance mGluR-dependent long-term depression (LTD). Herein, we demonstrate that mGluR-LTD induces a transient, translation-dependent increase in FMRP that is rapidly degraded by the ubiquitin-proteasome pathway. Moreover, proteasome inhibitors abolished mGluR-LTD, and LTD was absent in mice that overexpress human FMRP. Neither translation nor proteasome inhibitors blocked the augmentation of mGluR-LTD in FMRP-deficient mice. In addition, mGluR-LTD is associated with rapid increases in the protein levels of FMRP target mRNAs in wild-type mice. Interestingly, the basal levels of these proteins were elevated and their synthesis was improperly regulated during mGluR-LTD in FMRP-deficient mice. Our findings indicate that hippocampal mGluR-LTD requires the rapid synthesis and degradation of FMRP and that mGluR-LTD triggers the synthesis of FMRP binding mRNAs. These findings indicate that the translation, ubiquitination, and proteolysis of FMRP functions as a dynamic regulatory system for controlling synaptic plasticity.

Animals↗

PubMed2006

Regulation of eukaryotic initiation factor 4E by converging signaling pathways during metabotropic glutamate receptor-dependent long-term depression.

Long-term depression (LTD) is an activity-dependent decrease in synaptic efficacy that can be induced in hippocampal area CA1 by pharmacological application of the selective group I metabotropic glutamate receptor (mGluR) agonist 3,5-diyhroxyphenylglycine (DHPG). Recent work has demonstrated that DHPG-induced LTD recruits at least two signal transduction pathways known to couple to translation, the mitogen-activated protein kinase kinase (MEK)-extracellular signal-regulated kinase (ERK) signaling pathway and the phosphoinositide 3-kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR) signaling pathway. However, it remains unclear which translation factors are engaged by these two signaling pathways during mGluR-LTD. In this study, we investigated whether the group I mGluRs couple to the cap-dependent translation proteins: Mnk1, eIF4E, and 4E-BP. We found that both the MEK-ERK and PI3K-mTOR signaling pathways are critical for the DHPG-induced regulation of these translation factors. Furthermore, we demonstrate that increasing eIF4F complex availability via the genetic elimination of 4E-BP2 can enhance the degree of LTD achieved by DHPG application in an ERK-dependent manner. Our results provide direct evidence that cap-dependent translation is engaged during mGluR-LTD and demonstrate that the MEK-ERK and PI3K-mTOR signaling pathways converge to regulate eIF4E activity after induction of DHPG-LTD.

Animals↗

PubMed2005

The translation repressor 4E-BP2 is critical for eIF4F complex formation, synaptic plasticity, and memory in the hippocampus.

Long-lasting synaptic plasticity and memory requires mRNA translation, yet little is known as to how this process is regulated. To explore the role that the translation repressor 4E-BP2 plays in hippocampal long-term potentiation (LTP) and learning and memory, we examined 4E-BP2 knock-out mice. Interestingly, genetic elimination of 4E-BP2 converted early-phase LTP to late-phase LTP (L-LTP) in the Schaffer collateral pathway, likely as a result of increased eIF4F complex formation and translation initiation. A critical limit for activity-induced translation was revealed in the 4E-BP2 knock-out mice because L-LTP elicited by traditional stimulation paradigms was obstructed. Moreover, the 4E-BP2 knock-out mice also exhibited impaired spatial learning and memory and conditioned fear-associative memory deficits. These results suggest a crucial role for proper regulation of the eIF4F complex by 4E-BP2 during LTP and learning and memory in the mouse hippocampus.

Animals↗

PubMed2004

Interleukin-1beta induces beta-calcitonin gene-related peptide secretion in human type II alveolar epithelial cells.

Calcitonin gene-related peptide (CGRP) is a 37-amino acid neuropeptide mainly present in sensory nerve fibers, which is present in almost all organs, but it is also found in cultured rat type II alveolar epithelial cells (AEII). Our data have previously shown that CGRP may play an important role in inflammation as an immunomodulator. Proinflammatory factor IL-1beta induces CGRP release from neuron-derived sources. However, whether IL-1beta can induce CGRP secretion from a nonneural source, AEII cells, is not known. In the present study, we demonstrated that human AEII A549 cells expressed beta-CGRP, and IL-1beta (0.001-50 ng/ml) directly increased CGRP secretion from these cells in a time- and concentration-dependent manner. The mRNA level of beta-CGRP was also elevated by IL-1beta (1 ng/ml). In addition, we found that IL-1beta-induced CGRP production was mediated through the PKC-p38 mitogen-activated protein (MAP) kinase-NF-kappaB signaling pathway. Furthermore, IL-1beta-induced chemokines MCP-1 and IL-8 were partially inhibited by exogenous hCGRP (0.1-10 nM) and potentiated by hCGRP8-37 (0.1-10 nM), a CGRP1-receptor antagonist. In addition, the CGRP-inhibited chemokine effect was partially reduced by Rp-cAMP, a cAMP-PK inhibitor. These results suggest that AEII-derived CGRP may act in an autocrine/paracrine mode and play an important inhibitory role in the local area in lung inflammatory diseases.

Calcitonin Gene-Related Peptide↗

PubMed2004

Synaptic plasticity and translation initiation.

It is widely accepted that protein synthesis, including local protein synthesis at synapses, is required for several forms of synaptic plasticity. Local protein synthesis enables synapses to control synaptic strength independent of the cell body via rapid protein production from pre-existing mRNA. Therefore, regulation of translation initiation is likely to be intimately involved in modulating synaptic strength. Our understanding of the translation-initiation process has expanded greatly in recent years. In this review, we discuss various aspects of translation initiation, as well as signaling pathways that might be involved in coupling neurotransmitter and neurotrophin receptors to the translation machinery during various forms of synaptic plasticity.

Animals↗

PubMed2004

Activation of the phosphoinositide 3-kinase-Akt-mammalian target of rapamycin signaling pathway is required for metabotropic glutamate receptor-dependent long-term depression.

Hippocampal long-term depression (LTD) is a long-lasting decrease in synaptic strength that is most commonly studied at glutamatergic inputs to pyramidal cells in hippocampal area CA1. Activation of G-protein-coupled group I (including types 1 and 5) metabotropic glutamate receptors (mGluRs) by the pharmacological agonist (RS)-3,5-dihydroxyphenylglycine (DHPG) elicits LTD in area CA1 of the hippocampus. Recent reports have shown that de novo protein synthesis is necessary for DHPG-induced LTD. However, relatively little is known about the signaling pathways that couple mGluRs to translation initiation. In this study, we investigated whether the activation of the phosphoinositide 3-kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR) pathway, which has been shown to regulate translation initiation, is necessary for mGluR-LTD induced by DHPG. We found that brief incubations of mouse hippocampal slices with DHPG resulted in increased phosphorylation of Akt and mTOR in hippocampal area CA1. Two structurally unrelated PI3K inhibitors, LY294002 and wortmannin, blocked the DHPG-induced increases in phosphorylation of Akt and mTOR. Biochemical fractionation studies showed that the DHPG-induced increase in the phosphorylation of Akt and mTOR could be detected in synaptoneurosome preparations, and immunohistochemical analysis revealed that similar increases could be detected in both stratum pyramidale and stratum radiatum in area CA1. Finally, we observed that both PI3K inhibitors and rapamycin, an mTOR inhibitor, prevented mGluR-LTD induced by DHPG. Together, our findings indicate that activation of the PI3K-Akt-mTOR signaling cascade is required for mGluR-LTD and suggest that this pathway may couple group I mGluRs to translation initiation in hippocampal area CA1.

3-Phosphoinositide-Dependent Protein Kinases↗

PubMed2004

Lipopolysaccharide evoked peptide release by calcium-induced calcium release.

Calcium may play a key role in the lipopolysaccharide (LPS)-induced release of calcitonin gene-related peptide in rat dorsal root ganglion neurons. Both calcium entry via voltage-activated calcium channels sensitive to either omega-conotoxin GVIA or omega-agatoxin IVA, and calcium release from ryanodine-sensitive calcium stores were involved in this process. Cyclic ADP-ribose antagonist affected neither the enhancement of cytoplasmic free calcium nor the release of calcitonin gene-related peptide induced by LPS. These findings underscore a pivotal role of calcium-induced calcium release in lipopolysaccharide-stimulated calcitonin gene-related peptide release from nociceptive neurons.

Animals↗

PubMed2004

NMDA receptor activation results in PKA- and ERK-dependent Mnk1 activation and increased eIF4E phosphorylation in hippocampal area CA1.

Protein synthesis is essential for the stabilization of glutamate receptor-dependent forms of long-lasting hippocampal synaptic plasticity and for the consolidation of memory, but the signal transduction mechanisms that regulate translation factors during these processes are not well understood. As a first step towards understanding how translation is activated during synaptic plasticity, we investigated how the eukaryotic initiation factor 4E (eIF4E), a rate-limiting mRNA cap-binding protein, and its kinase, Mnk1, are regulated by protein kinase C (PKC), cAMP-dependent protein kinase (PKA) and N-methyl-D-aspartate (NMDA) receptor activation in hippocampal area CA1. We found that treatment of mouse hippocampal slices with either phorbol ester, to activate PKC, or forskolin, to activate PKA, resulted in activation of Mnk1 and increased eIF4E phosphorylation that was dependent on extracellular signal-regulated kinase (ERK). Similarly, brief treatment of hippocampal slices with NMDA resulted in activation of Mnk1 and increased phosphorylation of eIF4E. The NMDA-induced activation of Mnk1 and increased phosphorylation of eIF4E were dependent on PKA and ERK, but not PKC, and were present in synaptoneurosome preparations. Immunohistochemical analysis revealed that the PKA- and ERK-dependent increases in Mnk1 activation induced by NMDA also occurred in dendrites. These findings identify a specific regulatory pathway that can couple NMDA receptor activation to translation initiation factors in the hippocampus, and may represent a mechanism for triggering dendritic protein synthesis during long-term potentiation and long-term memory formation.

Animals↗

PubMed2003

Mechanism of interleukin-1 beta-induced calcitonin gene-related peptide production from dorsal root ganglion neurons of neonatal rats.

Calcitonin gene-related peptide (CGRP) is synthesized in dorsal root ganglion (DRG) neurons and released from primary afferent neurons to mediate hemodynamic effects and neurogenic inflammation. The effect of the proinflammatory cytokine interleukin-1 (IL-1)-beta on CGRP release from these sensory neurons was investigated. The results showed that IL-1beta (1 ng/ml) could directly induce CGRP release following prolonged incubation (24 hr) with these neurons. Treatment with IL-1beta (0.1-1.0 ng/ml) significantly increased CGRP release in a concentration-dependent manner. In addition, pretreatment of DRG cells with actinomycin D at 1 microM or cyclohexamide at 10 microM for 30 min inhibited 1 ng/ml IL-1beta-induced CGRP release in DRG neurons of neonatal rats. The inhibitors of PKC, JNK MAPK and NF-kappaB, but not p38 or ERK1/2 MAPK, blocked IL-1beta-induced CGRP release. RNase protection assay showed that IL-1beta could cause alpha-CGRP mRNA increase in a time- and concentration-dependent manner, although the level of beta-CGRP mRNA was not affected. These results indicate that IL-1beta may activate PKC, which in turn initiates JNK MAPK and activates NF-kappaB and finally induces alpha-CGRP gene expression and release from these sensory neurons.

Animals↗

PubMed2002

Comparison of calcitonin gene-related peptide release from rat lymphocytes and dorsal root ganglia neurons.

Calcitonin gene-related peptide (CGRP), a neuropeptide contained in primary sensory neurons, has been demonstrated to be synthesized and released by rat lymphocytes in our previous studies. In this study, the release properties and molecular characteristics of CGRP such as immunoreactivity (CGRP-LI) from lymphocytes were compared with those from dorsal root ganglia (DRG) neurons by using CGRP-specific RIA, reverse-phase HPLC, and RT-PCR. Con A and IL-2 could trigger CGRP-LI release from lymphocytes in a time-dependent manner. After 3 days stimulation with 4 microg/ml Con A, the level of CGRP-LI released by lymphocytes was increased from 77.4 +/- 9.6 pg/10(8) cells to 191.1 +/- 13.6 pg/10(8) cells and increased further to 374.5 +/- 38.3 pg/10(8) cells after 5 days. Stimulation with 750 U/ml human IL-2 recombinant (rhIL-2) caused a significantly elevated CGRP-LI release from 75.4 +/- 6.5 pg/10(8) cells to 266.2 +/- 16.2 pg/10(8) cells after 3 days and to 469.1 +/- 43.2 pg/10(8) cells after 5 days. Con A and IL-2 also augmented CGRP mRNA expression in lymphocytes. In the tested period (1-5 days), Con A and rhIL-2 had no stimulating effect on CGRP release from DRG neurons. In contrast, a high concentration of potassium and LPS could induce an acute release of CGRP from DRG neurons, but not from lymphocytes. Lymphocyte-released CGRP-LI was shown to coelute with synthetic rat CGRP (rCGRP) and DRG neuron-released CGRP by reverse-phase HPLC. In addition, to displace (125)I-CGRP from CGRP antibody by lymphocyte-released CGRP-LI was similar to that by synthetic rCGRP. These data suggest that lymphocyte- and nerve-derived CGRP-LI are similar in terms of immunological characteristics, molecular size, and polarity. However, lymphocytes secrete CGRP-LI in response to different stimuli compared to nerve-derived CGRP.

Animals↗

PubMed2002

Production and secretion of calcitonin gene-related peptide from human lymphocytes.

Calcitonin gene-related peptide (CGRP) is a 37-amino acid neuropeptide, which is mainly present in primary sensory nerves. Although our previous study has shown that rat lymphocytes can synthesize beta-CGRP, there is no evidence demonstrating whether CGRP can be synthesized by human lymphocytes. In this study, the production of CGRP from human lymphocytes from spleen and blood were investigated by using CGRP-specific radioimmunoassay (RIA), and RNase protection assay (RPA). The results showed that human T lymphocyte mitogen, such as phytohemagglutinin (PHA), could time- and dose-dependently induce hCGRP secretion; rhIL-2 alone did not effect hCGRP secretion, but it could potentiate PHA-evoked hCGRP secretion from human spleen lymphocytes. RPA showed that alpha- and beta-CGRP mRNA were both constitutively expressed in unstimulated human peripheral blood mononuclear cells (PBMC). PHA could cause beta-hCGRP but not alpha-hCGRP mRNA increase in a time-dependent manner. In addition, hCGRP(8-37), a CGRP(1) receptor antagonist, enhanced PHA or human interleukin-2 (rhIL-2), induced the proliferation of splenocytes and PBMC. These results suggest that hCGRP is produced and secreted by human lymphocyte. Lymphocyte mitogen can induce the elevation of beta-CGRP synthesis and secretion. The lymphocyte-derived beta-CGRP may inhibit, at least in part, lymphocytes proliferation, which are then involved in the modulation of human T lymphocyte function in response to immune stimulation.

Calcitonin Gene-Related Peptide↗