Attacking Lung Cancer, One Mutation at a Time

Lung cancers that carry the EML4-ALK translocation are uniquely sensitive to an ALK inhibitor.

Epidermal Growth Factor Receptor: Not Just Epidermal

Inhibition of epidermal growth factor receptor enhances granulocyte colony–stimulating factor–induced mobilization of hematopoietic stem and progenitor cells.

When the Guardian Looks Away

The same single-nucleotide polymorphism in the p53 regulator MDM2 increases cancer risk in mice but is a marker of less aggressive prostate cancer in humans.

A role for p11 in the antidepressant action of brain-derived neurotrophic factor

BACKGROUND

The protein p11 (also called S100A10) is downregulated in human and rodent depressive-like states. Considerable experimental evidence also implicates p11 in the mechanism of action of antidepressant drugs and electroconvulsive seizures, in part due to its interaction with specific serotonin receptors. Brain-derived neurotrophic factor (BDNF) has been linked to the therapeutic activity of antidepressants in rodent models and humans. In the current study, we investigated whether BDNF regulates p11 in vitro and in vivo.

METHODS

We utilized primary neuronal cultures, in vivo analyses of transgenic mice, and behavioral techniques to assess the effects of BDNF on p11.

RESULTS

Results indicate that BDNF stimulates p11 expression through tropomyosin-related kinase B (trkB) receptors and via the mitogen-activated protein kinase signaling pathway. Brain-derived neurotrophic factor-induced changes in p11 in vivo correlate with changes in ligand binding to the 5-hydroxytryptamine receptor 1B, the subcellular localization of which is known to be regulated by p11. Behavioral studies demonstrate that p11 knockout mice are insensitive to the antidepressant actions of BDNF.

CONCLUSIONS

Taken together, our data demonstrate that p11 levels are regulated by BDNF in vitro and in vivo and that the antidepressant-like effect of BDNF in two well-established behavioral models requires p11. These data support a role for p11 in the antidepressant activity of neurotrophins.

Small But Powerful

Lymphoma in mice is “addicted” to the microRNA miR-21, vanishing when the oncomir is removed.

The Heart of “Stemness”

A regulator of asymmetric cell division promotes the transition to blast crisis in chronic myelogenous leukemia.

Power in Numbers

A multidisciplinary effort begins to unravel the genomic portrait of prostate cancer.

Divide and Conquer

Expression of genes involved in chromosomal stability may be a better marker of tumor aggressiveness than tumor grade.

Hidden in Plain Sight

Ras pathway activation through chromosomal translocations involving RAF defines another group of patients who may benefit from RAF inhibitors.

Differentiation Block in Glioma

The glioma genome project leads to the discovery of an oncogene that may promote tumor formation by blocking differentiation of neural stem cells.

Your Genome Is Ready

Whole-genome sequencing will soon become easily available, but many challenges lie ahead.

Abstract LB-62: Direct visualization of circulating sarcoma cells by whole-blood fluorescence in-situ hybridization

Background: Several sarcoma subtypes are characterized by well-defined genetic events such as chromosomal translocations or gene amplification. In translocation-associated sarcomas, the presence of the fusion transcript can be detected in peripheral blood by RT-PCR. However, sarcoma cells have never been directly visualized in peripheral blood due to the absence of specific immunocytochemical markers.

Methods: We developed a novel method to examine large numbers of peripheral blood cells for the presence of sarcoma-associated genetic changes. Using an IRB-approved biospecimen collection protocol, peripheral blood was collected from 20 patients with translocation-associated sarcomas or well-differentiated/dedifferentiated liposarcomas (WD/DD LS), which are characterized by MDM2 amplification. In this exploratory phase, the analysis was limited to patients with high burden of disease, evidence of disease progression or recurrence. Immuno-FISH was performed using CD45 immunostaining to identify hematopoietic cells and the corresponding FISH probe, either a break-apart probe (SYT, DDIT3) or MDM2 probe to detect amplification.

Results: ADW2-amplified cells were detected in a subset of WD/DD LS peripheral blood samples, while translocation-positive cells were detected in samples of synovial sarcoma (using the SYT breakapart probe) and myxoid/round cell liposarcoma (using the DDIT3 breakapart probe). We are currently developing the techniques to quantitate the frequencies of such CD45(-) Probe(+) cells.

Conclusions: To our knowledge this is the first report of direct visualization of sarcoma cells in peripheral blood using whole-blood FISH analysis. We are currently characterizing these cells morphologically and immunocytochemically. In addition, we are developing tools necessary to perform quantitative analysis of circulating tumor cell frequencies in peripheral blood samples, to begin to establish whether the levels of circulating tumor cells correlate with tumor burden and response to therapy. This method may be applicable to other tumors where defined genetic lesions exist that are amenable to FISH analysis, such as chromosomal translocations or genomic gains or losses. The goal is to use such genotype-based analysis to explore the phenotypic diversity of circulating tumor cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-62.

Abstract 4814: Tunneling nanotubes facilitate intercellular communication and trafficking between mesothelioma cells

Introduction: Mesothelioma is an aggressive malignancy which spreads via local invasion. We have observed fine, long, non-adherent cable-like structures connecting mesothelioma cells in vitro which are consistent with tunneling nanotubes, an entity recently described in malignant as well as neuronal and immune cells. We hypothesized that tunneling nanotubes facilitate intercellular communication between distant and neighboring cells via transfer of intracellular components. Materials and Methods: Biphasic and sarcomatoid mesothelioma cells, as well as primary mesothelioma and lung cancer cells, were grown using medium of variable concentrations of serum, glucose, and cytokines at low or normal pH. Fluorescent lipophilic dyes were used to stain cytoplasmic membranes and mitochondria. Red and green fluorescent protein-expressing cells were examined following mixing of the two populations. Brightfield and fluorescent microscopy were performed, as was time-lapse imaging to determine time frames for transport via the nanotubes. To determine composition, nanotubes and cells were fixed and immunofluorescent staining was performed. Electron microscopy was also performed to elucidate nanotube structure and cell membrane insertions. Results: Nanotubes connected cells in close and distant proximity. The proportion of cells growing one or more nanotubes was highest in medium with low pH and/or low serum, high glucose, and cytokines. We have reproduced this finding in primary tumor cells from resected mesothelioma cells following surgery, as well as mesothelioma and lung cancer cells from pleural effusions. Brightfield and fluorescent microscopy revealed transfer of material (including mitochondria and proteins) between cells following nanotube formation, confirming the tubes are tunneling. Cells positive for both GFP and RFP and connected by nanotubes were observed, indicating protein transfer was bidirectional. Fluorescent immunostaining elucidated the presence of actin, vimentin, Zo-1, and fascin in nanotubes, supporting actin as a key component. Electron microscopy demonstrated the presence of early nanotubes and insertion of mature nanotubes into receptive cells. Conclusions: Tunneling nanotubes facilitate intercellular communication and trafficking between cells from cell lines and primary tumors. For the first time, we demonstrate that specific medium conditions can reproducibly promote increased growth of nanotubes to accelerate cell-to-cell communication via these structures, as well the ability to fix these sensitive structures for immunostaining. We also demonstrate that proteins and mitochondria are among cell components transported bidirectionally via nanotubes. Tunneling nanotubes provide a significant alternative for cell-to-cell communication between invasive cancer cells, as well as a plausible mechanism for tumoral resistance to therapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4814.

Addicted to Cancer

While EGFR (ErbB1) and Her2 (ErbB2) have long been known as targets for cancer therapeutics, the third family member, ErbB3, now comes to the forefront in ovarian cancer.

The Enemy Within

Collagen-secreting cells in kidney fibrosis may be derived from microvascular pericytes in the stroma rather than through an epithelial-to-mesenchymal transition.

The Double Life of RAF

Drugs that inhibit RAF kinase in cancer cells show success in the clinic. But how exactly do they work?

A Preemptive Strike Against Resistant Tumor Cells

A few cells within a tumor carry drug-resistance mutations even before treatment is initiated, providing an opportunity to squelch them early.

Round-Trip Ticket for Circulating Tumor Cells

In addition to forming distant metastases, circulating tumor cells may return to established tumors to help fuel their growth.

Abstract C250: The pericyte as a novel stromal element and therapeutic target in sarcoma

Background: Mesenchymal Stem Cells (MSCs) have been proposed as the cell of origin of sarcoma. In soft tissues, the microvascular pericyte has been recently shown to have MSC properties (Crisan et al, Cell Stem Cell 3:301). We have previously reported the isolation of benign mesenchymal cultures from sarcoma surgical samples. These cells have the immunophenotype (CD45-CD31- CD73+CD105+CD90+) and in vitro differentiation potential characteristic of MSCs. We hypothesized that these sarcoma-associated MSCs (SA-MSCs) are derived from pericytes associated with the sarcoma vasculature.

Methods: We examined whether benign SA-MSCs have surface markers characteristic of pericytes and cooperate with endothelial cells in tube formation assays. We also examined expression of CD146, a pericyte marker, and CD105, an MSC marker, in sarcoma archived tissue by IHC.

Results: Benign SA-MSCs indeed demonstrated properties of pericytes, such as characteristic cytoplasmic projections at low density, surface expression of pericyte markers (CD146, PDGFR-beta, NG2 and endosialin) and cooperation with endothelial cells in tube formation assays in matrigel. To demonstrate the existence of pericytes in sarcoma archived tissue, we used CD146 that has been shown to be restricted to the vasculature in sarcoma, but thought to be an endothelial marker (Shih et al, CCR 2:569). We demonstrate for the first time the existence of CD146+ pericytes in diverse sarcoma subtypes. In addition, we examined sarcoma archived material for expression of CD105 (endoglin), an MSC marker and a known tumor-specific endothelial marker in carcinoma. We found that CD105 was expressed in sarcoma endothelium similarly to its expression on carcinoma endothelium. In addition, by three-color immunofluorescence, CD105 was expressed in a subset of sarcoma pericytes. It was not expressed in normal surrounding tissues.

Conclusion: We show that SA-MSC cultures have properties of pericytes. Using a novel combination of markers we demonstrate that pericytes are abundant in sarcoma. Being in contact with both the endothelial cells and the malignant sarcoma cells, pericytes represent a novel stromal element in sarcoma and a potential therapeutic target. Based on these findings we are evaluating endosialin (CD248) and CD105 antibodies, both of which are in clinical development, for effectiveness in preclinical models of sarcoma.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C250.

Conditional deletion of neuronal cyclin-dependent kinase 5 in developing forebrain results in microglial activation and neurodegeneration

Neuronal migration disorders are often identified in patients with epilepsy refractory to medical treatment. The prolonged or repeated seizures are known to cause neuronal death; however, the mechanism underlying seizure-induced neuronal death remains to be elucidated. An essential role of cyclin-dependent kinase 5 (Cdk5) in brain development has been demonstrated in Cdk5(-/-) mice, which show neuronal migration defects and perinatal lethality. Here, we show the consequences of Cdk5 deficiency in the postnatal brain by generating Cdk5 conditional knockout mice, in which Cdk5is selectively eliminated from neurons in the developing forebrain. The conditional mutant mice were viable, but exhibited complex neurological deficits including seizures, tremors, and growth retardation. The forebrain not only showed disruption of layering, but also neurodegenerative changes accompanied by neuronal loss and microglial activation. The neurodegenerative changes progressed with age and were accompanied by up-regulation of the neuronal tissue-type plasminogen activator, a serine protease known to mediate microglial activation. Thus age-dependent neurodegeneration in the Cdk5 conditional knockout mouse brain invoked a massive inflammatory reaction. These findings indicate an important role of Cdk5 in inflammation, and also provide a mouse model to examine the possible involvement of inflammation in the pathogenesis of progressive cognitive decline in patients with neuronal migration disorders.

Divergence between thalamic and cortical inputs to lateral amygdala during juvenile-adult transition in mice

BACKGROUND

Adolescence is considered a critical time of life for emotional development in humans. During this period the amygdala, which regulates emotions, undergoes structural reorganization. Auditory fear conditioning, a form of amygdala-dependent emotional learning, occurs differently in juvenile and adult rodents. Because this learning is mediated by plastic changes in the thalamic and cortical inputs to lateral amygdala (LA), we investigated changes in synaptic properties of these inputs during juvenile-to-adult transition.

METHODS

Whole-cell patch clamp recording in amygdala slices from juvenile and young adult mice was conducted to investigate long-term potentiation and basal synaptic transmission in the thalamic and cortical inputs to LA.

RESULTS

We show that physiological differences develop between thalamic and cortical afferents to LA during the juvenile-to-adult transition. Although in juvenile mice the two pathways have similar properties, in young adult mice the thalamic pathway has reduced plasticity, increased number of quanta released by a single action potential, and decreased proportion of silent synapses.

CONCLUSIONS

Changes in thalamic but not cortical inputs to amygdala take place during late development and might contribute to differences in auditory fear conditioning between juveniles and adults.

Selective gating of glutamatergic inputs to excitatory neurons of amygdala by presynaptic GABAb receptor

GABAb receptor (GABAbR)-mediated suppression of glutamate release is critical for limiting glutamatergic transmission across the central nervous system (CNS). Here we show that, upon tetanic stimulation of afferents to lateral amygdala, presynaptic GABAbR-mediated inhibition only occurs in glutamatergic inputs to principle neurons (PNs), not to interneurons (INs), despite the presence of GABAbR in terminals to both types of neurons. The selectivity is caused by differential local GABA accumulation; it requires GABA reuptake and parallels distinct spatial distributions of presynaptic GABAbR in terminals to PNs and INs. Moreover, GABAbR-mediated suppression of theta-burst-induced long-term potentiation (LTP) occurs only in the inputs to PNs, not to INs. Thus, target-cell-specific control of glutamate release by presynaptic GABAbR orchestrates the inhibitory dominance inside amygdala and might contribute to prevention of nonadaptive defensive behaviors.

Enhanced generalization of auditory conditioned fear in juvenile mice

Increased emotionality is a characteristic of human adolescence, but its animal models are limited. Here we report that generalization of auditory conditioned fear between a conditional stimulus (CS+) and a novel auditory stimulus is stronger in 4-5-wk-old mice (juveniles) than in their 9-10-wk-old counterparts (adults), whereas nonassociative sensitization induced by foot shock (US) and the ability to discriminate CS+ from an explicitly unpaired stimulus (CS-) are not dependent on age. These results suggest that aversive associations are less precise in juvenile mice and can more easily produce conditional responses to stimuli different from CS+. Yet, through the explicit unpairing of CS- from US during training, juveniles are able to overcome this greater fear generalization and learn that CS- is not associated with foot shock.

Conditional gene expression and targeting in neuroscience research

Recently developed techniques for spatially and temporally controlled genetic manipulations based on regulated homologous recombination and/or transcription are extensively used in brain research. In addition to being important for testing the role of specific proteins in the central nervous system, these techniques allow analysis of brain functions at the neuronal circuit level. This overview discusses principles of conditional inactivation and expression of genes, and their specific applications to studies of the mammalian brain.

Mitigation of the plasma-implosion inhomogeneity in starlike wire-array Z pinches

Implosions in starlike triple and quadruple wire arrays were investigated in a 1 MA Zebra generator. Implosion in these loads is directed along the rays of the star and cascades from wire to wire to the center. Shadowgraphy shows improved homogeneity of imploding plasma and mitigation of instabilities. Despite the low azimuthal symmetry, starlike wire arrays produce a stable x-ray pulse with the highest peak power of >0.4 TW and the shortest duration of 8-12 ns among different types of tested loads. This can be linked to stabilization of instabilities due to the multiple nesting.

INI1 induces interferon signaling and spindle checkpoint in rhabdoid tumors

PURPOSE

Rhabdoid tumors are rare but aggressive pediatric malignancies characterized by biallelic loss of INI1/hSNF5. Reintroduction of INI1 causes cell arrest and senescence in rhabdoid cells. Our purpose was to identify INI1-downstream genes and to determine their functional and therapeutic significance for rhabdoid tumors.

EXPERIMENTAL DESIGN

INI1 downstream targets in rhabdoid cells were identified using a cDNA microarray analysis and the expression of selected INI1 targets was confirmed by quantitative reverse transcription-PCR, Western analysis, and/or immunohistochemical analysis of rhabdoid cells and primary rhabdoid tumors. To determine the functional significance of downstream targets, activated targets of INI1 were induced and repressed targets of INI1 were knocked down (by using RNA interference) in rhabdoid cells, in the absence of INI1. Consequence of altered expression of INI1 downstream targets for rhabdoid cell survival, cell cycle, and apoptosis was assessed.

RESULTS

Microarray studies indicated that INI1 activated IFN-stimulated genes at early time points and senescence markers at late time points and repressed mitotic genes such as Polo like kinase 1 (PLK1), selectively in rhabdoid cells. Treatment of rhabdoid cells with recombinant IFNs resulted in induction of IFN-stimulated genes, G1 arrest, and flat cell formation. PLK1 was overexpressed in primary human and mouse rhabdoid tumors. RNA interference-mediated knock down of PLK1 in rhabdoid cells resulted in mitotic arrest, aberrant nuclear division, decreased survival, and induction of apoptosis.

CONCLUSIONS

Targeting downstream effectors of INI1 such as IFN pathway and mitotic genes leads to antiproliferative effects in rhabdoid cells. IFN treatment and down-modulation of PLK1 constitute potential novel therapeutic strategies for rhabdoid tumors.

Excimer laser pumped by an intense, high-energy heavy-ion beam

High-energy heavy ions are an ideal tool to generate homogeneously excited, extended volumes of nonthermal plasmas. Here, the high-energy loss (dE/dx) and absolute power deposition of heavy ions interacting with matter has been used to pump an ultraviolet laser. A pulsed 70 MeV/u 238U beam with up to 2.5 x 10(9) particles in approximately 100 ns beam bunches was stopped in a 1.2 m long laser cell filled with a 1.6 bar Ar-Kr-F2 mixture (typically 50%:49.9%:0.1%). Laser effect on the 248 nm KrF* excimer transition is clearly demonstrated.

Stem cells and cancer

The cell of origin of cancer has been a strongly debated topic through out the history of cancer research. This review provides a historic framework and a synopsis of how the theories of cancer initiation and progression evolved from early times to the present day. We present the concept of a cancer stem cell, and review for you the literature supporting the existence of cancer stem cells in addition to a brief discussion on our own work supporting a bone marrow-derived source for the cancer stem cell, as well as cells of the cancer stroma.

Energy-transfer processes in neon-hydrogen mixtures excited by electron beams

Energy- and charge-transfer processes in neon-hydrogen mixtures (500-1400 hPa neon and 0.001-3 hPa hydrogen partial pressures) excited by a pulsed low-energy (approximately 10 keV) electron beam were investigated using time-resolved spectroscopy. Time spectra of the hydrogen Lyman-alpha line, neon excimer emission (second continuum), and neon atomic lines (3p-3s transitions) were recorded. The time-integrated intensity of the Lyman-alpha emission was measured for the same range of gas mixtures. It is shown that direct energy transfer from Ne*2 excimers and neon atoms in the four lowest excited states as well as recombination of H3+ ions are the main channels populating atomic hydrogen in the n=2 state. A rate constant of (4.2+/-1.4)x10(-11) cm3 s(-1) was obtained for the charge transfer from Ne2+ ions to molecular hydrogen. A lower limit for the depopulation rate constant of Ne*2 excimers by molecular hydrogen (combination of energy transfer and ionization) was found to be 1.0 x 10(-10) cm3 s(-1).

Gene Expression Profiling of Facilitated L-LTP in VP16-CREB Mice Reveals that BDNF Is Critical for the Maintenance of LTP and Its Synaptic Capture

Expression of VP16-CREB, a constitutively active form of CREB, in hippocampal neurons of the CA1 region lowers the threshold for eliciting the late, persistent phase of long-term potentiation (L-LTP) in the Schaffer collateral pathway. This VP16-CREB-mediated L-LTP differs from the conventional late phase of LTP in not being dependent on new transcription. This finding suggests that in the transgenic mice the mRNA transcript(s) encoding the protein(s) necessary for this form of L-LTP might already be present in CA1 neurons in the basal condition. We used high-density oligonucleotide arrays to identify the mRNAs differentially expressed in the hippocampus of transgenic and wild-type mice. We then explored the contribution of the most prominent candidate genes revealed by our screening, namely prodynorphin, BDNF, and MHC class I molecules, to the facilitated LTP of VP16-CREB mice. We found that the overexpression of brain-derived neurotrophic factor accounts for an important component of this phenotype.

Single-Photon Ionization Quadrupole Mass Spectrometry with an Electron Beam Pumped Excimer Light Source

The application of soft ionization methods for mass spectrometry (MS), such as single-photon ionization (SPI) using vacuum ultraviolet (VUV) light, provides powerful analytical instrumentation for real-time on-line monitoring of organic substances in gaseous matrixes. A compact and mobile quadrupole mass spectrometer (QMS) system using a novel electron beam pumped rare gas VUV lamp for SPI has been developed for on-line analysis of organic trace compounds (ppb concentrations). The VUV radiation of the light source is employed for SPI in the ion source of the QMS. The concept of the interfacing of the VUV light source with the QMS is described and the SPI-QMS is characterized. On-line detection limits down to 50 ppb for benzene, toluene, and m-xylene were achieved. The instrument is well suited for continuous measurements of aromatic and aliphatic trace compounds and can therefore be used for on-line monitoring of trace compounds in dynamically fluctuating process gases. First measurements of gas standards, petrochemical samples, and on-line monitoring of automotive exhaust are presented.

A behavioral role for dendritic integration: HCN1 channels constrain spatial memory and plasticity at inputs to distal dendrites of CA1 pyramidal neurons

The importance of long-term synaptic plasticity as a cellular substrate for learning and memory is well established. By contrast, little is known about how learning and memory are regulated by voltage-gated ion channels that integrate synaptic information. We investigated this question using mice with general or forebrain-restricted knockout of the HCN1 gene, which we find encodes a major component of the hyperpolarization-activated inward current (Ih) and is an important determinant of dendritic integration in hippocampal CA1 pyramidal cells. Deletion of HCN1 from forebrain neurons enhances hippocampal-dependent learning and memory, augments the power of theta oscillations, and enhances long-term potentiation (LTP) at the direct perforant path input to the distal dendrites of CA1 pyramidal neurons, but has little effect on LTP at the more proximal Schaffer collateral inputs. We suggest that HCN1 channels constrain learning and memory by regulating dendritic integration of distal synaptic inputs to pyramidal cells.

The hyperpolarization-activated HCN1 channel is important for motor learning and neuronal integration by cerebellar Purkinje cells

In contrast to our increasingly detailed understanding of how synaptic plasticity provides a cellular substrate for learning and memory, it is less clear how a neuron's voltage-gated ion channels interact with plastic changes in synaptic strength to influence behavior. We find, using generalized and regional knockout mice, that deletion of the HCN1 channel causes profound motor learning and memory deficits in swimming and rotarod tasks. In cerebellar Purkinje cells, which are a key component of the cerebellar circuit for learning of correctly timed movements, HCN1 mediates an inward current that stabilizes the integrative properties of Purkinje cells and ensures that their input-output function is independent of the previous history of their activity. We suggest that this nonsynaptic integrative function of HCN1 is required for accurate decoding of input patterns and thereby enables synaptic plasticity to appropriately influence the performance of motor activity.

Using conditional mutagenesis to study the brain

Conditional genetic modifications are used to determine how individual molecules contribute to the function of defined neuronal circuits in the mouse brain. Among various techniques for these genetic modifications, the tetracycline transactivator and the Cre-loxP systems have proved to be most successful in recent years. Here we describe the basic principles, recent developments, and potential applications of these methodologies. We discuss their impact on the study of general brain function and their use for modeling different brain disorders.

Presynaptic BDNF required for a presynaptic but not postsynaptic component of LTP at hippocampal CA1-CA3 synapses

Brain-derived neurotrophic factor (BDNF) has been implicated in several forms of long-term potentiation (LTP) at different hippocampal synapses. Using two-photon imaging of FM 1-43, a fluorescent marker of synaptic vesicle cycling, we find that BDNF is selectively required for those forms of LTP at Schaffer collateral synapses that recruit a presynaptic component of expression. BDNF-dependent forms of LTP also require activation of L-type voltage-gated calcium channels. One form of LTP with presynaptic expression, theta burst LTP, is thought to be of particular behavioral importance. Using restricted genetic deletion to selectively disrupt BDNF production in either the entire forebrain (CA3 and CA1) or in only the postsynaptic CA1 neuron, we localize the source of BDNF required for LTP to presynaptic neurons. These results suggest that long-term synaptic plasticity has distinct presynaptic and postsynaptic modules. Release of BDNF from CA3 neurons is required to recruit the presynaptic, but not postsynaptic, module of plasticity.

Rap1 couples cAMP signaling to a distinct pool of p42/44MAPK regulating excitability, synaptic plasticity, learning, and memory

Learning-induced synaptic plasticity commonly involves the interaction between cAMP and p42/44MAPK. To investigate the role of Rap1 as a potential signaling molecule coupling cAMP and p42/44MAPK, we expressed an interfering Rap1 mutant (iRap1) in the mouse forebrain. This expression selectively decreased basal phosphorylation of a membrane-associated pool of p42/44MAPK, impaired cAMP-dependent LTP in the hippocampal Schaffer collateral pathway induced by either forskolin or theta frequency stimulation, decreased complex spike firing, and reduced the p42/44MAPK-mediated phosphorylation of the A-type potassium channel Kv4.2. These changes correlated with impaired spatial memory and context discrimination. These results indicate that Rap1 couples cAMP signaling to a selective membrane-associated pool of p42/44MAPK to control excitability of pyramidal cells, the early and late phases of LTP, and the storage of spatial memory.

Hippocampal network patterns of activity in the mouse

Genetic engineering of the mouse brain allows investigators to address novel hypotheses in vivo. Because of the paucity of information on the network patterns of the mouse hippocampus, we investigated the electrical patterns in the behaving animal using multisite silicon probes and wire tetrodes. Theta (6-9 Hz) and gamma (40-100 Hz) oscillations were present during exploration and rapid eye movement sleep. Gamma power and theta power were comodulated and gamma power varied as a function of the theta cycle. Pyramidal cells and putative interneurons were phase-locked to theta oscillations. During immobility, consummatory behaviors and slow-wave sleep, sharp waves were present in cornu ammonis region CA1 of the hippocampus stratum radiatum associated with 140-200-Hz "ripples" in the pyramidal cell layer and population burst of CA1 neurons. In the hilus, large-amplitude "dentate spikes" occurred in association with increased discharge of hilar neurons. The amplitude of field patterns was larger in the mouse than in the rat, likely reflecting the higher neuron density in a smaller brain. We suggest that the main hippocampal network patterns are mediated by similar pathways and mechanisms in mouse and rat.

Raman amplification of ultrashort laser pulses in microcapillary plasmas

Experimental evidences of Raman amplification of ultrashort pulses in microcapillary plasmas are presented. The amplification of 100-500 fs pulses was investigated in microcapillaries with different lengths. The experimental data, together with simulation results, indicate that the resonance condition for Raman amplification in high-density plasma, n(e) approximately 1-3x10(20) cm(-3), existed only in a very short plasma column. Such an assumption makes it possible to reconcile the experimental results and theoretical predictions. Investigations in very short microcapillaries (0.2-0.5 mm) with a broadband seed pulse further support this hypothesis and the amplification factor is in agreement with the linear growth rate.

Some forms of cAMP-mediated long-lasting potentiation are associated with release of BDNF and nuclear translocation of phospho-MAP kinase

Long-lasting forms of synaptic plasticity like the late phase of LTP (L-LTP) typically require an elevation of cAMP, the recruitment of the cAMP-dependent protein kinase (PKA), and ultimately the activation of transcription and translation; some forms also require brain-derived neurotrophic factor (BDNF). Both cAMP and BDNF can activate mitogen-activated protein kinase (MAPK/ERK), which also plays a role in LTP. However, little is known about the mechanisms whereby cAMP, BDNF, and MAPK interact. We find that increases in cAMP can rapidly activate the BDNF receptor TrkB and induce BDNF-dependent long-lasting potentiation at the Schaffer collateral-CA1 synapse in hippocampus. Surprisingly, in these BDNF-dependent forms of potentiation, which are also MAPK dependent, TrkB activation is not critical for the activation of MAPK but instead appears to modulate the subcellular distribution and nuclear translocation of the activated MAPK.

Inhibition of HIV-1 virion production by a transdominant mutant of integrase interactor 1

Integase interactor 1 (INI1), also known as hSNF5, is a protein that interacts with HIV-1 integrase. We report here that a cytoplasmically localized fragment of INI1 (S6; aa183-294) containing the minimal integrase-interaction domain potently inhibits HIV-1 particle production and replication. Mutations in S6 or integrase that disrupt integrase-INI1 interaction abrogated the inhibitory effect. An integrase-deficient HIV-1 transcomplemented with integrase fused to Vpr was not affected by S6. INI1 was specifically incorporated into virions and was required for efficient HIV-1 particle production. These results indicate that INI1 is required for late events in the viral life cycle, and that ectopic expression of S6 inhibits HIV-1 replication in a transdominant manner via its specific interaction with integrase within the context of Gag-Pol, providing a novel strategy to control HIV-1 replication.

Structure-function analysis of integrase interactor 1/hSNF5L1 reveals differential properties of two repeat motifs present in the highly conserved region

Retroviral integrase (IN) catalyzes the integration of retroviral cDNA into host chromosome. Ini1 (integrase interactor 1) is a host protein that specifically binds and stimulates in vitro joining activity of HIV-1 IN. Ini1 has homology to yeast transcription factor SNF5 and is a component of the analogous mammalian SWI/SNF complex that can remodel chromatin. Little is known about the function of Ini1 in mammalian cells. To gain insight into the functional domains of Ini1, and to understand the details of protein-protein interactions of IN and Ini1, a structure-function analysis of Ini1 was initiated. By means of the yeast two-hybrid system, the minimal IN binding domain of Ini1 was characterized. One of the two repeat motifs present in the highly conserved regions of Ini1 was found necessary and sufficient to bind to IN in yeast as well as in vitro. Because IN binds to only one of the two repeat motifs in this conserved region of Ini1, it appears that the IN-Ini1 interaction is very specific and functionally significant. Characterization of DNA-binding properties of Ini1 revealed that Ini1 can bind to plasmid DNA, binding more readily to supercoiled DNA than to the relaxed circular DNA. The minimal domain for DNA binding was localized to a region upstream of repeat 1. The DNA binding activity of Ini1 is not required for its ability to interact with IN. The finding that the two repeat motifs of Ini1 display differential binding to HIV-1 IN and that this discrete component of mammalian SWI/SNF complex binds to DNA will help understand the role of Ini1 in HIV-1 integration and in cellular process.

Differential regulation of the pocket domains of the retinoblastoma family proteins by the HPV16 E7 oncoprotein

The human papillomavirus E7 oncoprotein binds to the retinoblastoma (Rb) tumor suppressor protein, and the binding to Rb correlates with the oncogenic potential of E7. Recent studies from several laboratories indicated that the half-life of the Rb protein is reduced in cells that are stably transformed with E7, suggesting that E7 could induce the proteolytic degradation of Rb. To investigate whether the Rb degradation is a primary effect of E7 or a result of altered cell phenotype, we sought to develop assays that can distinguish between the two possibilities. Using recombinant adenovirus expressing the human papillomavirus type 16 E7 protein, we show that the expression of E7 leads to an increased rate of decay of the Rb protein. Moreover, Rb degradation immediately follows the expression of E7 suggesting that it is an early and primary effect. Consistent with a previous study, we observed that the E7-induced degradation of Rb can be blocked by the inhibitors of the 26S proteasome. We have also developed a transient transfection assay for the E7-induced degradation of Rb. Using this assay, we show that the pocket domain of Rb is necessary and sufficient for the E7-induced degradation. However, the proteolysis is relatively specific for Rb because the level of p107 or p130 was not significantly altered by the expression of E7. Thus, although E7 binds to all three members of the Rb family of proteins, the proteolysis is much more efficient in the case of Rb. In the transient transfection assays, adenovirus E1A and SV40 large T antigen failed to induce degradation of Rb, suggesting that the Rb degradation is a unique property of the E7 oncoprotein.

Accumulation of human papillomavirus type 16 E7 protein bypasses G1 arrest induced by serum deprivation and by the cell cycle inhibitor p21

The E7 oncoproteins encoded by the high-risk type of human papillomaviruses (HPVs) interact with the Rb family proteins Rb, p107, and p130. The Rb family proteins associate with the factors of the E2F family to form transcription repressor complexes, which control expression of several genes essential for S-phase entry and DNA replication. The E7 oncoproteins, by interacting with the Rb family proteins, dissociate the repressor complexes involving the factors of the E2F and Rb families, leading to a release of the E2F factors in their activator forms. In this study, we have addressed the mechanism by which the HPV type 16 (HPV16) E7 stimulates the cell cycle. Using a cell line that inducibly expresses the HPV16 E7 protein, we show that an accumulation of E7 induces quiescent cells to enter S phase and that this function of E7 depends on retention of the motif involved in binding to the Rb family proteins. To study the effects of E7 on normal human cells, we generated a recombinant adenovirus that expresses the HPV16 E7 protein. Infection of normal human fibroblasts, which were arrested in G1 phase by serum deprivation, with the E7-expressing virus induced the cells to enter S phase. The E7-induced S phase entry was accompanied by an increase in the activator form of E2F, but no increase in the cyclin-dependent kinase (cdk) activity was detected. Infection of serum-stimulated fibroblasts with a recombinant adenovirus expressing the cdk inhibitor p21 inhibited progression into S phase. Coinfection with the E7-expressing virus abrogated the p21 inhibition of progression into S phase without increasing the cdk activity. These results are consistent with the notion that E7 stimulates entry into S phase through targets downstream of the cdks such as the proteins of the E2F and Rb families.