Hydrogen mapping of the lunar south pole using the LRO neutron detector experiment LEND

Hydrogen has been inferred to occur in enhanced concentrations within permanently shadowed regions and, hence, the coldest areas of the lunar poles. The Lunar Crater Observation and Sensing Satellite (LCROSS) mission was designed to detect hydrogen-bearing volatiles directly. Neutron flux measurements of the Moon's south polar region from the Lunar Exploration Neutron Detector (LEND) on the Lunar Reconnaissance Orbiter (LRO) spacecraft were used to select the optimal impact site for LCROSS. LEND data show several regions where the epithermal neutron flux from the surface is suppressed, which is indicative of enhanced hydrogen content. These regions are not spatially coincident with permanently shadowed regions of the Moon. The LCROSS impact site inside the Cabeus crater demonstrates the highest hydrogen concentration in the lunar south polar region, corresponding to an estimated content of 0.5 to 4.0% water ice by weight, depending on the thickness of any overlying dry regolith layer. The distribution of hydrogen across the region is consistent with buried water ice from cometary impacts, hydrogen implantation from the solar wind, and/or other as yet unknown sources.

Experiment LEND of the NASA Lunar Reconnaissance Orbiter for high-resolution mapping of neutron emission of the Moon

The scientific objectives of neutron mapping of the Moon are presented as 3 investigation tasks of NASA's Lunar Reconnaissance Orbiter mission. Two tasks focus on mapping hydrogen content over the entire Moon and on testing the presence of water-ice deposits at the bottom of permanently shadowed craters at the lunar poles. The third task corresponds to the determination of neutron contribution to the total radiation dose at an altitude of 50 km above the Moon. We show that the Lunar Exploration Neutron Detector (LEND) will be capable of carrying out all 3 investigations. The design concept of LEND is presented together with results of numerical simulations of the instrument's sensitivity for hydrogen detection. The sensitivity of LEND is shown to be characterized by a hydrogen detection limit of about 100 ppm for a polar reference area with a radius of 5 km. If the presence of ice deposits in polar "cold traps" is confirmed, a unique record of many millions of years of lunar history would be obtained, by which the history of lunar impacts could be discerned from the layers of water ice and dust. Future applications of a LEND-type instrument for Mars orbital observations are also discussed.

SOCS1: a potent and multifaceted regulator of cytokines and cell-mediated inflammation

Suppressor of cytokine signalling-1 (SOCS1), as the name implies, is a protein that functions as a negative regulator of cytokine signalling. Initially characterized for its ability to inhibit JAK phosphorylation and function, SOCS1 also targets proteins for degradation by the proteosome machinery. The expression of SOCS1 can be regulated at the transcription, translation and protein level. Despite the broad spectrum of cytokines that can induce SOCS1 expression and/or be inhibited by SOCS1 in vitro, the use of genetically modified mice has revealed a more specific role for SOCS1 in vivo including a critical role in the regulation of IFNgamma signalling. In addition, SOCS1 has a complex role in T cell activation, and studies have revealed significant roles for SOCS1 in the regulation of IL-4, IL-12 and IL-15 in vivo. Interestingly, SOCS1 action is not limited to the regulation of the classical JAK/STAT-signalling pathway, because SOCS1 also inhibits cytokines like insulin and toll-like receptor signal transduction, neither of which activates the JAK/STAT pathway. Evidence is emerging for a role for aberrant SOCS1 expression in human disease, particularly in a number of malignancies.

SOCS1: a potent and multifaceted regulator of cytokines and cell-mediated inflammation

Suppressor of cytokine signalling-1 (SOCS1), as the name implies, is a protein that functions as a negative regulator of cytokine signalling. Initially characterized for its ability to inhibit JAK phosphorylation and function, SOCS1 also targets proteins for degradation by the proteosome machinery. The expression of SOCS1 can be regulated at the transcription, translation and protein level. Despite the broad spectrum of cytokines that can induce SOCS1 expression and/or be inhibited by SOCS1 in vitro, the use of genetically modified mice has revealed a more specific role for SOCS1 in vivo including a critical role in the regulation of IFNgamma signalling. In addition, SOCS1 has a complex role in T cell activation, and studies have revealed significant roles for SOCS1 in the regulation of IL-4, IL-12 and IL-15 in vivo. Interestingly, SOCS1 action is not limited to the regulation of the classical JAK/STAT-signalling pathway, because SOCS1 also inhibits cytokines like insulin and toll-like receptor signal transduction, neither of which activates the JAK/STAT pathway. Evidence is emerging for a role for aberrant SOCS1 expression in human disease, particularly in a number of malignancies.

Functional expression cloning reveals proapoptotic role for protein phosphatase 4

Functional expression cloning strategies are highly suitable for the analysis of the molecular control of apoptosis. This approach has two critical advantages. Firstly, it eliminates prior assumptions about the properties of the proteins involved, and, secondly, it selectively targets proteins that are causally involved in apoptosis control and which affect the crucial cellular decision between survival and death. The application of this strategy to the isolation of cDNAs conferring resistance to dexamethasone and gamma-irradiation resulted in the isolation of a partial cDNA for the catalytic subunit of protein phosphatase 4 (PP4). Cells transfected with this partial cDNA in an expression vector downregulated PP4 and were resistant to both dexamethasone and UV radiation, as demonstrated by both membrane integrity and colony-forming assays. These observations suggest that PP4 plays an important proapoptotic role in T lymphocytes.

Distribution of hydrogen in the near surface of Mars: evidence for subsurface ice deposits

Using the Gamma-Ray Spectrometer on the Mars Odyssey, we have identified two regions near the poles that are enriched in hydrogen. The data indicate the presence of a subsurface layer enriched in hydrogen overlain by a hydrogen-poor layer. The thickness of the upper layer decreases with decreasing distance to the pole, ranging from a column density of about 150 grams per square centimeter at -42 degrees latitude to about 40 grams per square centimeter at -77 degrees. The hydrogen-rich regions correlate with regions of predicted ice stability. We suggest that the host of the hydrogen in the subsurface layer is ice, which constitutes 35 +/- 15% of the layer by weight.

SOCS1 regulates interferon-gamma mediated sensory neuron survival

Differentiation and survival of sensory neurons is regulated by factors such as NGF and LIF. Regulation of signal transduction pathways downstream of such factor signalling by suppressor of cytokine signalling (SOCS) proteins, which negatively regulate the JAK/STAT pathway, may modulate biological outcome. In this study, SOCS1 regulation of growth factor mediated sensory neuron survival was examined. SOCS1 expression by sensory neurons was up-regulated by IFNgamma. Survival of sensory neurons from SOCS1 null mice in NGF or LIF was similar to wildtype mice. IFNgamma partially supported survival of wildtype neurons but supported survival of SOCS1 null neurons as effectively as NGF or LIF. Thus it appears that SOCS1 is a major regulator of sensory neuron responses to the inflammatory cytokine, IFNgamma.

The SOCS box of suppressor of cytokine signaling-1 is important for inhibition of cytokine action in vivo

Suppressor of Cytokine Signaling-1 (SOCS-1) is an essential physiological inhibitor of IFN-gamma signaling. Mice lacking this gene die in the early postnatal period from a disease characterized by hyperresponsiveness to endogenous IFN-gamma. The SOCS box is a C-terminal domain shared with over 30 other proteins that links SOCS proteins to an E3 ubiquitin ligase activity and the proteasome, but whether it contributes to inhibition of cytokine signaling is currently disputed. We have deleted only the SOCS box of the SOCS-1 gene in mice and show that such mice have an increased responsiveness to IFN-gamma and slowly develop a fatal inflammatory disease. These results demonstrate that deletion of the SOCS box leads to a partial loss of function of SOCS-1.

A comparison of overground and treadmill running for measuring the three-dimensional kinematics of the lumbo-pelvic-hip complex

OBJECTIVE

To compare overground and treadmill running for differences in the three-dimensional angular kinematics of the lumbo-pelvic-hip complex.

DESIGN

A within-subject repeated measures design.

BACKGROUND

The treadmill is an attractive research instrument as speed and slope are easily controlled and the required calibration volume is reduced. However, the degree to which treadmill running simulates overground running has not been resolved in the literature to date.

METHODS

10 able-bodied subjects ran overground and on a treadmill at a self-selected speed. The treadmill speed was matched to each subjects respective average overground speed. The time-distance and the three-dimensional angular kinematic data were captured using a passive marker based motion analysis system. A set of angular and temporal kinematic parameters were extracted from the data and subjected to statistical analyses.

RESULTS

Significant differences were found between overground and treadmill running for all the time-distance parameters. Despite this, the kinematics of the lumbar spine and pelvis were similar between the two running conditions, with only three parameters being significantly different. These were lumbar extension at initial contact, anterior pelvic tilt at initial contact and the first maximum anterior pelvic tilt. Hip flexion-extension parameters were also only found to display subtle differences. Of the 17 hip parameters analysed, only hip flexion at initial contact, maximum hip flexion at loading response, hip extension at toe off, maximum hip extension and hip flexion-extension range of motion were found to be significantly different.

CONCLUSION

A high powered treadmill with a minimal belt speed fluctuation is capable of being used to obtain a representation of the typical three-dimensional kinematic pattern of the lumbo-pelvic-hip complex during running.

RELEVANCE

In order for the treadmill to be accepted as a useful research and/or clinical assessment instrument, it must be demonstrated that it does not significantly alter the performance of the evaluated activity. In this respect, a treadmill with minimal intra-stride belt speed variability and similar surface stiffness to the relevant overground condition is likely to be capable of being used to obtain a representation of the typical human running action for well accommodated subjects.

The effect of differing Cardan angle sequences on three dimensional lumbo-pelvic angular kinematics during running

The variability in the three dimensional (3D) lumbo-pelvic angular kinematic patterns during running when using differing Cardan angle sequences was quantified. Data for four able-bodied subjects running on a treadmill at 4.0 m/s were captured using a motion analysis system with six cameras operating at 200 Hz. The adjusted coefficient of multiple correlation was used to compare graphical waveforms whilst the maximum root mean square of the differences was used to express the magnitude of any discrepancy in absolute units. Minimal qualitative differences were found between the various sequences. Quantitative differences between each of the Cardan angle sequences were not found to exceed 7.0 degrees and 2.8 degrees for the lumbar spine and pelvic rotations respectively. It was concluded that different Cardan angle sequences were not found to substantially affect typical 3D lumbo-pelvic angular kinematic patterns during running.

SOCS1 deficiency results in accelerated mammary gland development and rescues lactation in prolactin receptor-deficient mice

Prolactin is essential for proliferation and differentiation of the developing mammary gland. We have explored a role for Suppressor of Cytokine Signaling 1 (SOCS1) as a modulator of the prolactin response using mice deficient in SOCS1, which were rescued from neonatal death by deletion of the Interferon gamma (IFN gamma) gene. SOCS1(-/-)/IFN gamma(-/-) mice exhibited accelerated lobuloalveolar development in the mammary gland during late pregnancy and precocious lactation. Significantly, the lactogenic defect in prolactin receptor heterozygous females could be rescued by deletion of a single SOCS1 allele. These findings establish a role for SOCS1 as a negative regulator of prolactin signaling and suggest that SOCS1 is required for the prevention of lactation prior to parturition.

Suppressor of cytokine signaling-1 attenuates the duration of interferon gamma signal transduction in vitro and in vivo

Suppressor of cytokine signaling-1 (SOCS-1) is a cytokine-inducible intracellular protein that functions to negatively regulate cytokine signal transduction pathways. Studies in vitro have shown that constitutive overexpression of SOCS-1 inhibits signaling in response to a range of cytokines, including interferons (IFN). Mice lacking SOCS-1 die from a complex disease characterized by liver degeneration and massive inflammation. Whereas there is clear evidence of increased IFNgamma signaling in SOCS-1(-/-) mice, it is unclear to what extent this is due to increased IFNgamma levels or to increased IFNgamma sensitivity. Here we have used SOCS-1(-/-) IFNgamma(-/-) mice, which remain healthy and produce no endogenous IFNgamma, to demonstrate that in vitro and in vivo hepatocytes lacking SOCS-1 exhibit a prolonged response to IFNgamma and that this correlates with a dramatically increased sensitivity to the toxic effects of IFNgamma in vivo. Thus, SOCS-1 is required for the timely attenuation of IFNgamma signaling in vivo.

The elemental composition of asteroid 433 eros: results of the NEAR-shoemaker X-ray spectrometer

We report major element composition ratios for regions of the asteroid 433 Eros imaged during two solar flares and quiet sun conditions during the period of May to July 2000. Low aluminum abundances for all regions argue against global differentiation of Eros. Magnesium/silicon, aluminum/silicon, calcium/silicon, and iron/silicon ratios are best interpreted as a relatively primitive, chondritic composition. Marked depletions in sulfur and possible aluminum and calcium depletions, relative to ordinary chondrites, may represent signatures of limited partial melting or impact volatilization.

Gigantism in mice lacking suppressor of cytokine signalling-2

Suppressor of cytokine signalling-2 (SOCS-2) is a member of the suppressor of cytokine signalling family, a group of related proteins implicated in the negative regulation of cytokine action through inhibition of the Janus kinase (JAK) signal transducers and activators of transcription (STAT) signal-transduction pathway. Here we use mice unable to express SOCS-2 to examine its function in vivo. SOCS-2(-/-) mice grew significantly larger than their wild-type littermates. Increased body weight became evident after weaning and was associated with significantly increased long bone lengths and the proportionate enlargement of most organs. Characteristics of deregulated growth hormone and insulin-like growth factor-I (IGF-I) signalling, including decreased production of major urinary protein, increased local IGF-I production, and collagen accumulation in the dermis, were observed in SOCS-2-deficient mice, indicating that SOCS-2 may have an essential negative regulatory role in the growth hormone/IGF-I pathway.

Interplanetary Network Localization of GRB 991208 and the Discovery of its Afterglow

The extremely energetic ( approximately 10-4 ergs cm-2) gamma-ray burst (GRB) of 1999 December 8 was triangulated to an approximately 14 arcmin2 error box approximately 1.8 days after its arrival at Earth with the third interplanetary network (IPN), which consists of the Ulysses, Near-Earth Asteroid Rendezvous, and Wind spacecraft. Radio observations with the Very Large Array approximately 2.7 days after the burst revealed a bright fading counterpart whose position is consistent with that of an optical transient source with a redshift of 0.707. We present the time history, peak flux, fluence, and refined 1.3 arcmin2 error box of this event and discuss its energetics. This is the first time that a counterpart has been found for a GRB localized only by the IPN.

Biomechanical transformation of the gastroc-soleus muscle with botulinum toxin A in children with cerebral palsy

Objective measures (kinematics and kinetics) were used to study prospectively the effects of botulinum toxin A (BTX/A) on the gastro-soleus muscle in ambulant children with cerebral palsy. In this prospective before and after trial, 15 children with diplegia and 10 children with hemiplegia were studied (mean age 5 years 7 months, range 4 years to 9 years). A range of standardized clinical measures was undertaken but the emphasis for this report is on the three-dimensional gait analysis (3DGA) results. All children showed improvements in sagittal ankle kinematics, as has been previously reported. Two new measures of ankle kinetics were devised: ankle moment quotient (AMQ), and ankle power quotient (APQ). Before intervention, ankle moments were characterized by a 'double bump' ankle moment. A typical abnormal baseline ankle-power curve was triphasic with an initial trough of absorption followed by abnormal mid-stance power generation, instead of the usual A1 pattern, and reduced terminal stance power generation (A2). Three weeks after treatment with BTX/A alone there was a statistically significant improvement of AMQ and APQ; some patients required potentiation of BTX/A with a short period of serial casts. Both groups (BTX/A alone and BTX/A plus casting) continued to show improvement in ankle kinetics from baseline after 12 and 24 weeks. This is the first study to demonstrate improvements in the typical abnormal ankle kinetics which we believe provides evidence of the 'biomechanical transformation of muscle'.

Different protein turnover of interleukin-6-type cytokine signalling components

Interleukin (IL)-6 and IL-6-type cytokines signal through the gp130/Jak/STAT signal transduction pathway. The key components involved are the signal transducing receptor subunit gp130, the Janus kinases Jak1, Jak2 and Tyk2, STAT1 and STAT3 of the family of signal transducers and activators of transcription, the protein tyrosine phosphatase SHP2 and the suppressors of cytokine signalling SOCS1, SOCS2 and SOCS3. Whereas considerable information has been accumulated concerning the time-course of activation for the individual signalling molecules, data on the availability of the proteins involved in IL-6-type cytokine signal transduction are scarce. Nevertheless, availability of these molecules, determined by the balance of protein synthesis and degradation, also influences IL-6-type cytokine signal transduction. Here, we present a comprehensive set of data on the half-lives of the key molecules involved in the IL-6 signal transduction pathway. The turnover rates for the various proteins differ substantially. Three groups of signalling proteins can be discriminated: whereas the feedback inhibitors SOCS1, SOCS2 and SOCS3 are very short-lived, STAT1, STAT3 and SHP2 have an extremely slow turnover rate. Interestingly, the half-life of STAT3beta, a splice variant of STAT3alpha, is reduced to almost 50% of the half-life of STAT3alpha. The Janus kinases Jak1, Jak2, Tyk2 and gp130 show intermediate half-lives. Our data imply that signalling components activated by post-translational modifications are long-lived whereas the activity of very short-lived proteins is regulated mainly at the transcriptional level.

High- or low- technology measurements of energy expenditure in clinical gait analysis?

The repeatability of energy-expenditure measurements were studied in five children and four adults without disabilities using the Cosmed K4 (high technology). The ability to detect change in measurements was compared between this instrument and the Physiological Cost Index (PCI; low technology). The results of repeatability (95% range) for oxygen cost were 13.1% in children and 13% in adults. In contrast, the SD of PCI was 6 to 72% of the mean in adults and wider in children (91%; 95% range). The validity of PCI as an outcome measure was questioned. In addition, 177 children with motor disability were prospectively studied using the Cosmed K4. Previous experience with the Cosmed K2 (intermediate technology) helped to develop a practical and repeatable protocol for testing children with disability using the Cosmed K4. The protocol commenced with 5 minutes of rest to achieve baseline values of heart rate and oxygen consumption, followed by 10 minutes of continuous walking at a self-selected speed on a 10-metre level oval walking track. The test concluded with 5 minutes of rest to monitor the return to baseline values. Ninety-one percent of the children with disability quickly reached a steady-state of oxygen consumption and carbon-dioxide production. The carbon-dioxide sensor in the Cosmed K4 has enabled a new group of severely involved children with cerebral palsy (9%) to be defined. These children have been termed 'physiologically marginal ambulators'.

Suppressors of cytokine signaling (SOCS): negative regulators of signal transduction

SOCS-1 was originally identified as an inhibitor of interleukin-6 signal transduction and is a member of a family of proteins (SOCS-1 to SOCS-7 and CIS) that contain an SH2 domain and a conserved carboxyl-terminal SOCS box motif. Mutation studies have established that critical contributions from both the amino-terminal and SH2 domains are essential for SOCS-1 and SOCS-3 to inhibit cytokine signaling. Inhibition of cytokine-dependent activation of STAT3 occurred in cells expressing either SOCS-1 or SOCS-3, but unlike SOCS-1, SOCS-3 did not directly interact with or inhibit the activity of JAK kinases. Although the conserved SOCS box motif appeared to be dispensable for SOCS-1 and SOCS-3 action when overexpressed, this domain interacts with elongin proteins and may be important in regulating protein turnover. In gene knockout studies, SOCS-1(-/-) mice were born but failed to thrive and died within 3 weeks of age with fatty degeneration of the liver and hemopoietic infiltration of several organs. The thymus in SOCS-1(-/-) mice was small, the animals were lymphopenic, and deficiencies in B lymphocytes were evident within hemopoietic organs. We propose that the absence of SOCS-1 in these mice prevents lymphocytes and liver cells from appropriately controlling signals from cytokines with cytotoxic side effects.

SOCS1 is a critical inhibitor of interferon gamma signaling and prevents the potentially fatal neonatal actions of this cytokine

Mice lacking suppressor of cytokine signaling-1 (SOCS1) develop a complex fatal neonatal disease. In this study, SOCS1-/- mice were shown to exhibit excessive responses typical of those induced by interferon gamma (IFNgamma), were hyperresponsive to viral infection, and yielded macrophages with an enhanced IFNgamma-dependent capacity to kill L. major parasites. The complex disease in SOCS1-/- mice was prevented by administration of anti-IFNgamma antibodies and did not occur in SOCS1-/- mice also lacking the IFNgamma gene. Although IFNgamma is essential for resistance to a variety of infections, the potential toxic action of IFNgamma, particularly in neonatal mice, appears to require regulation. Our data indicate that SOCS1 is a key modulator of IFNgamma action, allowing the protective effects of this cytokine to occur without the risk of associated pathological responses.

Aberrant hematopoiesis in mice with inactivation of the gene encoding SOCS-1

Mice with homozygous inactivation of the gene encoding the suppressor of cytokine signaling-1 (SOCS-1) protein die within 21 days of birth with low body weight, fatty degeneration and necrosis of the liver, infiltration of the lung, pancreas, heart and skin by macrophages and granulocytes and a profound depletion of T- and B-lymphocytes. In the present study, SOCS-1 -/- mice were found to have a moderate neutrophilia, and reduced platelet and hematocrit levels. Replacement of the SOCS-1 gene by a lac-Z reporter gene allowed documentation by FACS sorting that at least a proportion of granulocyte-macrophage progenitor cells transcribe SOCS-1. Most hematopoietic progenitor cell frequencies were normal in -/- marrow as were the size and cellular content of colonies formed by -/- progenitor cells in response to various stimulating factors. However, there was an increased frequency of macrophage progenitor cells in -/- mice and, abnormally, one quarter of all progenitor cells were located in the liver. Progenitor cells from -/- mice were hyper-responsive to stimulation by GM-CSF but not by M-CSF or Multi-CSF (IL-3). Progenitor cells from -/- mice were also hypersensitive to inhibition by interferon-gamma (IFN-gamma), the degree of inhibition varying markedly with the stimulating factor used. The suppressive effects of IFN-gamma therefore appear to involve interactions with particular growth factor-initiated signals in -/- cells--interactions that are strongly modulated by the action of the SOCS-1 protein.

Negative regulation of the JAK/STAT pathway

Cytokines induce a variety of biological responses by binding to specific cell surface receptors and activating cytoplasmic signal transduction pathways, such as the JAK/STAT pathway. Although these responses are generally transient, few molecules have been characterised that switch the signal off. Several different steps of the signal transduction pathway appear to be targeted by negative regulators, including the receptor/ligand complex, JAK kinases, and STAT transcription factors. Negative regulation is achieved by dephosphorylation of signalling intermediates by protein tyrosine phosphatases such as SHP-1, and by proteolytic degradation. Recent studies have identified two new families of negative regulatory molecules, SOCS and PIAS, which function in novel ways to suppress signal transduction pathways. The duration and intensity of a cell's response to cytokine therefore appear to be determined by the net effect of several regulatory mechanisms.

Mutational analyses of the SOCS proteins suggest a dual domain requirement but distinct mechanisms for inhibition of LIF and IL-6 signal transduction

SOCS-1 (suppressor of cytokine signaling-1) is a representative of a family of negative regulators of cytokine signaling (SOCS-1 to SOCS-7 and CIS) characterized by a highly conserved C-terminal SOCS box preceded by an SH2 domain. This study comprehensively examined the ability of several SOCS family members to negatively regulate the gp130 signaling pathway. SOCS-1 and SOCS-3 inhibited both interleukin-6 (IL-6)- and leukemia inhibitory factor (LIF)-induced macrophage differentiation of murine monocytic leukemic M1 cells and LIF induction of a Stat3-responsive reporter construct in 293T fibroblasts. Deletion of amino acids 51-78 in the N-terminal region of SOCS-1 prevented inhibition of LIF signaling. The SOCS-1 and SOCS-3 N-terminal regions were functionally interchangeable, but this did not extend to other SOCS family members. Mutation of SH2 domains abrogated the ability of both SOCS-1 and SOCS-3 to inhibit LIF signal transduction. Unlike SOCS-1, SOCS-3 was unable to inhibit JAK kinase activity in vitro, suggesting that SOCS-1 and SOCS-3 act on the JAK-STAT pathway in different ways. Thus, although inhibition of signaling by SOCS-1 and SOCS-3 requires both the SH2 and N-terminal domains, their mechanisms of action appear to be biochemically different.

Negative regulation of the JAK/STAT pathway

Cytokines induce a variety of biological responses by binding to specific cell surface receptors and activating cytoplasmic signal transduction pathways, such as the JAK/STAT pathway. Although these responses are generally transient, few molecules have been characterised that switch the signal off. Several different steps of the signal transduction pathway appear to be targeted by negative regulators, including the receptor/ligand complex, JAK kinases, and STAT transcription factors. Negative regulation is achieved by dephosphorylation of signalling intermediates by protein tyrosine phosphatases such as SHP-1, and by proteolytic degradation. Recent studies have identified two new families of negative regulatory molecules, SOCS and PIAS, which function in novel ways to suppress signal transduction pathways. The duration and intensity of a cell's response to cytokine therefore appear to be determined by the net effect of several regulatory mechanisms.

Liver degeneration and lymphoid deficiencies in mice lacking suppressor of cytokine signaling-1

SOCS-1, a member of the suppressor of cytokine signaling (SOCS) family, was identified in a genetic screen for inhibitors of interleukin 6 signal transduction. SOCS-1 transcription is induced by cytokines, and the protein binds and inhibits Janus kinases and reduces cytokine-stimulated tyrosine phosphorylation of signal transducers and activators of transcription 3 and the gp130 component of the interleukin 6 receptor. Thus, SOCS-1 forms part of a feedback loop that modulates signal transduction from cytokine receptors. To examine the role of SOCS-1 in vivo, we have used gene targeting to generate mice lacking this protein. SOCS-1(-/-) mice exhibited stunted growth and died before weaning with fatty degeneration of the liver and monocytic infiltration of several organs. In addition, the thymus of SOCS-1(-/-) mice was reduced markedly in size, and there was a progressive loss of maturing B lymphocytes in the bone marrow, spleen, and peripheral blood. Thus, SOCS-1 is required for in vivo regulation of multiple cell types and is indispensable for normal postnatal growth and survival.

SOCS: suppressors of cytokine signalling

Regulation of many aspects of cell behaviour occurs through the interaction of cytokines with specific cell surface receptors, resulting in the activation of cytoplasmic signal transduction pathways. Although cellular responses to cytokines are tightly controlled, few molecules have been identified which are able to switch these signals off. The suppressors of cytokine signalling (SOCS) proteins are a new family of negative regulators of cytokine signal transduction. SOCS proteins contain a variable amino-terminal region, a central Src-homology 2 (SH2) domain and a novel conserved carboxy-terminal motif termed the SOCS box. The expression of SOCS proteins is induced by cytokine. Once expressed, SOCS downregulate JAK/STAT pathways and hence the biological response. Recent studies, primarily reliant on overexpression of proteins, indicate that SOCS may be involved in modulating additional pathways, suggesting that they may play a more general role in regulating cellular responses to cytokine. The analysis of knockout mice will clarify the physiological role of SOCS in regulating cytokine responsiveness. Mutations leading to the loss of SOCS activity may give rise to cytokine hyperresponsiveness and may contribute to the development of diseases such as diabetes and cancer. Small molecule effectors which modify SOCS function may potentially be useful therapeutics for the treatment of certain diseases.

Growth hormone preferentially induces the rapid, transient expression of SOCS-3, a novel inhibitor of cytokine receptor signaling

Four members (SOCS-1, SOCS-2, SOCS-3, and CIS) of a family of cytokine-inducible, negative regulators of cytokine receptor signaling have recently been identified. To address whether any of these genes are induced in response to growth hormone (GH), serum-starved 3T3-F442A fibroblasts were incubated with GH for various time points, and the expression of the SOCS gene family was analyzed by Northern blotting. GH stimulated the rapid, transient induction of SOCS-3 mRNA, peaking 30 min after the initiation of GH exposure and declining to basal levels by 2 h. Expression of the other SOCS genes (SOCS-1, SOCS-2, CIS) was also up-regulated by GH, although to a lesser extent than SOCS-3 and with differing kinetics. SOCS-3 expression was also strongly induced in 3T3-F442A cells treated with leukemia-inhibitory factor (LIF), with weaker induction of SOCS-1 and CIS being observed. The preferential induction of SOCS-3 mRNA was also observed in hepatic RNA isolated from the livers of mice that had received a single supraphysiological dose of GH intraperitoneally. Co-transfection studies revealed that constitutive expression of SOCS-1 and SOCS-3, but not SOCS-2 or CIS, blocked GH-induced transactivation of the GH-responsive serine protease inhibitor 2.1 gene promoter.

Twenty proteins containing a C-terminal SOCS box form five structural classes

The four members of the recently identified suppressor of cytokines signaling family (SOCS-1, SOCS-2, SOCS-3, and CIS, where CIS is cytokine-inducible SH2-containing protein) appear, by various means, to negatively regulate cytokine signal transduction. Structurally, the SOCS proteins are composed of an N-terminal region of variable length and amino acid composition, a central SH2 domain, and a previously unrecognized C-terminal motif that we have called the SOCS box. By using the SOCS box amino acid sequence consensus, we have searched DNA databases and have identified a further 16 proteins that contain this motif. These proteins fall into five classes based on the protein motifs found N-terminal of the SOCS box. In addition to four new SOCS proteins (SOCS-4 to SOCS-7) containing an SH2 domain and a SOCS box, we describe three new families of proteins that contain either WD-40 repeats (WSB-1 and -2), SPRY domains (SSB-1 to -3) or ankyrin repeats (ASB-1 to -3) N-terminal of the SOCS box. In addition, we show that a class of small GTPases also contains a SOCS box. The expression of representative members of each class of proteins differs markedly, as does the regulation of expression by cytokines. The function of the WSB, SSB, and ASB protein families remains to be determined.

Distinct roles for leukemia inhibitory factor receptor alpha-chain and gp130 in cell type-specific signal transduction

Leukemia inhibitory factor (LIF) induces a variety of disparate biological responses in different cell types. These responses are thought to be mediated through the functional LIF receptor (LIFR), consisting of a heterodimeric complex of LIFR alpha-chain (LIFRalpha) and gp130. The present study investigated the relative capacity of the cytoplasmic domains of each receptor subunit to signal particular responses in several cell types. To monitor the signaling potential of LIFRalpha and gp130 individually, we constructed chimeric receptors by linking the extracellular domain of granulocyte colony-stimulating factor receptor (GCSFR) to the transmembrane and cytoplasmic regions of either LIFRalpha or gp130. Both chimeric receptors and the full-length GCSFR in expressed in M1 myeloid leukemic cells to measure differentiation induction, in embryonic stem cells to measure differentiation inhibition, and in Ba/F3 cells to measure cell proliferation. Our results demonstrated that whereas GCSFR-gp130 receptor homodimer mediated a GCSF-induced signal in all three cell types, the GCSFR-LIFRalpha receptor homodimer was only functional in embryonic stem cells. These findings suggest that the signaling potential of gp130 and LIFRalpha cytoplasmic domains may differ depending upon the tissue and cellular response initiated.

A family of cytokine-inducible inhibitors of signalling

Cytokines are secreted proteins that regulate important cellular responses such as proliferation and differentiation. Key events in cytokine signal transduction are well defined: cytokines induce receptor aggregation, leading to activation of members of the JAK family of cytoplasmic tyrosine kinases. In turn, members of the STAT family of transcription factors are phosphorylated, dimerize and increase the transcription of genes with STAT recognition sites in their promoters. Less is known of how cytokine signal transduction is switched off. We have cloned a complementary DNA encoding a protein SOCS-1, containing an SH2-domain, by its ability to inhibit the macrophage differentiation of M1 cells in response to interleukin-6. Expression of SOCS-1 inhibited both interleukin-6-induced receptor phosphorylation and STAT activation. We have also cloned two relatives of SOCS-1, named SOCS-2 and SOCS-3, which together with the previously described CIS form a new family of proteins. Transcription of all four SOCS genes is increased rapidly in response to interleukin-6, in vitro and in vivo, suggesting they may act in a classic negative feedback loop to regulate cytokine signal transduction.

Tyrosine residues in the granulocyte colony-stimulating factor (G-CSF) receptor mediate G-CSF-induced differentiation of murine myeloid leukemic (M1) cells

The cytoplasmic tyrosine residues of many growth factor receptors have been shown to be important for receptor signal transduction via the recruitment of proteins containing phosphotyrosine-binding domains. This study demonstrates the importance of specific tyrosine residues in the granulocyte colony-stimulating factor (G-CSF) receptor cytoplasmic domain in G-CSF-induced macrophage cell differentiation. Site-directed mutagenesis was used to generate a series of G-CSF receptor (G-CSF-R) mutants in which the tyrosine residues were replaced with phenylalanine either singly or in combination. The mouse myeloid leukemic cell line (M1) transfected with G-CSF-R cDNA can be induced to differentiate into macrophages in response to G-CSF. The effect of the tyrosine mutations on this differentiation response was assessed by examining cell morphology and differentiation in soft agar colony assays. Although three of the four cytoplasmic tyrosine residues appeared to contribute to the differentiation response, mutation of a single residue (Tyr744) significantly reduced the ability of the M1 cells to differentiate. The STAT family of signaling molecules (Stat1, Stat3, and Stat5) were activated by G-CSF in M1 cells expressing those G-CSF-R tyrosine mutants unable to mediate G-CSF-induced differentiation. Furthermore, activation of STAT proteins was shown to occur in the absence of all four cytoplasmic tyrosine residues, suggesting an alternative mechanism for STAT activation other than direct interaction with receptor phosphotyrosines.

Prolonged in vivo gene expression driven by a tyrosine hydroxylase promoter in a defective herpes simplex virus amplicon vector

A 9.0-kb fragment of the tyrosine hydroxylase (TH) promoter, previously shown to direct tissue-specific expression in transgenic mice, was fused to an Escherichia coli LacZ reporter gene in a defective herpes simplex virus type-1 (HSV-1) amplicon vector (THlac). The HSV immediate early (IE) 4/5 promoter (HSVlac) was used as a control. LacZ gene expression was visualized by X-Gal histochemical and TH immunocytochemical analysis. Two days and 10 weeks after THlac injection into rat caudate nucleus (CN), X-Gal-stained cells were observed in the substantia nigra (SN) and locus ceruleus (LC) ipsilateral to the injection site. These blue cells were TH-positive neurons as evidenced by double labeling with immunocytochemistry. Moreover, the number of X-Gal+, TH+ (double-positive) neurons in the SN increased at 10 weeks as compared to that seen 2 days after THlac injection. In marked contrast, few double-positive nigral neurons were observed either 2 days or 10 weeks after direct injection of THlac into SN. However, neither nigral nor striatal injection of HSVlac resulted in prolonged gene expression. These results suggest that a neuronal, but not a viral, promoter in an HSV vector can produce cell-type-specific, prolonged, and stable gene expression following retrograde transport. In addition, THlac produced infrequent gene expression in TH-negative cells (CN and dorsal to SN) after THlac injection into CN and SN, respectively. Overall, these results suggest that in some in vivo contexts cell-type-preferred expression can be achieved by a cellular promoter in an amplicon vector. Moreover, they underscore the need for the careful and systematic study of neuronal promoters in HSV vectors.

A cdc2-like kinase distinct from cdk5 is associated with neurofilaments

An immunoprecipitation assay was used to identify protein kinases which are physically associated with neurofilaments (NF) in mouse brain extracts. Using this approach, we show that a cdc2-related kinase is associated with NF. The cdc2-related kinase was found to be distinct from cdk5 and the authentic cdc2 by a number of criteria. Firstly, it has a molecular mass on SDS-PAGE gels of 34 kDa, similar to that of cdc2, but differing from cdk5 (31 kDa). Secondly, it is not recognized by an antibody specific for cdk5. Thirdly, it is recognized by an antibody raised against the C-terminal region of authentic cdc2, but not by an antibody specific for the PSTAIRE motif. Using immunoblotting, we further show that the cdc2-related kinase copurifies with NF isolated from rat tissues. In vitro kinase assays further demonstrated that immunoprecipitated cdc2-related kinase phosphorylates recombinant NF-H protein. Phosphorylation of NF-H by the cdc2-like activity was not affected by 3 microM olomoucine but was inhibited by 10 microM of this kinase inhibitor. Phosphoamino acid analysis of in vitro phosphorylated NF-H indicates that the immunoprecipitated cdc2-related kinase phosphorylates serine residues.

Neurofilament phosphorylation is modulated by myelination

Axons undergo substantial changes in radial growth during the course of development. Recent evidence suggests that axonal diameter may be controlled by the state of neurofilament (NF) phosphorylation. Using dorsal root ganglion (DRG)-Schwann cell co-cultures, we provide direct evidence that phosphorylation of NF is regulated by myelination. NF phosphorylation increased upon myelination of DRG neurons by Schwann cells. The increase in NF phosphorylation was reflected both as an increase in immunoreactivity with the antibody SMI31, specific for phosphorylation-dependent NF epitopes, and a concomitant decrease in immunoreactivity with SMI32, specific for nonphosphorylated NF epitopes. The increase in NF phosphorylation induced by myelination in the neuron-glia co-cultures was similar to NF phosphorylation seen in sciatic nerve extracts of mice with normal myelination compared to Trembler J mouse littermates in which myelination of peripheral nerves is compromised. Using an in situ gel kinase assay, we have detected changes in individual NF kinase activities during myelination. In particular, a 35-kDa kinase activity was induced by myelination, whereas a 42-kDa kinase decreased in activity. We discuss the possibility that these and other kinases may be involved in signaling processes between neurons and glia during myelination.

Nonresponsiveness of the metastatic human lung carcinoma MV522 xenograft to conventional anticancer agents

The human lung carcinoma cell line MV522 was previously noted to produce extensive metastasis to the lungs, spleen and lymph nodes after subcutaneous transplantation into athymic nude mice. Animals eventually succumb to these metastases, and not primary tumor growth. The ability to produce extensive metastasis after a simple subcutaneous injection in 100% of animals (> 100 tested to date) would be an advantage when screening compounds for anticancer activity. To validate the utility of this xenograft model for testing anticancer agents, we tested the ability of 10 anticancer drugs to either inhibit primary tumor growth and/or prolong life span of MV522-bearing animals. Among the 10 antitumor conventional agents, only mitomycin C and taxol demonstrated primary tumor growth inhibition. Mitomycin C produced a mild increase in median life span of 41% to 63%, while taxol had inconsistent effects. The metastatic MV522 carcinoma model appears to reflect clinical resistance of primary non-small cell lung cancer to conventional chemotherapeutic agents and should be useful for testing new anti-cancer drugs.

Production of monoclonal antibodies against neurofilament-associated proteins: demonstration of association with neurofilaments by a coimmunoprecipitation method

A panel of monoclonal antibodies (MAbs) was produced against mouse brain proteins that bind to the tail domain of the neurofilament (NF) heavy (200-kDa) subunit (NF-H) in vitro. An in vivo association of the MAb ligands with NFs was confirmed by examining reactivity of the MAbs with immunoprecipitated NF-H complexes. Using this method we demonstrated association of the ligands of three of the MAbs with NFs. In contrast, glial fibrillary acidic protein and an unknown 97-kDa brain protein were not associated with NFs by this criterion. An 80-kDa doublet that coimmunoprecipitated with NF-H complexes, recognized by MAb 223, was shown by immunocytochemistry and immunoblotting to be synapsin Ia and Ib. Using a complementary approach, we confirmed an association of synapsin with NFs by demonstrating that immunoprecipitated synapsin I complexes contained NF-H and NF medium (160-kDa) subunits. MAbs 63 and 105 recognized a more complex set of proteins that had predominantly synaptic localizations. These data suggest that NFs may provide important support for attachment and/or transport of synaptic proteins in brain.

Characterization of illudin S sensitivity in DNA repair-deficient Chinese hamster cells. Unusually high sensitivity of ERCC2 and ERCC3 DNA helicase-deficient mutants in comparison to other chemotherapeutic agents

Illudins, novel natural products with a structure unrelated to any other known chemical, display potent in vitro and in vivo anti-cancer activity against even multi-drug resistant tumors, and are metabolically activated to an unstable intermediate that binds to DNA. The DNA damage produced by illudins, however, appears to differ from that of other known DNA damaging toxins. The sensitivity pattern of the various UV-sensitive cell lines differs from previously studied DNA cross-linking agents. Normally, the ERCC1- (excision repair cross complementing) and ERCC4-deficient cell lines are most sensitive to DNA cross-linking agents, with ERCC2-, ERCC3- and ERCC5-deficient cell lines having minimal sensitivity. With illudins the pattern is reversed, with ERCC2 and ERCC3 being the most sensitive. The sensitivity to illudins in complementation groups 1 through 3 is due to a deficiency of the ERCC1-3 gene products, as cellular drug accumulation studies revealed no differences in transport capacity or total drug accumulation. Also, a transgenic cell line in which ERCC2 activity was expressed through an expression vector regained its relative resistance to the illudins. The EM9 cell line, which displays sensitivity to monoadduct producing chemicals, was not sensitive. Thus, excision repair is involved in repair of illudin-induced damage and, unlike other anti-cancer agents, the involvement of ERCC2 and ERCC3 helicases is critical for repair to occur. The requirement for ERCC2 and ERCC3, combined with the finding that ERCC1 but not ERCC2 is upregulated in drug-resistant tumors, may explain the efficacy of illudins against drug-resistant tumors. The inhibition of DNA synthesis in cells within minutes after exposure to illudins at nanomolar concentrations may be related to the finding that the ERCC3 gene product is actually the p89 helicase component of the BTF2 (TFII) basic transcription factor and the high sensitivity of ERCC3-deficient cells to illudins.

A 17S multiprotein form of murine cell DNA polymerase mediates polyomavirus DNA replication in vitro

We have identified and purified a multiprotein form of DNA polymerase from the murine mammary carcinoma cell line (FM3A) using a series of centrifugation, polyethylene glycol precipitation, and ion-exchange chromatography steps. Proteins and enzymatic activities associated with this mouse cell multiprotein form of DNA polymerase include the DNA polymerases alpha and delta, DNA primase, proliferating cell nuclear antigen (PCNA), DNA ligase I, DNA helicase, and DNA topoisomerases I and II. The sedimentation coefficient of the multiprotein form of DNA polymerase is 17S, as determined by sucrose density gradient analysis. The integrity of the murine cell multiprotein form of DNA polymerase is maintained after treatment with detergents, salt, RNase, DNase, and after chromatography on DE52-cellulose, suggesting that the association of the proteins with one another is independent of nonspecific interaction with other cellular macromolecular components. Most importantly, we have demonstrated that this complex of proteins is fully competent to replicate polyomavirus DNA in vitro. This result implies that all of the cellular activities required for large T-antigen dependent in vitro polyomavirus DNA synthesis are present within the isolated 17S multiprotein form of the mouse cell DNA replication activities. A model is proposed to represent the mammalian Multiprotein DNA Replication Complex (MRC) based on the fractionation and chromatographic profiles of the individual proteins found to co-purify with the complex.