The ubiquitously expressed DNA-binding protein late SV40 factor binds Ig switch regions and represses class switching to IgA

Ig heavy chain class switch recombination (CSR) determines the expression of Ig isotypes. The molecular mechanism of CSR and the factors regulating this process have remained elusive. Recombination occurs primarily within switch (S) regions, located upstream of each heavy chain gene (except Cdelta). These repetitive sequences contain consensus DNA-binding sites for the DNA-binding protein late SV40 factor (LSF) (CP2/leader-binding protein-1c). In this study, we demonstrate by EMSA that purified rLSF, as well as LSF within B cell extracts, directly binds both Smu and Salpha sequences. To determine whether LSF is involved in regulating CSR, two different LSF dominant negative variants were stably expressed in the mouse B cell line I.29 mu, which can be induced to switch from IgM to IgA. Overexpression of these dominant negative LSF proteins results in decreased levels of endogenous LSF DNA-binding activity and an increase in cells undergoing CSR. Thus, LSF represses class switching to IgA. In agreement, LSF DNA-binding activity was found to decrease in whole cell extracts from splenic B cells induced to undergo class switching. To elucidate the mechanism of CSR regulation by LSF, the interactions of LSF with proteins involved in chromatin modification were tested in vitro. LSF interacts with both histone deacetylases and the corepressor Sin3A. We propose that LSF represses CSR by histone deacetylation of chromatin within S regions, thereby limiting accessibility to the switch recombination machinery.     

Labile Serum Factor and Its Effect on Arbovirus Neutralization

Enhancement of neutralization of Sindbis, Venezuelan equine encephalitis, Eastern equine encephalitis, Western equine encephalitis, and St. Louis encephalitis viruses by labile serum factor (LSF) in human serum and plasma was demonstrated. Human serum and plasma could be diluted 1:8 and 1:16 and still retain some LSF activity. Satisfactory storage temperatures for retention of LSF activity were −20 or −56 C. Repeated freeze-thaw cycles of serum did not alter LSF activity, but the activity was completely eliminated by heating at 56 C for 5 min. LSF of human serum equally enhanced neutralization by Sindbis immune mouse and rabbit sera; these results suggest a lack of species specificity. Rehydrated lyophilized gunea pig complement did not restore LSF activity to heated human plasma. Serum components responsible for LSF activity were not dialyzable. Discovery of fresh serum without LSF activity established the need to pretest all sera used as LSF sources.     

A series of murine interleukin molecules which stimulate both murine and human lymphocytes: I. Production by Phytolacca americana (pokeweed) lectin 2 (Pa-2)-stimulated thymus and thymus-derived cells

Cell-free supernatant fluid, from cultures of Phytolacca americana (pokeweed) lectin 2 (Pa-2)-pulsed murine spleen or thymus cells, contains factors which induce cultured lymphocytes to differentiate into IgM-secreting cells (assayed by a reverse plaque technique) and to proliferate (measured by the incorporation of tritiated thymidine) without the addition of mitogen. The factors in this supernatant fluid responsible for these activities have been designated as lymphocyte stimulating factors (LSF). LSF showed no genetic restrictions related to the major histocompatability complex; LSF made in one strain of mice worked in other strains. Indeed, LSF is not restricted by species barriers; human peripheral blood mononuclear cells were also stimulated by murine LSF to proliferate and differentiate into immunoglobulin-secreting cells without further addition of antigen or mitogen. Maximum production of LSF was achieved within 12 hr of culture and was independent of cell division. In contrast to TRF, no further production of LSF was detectable after 24 hr of culture. Unlike T-cell growth factor, this material stimulated increased mitosis of thymic, T, and B lymphocytes without the addition of mitogen or antigen. LSF also stimulated polyclonal B-cell differentiation into IgM-secreting cells. Maximal numbers of immunoglobulin-secreting cells were generated when LSF was added at the initiation of the culture. Indeed, unlike TRF, LSF needed to be present only during the first 6 hr of culture to achieve maximum stimulation, and did not require the presence of antigen. The production of LSF by a T-cell population in the spleen was shown by two independent methods. Spleen cells treated with anti-Thy 1 plus complement failed to produce detectable levels of LSF. On the other hand, purified populations of surface immunoglobulin-negative spleen cells produced LSF. Furthermore, the subset of thymocytes responsible for LSF production was the small population (approximately 10%) of cells in the thymus, which are not agglutinated by peanut agglutinin.     

Synthesis and biological evaluation of lisofylline (LSF) analogs as a potential treatment for Type 1 diabetes

Lisofylline (LSF, 1-(5-R-hydroxyhexyl)-3,7-dimethylxanthine) is an anti-inflammatory agent that protects beta-cells from Th1 cytokine-induced dysfunction and reduces the onset of Type 1 diabetes in non-obese diabetic (NOD) mice. Due to its low potency, poor oral bioavailability, and short half-life, the widespread clinical utility of LSF may be limited. Our goal has been to develop new agents based on the LSF structural motif that resolve the potency and pharmacokinetic liabilities of LSF. In this study, we have generated a focused library of LSF analogs that maintain the side chain (5-R-hydroxyhexyl) constant, while substituting a variety of nitrogen-containing heterocyclic substructures for the xanthine moiety of LSF. This library includes the xanthine-like (5-aza-7-deazaxanthine), as well as non-xanthine-like skeletons. The LSF analogs were evaluated in a pancreatic beta-cell line for the effects on apoptosis protection and insulin release. The metabolic stability of selected compounds was also tested.     

Structure of the Arabidopsis Glucan Phosphatase LIKE SEX FOUR2 Reveals a Unique Mechanism for Starch Dephosphorylation

Starch is a water-insoluble, Glc-based biopolymer that is used for energy storage and is synthesized and degraded in a diurnal manner in plant leaves. Reversible phosphorylation is the only known natural starch modification and is required for starch degradation in planta. Critical to starch energy release is the activity of glucan phosphatases; however, the structural basis of dephosphorylation by glucan phosphatases is unknown. Here, we describe the structure of the Arabidopsis thaliana starch glucan phosphatase LIKE SEX FOUR2 (LSF2) both with and without phospho-glucan product bound at 2.3Å and 1.65Å, respectively. LSF2 binds maltohexaose-phosphate using an aromatic channel within an extended phosphatase active site and positions maltohexaose in a C3-specific orientation, which we show is critical for the specific glucan phosphatase activity of LSF2 toward native Arabidopsis starch. However, unlike other starch binding enzymes, LSF2 does not possess a carbohydrate binding module domain. Instead we identify two additional glucan binding sites located within the core LSF2 phosphatase domain. This structure is the first of a glucan-bound glucan phosphatase and provides new insights into the molecular basis of this agriculturally and industrially relevant enzyme family as well as the unique mechanism of LSF2 catalysis, substrate specificity, and interaction with starch granules.     

The effects of petroleum oil and lime sulfur on the mortality of Unaspis yanonensis and Aculops pelekassi in the laboratory

Arrowhead scale (AHS), Unaspis yanonensis (Kuwana) (Hemiptera: Diaspididae), and pink citrus rust mite (PCRM), Aculops pelekassi (Keifer) (Acari: Eriophyoidae), are important arthropod pests of organic citrus orchards in Jeju. This study was conducted to evaluate the stage-specific mortality effects of petroleum spray oil (PSO) (AI 95%) and lime sulfur (LSF) (AI 22%) against AHS and PCRM in the laboratory. The developmental stages of AHS were divided into the 1st nymph, the three sub-stages of the 2nd nymph (N2a = early soft body, N2b = hardened body, and N2c = late apolysis), and the two sub-stages of adult females (A3a = early age, and A3b = middle age). The developmental stages of PCRM were divided into eggs, the 2nd nymphs, and adults. PSO 100× and LSF 80× resulted in high mortality against the 1st nymphs of AHS. The effects of PSO and LSF were significantly different among the application rates on 2nd nymphs of AHS and were higher on N2a. The PSO and LSF treatments significantly affected egg hatch rate of PCRM: LSF 50× (2.4%), LSF 100× and PSO of 50× and 200× (17.8% to 20.4%), and LSF 200× (39.0%). PSO and LSF also significantly affected the mortality of the 2nd nymphs and adults of PCRM. PSO and LSF resulted in low direct mortality on A3a and A3b of AHS, but induced an abnormal morphology. PSO treatment resulted in a loose attachment of AHS scale cover on the leaf surface and LSF treatment resulted in an abnormal or lacking scale cover.     

Age-Related Differences in Spatial Frequency Processing during Scene Categorization

Visual analysis of real-life scenes starts with the parallel extraction of different visual elementary features at different spatial frequencies. The global shape of the scene is mainly contained in low spatial frequencies (LSF), and the edges and borders of objects are mainly contained in high spatial frequencies (HSF). The present fMRI study investigates the effect of age on the spatial frequency processing in scenes. Young and elderly participants performed a categorization task (indoor vs. outdoor) on LSF and HSF scenes. Behavioral results revealed performance degradation for elderly participants only when categorizing HSF scenes. At the cortical level, young participants exhibited retinotopic organization of spatial frequency processing, characterized by medial activation in the anterior part of the occipital lobe for LSF scenes (compared to HSF), and the lateral activation in the posterior part of the occipital lobe for HSF scenes (compared to LSF). Elderly participants showed activation only in the anterior part of the occipital lobe for LSF scenes (compared to HSF), but not significant activation for HSF (compared to LSF). Furthermore, a ROI analysis revealed that the parahippocampal place area, a scene-selective region, was less activated for HSF than LSF for elderly participants only. Comparison between groups revealed greater activation of the right inferior occipital gyrus in young participants than in elderly participants for HSF. Activation of temporo-parietal regions was greater in elderly participants irrespective of spatial frequencies. The present findings indicate a specific low-contrasted HSF deficit for normal elderly people, in association with an occipito-temporal cortex dysfunction, and a functional reorganization of the categorization of filtered scenes.     

Developmental Changes in ERP Responses to Spatial Frequencies

Social interaction starts with perception of other persons. One of the first steps in perception is processing of basic information such as spatial frequencies (SF), which represent details and global information. However, although behavioural perception of SF is well investigated, the developmental trajectory of the temporal characteristics of SF processing is not yet well understood. The speed of processing of this basic visual information is crucial, as it determines the speed and possibly accuracy of subsequent visual and social processes. The current study investigated developmental changes in the temporal characteristics of selective processing of high SF (HSF; details) versus low SF (LSF; global). To this end, brain activity was measured using EEG in 108 children aged 3–15 years, while HSF or LSF grating stimuli were presented. Interest was in the temporal characteristics of brain activity related to LSF and HSF processing, specifically at early (N80) or later (P1 or N2) peaks in brain activity. Analyses revealed that from 7–8 years onwards HSF but not LSF stimuli evoked an N80 peak. In younger children, aged 3–8 years, the visual manipulation mainly affected the visual N2 peak. Selective processing of HSF versus LSF thus occurs at a rather late time-point (N2 peak) in young children. Although behavioural research previously showed that 3–6 year-olds can perceive detailed information, the current results point out that selective processing of HSF versus LSF is still delayed in these children. The delayed processing in younger children could impede the use of LSF and HSF for emotional face processing. Thus, the current study is a starting point for understanding changes in basic visual processing which underlie social development.