Guanine nucleotide exchange factors of the cytohesin family and their roles in signal transduction

Summary:  Members of the cytohesin protein family, a group of guanine nucleotide exchange factors for adenosine diphosphate ribosylation factor (ARF) guanosine triphosphatases, have recently emerged as important regulators of signal transduction in vertebrate and invertebrate biology. These proteins share a modular domain structure, comprising carboxy-terminal membrane recruitment elements, a Sec7 homology effector domain, and an amino-terminal coiled-coil domain that serve as a platform for their integration into larger signaling complexes. Although these proteins have a highly similar overall build, their individual biological functions appear to be at least partly specific. Cytohesin-1 had been identified as a regulator of β2 integrin inside-out regulation in immune cells and was subsequently shown to be involved in mitogen-associated protein kinase signaling in tumor cell proliferation as well as in T-helper cell activation and differentiation. Cytohesin-3, which had been discovered to be strongly associated with T-cell anergy, was very recently described as an essential component of insulin signal transduction in Drosophila and in human and murine liver cells. Future work will aim to dissect the mechanistic details of the modes of action of the cytohesins as well as to define the precise roles of these versatile proteins in vertebrates at the genetic level.     

The major histocompatibility complex (CyLA) of the cynomolgus monkey. I. Serologic definition of 21 specificities

Thirty-seven lymphocytotoxic antisera, 27 of which were raised by immunization with skin grafts and blood from partially matched donors, were tested against cells obtained from 218 unrelated animals and 205 offspring from a colony of cynomolgus monkey (Macaca fascicularis). Evidence was obtained for the presence of at least 21 specificities defined by cluster analysis and segregation within families. Allelic relationships between 16 specificities was suggested by segregation patterns, the absence of triplets and statistical analysis of association in the unrelated population sample. The data support a two-locus model, with tentative assignment of seven specificities to the A locus and six to the B locus. That these lymphocyte alloantigens constitute the major histocompatibility complex (MHC) of the cynomolgus monkey is suggested by analogy with other known MHCs and by the increased survival times of skin grafts between paternally matched half sibs compared to haplodistinct full sibs.     

Cell-Growth Kinetics and Karyotype Analysis of Human Memory Lymphocytes Responding to Alloantigen and Mitogen

Peripheral-blood lymphocytes were primed in vitro with the mitogen phytohemagglutinin (PHA) or with allogeneic cells and their memory responses studied following sequential restimulation with either mitogen or alloantigen. Chromosome preparations were made every 12 hours following exposure to the stimulating agents. Cultures were labeled with BUdR for sister-chromatid staining of the chromosomes which provided information about the kinetics of cell growth and rates of sister chromatid exchange. Cultures containing no BUdR were used for the investigation of cell karyotypes after chromosome-banding.Following PHA as well as alloantigen restimulation, an earlier reaction of the responding cells was observed. The peak response after the first stimulation was found at 120 h with allogeneic stimulation and at 60 h with mitogen stimulation. In the second round of stimulation, the peak occurred after 48 h (allogeneic) and 36 h (PHA) and following the third stimulation after 36 h (allogeneic) and 24 h (PHA). The speed of cell growth was decreased following restimulation with either alloantigen and mitogen. In contrast to the allogeneic restimulation, the number of cells responding after PHA restimulation was decreased.No systematic numerical or structural aberration of the karyotype was detected following repeated stimulation with either alloantigen or mitogen. In this sense, the lymphocyte subpopulations selected by repeated stimulation did not differ from the starting material. On the other hand, the sister-chromatid exchange (SCE) frequency was increased following allogeneic restimulation, whereas it remained constant with PHA restimulation.     

Intraduodenal neuropeptide levels,but not plasma levels,vary in a cyclic fashion with the migrating motor complex

The neurohormonal control of the migrating motor complex (MMC) is not fully understood. The hypothesis of the present study was that neuropeptide levels might vary with the different phases of the MMC and that a similar variation might be found in the secretions of the gastrointestinal tract. Thus, plasma and intraduodenal concentrations of vasoactive intestinal peptide (VIP), somatostatin (SOM), substance P (SP) and neurokinin A (NKA) were determined by radioimmunoassay every 10 min during two complete MMC cycles in eight male subjects. For comparison, plasma motilin (MOT) concentrations were measured. Plasma concentrations of MOT (mean peak value ± SEM; 39 ± 6 pmol L^?1), but none of the neuropeptides studied, showed a cyclic variation in plasma with the different phases of the MMC. Peak intraduodenal concentrations of VIP (79 ± 23 pmol L^?1),?SOM (2437 ± 432 pmol L^?1) and SP (718 ± 326 pmol L^?1) occurred at or at the time point before the onset of phase III of the MMC. No such correlation was observed for NKA. These results demonstrate that intraduodenal but not plasma concentrations of the neuropeptides VIP, SOM and SP show an association with phase III of the MMC. The biological relevance of this finding is yet unclear, but the results raise the possibility that gut neuropeptides may regulate fasting motility through a luminal release.     

Visceral leishmaniasis in the acquired immunodeficiency syndrome: Report of two cases

Core biopsies of the bone marrow are indispensable in the evaluation of fever of unknown etiology in human immunodeficiency virus-positive patients. We report two patients in whom visceral leishmaniasis was diagnosed based on the typical morphology, staining characteristics, and ultrastructure of the organisms.     

Adhesion of carcinoma cells to rat hepatocytes and rat fibronectin is inhibited by the OPAR monoclonal antibody,which is directed against a rat liver-specific carbohydrate epitope

The OPAR mouse monoclonal antibody (mAb) directed against rat hepatocytes was previously shown to inhibit adhesion of TA3/Ha mammary carcinoma cells to hepatocytes. The antigen is abundantly present at the surface of hepatocytes beneath the endothelium of liver capillaries where we have observed invasion of carcinoma cells to occur. The OPAR mAb reacted with three major bands on a Western blot of liver plasma membrane proteins. The same proteins were also seen upon immunoprecipitation from iodinated liver plasma membrane proteins. We have isolated OPAR antigens by lectin wheat germ agglutinin (WGA) and OPAR affinity chromatography. Amino acid sequence analysis revealed that two of the bands were 1-macroglobulin and C4-binding protein, which are serum components produced by hepatocytes. The presence of the epitope on distinct proteins and our previous observation that it can be detected in the Golgi apparatus but not in the endoplasmic reticulum, suggested that OPAR reacts with a liver-specific glycoconjugate. Loss of OPAR reactivity after neuraminidase and N-glycosidase F treatment showed that the epitope contains sialic acid residues on N-linked sugar moieties. OPAR also reacted with rat fibronectin, and inhibited adhesion of TA3/St cells to fibronectin. This explains the inhibition by the OPAR mAb of TA3/St cell adhesion to hepatocytes, which we have shown to be due mainly to interaction with hepatocyte surface-associated fibronectin. However, adhesion of the related TA3/Ha cells to hepatocytes, which is mediated by the ₆P4 integrin, and does not involve binding to fibronectin, is also inhibited. This suggests that ₆₄ on liver-metastasizing carcinoma cells binds to an OPAR epitope-carrying glycoprotein produced by hepatocytes.     

Reelin-immunoreactivity in the hippocampal formation of 9-month-old wildtype mouse: effects of APP/PS1 genotype and ovariectomy

Reelin, an extracellular matrix protein has an important role in the migration, correct positioning and maturation of neurons during development. Though it is generally down-regulated in the postnatal period, expression of this large glycoprotein continues in the adult brain in some cell populations. In the present study, we examined the distribution of reelin-immunoreactivity (-ir) in the hippocampal formation of 9-month-old wildtype mice (WT). Then, reelin-ir in normal mice was compared to that of transgenic mice (APP/PS1) carrying mutated human APP and PS1 genes, which are linked to the familial form of Alzheimer's disease (AD). The APP/PS1 mice were additionally burdened with a second risk factor for AD, namely depletion of circulating gonadal hormones by ovariectomy (APP/PS1 + OVX). The analyses revealed that in adult WT reelin-ir is expressed by Cajal-Retzius cells and a subgroup of interneurons throughout the hippocampal formation. In addition, layer II projection neurons in the lateral entorhinal subfields are reelin-ir. Interestingly, ovariectomy decreases the number of reelin-ir cells in the hilus in WT mice, whereas AD-related genotype alone induces only a non-significant reduction. Unexpectedly, additional stress, e.g., depletion of gonadal hormones, does not aggravate the slight reduction in the reelin cell number in the APP/PS1 mice. We propose that the changes in normal reelin-ir are linked to disturbances in repair mechanisms in which APP/PS1 and gonadal hormones are involved and which are perturbed in neurodegenerative conditions, namely AD.     

人脐静脉内皮细胞清除补体攻膜复合物的机制

目的：探讨内皮细胞清除补体攻膜复合物（MAC）的途径及其清除动力学，方法：原代培养的人脐静脉内皮细胞以RH414荧光标记质膜双层，0℃组装亚溶剂量的MAC，37℃复苏后，LSCM实时监MAC沉积诱导的质膜囊泡化形成和胞吞，胞吐情况,流式细胞仪定量检测内皮细胞表面MAC抗原的清除情况，结果：MAC沉积后，内皮细胞有的质膜囊泡化形成，囊泡以胞吞和胞吐2种方式离开细胞，并以前者占优，37度条件下，内皮细胞清除表面MAC的半衰期约为5min。结论：内皮细胞可通过胞吞和胞吐2种机制清除细胞表面沉积的MAC，并以胞吞方式为主。