The sphingolipid metabolite sphingosine-1-phosphate (SPP) has been implicated as a second messenger in cell proliferation and survival. However, many of its biological effects are due to binding to unidentified receptors on the cell surface. SPP activated the heterotrimeric guanine nucleotide binding protein (G protein)-coupled orphan receptor EDG-1, originally cloned as Endothelial Differentiation Gene-1. EDG-1 bound SPP with high affinity (dissociation constant = 8.1 nM) and high specificity. Overexpression of EDG-1 induced exaggerated cell-cell aggregation, enhanced expression of cadherins, and formation of well-developed adherens junctions in a manner dependent on SPP and the small guanine nucleotide binding protein Rho.

The proper placement of the cell division site in Escherichia coli requires the site‐specific inactivation of potential division sites at the cell poles in a process that is mediated by the MinC, MinD and MinE proteins. During the normal division cycle MinD plays two roles. It activates the MinC‐dependent mechanism that is responsible for the inactivation of potential division sites and it also renders the division inhibition system sensitive to the topological specificity factor MinE. MinE suppresses the division block at the normal division site at mid‐cell but not all cell poles, thereby ensuring the normal division pattern. In this study the MinD protein was purified to homogeneity and shown to bind ATP and to have ATPase activity. When the putative ATP binding domain of MinD was altered by site‐directed mutagenesis, the mutant protein was no longer able to activate the MinC‐dependent division inhibition system. Immunoelectron microscopy showed that MinD was located in the inner membrane region of the cell envelope. These results show that MinD is a membrane ATPase and suggest that the ATPase activity plays an essential role in the functions of the MinD protein during the normal division process.

The endoplasmic reticulum (ER) often forms stacked membrane sheets, an arrangement that is likely required to accommodate a maximum of membrane-bound polysomes for secretory protein synthesis. How sheets are stacked is unknown. Here, we used novel staining and automated ultra-thin sectioning electron microscopy methods to analyze stacked ER sheets in neuronal cells and secretory salivary gland cells of mice. Our results show that stacked ER sheets form a continuous membrane system in which the sheets are connected by twisted membrane surfaces with helical edges of left- or right-handedness. The three-dimensional structure of tightly stacked ER sheets resembles a parking garage, in which the different levels are connected by helicoidal ramps. A theoretical model explains the experimental observations and indicates that the structure corresponds to a minimum of elastic energy of sheet edges and surfaces. The structure allows the dense packing of ER sheets in the restricted space of a cell.

Human ductal saliva contributes over a thousand unique proteins to whole saliva. The mechanism by which most of these proteins are secreted by salivary glands remains to be determined. The present study used a mass spectrometry-based, shotgun proteomics approach to explore the possibility that many of the proteins found in saliva are derived from exosomes, membrane-bound vesicles of endosomal origin within multivesicular endosomes. Using MudPIT (multidimensional protein identification technology) mass spectrometry, we catalogued 491 proteins in the exosome fraction of human parotid saliva. Many of these proteins were previously observed in ductal saliva from parotid glands (265 proteins). Furthermore, 72 of the proteins in parotid exosomes overlap with those previously identified as urinary exosome proteins, proteins which are also frequently associated with exosomes from other tissues and cell types. Gene Ontology (GO) and KEGG pathway analyses found that cytosolic proteins comprise the largest category of proteins in parotid exosomes (43%), involved in such processes as phosphatidylinositol signaling system, calcium signaling pathway, inositol metabolism, protein export, and signal transduction among others; whereas the integral plasma membrane proteins and associated/peripheral plasma membrane proteins (26%) were associated with extracellular matrix-receptor interaction, epithelial cell signaling, T-cell and B-cell receptor signaling, cytokine receptor interaction, and antigen processing and presentation among other biological functions. In addition, exosomal proteins were linked to specific diseases (e.g. neurodegenerative disorders, prion disease, cancers, type I and II diabetes). Consequently, parotid glands secrete exosomes that reflect the metabolic and functional status of the gland and may also carry informative protein markers useful in the diagnosis and treatment of systemic diseases. KeywordsExosomes; parotid saliva; acinar cells; MudPIT; protein markers

In this report, sphingosine-1-phosphate (S1P), a serum-borne bioactive lipid, is shown to activate tight-junction-associated protein Zonula Occludens-1 (ZO-1), which in turn plays a critical role in regulating endothelial chemotaxis and barrier integrity. After S1P stimulation, ZO-1 was redistributed to the lamellipodia and cell-cell junctions via the S1P1/G i /Akt/Rac pathway. Similarly, both endothelial barrier integrity and cell motility were significantly enhanced in S1P-treated cells through the G i /Akt/Rac pathway. Importantly, S1P-enhanced barrier integrity and cell migration were abrogated in ZO-1 knockdown cells, indicating ZO-1 is functionally indispensable for these processes. To investigate the underlying mechanisms, we demonstrated that cortactin plays a critical role in S1P-induced ZO-1 redistribution to the lamellipodia. In addition, S1P significantly induced the formation of endothelial tight junctions. ZO-1 and ␣-catenin polypeptides were colocalized in S1P-induced junctional structures; whereas, cortactin was not observed in these regions. Together, these results suggest that S1P induces the formation of two distinct ZO-1 complexes to regulate two different endothelial functions: ZO-1/cortactin complexes to regulate chemotactic response and ZO-1/␣-catenin complexes to regulate endothelial barrier integrity. The concerted operation of these two ZO-1 complexes may coordinate two important S1P-mediated functions, i.e. migration and barrier integrity, in vascular endothelial cells.Endothelial barrier integrity is an important physiological function of the endothelium in vivo. Dysregulated barrier integrity is implicated in a variety of pathological conditions, such as stroke, inflammation, various immune responses, etc. (1). To elucidate the function and regulation of endothelial barrier integrity, cultured brain microvascular endothelial cells have been widely employed as an in vitro model system to study the blood-brain barrier (BBB) 2 (2). Evidence from these studies indicates that BBB plays a critical role in regulating the homeostatic environment of the brain and the transportation of plasma constituents into brain. Furthermore, it has been shown that severely impaired blood-brain barrier integrity is attributed to the pathological states of various neurological disorders, such as multiple sclerosis (3, 4), Alzheimer disease (5, 6), and human immunodeficiency virus-1-associated encephalitis or dementia (7,8).Sphingosine 1-phosphate (S1P), a serum-borne bioactive lipid mediator secreted by activated platelets (9), enhances barrier formation in cultured pulmonary endothelial cells (ECs) (10). However, the molecular details for the formation and maintenance of endothelial barrier integrity are poorly understood. It was recently reported that the association of cortactin, an F-actin cross-linking polypeptide, and myosin light chain kinase is crucial in S1P-enhanced endothelial barrier integrity (11). Furthermore, it is well documented that tight junctions are important in regulating BBB formation...

The organization of the endoplasmic reticulum (ER) in the cortex of Xenopus oocytes was investigated during maturation and activation using a green fluorescent protein chimera, immunofluorescence, and electron microscopy. Dense clusters of ER developed on the vegetal side (the side opposite the meiotic spindle) during maturation. Small clusters appeared transiently at the time of nuclear envelope breakdown, disappeared at the time of first polar body formation, and then reappeared as larger clusters in mature eggs. The appearance of the large ER clusters was correlated with an increase in releaseability of Ca 2ϩ by IP 3 . The clusters dispersed during the Ca 2ϩ wave at activation. Possible relationships of ER structure and Ca 2ϩ regulation are discussed.

Transforming growth factor /3 (TGF (3),t originally isolated from platelets as a 25-kD peptide (1, 2), has been shown to be a product of other inflammatory cells, including lymphocytes (3, 4) and macrophages (5, 6), and to have potent immunomodulatory effects (7). Although five different forms of TGFJ3 have now been characterized (1), only TGF01 and its homologue, TGF02 (8, 9), have thus far been identified in hemopoietic cells (6). Each ofthese peptides has been cloned, demonstrating that TGF01 is encoded as a 390 amino acid precursor (10), TGFs2 as a 412 amino acid precursor (11,12), and that both have a signal peptide of 20-23 amino acids at the NH2 terminus . The processed 112 amino acid chains of the two peptides share 72% sequence homology and appear to bind equally well to TGFS class III receptors (13), although TGFS1 binds with greater affinity than TGF02 to class I and II receptors (14, 15). Interestingly, lymphoid cells appear to possess only class I and II TGF,6 receptors (16), although in vitro, lymphocyte and monocyte responses to TGF01 and 02 appear comparable (6,17,18). The secretion of TGFa peptides by lymphocytes and monocytes only after activation (3-6) implicates these polypeptides in the evolution of immunologic processes, and in recent studies TGFR has been identified in chronic inflammatory tissues (19)(20)(21)(22), including the synovium of rheumatoid arthritis patients (7,22) and in experimentally induced arthritis in rodents (22). To define the role of TGFS in such lesions, we injected natural or recombinant TGF0 directly into the joint cavity of Lewis rats and monitored its effect on cellular recruitment and activation, and on its potential modulation of pathogenic effects. TGF01 and TGF02 were both found to induce synovial erythema, swelling, and leukocyte infiltration . The infiltrating mononuclear cells, activated to express growth factors, likely regulated the pronounced synovial hyperplasia that was apparent within 2-3 d. Based on these observations, it appears that TGF0, released by platelets and inflammatory cells in the arthritic synovium, may directly contribute to the events associated with inflammatory arthropathies.

Chromosome capture by microtubules is widely accepted as the universal mechanism of spindle assembly in dividing cells. However, the observed length of spindle microtubules and computer simulations of spindle assembly predict that chromosome capture is efficient in small cells, but may fail in cells with large nuclear volumes such as animal oocytes. Here we investigate chromosome congression during the first meiotic division in starfish oocytes. We show that microtubules are not sufficient for capturing chromosomes. Instead, chromosome congression requires actin polymerization. After nuclear envelope breakdown, we observe the formation of a filamentous actin mesh in the nuclear region, and find that contraction of this network delivers chromosomes to the microtubule spindle. We show that this mechanism is essential for preventing chromosome loss and aneuploidy of the egg--a leading cause of pregnancy loss and birth defects in humans.