摘要:

AbstractCell surface carbohydrates undergo marked alterations during mouse embryogenesis. In preimplantation embryos, many carbohydrate markers show stage‐specific expression in diverse ways. In early postimplantation embryos, certain carbohydrate markers are localized in defined regions in the embryo. Important carriers of stage‐specific carbohydrates are the lactoseries structure (Galβ1→4GlcNAc) and the globoseries structure (Galα1→4Gal). Notably, the glycoprotein‐bound large carbohydrate of poly‐N‐acetyllactosamine‐type ([Galβ1→4GlcNAcβ1 → 3]n) carries a number of markers preferentially expressed in early embryonic cells. These markers are of practical value in analyzing embryogenesis and cell differentiation. For example, in order to monitor in vitro differentiation of multipotential embryonal carcinoma cells, stage‐specific embryonic antigen‐1 (SSEA‐1) and theLotusagglutinin receptor have been used as markers of the undifferentiated cells, and theDolichosagglutinin receptor has been used as a marker of extraembryonic endoderm cells. Developmental control of cell surface carbohydrates is attained by controlled expression of activities of key glycosyltransferases; for example, the activity of N‐acetylglucosaminide αl → 3 fucosyltransferase is lost during in vitro differentiation of embryonal carcinoma cells to parietal endoderm cells, in parallel to the disappearance of SSEA‐1. Accumulating evidence suggests that poly‐N‐acetyllactosamine‐type glycans that are abundant in early embryonic cells are involved

ISSN:0730-2312    

DOI:10.1002/jcb.240360102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractReceptor‐mediated activation of many cells, including blood platelets, leads to changes at the cytoplasmic side of the membrane. In platelets, phospholipases, such as phospholipase C and phospholipase A2, have been shown to become activated. From phospholipids they generate the second messengers diacylglycerol and inositol phosphate(s) and fatty acids, respectively. At the same time, actin polymerization and reorganization of actin filaments into bundles and networks occurs. Here, the association of lipids, radiolabeled either with saturated (palmitic acid) or unsaturated (arachidonic acid) fatty acids, with the cytoskeletons of resting and activated human blood platelets was studied. The relative binding of lipid components to the cytoskeleton of activated platelets labeled with palmitic acid is six times higher than that of platelets labeled with arachidonic acid. Analysis of lipids associated with isolated cytoskeletons of resting and activated platelets (labeled with palmitic acid) showed a 30‐fold increase in the binding of labeled lipids to the cytoskeletal structures during activation. Both diacylglycerol and fatty acids were found to be associated with the cytoskeleton of activated platelets. Gel filtration, chromatofocusing, and immunoprecipitation studies demonstrated tight binding of these lipids to α‐actinin. α‐Actinin is one of the proteins that rapidly becomes associated with the cytoskeleton during platelet aggregation; it is also one of the molecules proposed to act as an actin‐membrane linker. The results, reported indicate a possible participation of α‐actinin, fatty acids, and the phosphoinositide‐derived second messenger diacylglycerol in the regulation of cytoskeleton‐membrane interactions. Together with the results of others they suggest a possible involvement of the phosphatidylinositol cycle in the assembly of actin filaments and their anch

ISSN:0730-2312    

DOI:10.1002/jcb.240360103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractSynapsin I is a neuronal phosphoprotein that can bundle actin filaments in vitro. This activity is under phosphorylation control, and may be related to its putative in vivo role of regulating the clustering and release of small synaptic vesicles. We have compared human and bovine synapsin I by peptide mapping, and have used NTCB (2‐nitro‐5‐thiocyano benzoic acid) cleavage to generate a series of peptide fragments from bovine synapsin I. After chymotryptic digestion, 88% of the tyrosine‐containing fragments appear to be structurally identical in human and bovine synapsin I, as judged by their positions on high‐resolution two‐dimensional peptide maps. The alignment of the NTCB peptides within the parent protein have been determined by peptide mapping, and the ability of these fragments to precipitate with actin bundles has been measured. Only peptides that are derived from regions near the ends of the protein are active. One such 25‐kDa peptide which sediments with actin also cross‐reacts with antibodies to chicken villin, an actin binding and bundling protein derived from the intestinal microvillus. Since in other respects villin appears to be an unrelated protein, these results suggest the possibility that certain actin binding proteins may show immunologic cross‐reactivity due to convergent evolution within the acti

ISSN:0730-2312    

DOI:10.1002/jcb.240360104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractMyosins IA and IB are globular proteins with only a single, short (for myosins) heavy chain (140,000 and 125,000 daltons for IA and IB, respectively) and are unable to form bipolar filaments. The amino acid sequence of IB heavy chain shows 55% similarity to muscle myosins in the N‐terminal 670 residues, which contain the active sites, and a unique 500‐residue C‐terminus highly enriched in proline, glycine, and alanine. The C‐terminal region contains a second actin‐binding site which allows myosins IA and IB to cross‐link actin filaments and support contractile activity. Myosins IA and IB are regulated solely by phosphorylation of one serine on the heavy chain positioned between the catalytic site and the actin‐binding site that activates ATPase.Myosins II is a more conventional myosin in composition (two heavy chains and two pairs of light chains), heavy chain sequence (globular head 45% identical to muscle myosins and a coiled‐coil helical tail), and structure (bipolar filaments). The tail of myosin II is much shorter than that of other conventional myosins, and it contains a 25 amino acid sequence in which helical structure is predicted to be weak or absent. The position of this sequence corresponds to the position of a bend in the monomer. Myosin II heavy chains also have a 29‐residue nonhelical tailpiece which contains three regulatory, phosphorylatable serines. Phosphorylation at the tip of the tail regulates ATPase activity in the globular head apparently through an effect on f

ISSN:0730-2312    

DOI:10.1002/jcb.240360105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractApical and basolateral membrane domains of epithelial cell plasma membranes possess unique lipid compositions. The tight junction, the structure separating the two domains, forms a diffusion barrier for membrane components and thereby prevents intermixing of the two sets of lipids. The barrier apparently resides in the outer, exoplasmic leaflet of the plasma membrane bilayer. First data are now available on the generation of these differences in Madin‐Darby canine kidney (MDCK) cells, grown on filter supports. Experiments in which fluorescent precursors of apical lipids were introduced into the cell have demonstrated that upon biosynthesis apical lipids are sorted from basolateral lipids in an intracellular compartment. In this paper we present a model for the sorting process, the central point of which is that the two sets of lipids laterally segregate into microdomains that bud to form vesicles delivering the lipids to the apical and the basolateral plasma membrane domains, respectivel

ISSN:0730-2312    

DOI:10.1002/jcb.240360106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe amino‐terminal sequences of several imported mitochondrial precursor proteins have been shown to contain all the information required for transport to and sorting within mitochondria. Proteins transported into the matrix contain a matrix‐targeting sequence. Proteins destined for other submitochondrial compartments contain, in addition, an intramitochondrial sorting sequence. The sorting sequence in the cytochromec1presequence is a stop‐transport sequence for the inner mitochondrial membrane. Proteins containing cleavable presequences can reach the intermembrane space by either of two pathways: (1) Part of the presequence is transported into the matrix; the attached protein, however, is transported across the outer but not the inner membrane (eg, the cytochromec1presequence). (2) The precursor is first transported into the matrix; part of the presequence is then removed, and the protein is reexported across the inner membrane (eg, the precursor of the iron‐sulphur protein of the cytochromebc1complex).Matrix‐targeting sequences lack primary amino acid sequence homology, but they share structural characteristics. Many DNA sequences in a genome can potentially encode a matrix‐targeting sequence. These sequences become active if positioned upstream of a protein coding sequence. Artificial matrix‐targeting sequences include synthetic presequences consisting of only a few different amino acids, a known amphiphilic helix found inside a cytosolic protein, and the presequence of an imported chloroplast protein.Transport of proteins across mitochrondrial membranes requires a membranes requires a membrane potential, ATP, and a 45‐kd protein of the mitochondrial outer membrane. The ATP requirement for import is correlated with a stable structure in the imported precursor molecule. We suggest that transmembrane transport of a stably folded precursor requires an ATP‐dependent unfolding of the

ISSN:0730-2312    

DOI:10.1002/jcb.240360107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractBinding and endocytosis of the ligands transferrin, epidermal growth factor (EGF), and ricin were measured in a number of different cell lines after treatment of cells with compounds that react with SH‐groups and under conditions where the cytosolic pH was lowered. N‐ethylmalemide and diamide irreversibly inhibited endocytosis of all ligands tested, whereas low pH in the cytosol strongly inhibited endocytosis of transferrin and EGF. Data obtained by electron microscopy indicated that the formation of coated vesicles from coated pits is inhibited in acidified cells. Entry of ricin was much less affected, and ricin endocytosed under these conditions was able to intoxicate the cells. At low pH in the cytosol there was a calcium‐dependent increase in the number of transferrin receptors at the cell surface. The increase was even larger in the presence of the calcium ionophore A23187, whereas it was completely blocked by the calmodulin antagonists trifluoperazine and W7. The results show that endocytosis from coated pits can be inhibited in a reversible way by acidification of the cytosol and they suggest that a second pathway of endocytosis exists, possibly involving formation of vesicles from uncoated areas of the mem

ISSN:0730-2312    

DOI:10.1002/jcb.240360108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractProgression from a steroid sensitive to insensitive state is characteristic of breast tumors, but little is known about the molecular mechanisms involved. Changes in steroid receptor can be associated with the progression. This paper reviews the cell culture data pertaining to loss of response and concludes that loss of receptor is a consequence rather than a cause of insensitivity. This view is based on evidence that loss of all response parameters occurs despite the presence of fully functional receptors as determined by transfection experiments. The postreceptor defect appears to be at the level of the hormone response element of the responsive genes arid may involve DNA methylation. The implications of the model for human breast cancer biology are discussed.

ISSN:0730-2312    

DOI:10.1002/jcb.240360109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractTyrosine protein kinase activity has been detected in the mitochondrial fraction purified from sarcoma 180 tumor cells. Following hypotonic disruption of mitochondria, tyrosine kinase activity appeared to cosediment with monoamine oxidase, marker enzyme of mitochondrial outer membrane; meanwhile, serine and threonine kinases were found to be associated with the inner membrane and matrix of mitochondria. Mitochondrial tyrosine kinase(s) showed thermosensitivity and Mn2+dependence, useful properties for its characterization and separation from tyrosine kinases associated with other particulate fractions and from serine and threonine kinases associated with mitochondria. Following in vitro incubation of mitochondria with labelled ATP as substrate and analysis by PAGE, a complex pattern of phosphotyrosine containing proteins with a major band of 50–55 kilo‐daltons resul

ISSN:0730-2312    

DOI:10.1002/jcb.240360110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

ISSN:0730-2312    

DOI:10.1002/jcb.240360101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY