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At least 1,279 records · Page 71Linked to original sources
PubMed1981

Effect of dimyristoyl phosphatidylcholine on intact erythrocytes. Release of spectrin-free vesicles without ATP depletion.

Incubation of human erythrocytes with suspensions of sonicated dimyristoyl phosphatidylcholine resulted in dramatic morphological changes of the cells and release of membrane vesicles. The shedding of membrane vesicles was not preceded by ATP depletion and only occurred at temperatures of incubation that were above the phase transition temperature of dimyristoyl phosphatidylcholine. Membrane vesicles were separated from intact erythrocytes and exogenous dimyristoyl phosphatidylcholine by a series of centrifugation steps. The lipid composition of the membrane vesicles was similar to that of the native erythrocyte, and the predominant membrane proteins were band 3, glycophorin and acetylcholinesterase. Spectrin was not detected. Freeze-fracture electron microscopy showed vesicles (150 nm in diameter) with protein particles embedded in the lipid bilayer.

Acetylcholinesterase↗
PubMed1989

Alpha-actinins, calspectin (brain spectrin or fodrin), and actin participate in adhesion and movement of growth cones.

We have used biochemical and immunocytochemical techniques to investigate the possible involvement of membrane cytoskeletal elements such as alpha-actinin, calspectin (brain spectrin or fodrin), and actin in growth cone activities. During NGF-induced differentiation of PC12 cells, alpha-actinin increased in association with neurite outgrowth and was predominantly distributed throughout the entire growth cone and the distal portion of neurites. Filopodial movements were sensitive to Ca2+ flux. Two types of alpha-actinin, with Ca2(+)-sensitive and -insensitive actin binding abilities, were identified in the differentiated cells. Ca2(+)-sensitive alpha-actinin and actin filaments were concentrated in filopodia. The Ca2(+)-insensitive protein was distributed from the body of the growth cone to the distal portion of neurites, corresponding to the substratum-adhesive sites. The location of calspectin in growth cones was similar to that of the Ca2(+)-insensitive alpha-actinin. These results are consistent with the hypothesis that Ca2(+)-sensitive alpha-actinin and actin filaments are involved in Ca2(+)-dependent filopodial movement and Ca2(+)-insensitive alpha-actinin and calspectin are associated with adhesion of growth cones.

Actinin↗
PubMed2004

The spectrin family member Syne-1 functions in retrograde transport from Golgi to ER.

To address the function of the Golgi- and nuclear envelope-localized spectrin family member synaptic nuclear envelope protein-1 (Syne-1), we expressed two separate recombinant fragments derived from the central portion of the molecule. Both of these fragments were predicted to act as dominant negative inhibitors of Syne-1 function at the Golgi. One of the fragments was previously shown to bind the Golgi complex. The other fragment was found to form microtubule-associated puncta that sequester endogenous Syne-1. Expression of either fragment resulted in a cell type-specific alteration in the structure of the Golgi complex, which appeared to collapse into a compact juxtanuclear structure in some cell types but not others. These fragments were expressed in cultured cells and their effects on Golgi function were examined. Expression of both dominant negative Syne-1 fragments blocked recycling of the endoplasmic reticulum (ER) resident protein disulfide isomerase (PDI), which accumulated in the Golgi complex. In addition, we found that fragment expression altered the distribution of the KDEL receptor and the COP-I coat protein beta-COP, two proteins known to be involved in regulating the retrograde pathway. We conclude that these results indicate a role for Syne-1 in facilitating retrograde vesicular trafficking from the Golgi to the ER.

Animals↗
PubMed1988

Tumor promoter induces reorganization of actin filaments and calspectin (fodrin or nonerythroid spectrin) in 3T3 cells.

We have used immunofluorescence, differential-interference-contrast, and interference-reflection microscopy to examine the translocation of actin filaments and calspectin (fodrin or nonerythroid spectrin) in 3T3 cells induced by phorbol 12-myristate 13-acetate (PMA). The two cytoskeletal proteins were observed to localize in dot structures that corresponded to the cell-substratum contact sites (focal contact) of the cytoplasmic surface of the plasma membrane. The induction of these cytoskeletal changes was specific for tumor promoters. High-resolution microscopy revealed that calspectin was intensely concentrated in ring-like structures surrounding actin dots. It was also located within the areas of actin dots, but to a lesser extent. Trifluoperazine and other phenothiazine derivatives inhibited the formation of those dot structures that appeared after the addition of PMA. Some serine protease inhibitors were also demonstrated to influence cytoskeletal changes by PMA. Our results provide evidence that calspectin is closely associated with actin filaments in dot structures induced by PMA. Possible mechanisms for these cytoskeletal changes produced by PMA are discussed.

Actins↗
PubMed1983

The spectrin-related molecule, TW-260/240, cross-links the actin bundles of the microvillus rootlets in the brush borders of intestinal epithelial cells.

Previous studies have shown that molecules related to erythrocyte spectrin are present in the cortical cytoplasm of nonerythroid cells. We report here the localization by immunoelectron microscopy of one such molecule, TW-260/240, in the brush border of intestinal epithelial cells. Using highly specific antibodies against TW-260 and TW-240 as well as antibodies against fodrin, another spectrinlike molecule, we have found that the TW-260/240 molecules are displayed between rootlets at all levels of the terminal web. Occasionally, extended structures appear labeled suggestive of the fine filaments known to cross-link actin bundles. These results are in line with previous in vitro studies showing that TW-260/240 binds to, and cross-links, actin filaments. The results are discussed in terms of a model in which rootlets are immobilized in the terminal web in a matrix of TW-260/240.

Actins↗
PubMed1995

Reperfusion of rat heart after brief ischemia induces proteolysis of calspectin (nonerythroid spectrin or fodrin) by calpain.

Rat myocardium expresses the 240- and 235-kD polypeptides antigenically related to alpha- and beta-subunits of brain calspectin (nonerythroid spectrin or fodrin), respectively. In the subcellular fractions of the myocardium, alpha-calspectin was found in the 600g, 10,000g, and 100,000g pellets, whereas beta-calspectin was localized to the 10,000g pellet. On the basis of the Na+,K(+)-ATPase activity and the contents of a gap junction protein, the sarcolemma was distributed to the 10,000g and 100,000g pellets, and the intercalated disks were enriched in the 10,000g pellet. Both alpha- and beta-calspectin were proteolyzed by calpain in vitro. The two subunits were also proteolyzed in vivo, when the rat hearts underwent 10 to 60 minutes of global ischemia followed by 30 minutes of reperfusion. The reperfusion following the ischemia induced the proteolysis of alpha-calspectin in the 10,000g and 100,000g pellets, producing the 150-kD fragment. A synthetic calpain inhibitor, calpain inhibitor-1, suppressed the degradation of calspectin in vivo, which indicates that calpain is responsible for the reperfusion-induced proteolysis of calspectin. The inhibitor also improved myocardial stunning. Immunohistochemical study revealed that the proteolysis of alpha-calspectin occurs at the intercalated disks and the sarcolemma after postischemic reperfusion, in accord with the biochemical data. These results suggest that degradation of calspectin partly accounts for the contractile failure of the myocardium after postischemic reperfusion by disrupting the membrane skeleton and the intercalated disks.

Animals↗
PubMed2004

A role for the spectrin superfamily member Syne-1 and kinesin II in cytokinesis.

Expression of a dominant negative fragment of the spectrin family member Syne-1 causes an accumulation of binucleate cells, suggesting a role for this protein in cytokinesis. An association of this fragment with the C-terminal tail domain of the kinesin II subunit KIF3B was identified by yeast two-hybrid and co-precipitation assays, suggesting that the role of Syne-1 in cytokinesis involves an interaction with kinesin II. In support of this we found that (1) expression of KIF3B tail domain also gives rise to multinucleate cells, (2) both Syne-1 and KIF3B localize to the central spindle and midbody during cytokinesis in a detergent resistant and ATP sensitive manner and (3) Syne-1 localization is blocked by expression of KIF3B tail. Also, membrane vesicles containing syntaxin associate with the spindle midbody with identical properties. We conclude that Syne-1 and KIF3B function together in cytokinesis by facilitating the accumulation of membrane vesicles at the spindle midbody.

Animals↗
PubMed1975

Absence of one component of spectrin adenosine triphosphatase in hereditary spherocytosis.

The stimulation by calcium and magnesium of ATPase activity of isolated ghosts, of water-soluble protein (spectrin), and of residual vesicles, derived from normal erythrocytes and from hereditary spherocytes (H.S.), has been measured. The ATPase activity found in normal water-soluble protein (WSP) at low levels of calcium (0.1-2.0 mM) is essentially absent in H.S. water-soluble protein, but the ATPase activity with magnesium and with high levels of calcium (60-100 mM) is the same in H.S. and normal WSP. Compared to normal, H.S. ghosts have increased Mg2+-stimulated activity. This increased activity is retained by the sedimentable vesicles ("residue") after extraction of the ghosts with 0.025 mM EDTA. The Ca2+, Mg2+-ATPase associated with the calcium pump is not significantly different in H.S.

Adenosine Triphosphatases↗
PubMed1987

Amelin: a 4.1-related spectrin-binding protein found in neuronal cell bodies and dendrites.

An immunoreactive, structural, and functional analog of erythrocyte protein 4.1 is present in neuronal cell bodies and dendrites. Other investigators have described the isolation of a 4.1 analog in brain with structural characteristics suggesting that its identity was synapsin I, a neuronal phosphoprotein localized in the presynaptic terminal in association with small synaptic vesicles. In this report we demonstrate that the cell body/dendritic form of brain protein 4.1, which we have named amelin, is distinct from that of synapsin I on the basis of subcellular localization, migration in 2-dimensional gel electrophoresis, and structural criteria. We also demonstrate that amelin, like synapsin I, can bind brain spectrin on nitrocellulose paper. Neither amelin nor synapsin I binds calmodulin, as determined by a blot binding assay. We hypothesize that there exists in brain a family of 4.1-related proteins with distinct subcellular localization and function.

Animals↗
PubMed1997

Characterization of the interaction between synapsin I and calspectin (brain spectrin or fodrin).

We characterized the properties of the interaction between synapsin I and calspectin using purified proteins. The binding assay in the native state using antibodies specific to the tail region of synapsin I revealed that the binding is a high affinity with Kd of 9 nM, which is almost comparable to that of synapsin I to synaptic vesicles and to F-actin. We demonstrated that the head-middle region of synapsin I binds the NH2-terminal domain of beta subunit of calspectin, which also contains an actin binding site. Furthermore, the interaction was significantly inhibited by phosphorylation of synapsin I by cAMP-dependent protein kinase or by Ca2+, calmodulin-dependent protein kinase II. These properties of the interaction between synapsin I and calspectin may help understanding of its modulatory roles in neurotransmitter release.

Animals↗