Redistribution of phosphatidylethanolamine at the cleavage furrow of dividing cells during cytokinesis

Membrane phospholipid dynamics during cytokinesis: regulation of actin filament assembly by redistribution of membrane surface phospholipid

To study molecular motion and function of membrane phospholipids, we have developed various probes which bind specifically to certain phospholipids. Using a novel peptide probe, RoO9-0198, which binds specifically to phosphatidylethanolamine (PE) in biological membranes, we have analyzed the cell surface movement of PE in dividing CHO cells. We found that PE was exposed on the cell surface specifically at the cleavage furrow during the late telophase of cytokinesis. PE was exposed on the cell surface only during the late telophase and no alteration in the distribution of the plasma membranebound peptide was observed during the cytokinesis, suggesting that the surface exposure of PE reflects the enhanced transbilayer movement of PE at the cleavage furrow. Furthermore, cell surface immobilization of PE induced by adding of the cyclic peptide coupled with streptavidin to prometaphase cells effectively blocked the cytokinesis at late telophase. The peptide-streptavidin complex bound specifically to cleavage furrow and inhibited both actin filament disassembly at cleavage furrow and subsequent plasma membrane fusion. Binding of the peptide complex to interphase cells also induced immediate disassembly of stress fibers followed by assembly of cortical actin filaments to the local area of plasma membrane where the peptide complex bound. The cytoskeletal reorganizations caused by the peptide complex were fully reversible; removal of the surface-bound peptide complex by incubating with PE-containing liposome caused gradual disassembly of the cortical actin filaments and subsequent formation of stress fibers. These observations suggest that the redistribution of plasma membrane phospholipids act as a regulator of actin cytoskeleton organization and may play a crucial role in mediating a coordinate movement between plasma membrane and actin cytoskeleton to achieve successful cell division.

Phospholipid-assisted refolding of an integral membrane protein. Minimum structural features for phosphatidylethanolamine to act as a molecular chaperone

Escherichia coli-derived phosphatidylethanolamine (PE) or PE with fully saturated fatty acids was able to correct in vitro a defect in folding in the lipid-dependent epitope 4B1 of lactose permease (LacY) resulting from in vivo assembly in the absence of PE. PE plasmalogen, PE with two unsaturated fatty acids, and lyso-PE, which all do not favor bilayer organization, did not support proper refolding. Proper refolding occurred when these latter lipids were mixed with a bilayer-forming lipid (phosphatidylglycerol), which alone could not support refolding. L-Phosphatidylserine (PS; natural diastereomer) did support proper refolding. PE derivatives of increasing degrees of methylation were progressively less effective in supporting refolding, with phosphatidylcholine being completely ineffective. Therefore, the properties of nonmethylated aminophospholipids capable of organization into a bilayer configuration are essential for the recovery of the native state of epitope 4B1 after misassembly in vivo in the absence of PE. Neither D-PS (sn-glycero-1-phosphate backbone) nor P-D-S (D-serine in the head group) is competent in supporting proper refolding unless used in binary mixtures with phosphatidylglycerol. The detailed characterization of phospholipid-assisted refolding reported here further supports a specific rather than nonspecific role for PE in structural maturation of lactose permease in vivo (Bogdanov, M., and Dowhan, W. (1998) EMBO J. 17, 5255-5264).

Effects of docosahexaenoic and arachidonic acids on the synthesis and distribution of aminophospholipids during neuronal differentiation of PC12 cells

We have shown previously that docosahexaenoic acid (DHA) promotes and arachidonic acid (AA) suppresses neurite outgrowth of PC12 cells induced by nerve growth factor (NGF) and that incorporation of [3H]ethanolamine into phosphatidylethanolamine (PE) is suppressed in PC12 cells by AA while DHA has no effect. In the present study, the effects of these fatty acids on PE synthesis via decarboxylation of phosphatidylserine (PS), another pathway of PE synthesis, and distribution of aminophospholipids were examined. Incorporation of [3H]serine into PS and PE was elevated in the course of NGF-induced differentiation and was further stimulated significantly by DHA, but not by AA. [3H]Ethanolamine uptake by PC12 cells was significantly suppressed by AA but not by DHA while these fatty acids did not affect [3H]serine uptake, indicating that the suppression by AA of [3H]ethanolamine incorporation into phosphatidylethanolamine is attributable, at least in part, to a reduction in [3H]ethanolamine uptake. The distribution of PE in the outer leaflet of plasma membrane decreased during differentiation, which is known to be accompanied by an increase in the surface area of plasma membrane. Supplementation of PC12 cells with DHA or AA did not affect the distribution of aminophospholipids. Thus, DHA and AA affected aminophospholipid synthesis and neurite outgrowth differently, but not the transport and distribution of aminophospholipids, while the PE concentration in the outer leaflet of the plasma membrane decreased in association with morphological changes in PC12 cells induced by NGF.

Localization and function of early cell division proteins in filamentous Escherichia coli cells lacking phosphatidylethanolamine

Escherichia coli cells that contain the pss-93 null mutation are completely deficient in the major membrane phospholipid phosphatidylethanolamine (PE). Such cells are defective in cell division. To gain insight into how a phospholipid defect could block cytokinesis, we used fluorescence techniques on whole cells to investigate which step of the cell division cycle was affected. Several proteins essential for early steps in cytokinesis, such as FtsZ, ZipA, and FtsA, were able to localize as bands to potential division sites in pss-93 filaments, indicating that the generation and localization of potential division sites was not grossly affected by the absence of PE. However, there was no evidence of constriction at most of these potential division sites. FtsZ and green fluorescent protein (GFP) fusions to FtsZ and ZipA often formed spiral structures in these mutant filaments. This is the first report of spirals formed by wild-type FtsZ expressed at normal levels and by ZipA-GFP. The results suggest that the lack of PE may affect the correct interaction of FtsZ with membrane nucleation sites and alter FtsZ ring structure so as to prevent or delay its constriction.

Lysenin, a novel sphingomyelin-specific binding protein

Lysenin, a novel 41-kDa protein purified from coelomic fluid of the earthworm Eisenia foetida, induced erythrocyte lysis. Preincubation of lysenin with vesicles containing sphingomyelin inhibited lysenin-induced hemolysis completely, whereas vesicles containing phospholipids other than sphingomyelin showed no inhibitory activity, suggesting that lysenin bound specifically to sphingomyelin on erythrocyte membranes. The specific binding of lysenin to sphingomyelin was confirmed by enzyme-linked immunosorbent assay, TLC immunostaining, and liposome lysis assay. In these assays, lysenin bound specifically to sphingomyelin and did not show any cross-reaction with other phospholipids including sphingomyelin analogs such as sphingosine, ceramide, and sphingosylphosphorylcholine, indicating that it recognized a precise molecular structure of sphingomyelin. Kinetic analysis of the lysenin-sphingomyelin interaction by surface plasmon resonance measurements using BIAcoreTM system showed that lysenin associated with membrane surfaces composed of sphingomyelin (kon = 3.2 x 10(4) M-1 s-1) and dissociated extremely slowly (koff = 1.7 x 10(-4) s-1), giving a low dissociation constant (KD = 5.3 x 10(-9) M). Incorporation of cholesterol into the sphingomyelin membrane significantly increased the total amount of lysenin bound to the membrane, whereas it did not change the kinetic parameters of the lysenin-membrane interaction, suggesting that lysenin specifically recognized sphingomyelin and cholesterol incorporation changed the topological distribution of sphingomyelin in the membranes, thereby increasing the accessibility of sphingomyelin to lysenin. Immunofluorescence staining of fibroblasts derived from a patient with Niemann-Pick disease type A showed that lysenin stained the surfaces of the fibroblasts uniformly, whereas intense lysosomal staining was observed when the cells were permeabilized by digitonin treatment. Preincubation of lysenin with vesicles containing sphingomyelin abolished lysenin immunostaining. This study demonstrated that lysenin bound specifically to sphingomyelin on cellular membranes and should be a useful tool to probe the molecular motion and function of sphingomyelin in biological membranes.

The mechanism and control of cytokinesis

Cytokinesis is under active investigation in each of the dominant experimental model systems. During 1996 and 1997, several developments necessitated the reassessment of the prevailing model for cytokinesis. In addition, the inventory of proteins required for cytokinesis has grown considerably. However, a molecular understanding of cytokinesis still remains elusive.

Role of lipid polymorphism in G protein-membrane interactions: nonlamellar-prone phospholipids and peripheral protein binding to membranes

Heterotrimeric G proteins (peripheral proteins) conduct signals from membrane receptors (integral proteins) to regulatory proteins localized to various cellular compartments. They are in excess over any G protein-coupled receptor type on the cell membrane, which is necessary for signal amplification. These facts account for the large number of G protein molecules bound to membrane lipids. Thus, the protein-lipid interactions are crucial for their cellular localization, and consequently for signal transduction. In this work, the binding of G protein subunits to model membranes (liposomes), formed with defined membrane lipids, has been studied. It is shown that although G protein alpha-subunits were able to bind to lipid bilayers, the presence of nonlamellar-prone phospholipids (phosphatidylethanolamines) enhanced their binding to model membranes. This mechanism also appears to be used by other (structurally and functionally unrelated) peripheral proteins, such as protein kinase C and the insect protein apolipophorin III, indicating that it could constitute a general mode of protein-lipid interactions, relevant in the activity and translocation of some peripheral (amphitropic) proteins from soluble to particulate compartments. Other factors, such as the presence of cholesterol or the vesicle surface charge, also modulated the binding of the G protein subunits to lipid bilayers. Conversely, the binding of G protein-coupled receptor kinase 2 and the G protein beta-subunit to liposomes was not increased by hexagonally prone lipids. Their distinct interactions with membrane lipids may, in part, explain the different cellular localizations of all of these proteins during the signaling process.

Exposure of phosphatidylethanolamine on the surface of apoptotic cells

In the early stages of apoptosis, phosphatidylserine (PS) is translocated from the inner side of the plasma membrane to the outer layer, which allows phagocytes to recognize and engulf the apoptotic cells. In this study we have analyzed the cell surface exposure of phosphatidylethanolamine (PE) in apoptotic CTLL-2 cells, a cytotoxic T cell line, using a tetracyclic polypeptide of 19 amino acids (Ro09-0198) which specifically recognizes the structure of PE and forms a tight equimolar complex with the phospholipid. Fluorescence microscopic analysis showed that the peptide, conjugated with fluorescence-labeled streptavidin (FL-SA-Ro), bound effectively to the cell surface of cells undergoing apoptosis in response to withdrawal of interleukin-2 from the culture media, but not to nonapoptotic cells. The binding of FL-SA-Ro to apoptotic cells was not uniform and the intense staining was observed on surface blebs of apoptotic cells. The FL-SA-Ro binding was inhibited specifically by liposomes containing PE, suggesting that PE is mainly exposed on the surface blebs of apoptotic cells. The specific binding of FL-SA-Ro to the apoptotic cells was also confirmed using a flourescence-activated cell sorter and the time-dependent cell surface exposure of PE correlated well with the exposure of PS, as detected by the binding of annexin V. This study provides the first direct evidence that PE as well as PS is exposed on the cell surface during the early stages of apoptosis, resulting in the total loss of asymmetric distribution of aminophospholipids in the plasma membrane bilayer.