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Wang Z, Zhang J, Ye M, Zhu M, Zhang B, Roy M, Liu J, An X. Tumor suppressor role of protein 4.1B/DAL-1. Cell Mol Life Sci 2014; 71:4815-30. [PMID: 25183197 PMCID: PMC11113756 DOI: 10.1007/s00018-014-1707-z] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Revised: 07/21/2014] [Accepted: 08/15/2014] [Indexed: 12/14/2022]
Abstract
Protein 4.1B/DAL-1 is a membrane skeletal protein that belongs to the protein 4.1 family. Protein 4.1B/DAL-1 is localized to sites of cell-cell contact and functions as an adapter protein, linking the plasma membrane to the cytoskeleton or associated cytoplasmic signaling effectors and facilitating their activities in various pathways. Protein 4.1B/DAL-1 is involved in various cytoskeleton-associated processes, such as cell motility and adhesion. Moreover, protein 4.1B/DAL-1 also plays a regulatory role in cell growth, differentiation, and the establishment of epithelial-like cell structures. Protein 4.1B/DAL-1 is normally expressed in multiple human tissues, but loss of its expression or prominent down-regulation of its expression is frequently observed in corresponding tumor tissues and tumor cell lines, suggesting that protein 4.1B/DAL-1 is involved in the molecular pathogenesis of these tumors and acts as a potential tumor suppressor. This review will focus on the structure of protein 4.1B/DAL-1, 4.1B/DAL-1-interacting molecules, 4.1B/DAL-1 inactivation and tumor progression, and anti-tumor activity of the 4.1B/DAL-1.
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Affiliation(s)
- Zi Wang
- Molecular Biology Research Center, School of Life Sciences, Central South University, 110 Xiangya Road, Changsha, 410078 China
| | - Ji Zhang
- Molecular Biology Research Center, School of Life Sciences, Central South University, 110 Xiangya Road, Changsha, 410078 China
- Department of Hematology, The First Affiliated Hospital, University of South China, Hengyang, 421001 China
| | - Mao Ye
- State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Biology, Hunan University, Changsha, 410082 China
| | - Min Zhu
- Molecular Biology Research Center, School of Life Sciences, Central South University, 110 Xiangya Road, Changsha, 410078 China
| | - Bin Zhang
- Department of Histology and Embryology, Xiangya School Medicine, Central South University, Changsha, 410083 China
| | - Mridul Roy
- Molecular Biology Research Center, School of Life Sciences, Central South University, 110 Xiangya Road, Changsha, 410078 China
| | - Jing Liu
- Molecular Biology Research Center, School of Life Sciences, Central South University, 110 Xiangya Road, Changsha, 410078 China
- State Key Laboratory of Medical Genetics, Central South University, 110 Xiangya Road, Changsha, 410078 China
| | - Xiuli An
- Laboratory of Membrane Biology, New York Blood Center, 310 E 67th Street, New York, 10065 USA
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Bosanquet DC, Ye L, Harding KG, Jiang WG. FERM family proteins and their importance in cellular movements and wound healing (review). Int J Mol Med 2014; 34:3-12. [PMID: 24820650 DOI: 10.3892/ijmm.2014.1775] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2014] [Accepted: 03/10/2014] [Indexed: 11/06/2022] Open
Abstract
Motility is a requirement for a number of biological processes, including embryonic development, neuronal development, immune responses, cancer progression and wound healing. Specific to wound healing is the migration of endothelial cells, fibroblasts and other key cellular players into the wound space. Aberrations in wound healing can result in either chronic wounds or abnormally healed wounds. The protein 4.1R, ezrin, radixin, moesin (FERM) superfamily consists of over 40 proteins all containing a three lobed N-terminal FERM domain which binds a variety of cell-membrane associated proteins and lipids. The C-terminal ends of these proteins typically contain an actin-binding domain (ABD). These proteins therefore mediate the linkage between the cell membrane and the actin cytoskeleton, and are involved in cellular movements and migration. Certain FERM proteins have been shown to promote cancer metastasis via this very mechanism. Herein we review the effects of a number of FERM proteins on wound healing and cancer. We show how these proteins typically aid wound healing through their effects on increasing cellular migration and movements, but also typically promote metastasis in cancer. We conclude that FERM proteins play important roles in cellular migration, with markedly different outcomes in the context of cancer and wound healing.
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Affiliation(s)
- David C Bosanquet
- Departments of Surgery and Wound Healing, Cardiff University School of Medicine, Heath Park, Cardiff CF14 4XW, UK
| | - Lin Ye
- Departments of Surgery and Wound Healing, Cardiff University School of Medicine, Heath Park, Cardiff CF14 4XW, UK
| | - Keith G Harding
- Departments of Surgery and Wound Healing, Cardiff University School of Medicine, Heath Park, Cardiff CF14 4XW, UK
| | - Wen G Jiang
- Departments of Surgery and Wound Healing, Cardiff University School of Medicine, Heath Park, Cardiff CF14 4XW, UK
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The linoleic acid derivative DCP-LA increases membrane surface localization of the α7 ACh receptor in a protein 4.1N-dependent manner. Biochem J 2013; 450:303-9. [DOI: 10.1042/bj20121348] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In yeast two-hybrid screening, protein 4.1N, a scaffolding protein, was identified as a binding partner of the α7 ACh (acetylcholine) receptor. For rat hippocampal slices, the linoleic acid derivative DCP-LA {8-[2-(2-pentyl-cyclopropylmethyl)-cyclopropyl]-octanoic acid} increased the association of the α7 ACh receptor with 4.1N, and the effect was inhibited by GF109203X, an inhibitor of PKC (protein kinase C), although DCP-LA did not induce PKC phosphorylation of 4.1N. For PC-12 cells, the presence of the α7 ACh receptor in the plasma membrane fraction was significantly suppressed by knocking down 4.1N. DCP-LA increased the presence of the α7 ACh receptor in the plasma membrane fraction, and the effect was still inhibited by knocking down 4.1N. In the monitoring of α7 ACh receptor mobilization, DCP-LA enhanced signal intensities for the α7 ACh receptor at the membrane surface in PC-12 cells, which was clearly prevented by knocking down 4.1N. Taken together, the results of the present study show that 4.1N interacts with the α7 ACh receptor and participates in the receptor tethering to the plasma membrane. The results also indicate that DCP-LA increases membrane surface localization of the α7 ACh receptor in a 4.1N-dependent manner under the control of PKC, but without phosphorylating 4.1N.
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Baines AJ. A FERM-adjacent (FA) region defines a subset of the 4.1 superfamily and is a potential regulator of FERM domain function. BMC Genomics 2006; 7:85. [PMID: 16626485 PMCID: PMC1459144 DOI: 10.1186/1471-2164-7-85] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2005] [Accepted: 04/20/2006] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Proteins containing FERM domains comprise a diverse group of eukaryotic proteins that bind membrane proteins and lipids. In doing so, they organise membrane microstructure, and coordinate the disposition of signalling and cell adhesion complexes. In protein 4.1R, phosphorylation adjacent to the FERM domain regulates its activity, and membrane mechanical properties. RESULTS A novel sequence domain has been detected in a subset of proteins that contain FERM domains. This subset includes the true 4.1 proteins, some tyrosine phosphatases, rho-GEF proteins and type II transmembrane proteins, as well as some uncharacterised FERM proteins. This FERM-adjacent region is always closely proximate to the C-terminal of the FERM domain. This sequence is likely to be folded with elements of alpha and beta structure. The FERM-adjacent region of 4.1R contains serine residues phosphorylated by PKC and PKA; these appear conserved in about half of all other FERM-adjacent regions. Phylogenetic analyses indicate that all proteins containing a FERM-adjacent region arose from a single ancestor after FERM domains had started to proliferate in genomes of animals, plants and mycetozoa. CONCLUSION The FERM-adjacent region defines a subset of the FERM proteins in animals. The conservation of motifs in this region that are potential substrates for kinases together with the known regulatory phosphorylation of 4.1R in this region raises the possibility that the FERM-adjacent region is a regulatory adaptation in this subset of the FERM proteins.
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Affiliation(s)
- Anthony J Baines
- Department of Biosciences, University of Kent, Canterbury, CT2 7NJ, UK.
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Manno S, Takakuwa Y, Mohandas N. Modulation of erythrocyte membrane mechanical function by protein 4.1 phosphorylation. J Biol Chem 2004; 280:7581-7. [PMID: 15611095 DOI: 10.1074/jbc.m410650200] [Citation(s) in RCA: 133] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Erythrocyte membrane mechanical function is regulated by the spectrin-based membrane skeleton composed of alpha- and beta-spectrin, actin, protein 4.1R (4.1R), and adducin. Post-translational modifications of these proteins have been suggested to modulate membrane mechanical function. Indeed, beta-spectrin phosphorylation by casein kinase I has been shown to decrease membrane mechanical stability. However, the effects of the phosphorylation of skeletal proteins by protein kinase C (PKC), a serine/threonine kinase, have not been elucidated. In the present study, we explored the functional consequences of the phosphorylation of 4.1R and adducin by PKC. We identified Ser-312 in 4.1R as the PKC phosphorylation site. Using antibodies raised against phosphopeptides of 4.1R and adducin, we documented significant differences in the time course of phosphorylation of adducin and 4.1R by PKC. Although adducin was phosphorylated rapidly by the activation of membrane-bound atypical PKC by phorbol 12-myristate 13-acetate stimulation, there was a significant delay in the phosphorylation of 4.1R because of delayed recruitment of conventional PKC from cytosol to the membrane. This differential time course in the phosphorylation of 4.1R and adducin in conjunction with membrane mechanical stability measurements enabled us to document that, although phosphorylation of adducin by PKC has little effect on membrane mechanical stability, additional phosphorylation of 4.1R results in a marked decrease in membrane mechanical stability. We further showed that the phosphorylation of 4.1R by PKC results in its decreased ability to form a ternary complex with spectrin and actin as well as dissociation of glycophorin C from the membrane skeleton. These findings have enabled us to define a regulatory role for 4.1R phosphorylation in dynamic regulation of red cell membrane properties.
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Affiliation(s)
- Sumie Manno
- Department of Biochemistry, Tokyo Women's Medical University, 8-1 Kawada-Cho, Shinjuku-Ku, Tokyo 162-8666, Japan
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Kaczmarek J, Thieleman A, Kopczyński Z, Goslar J, Hoffmann SK, Rybczyńska M. Alterations in skeletal protein, distribution of PKCalpha, and level of phospholipids in erythrocyte membranes of women with primary breast cancer. Blood Cells Mol Dis 2002; 29:225-35. [PMID: 12490289 DOI: 10.1006/bcmd.2002.0562] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The aim of our work was to study the influence of primary breast cancer on mature erythrocyte membranes. Blood was sampled from 29 women with primary breast cancer, aged 35-86 years, in different stages of clinical progression of the disease. In red blood cell membranes an increase of phosphatidylinositol-4-phosphate and phosphatidylinositol-4,5-diphosphate levels was observed. These changes were accompanied by a decrease in phospholipase C activity. Simultaneously, a significant decrease in concentration of phosphatidylserine, sphingomyelin, and phosphatidylinositol was found. Quantitative protein evaluation showed an increase in band 4.1 protein content with no changes in the level of constitutive PKCalpha responsible for the phosphorylation of this protein and its affinity to glycophorine C. In parallel a greater increase of PKCalpha translocation after PMA treatment compared to controls was observed. Possible oxidative damage of erythrocyte membranes indicated by an increase in malonyldialdehyde level and decrease in SH-group content as well as by an increase in the w/ ratio was documented. From the results it is concluded that primary breast cancer seems to affect the membranes of mature erythrocytes.
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Affiliation(s)
- Jolanta Kaczmarek
- Department of Clinical Chemistry, Karol Marcinkowski University of Medical Sciences in Poznań, Poznań, Poland
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Bennett V, Baines AJ. Spectrin and ankyrin-based pathways: metazoan inventions for integrating cells into tissues. Physiol Rev 2001; 81:1353-92. [PMID: 11427698 DOI: 10.1152/physrev.2001.81.3.1353] [Citation(s) in RCA: 714] [Impact Index Per Article: 31.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The spectrin-based membrane skeleton of the humble mammalian erythrocyte has provided biologists with a set of interacting proteins with diverse roles in organization and survival of cells in metazoan organisms. This review deals with the molecular physiology of spectrin, ankyrin, which links spectrin to the anion exchanger, and two spectrin-associated proteins that promote spectrin interactions with actin: adducin and protein 4.1. The lack of essential functions for these proteins in generic cells grown in culture and the absence of their genes in the yeast genome have, until recently, limited advances in understanding their roles outside of erythrocytes. However, completion of the genomes of simple metazoans and application of homologous recombination in mice now are providing the first glimpses of the full scope of physiological roles for spectrin, ankyrin, and their associated proteins. These functions now include targeting of ion channels and cell adhesion molecules to specialized compartments within the plasma membrane and endoplasmic reticulum of striated muscle and the nervous system, mechanical stabilization at the tissue level based on transcellular protein assemblies, participation in epithelial morphogenesis, and orientation of mitotic spindles in asymmetric cell divisions. These studies, in addition to stretching the erythrocyte paradigm beyond recognition, also are revealing novel cellular pathways essential for metazoan life. Examples are ankyrin-dependent targeting of proteins to excitable membrane domains in the plasma membrane and the Ca(2+) homeostasis compartment of the endoplasmic reticulum. Exciting questions for the future relate to the molecular basis for these pathways and their roles in a clinical context, either as the basis for disease or more positively as therapeutic targets.
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Affiliation(s)
- V Bennett
- Howard Hughes Medical Institute, Duke University Medical Center, Durham, North Carolina 27710, USA.
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Chang SH, Low PS. Regulation of the glycophorin C-protein 4.1 membrane-to-skeleton bridge and evaluation of its contribution to erythrocyte membrane stability. J Biol Chem 2001; 276:22223-30. [PMID: 11294862 DOI: 10.1074/jbc.m100604200] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The band 3-ankyrin-spectrin bridge and the glycophorin C-protein 4.1-spectrin/actin bridge constitute the two major tethers between the erythrocyte membrane and its spectrin skeleton. Although a structural requirement for the band 3-ankyrin bridge is well established, the contribution of the glycophorin C-protein 4.1 bridge to red cell function remains to be defined. In order to explore this latter bridge further, we have identified and/or characterized five stimuli that sever the linkage in intact erythrocytes and have examined the impact of this rupture on membrane mechanical properties. We report here that elevation of cytosolic 2,3-bisphosphoglycerate, an increase in intracellular Ca(2+), removal of cell O(2), a decrease in intracellular pH, and activation of erythrocyte protein kinase C all promote dissociation of protein 4.1 from glycophorin C, leading to reduced retention of glycophorin C in detergent-extracted spectrin/actin skeletons. Significantly, where mechanical studies could be performed, we also observe that rupture of the membrane-to-skeleton bridge has little or no impact on the mechanical properties of the cell, as assayed by ektacytometry and nickel mesh filtration. We, therefore, suggest that, although regulation of the glycophorin C-protein 4.1-spectrin/actin bridge likely occurs physiologically, the role of the tether and the associated regulatory changes remain to be established.
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Affiliation(s)
- S H Chang
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA
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Regulation of AMPA receptor GluR1 subunit surface expression by a 4. 1N-linked actin cytoskeletal association. J Neurosci 2001. [PMID: 11050113 DOI: 10.1523/jneurosci.20-21-07932.2000] [Citation(s) in RCA: 199] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The synaptic localization, clustering, and immobilization of neurotransmitter receptors and ion channels play important roles in synapse formation and synaptic transmission. Although several proteins have been identified that interact with AMPA receptors and that may regulate their synaptic targeting, little is known about the interaction of AMPA receptors with the cytoskeleton. In studies examining the interaction of the AMPA receptor GluR1 subunit with neuronal proteins, we determined that GluR1 interacts with the 4.1G and 4.1N proteins, homologs of the erythrocyte membrane cytoskeletal protein 4.1. Using the yeast two-hybrid system and a heterologous cell system, we demonstrated that both 4.1G and 4.1N bind to a membrane proximal region of the GluR1 C terminus, and that a region within the C-terminal domain of 4.1G or 4.1N is sufficient to mediate the interaction. We also found that 4.1N can associate with GluR1 in vivo and colocalizes with AMPA receptors at excitatory synapses. Disruption of the interaction of GluR1 with 4.1N or disruption of actin filaments decreased the surface expression of GluR1 in heterologous cells. Moreover, disruption of actin filaments in cultured cortical neurons dramatically reduced the level of surface AMPA receptors. These results suggest that protein 4.1N may link AMPA receptors to the actin cytoskeleton.
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10
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Abstract
The short actin filaments in the erythrocyte's membrane skeleton are shown to be largely oriented tangent to the lipid bilayer. Actin "proto"-filaments have previously been described as junctional centers intertriangulated by spectrin; however, the protofilaments may simultaneously serve as pinning centers between the network and the overlying bilayer. The latter function now seems of particular importance because near-normal network assembly has been reported with transgenic mouse sphero-erythrocytes that lack the primary linkage protein Band 3. To assess possible physical constraints on actin protofilaments in intact membranes, fluorescence polarization microscopy (FPM) has been used to study rhodamine phalloidin-labeled red cell ghosts. A basis for interpreting FPM images of cells is provided by FPM applied to isolated actin filaments. These are labeled with the same rhodamine probes and imaged at various orientations with respect to the polarizers, including filament orientations perpendicular to the image plane. High aperture and fluorophore conjugation effects are found to be minimal, enabling development of a simple, semi-empirical model which indicates that protofilaments are generally within approximately 20 degrees of the membrane tangent plane.
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Affiliation(s)
- C Picart
- Institute for Medicine and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6315, USA
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11
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Workman RF, Low PS. Biochemical analysis of potential sites for protein 4.1-mediated anchoring of the spectrin-actin skeleton to the erythrocyte membrane. J Biol Chem 1998; 273:6171-6. [PMID: 9497338 DOI: 10.1074/jbc.273.11.6171] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Erythrocyte protein 4.1 has been hypothesized to link the spectrin-actin junctional complex directly to the cytoplasmic domain of glycophorin C, but this bridging function has never been directly demonstrated. Because an alternative protein-mediated bridge between the junctional complex and the cytoplasmic domain of band 3 is also plausible, we have undertaken to characterize the membrane sites to which protein 4.1 can anchor the spectrin and actin skeleton. We demonstrate that proteolytic removal of the cytoplasmic domain of band 3 has minimal effect on the ability of protein 4.1 to promote 125I-labeled spectrin and actin binding to KI-stripped erythrocyte membrane vesicles. We also show that quantitative blockade of all band 3 sites with either monoclonal or polyclonal antibodies to band 3 is equally ineffective in preventing protein 4.1-mediated association of spectrin and actin with the membrane. In contrast, obstruction of protein 4.1 binding to its docking site on the cytoplasmic pole of glycophorin C is demonstrated to reduce the same protein 4.1 bridging function by approximately 85%. We conclude from these data that (i) glycophorin C contributes the primary anchoring site of the protein 4.1-mediated bridge to the spectrin-actin skeleton; (ii) band 3 is incapable of serving the same function; and (iii) additional minor protein 4.1 bridging sites may exist on the human erythrocyte membrane.
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Affiliation(s)
- R F Workman
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-1393, USA
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Workman RF, Low PS. Effect of purification protocol on the functional properties of erythrocyte membrane protein 4.1. Protein Expr Purif 1998; 12:100-4. [PMID: 9473463 DOI: 10.1006/prep.1997.0812] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The inositol hexaphosphate (IHP) method for purification of the erythrocyte membrane protein 4.1 yields the largest quantity of pure protein of any published protocol. However, protein 4.1 isolated by this method was found to bind to KI-stripped inside-out red blood cell membrane vesicles (KIOVs) only 40% as well as protein 4.1 purified by other methods. While an improved Tyler method, the SP method, yields 30-40% less protein 4.1 than the IHP method, the SP preparation nevertheless exceeds the IHP method in that the protein 4.1 is fully functional. Unlike the Tyler method, the SP procedure is also free of contaminating spectrin, p55, and proteases.
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Affiliation(s)
- R F Workman
- Department of Chemistry, Purdue University, 1393 Brown Building, W. Lafayette, Indiana 47907, USA
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Abstract
Infection of human erythrocytes with the malaria parasite Plasmodium falciparum induces many morphological and biochemical changes in the host cell. Host serine/threonine protein kinases could be involved in some of these processes. The aim of this study was to determine the effect of infection on red blood cell protein kinase C (PKC) and establish the importance of this enzyme in parasite growth and sexual stage differentiation. Phorbol myristate acetate (PMA)-induced translocation of erythrocyte PKC activity is impaired in erythrocytes enriched for mature asexual stage infected cells. Western blotting shows that this is due to a relative reduction in membrane PKC protein levels rather than inhibition of enzyme activity and analysis of PKC activity isolated from whole cell lysates by DE52 chromatography suggests that total activatable PKC levels are lower in infected erythrocytes. A reduction in PMA-induced activation is also observed in PKC assays performed in situ. Downregulation of erythrocyte PKC by overnight incubation with PMA before infection causes a significant decrease in the rate of the asexual growth, suggesting that the enzyme, although lost later in infection, may be important in the earlier development of the parasite. By contrast, the lack of PKC had no effect on the production of sexual stage parasites.
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Abstract
AbstractInfection of human erythrocytes with the malaria parasite Plasmodium falciparum induces many morphological and biochemical changes in the host cell. Host serine/threonine protein kinases could be involved in some of these processes. The aim of this study was to determine the effect of infection on red blood cell protein kinase C (PKC) and establish the importance of this enzyme in parasite growth and sexual stage differentiation. Phorbol myristate acetate (PMA)-induced translocation of erythrocyte PKC activity is impaired in erythrocytes enriched for mature asexual stage infected cells. Western blotting shows that this is due to a relative reduction in membrane PKC protein levels rather than inhibition of enzyme activity and analysis of PKC activity isolated from whole cell lysates by DE52 chromatography suggests that total activatable PKC levels are lower in infected erythrocytes. A reduction in PMA-induced activation is also observed in PKC assays performed in situ. Downregulation of erythrocyte PKC by overnight incubation with PMA before infection causes a significant decrease in the rate of the asexual growth, suggesting that the enzyme, although lost later in infection, may be important in the earlier development of the parasite. By contrast, the lack of PKC had no effect on the production of sexual stage parasites.
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