Localization of the rat myosin I molecules myr 1 and myr 2 and in vivo targeting of their tail domains

1995 ◽  
Vol 108 (12) ◽  
pp. 3775-3786 ◽  
Author(s):  
C. Ruppert ◽  
J. Godel ◽  
R.T. Muller ◽  
R. Kroschewski ◽  
J. Reinhard ◽  
...  
Keyword(s):  
Subcellular Localization ◽  
Brush Border ◽  
Subcellular Fractionation ◽  
Actin Binding ◽  
Resting Cells ◽  
Medium Density ◽  
Subcellular Targeting ◽  
Myosin I ◽  
Punctate Pattern

Myr 1 is a widely distributed mammalian myosin I molecule related to brush border myosin 1. A second widely distributed myosin I molecule similar to myr 1 and brush border myosin I, called myr 2, has now been identified. Specific antibodies and expression of epitope-tagged molecules were used to determine the subcellular localization of myr 1 and myr 2 in NRK cells. Myr 1 was detected at the plasma membrane and was particularly enriched in cell protrusions like lamellipodia, membrane ruffles and filopodia. In dividing cells myr 1 localized to the cleavage furrow. Myr 2 was localized in a discrete punctate pattern in resting cells and in cells undergoing cytokinesis. In subcellular fractionation experiments myr 1 and myr 2 were both partly soluble and partly associated with smooth membranes of medium density. The tail domains of myosin I molecules have been proposed to interact with a receptor and thereby determine the subcellular localization. To test this hypothesis we expressed the tail domains of myr 1 and myr 2 that lack the F-actin-binding myosin head domain in NRK cells. These tail domains also partly copurified with smooth membranes of medium density and immunolocalized similar to the respective endogenous myosin I; however, they exhibited a lower affinity for membranes and an increased diffuse cytosolic localization. These results suggest that the tail domains of myr 1 and myr 2 are sufficient for subcellular targeting but that their head domains also contribute significantly to maintaining a proper subcellular localization.

scholarly journals Presenilin 1 Controls γ-Secretase Processing of Amyloid Precursor Protein in Pre-Golgi Compartments of Hippocampal Neurons

1999 ◽  
Vol 147 (2) ◽  
pp. 277-294 ◽  
Author(s):  
Wim G. Annaert ◽  
Lyne Levesque ◽  
Kathleen Craessaerts ◽  
Inge Dierinck ◽  
Greet Snellings ◽  
...  
Keyword(s):  
Subcellular Localization ◽  
Amyloid Precursor Protein ◽  
Hippocampal Neurons ◽  
Subcellular Fractionation ◽  
Precursor Protein ◽  
Presenilin 1 ◽  
Carboxy Terminal ◽  
Endocytic Pathways

Mutations of presenilin 1 (PS1) causing Alzheimer's disease selectively increase the secretion of the amyloidogenic βA4(1-42), whereas knocking out the gene results in decreased production of both βA4(1-40) and (1-42) amyloid peptides (De Strooper et al. 1998). Therefore, PS1 function is closely linked to the γ-secretase processing of the amyloid precursor protein (APP). Given the ongoing controversy on the subcellular localization of PS1, it remains unclear at what level of the secretory and endocytic pathways PS1 exerts its activity on APP and on the APP carboxy-terminal fragments that are the direct substrates for γ-secretase. Therefore, we have reinvestigated the subcellular localization of endogenously expressed PS1 in neurons in vitro and in vivo using confocal microscopy and fine-tuned subcellular fractionation. We show that uncleaved PS1 holoprotein is recovered in the nuclear envelope fraction, whereas the cleaved PS fragments are found mainly in post-ER membranes including the intermediate compartment (IC). PS1 is concentrated in discrete sec23p- and p58/ERGIC-53–positive patches, suggesting its localization in subdomains involved in ER export. PS1 is not found to significant amounts beyond the cis-Golgi. Surprisingly, we found that APP carboxy-terminal fragments also coenrich in the pre-Golgi membrane fractions, consistent with the idea that these fragments are the real substrates for γ-secretase. Functional evidence that PS1 exerts its effects on γ-secretase processing of APP in the ER/IC was obtained using a series of APP trafficking mutants. These mutants were investigated in hippocampal neurons derived from transgenic mice expressing PS1wt or PS1 containing clinical mutations (PS1M146L and PS1L286V) at physiologically relevant levels. We demonstrate that the APP-London and PS1 mutations have additive effects on the increased secretion of βA4(1-42) relative to βA4(1-40), indicating that both mutations operate independently. Overall, our data clearly establish that PS1 controls γ42-secretase activity in pre-Golgi compartments. We discuss models that reconcile this conclusion with the effects of PS1 deficiency on the generation of βA4(1-40) peptide in the late biosynthetic and endocytic pathways.

scholarly journals The subcellular localization of di- and tri-peptide hydrolase activity in guinea-pig small intestine

1970 ◽  
Vol 120 (1) ◽  
pp. 195-203 ◽  
Author(s):  
T. J. Peters
Keyword(s):  
Guinea Pig ◽  
Brush Border ◽  
Soluble Fraction ◽  
Subcellular Fractionation ◽  
Border Region ◽  
Protein Digestion ◽  
Kinetic Assay ◽  
Brush Borders

1. Two different subcellular fractionation techniques were applied to guinea-pig intestinal mucosa and the composition of the brush borders prepared by the two methods were compared. 2. By using a kinetic assay system the subcellular distribution of activity against ten dipeptides and five tripeptides was studied. 3. Only small amounts (5–10%) of activity against dipeptides were found in the brush-border region, the enzymes being concentrated in the cytosol. 4. Significant amounts (10–60%) of activity against tripeptides were found in the brush border with the remainder largely present in the soluble fraction. 5. The relevance of these studies to the localization in vivo and the possible role of peptidases in protein digestion is discussed.

Ouabain-induced Seizures in Rats: Regional and Subcellular Localization of 3H-Ouabain Associated with Na+–K+-ATPase in Brain

1972 ◽  
Vol 50 (8) ◽  
pp. 888-896 ◽  
Author(s):  
J. Donaldson ◽  
J. L. Minnich ◽  
A. Barbeau
Keyword(s):  
Subcellular Localization ◽  
Regional Distribution ◽  
Subcellular Fractionation ◽  
Synaptosomal Membrane ◽  
Intraventricular Injections ◽  
The Brain

Previous observations on clonic and tonic seizures in rats induced by intraventricular injections of ouabain, Zn2+, or Cu2+ have been expanded and confirmed. Tritiated ouabain was injected intraventricularly to rats and its regional distribution studied in the brain. The hippocampus and hypothalamus were found to be the regions with highest accumulation of radioactivity. This was supported by the in vitro finding that synaptosomes from both these regions demonstrate the highest uptake of the labelled ouabain. Subcellular fractionation experiments following in vivo injection of 3H-ouabain revealed that maximal radioactivity is associated with synaptosomal membrane fractions rich in Na+–K+-ATPase.

Characterization of the enterocyte-like brush border cytoskeleton of the C2BBe clones of the human intestinal cell line, Caco-2

1992 ◽  
Vol 102 (3) ◽  
pp. 581-600 ◽  
Author(s):  
M.D. Peterson ◽  
M.S. Mooseker
Keyword(s):  
Molecular Mass ◽  
Cell Line ◽  
Heavy Chain ◽  
Brush Border ◽  
Laser Scanning ◽  
Human Colon ◽  
Cell Types ◽  
Intestinal Cell ◽  
Myosin I

The brush border (BB) of the enterocyte is a well-studied example of the actin-based cytoskeleton. We describe here a cell culture model that expresses a faithful representation of the in vivo structure. Two clones (C2BBe 1 and 2) isolated from the cell line Caco-2 (derived from a human colonic adenocarcinoma) formed a polarized monolayer with an apical BB morphologically comparable to that of the human colon. BBs could be isolated by standard methods and contained the microvillar proteins villin, fimbrin, sucrase-isomaltase and BB myosin I, and the terminal web proteins fodrin and myosin II. The immunolocalization of these proteins in confluent, filter-grown monolayers was determined by laser scanning confocal microscopy; patterns of distribution comparable to those in human enterocytes were observed. Sedimentation analysis of cell homogenates derived from C2BBe cells and human colonic epithelial cells demonstrated similar patterns of fractionation of BB proteins; the physical association of those proteins, as determined by extraction from the BB, was also comparable between the two cell types. Like enterocytes of the human intestine, C2BBe cells expressed multiple myosin I immunogens reactive with a head domain-specific monoclonal antibody raised against avian BB myosin I, one of which co-migrated with the approximately 110 kilodalton (kDa) heavy chain of human BB myosin I. In addition, the C2BBe cells express a pair of higher molecular mass immunogens (130 and 140 kDa). These myosin I immunogens all exhibit ATP-dependent association with the C2BBe cytoskeleton. Although the higher molecular mass immunogens were detected in several other human intestinal lines examined, including the parent Caco-2 line, none of these other lines expressed detectable levels of the 110 kDa immunogen, which is presumed to be the heavy chain of human BB myosin I.

scholarly journals The Dictyostelium Carmil Protein Links Capping Protein and the Arp2/3 Complex to Type I Myosins through Their Sh3 Domains

2001 ◽  
Vol 153 (7) ◽  
pp. 1479-1498 ◽  
Author(s):  
Goeh Jung ◽  
Kirsten Remmert ◽  
Xufeng Wu ◽  
Joanne M. Volosky ◽  
John A. Hammer
Keyword(s):  
Fusion Proteins ◽  
Leading Edge ◽  
Fluid Phase ◽  
Actin Binding ◽  
Type I ◽  
Sh3 Domains ◽  
Capping Protein ◽  
Myosin I ◽  
Mutant Phenotypes

Fusion proteins containing the Src homology (SH)3 domains of Dictyostelium myosin IB (myoB) and IC (myoC) bind a 116-kD protein (p116), plus nine other proteins identified as the seven member Arp2/3 complex, and the α and β subunits of capping protein. Immunoprecipitation reactions indicate that myoB and myoC form a complex with p116, Arp2/3, and capping protein in vivo, that the myosins bind to p116 through their SH3 domains, and that capping protein and the Arp2/3 complex in turn bind to p116. Cloning of p116 reveals a protein dominated by leucine-rich repeats and proline-rich sequences, and indicates that it is a homologue of Acan 125. Studies using p116 fusion proteins confirm the location of the myosin I SH3 domain binding site, implicate NH2-terminal sequences in binding capping protein, and show that a region containing a short sequence found in several G-actin binding proteins, as well as an acidic stretch, can activate Arp2/3-dependent actin nucleation. p116 localizes along with the Arp2/3 complex, myoB, and myoC in dynamic actin-rich cellular extensions, including the leading edge of cells undergoing chemotactic migration, and dorsal, cup-like, macropinocytic extensions. Cells lacking p116 exhibit a striking defect in the formation of these macropinocytic structures, a concomitant reduction in the rate of fluid phase pinocytosis, a significant decrease in the efficiency of chemotactic aggregation, and a decrease in cellular F-actin content. These results identify a complex that links key players in the nucleation and termination of actin filament assembly with a ubiquitous barbed end–directed motor, indicate that the protein responsible for the formation of this complex is physiologically important, and suggest that previously reported myosin I mutant phenotypes in Dictyostelium may be due, at least in part, to defects in the assembly state of actin. We propose that p116 and Acan 125, along with homologues identified in Caenorhabditis elegans, Drosophila, mouse, and man, be named CARMIL proteins, for capping protein, Arp2/3, and myosin I linker.

Multiple unconventional myosin domains of the intestinal brush border cytoskeleton

1994 ◽  
Vol 107 (12) ◽  
pp. 3535-3543 ◽  
Author(s):  
M.B. Heintzelman ◽  
T. Hasson ◽  
M.S. Mooseker
Keyword(s):  
Brush Border ◽  
Myosin Ii ◽  
Actin Binding ◽  
Myosin Vi ◽  
Myosin V ◽  
Terminal Web ◽  
Intestinal Brush Border ◽  
Myosin I ◽  
Biochemical Fractionation

Representatives of class V and class VI unconventional myosins are identified as components of the intestinal brush border cytoskeleton. With brush border myosin-I and myosin-II, this brings to four the number of myosin classes associated with this one subcellular domain and represents the first characterization of four classes of myosins expressed in a single metazoan cell type. The distribution and cytoskeletal association of each myosin is distinct as assessed by both biochemical fractionation and immunofluorescence localization. Myosin-VI exists in both the microvillus and terminal web although the terminal web is the predominant site of concentration. Myosin-V is present in the terminal web and, most notably, at the distal ends of the microvilli, thus becoming the first actin-binding protein to be localized to this domain as assessed by both immunohistochemical and biochemical methods. In the undifferentiated enterocytes of the intestinal crypts, myosin-VI is expressed but not yet localized to the brush border, in contrast to myosin-V, which does demonstrate an apical distribution in these cells. An assessment of myosin abundance indicates that while myosin-II is the most abundant in the cell and in the brush border, brush border myosin-I is only slightly less abundant in contrast to myosins-V and -VI, both of which are two orders of magnitude less abundant than the others. Extraction studies indicate that of these four myosins, myosin-V is the most tightly associated with the brush border membrane, as detergent, in addition to ATP, is required for efficient solubilization.

scholarly journals Galectin-4 and Small Intestinal Brush Border Enzymes Form Clusters

1997 ◽  
Vol 8 (11) ◽  
pp. 2241-2251 ◽  
Author(s):  
E. Michael Danielsen ◽  
Bo van Deurs
Keyword(s):  
Brush Border ◽  
Gradient Centrifugation ◽  
Subcellular Fractionation ◽  
Aminopeptidase N ◽  
Intestinal Lumen ◽  
Immunogold Electron Microscopy ◽  
Brush Border Enzymes ◽  
Intestinal Brush Border ◽  
Mucosal Explants

Detergent-insoluble complexes prepared from pig small intestine are highly enriched in several transmembrane brush border enzymes including aminopeptidase N and sucrase-isomaltase, indicating that they reside in a glycolipid-rich environment in vivo. In the present work galectin-4, an animal lectin lacking a N-terminal signal peptide for membrane translocation, was discovered in these complexes as well, and in gradient centrifugation brush border enzymes and galectin-4 formed distinct soluble high molecular weight clusters. Immunoperoxidase cytochemistry and immunogold electron microscopy showed that galectin-4 is indeed an intestinal brush border protein; we also localized galectin-4 throughout the cell, mainly associated with membraneous structures, including small vesicles, and to the rootlets of microvillar actin filaments. This was confirmed by subcellular fractionation, showing about half the amount of galectin-4 to be in the microvillar fraction, the rest being associated with insoluble intracellular structures. A direct association between the lectin and aminopeptidase N was evidenced by a colocalization along microvilli in double immunogold labeling and by the ability of an antibody to galectin-4 to coimmunoprecipitate aminopeptidase N and sucrase-isomaltase. Furthermore, galectin-4 was released from microvillar, right-side-out vesicles as well as from mucosal explants by a brief wash with 100 mM lactose, confirming its extracellular localization. Galectin-4 is therefore secreted by a nonclassical pathway, and the brush border enzymes represent a novel class of natural ligands for a member of the galectin family. Newly synthesized galectin-4 is rapidly “trapped” by association with intracellular structures prior to its apical secretion, but once externalized, association with brush border enzymes prevents it from being released from the enterocyte into the intestinal lumen.

Disruption of the actin cytoskeleton of mammalian cells by the capping complex actin-fragmin is inhibited by actin phosphorylation and regulated by Ca2+ ions

1998 ◽  
Vol 111 (12) ◽  
pp. 1695-1706 ◽  
Author(s):  
B. Constantin ◽  
K. Meerschaert ◽  
J. Vandekerckhove ◽  
J. Gettemans
Keyword(s):  
Actin Cytoskeleton ◽  
Cell Morphology ◽  
Actin Filaments ◽  
Mammalian Cells ◽  
Actin Binding ◽  
General Mechanism ◽  
Resting Cells ◽  
Dependent Manner

Fragmin from Physarum polycephalum is a gelsolin-like actin-binding protein and interferes with the growth of actin filaments in vitro by severing actin filaments and capping their barbed ends through formation of an actin-fragmin dimer in a Ca2+-dependent manner. The actin-fragmin dimer is phosphorylated in vivo and in vitro on the actin subunit by the actin-fragmin kinase. We have studied the properties of these capping proteins and their regulation by actin phosphorylation and Ca2+ ions in living PtK2, CV1 and NIH3T3 cultured cells by microinjection or by expression in conjunction with immunostaining and fluorescence microscopy. Microinjection of the actin-fragmin dimer disintegrated the actin cytoskeleton and altered cell morphology. This in vivo effect could be blocked by phosphorylation of the actin subunit by the actin-fragmin kinase in low Ca2+ conditions, and the capping activity could be recovered by high Ca2+ concentration, probably through activation of the second actin-binding site in fragmin. This suggests that in Physarum microplasmodia, actin polymerization can be controlled in a Ca2+-dependent manner through the phosphorylation of actin. Microinjected or overexpressed recombinant fragmin did not affect the actin-based cytoskeleton or cell morphology of resting cells, unless the cytosolic free Ca2+ concentration was increased by microinjection of a Ca2+-containing buffer. The cells were able to revert to their normal phenotype which indicates that endogenous regulatory mechanisms counteracted fragmin activity, probably by uncapping fragmin from the barbed ends of filaments. Fragmin also antagonized formation of stress fibers induced by lysophosphatidic acid. Our findings demonstrate that the interactions between actin and fragmin are tightly regulated by the cytosolic Ca2+ concentration and this provides a basis for a more general mechanism in higher organisms to regulate microfilament organization.

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