Recycling domains in plant cell morphogenesis: small GTPase effectors, plasma membrane signalling and the exocyst

2010 ◽  
Vol 38 (2) ◽  
pp. 723-728 ◽  
Author(s):  
Viktor Žárský ◽  
Martin Potocký
Keyword(s):  
Plasma Membrane ◽  
Plant Cell ◽  
Secretory Pathway ◽  
Root Hairs ◽  
Small Gtpases ◽  
Small Gtpase ◽  
Cell Cortex ◽  
Membrane Phospholipids ◽  
Recycling Endosome ◽  
Regulatory Module

The Rho/Rop small GTPase regulatory module is central for initiating exocytotically ACDs (active cortical domains) in plant cell cortex, and a growing array of Rop regulators and effectors are being discovered in plants. Structural membrane phospholipids are important constituents of cells as well as signals, and phospholipid-modifying enzymes are well known effectors of small GTPases. We have shown that PLDs (phospholipases D) and their product, PA (phosphatidic acid), belong to the regulators of the secretory pathway in plants. We have also shown that specific NOXs (NADPH oxidases) producing ROS (reactive oxygen species) are involved in cell growth as exemplified by pollen tubes and root hairs. Most plant cells exhibit several distinct plasma membrane domains (ACDs), established and maintained by endocytosis/exocytosis-driven membrane protein recycling. We proposed recently the concept of a ‘recycling domain’ (RD), uniting the ACD and the connected endosomal recycling compartment (endosome), as a dynamic spatiotemporal entity. We have described a putative GTPase–effector complex exocyst involved in exocytic vesicle tethering in plants. Owing to the multiplicity of its Exo70 subunits, this complex, along with many RabA GTPases (putative recycling endosome organizers), may belong to core regulators of RD organization in plants.

scholarly journals Nanodomain-mediated lateral sorting drives polarization of the small GTPase ROP2 in the plasma membrane of root hair cells

2021 ◽  
Author(s):  
Vanessa Aphaia Fiona Fuchs ◽  
Philipp Denninger ◽  
Milan Župunski ◽  
Yvon Jaillais ◽  
Ulrike Engel ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Single Molecule ◽  
Root Hair ◽  
Root Hairs ◽  
Small Gtpases ◽  
Small Gtpase ◽  
Cellular Growth ◽  
Epifluorescence Microscopy ◽  
Anionic Phospholipids ◽  
Downstream Effectors

Formation of root hairs involves the targeted recruitment of the cellular growth machinery to the root hair initiation domain (RHID), a specialized site at the plasma membrane (PM) of trichoblast cells. Early determinants in RHID establishment are small GTPases of the Rho-of-plants (ROP) protein family, which are required for polarization of downstream effectors, membrane modification and targeted secretion during tip growth. It remains, however, not fully understood how ROP GTPases themselves are polarized. To investigate the mechanism underlying ROP2 recruitment, we employed Variable Angle Epifluorescence Microscopy (VAEM) and exploited mCitrine fluorophore blinking for single molecule localization, particle tracking and super-resolved imaging of the trichoblast plasma membrane. We observed the association of mCit-ROP2 within distinct membrane nanodomains, whose polar occurrence at the RHID was dependent on the presence of the RopGEF GEF3, and found a gradual, localized decrease of mCit-ROP2 protein mobility that preceded polarization. We provide evidence for a step-wise model of ROP2 polarization that involves (i) an initial non-polar recruitment to the plasma membrane via interactions with anionic phospholipids, (ii) ROP2 assembly into membrane nanodomains independent of nucleotide-binding state and, sub-sequently, (iii) lateral sorting into the RHID, driven by GEF3-mediated localized reduction of ROP2 mobility.

scholarly journals The Rab27a effector exophilin7 promotes fusion of secretory granules that have not been docked to the plasma membrane

2013 ◽  
Vol 24 (3) ◽  
pp. 319-330 ◽  
Author(s):  
Hao Wang ◽  
Ray Ishizaki ◽  
Jun Xu ◽  
Kazuo Kasai ◽  
Eri Kobayashi ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Knockout Mice ◽  
Secretory Granules ◽  
Small Gtpase ◽  
Membrane Phospholipids ◽  
Β Cells ◽  
Β Cell ◽  
Pancreatic Β Cells ◽  
Insulin Granules ◽  
Insulin Exocytosis

Granuphilin, an effector of the small GTPase Rab27a, mediates the stable attachment (docking) of insulin granules to the plasma membrane and inhibits subsequent fusion of docked granules, possibly through interaction with a fusion-inhibitory Munc18-1/syntaxin complex. However, phenotypes of insulin exocytosis differ considerably between Rab27a- and granuphilin-deficient pancreatic β cells, suggesting that other Rab27a effectors function in those cells. We found that one of the putative Rab27a effector family proteins, exophilin7/JFC1/Slp1, is expressed in β cells; however, unlike granuphilin, exophilin7 overexpressed in the β-cell line MIN6 failed to show granule-docking or fusion-inhibitory activity. Furthermore, exophilin7 has no affinities to either Munc18-1 or Munc18-1–interacting syntaxin-1a, in contrast to granuphilin. Although β cells of exophilin7-knockout mice show no apparent abnormalities in intracellular distribution or in ordinary glucose-induced exocytosis of insulin granules, they do show impaired fusion in response to some stronger stimuli, specifically from granules that have not been docked to the plasma membrane. Exophilin7 appears to mediate the fusion of undocked granules through the affinity of its C2A domain toward the plasma membrane phospholipids. These findings indicate that the two Rab27a effectors, granuphilin and exophilin7, differentially regulate the exocytosis of either stably or minimally docked granules, respectively.

scholarly journals Exophilin8 transiently clusters insulin granules at the actin-rich cell cortex prior to exocytosis

2011 ◽  
Vol 22 (10) ◽  
pp. 1716-1726 ◽  
Author(s):  
Kouichi Mizuno ◽  
José S. Ramalho ◽  
Tetsuro Izumi
Keyword(s):  
Plasma Membrane ◽  
Secretory Granules ◽  
Small Gtpase ◽  
Cell Cortex ◽  
Cortical Actin ◽  
Insulin Granules ◽  
Myosin Va ◽  
Exogenous Expression ◽  
Mutation Analyses

Exophilin8/MyRIP/Slac2-c is an effector protein of the small GTPase Rab27a and is specifically localized on retinal melanosomes and secretory granules. We investigated the role of exophilin8 in insulin granule trafficking. Exogenous expression of exophilin8 in pancreatic β cells or their cell line, MIN6, polarized (exophilin8-positive) insulin granules at the cell corners, where both cortical actin and the microtubule plus-end–binding protein, EB1, were present. Mutation analyses indicated that the ability of exophilin8 to act as a linker between Rab27a and myosin Va is essential for its granule-clustering activity. Moreover, exophilin8 and exophilin8-associated insulin granules were markedly stable and immobile. Total internal reflection fluorescence microscopy indicated that exophilin8 restricts the motion of insulin granules at a region deeper than that where another Rab27a effector, granuphilin, accumulates docked granules directly attached to the plasma membrane. However, the exophilin8-induced immobility of insulin granules was eliminated upon secretagogue stimulation and did not inhibit evoked exocytosis. Furthermore, exophilin8 depletion prevents insulin granules from being transported close to the plasma membrane and inhibits their fusion. These findings indicate that exophilin8 transiently traps insulin granules into the cortical actin network close to the microtubule plus-ends and supplies them for release during the stimulation.

scholarly journals Rho1 regulates apoptosis via activation of the JNK signaling pathway at the plasma membrane

2010 ◽  
Vol 189 (2) ◽  
pp. 311-323 ◽  
Author(s):  
Amanda L. Neisch ◽  
Olga Speck ◽  
Beth Stronach ◽  
Richard G. Fehon
Keyword(s):  
Plasma Membrane ◽  
Cell Survival ◽  
Cell Shape ◽  
Rho Kinase ◽  
Small Gtpase ◽  
Cell Cortex ◽  
Jnk Pathway ◽  
Jnk Signaling ◽  
Upstream Regulator ◽  
Jnk Signaling Pathway

Precisely controlled growth and morphogenesis of developing epithelial tissues require coordination of multiple factors, including proliferation, adhesion, cell shape, and apoptosis. RhoA, a small GTPase, is known to control epithelial morphogenesis and integrity through its ability to regulate the cytoskeleton. In this study, we examine a less well-characterized RhoA function in cell survival. We demonstrate that the Drosophila melanogaster RhoA, Rho1, promotes apoptosis independently of Rho kinase through its effects on c-Jun NH2-terminal kinase (JNK) signaling. In addition, Rho1 forms a complex with Slipper (Slpr), an upstream activator of the JNK pathway. Loss of Moesin (Moe), an upstream regulator of Rho1 activity, results in increased levels of Rho1 at the plasma membrane and cortical accumulation of Slpr. Together, these results suggest that Rho1 functions at the cell cortex to regulate JNK activity and implicate Rho1 and Moe in epithelial cell survival.

scholarly journals Mouse A6/Twinfilin Is an Actin Monomer-Binding Protein That Localizes to the Regions of Rapid Actin Dynamics

2000 ◽  
Vol 20 (5) ◽  
pp. 1772-1783 ◽  
Author(s):  
Maria Vartiainen ◽  
Pauli J. Ojala ◽  
Petri Auvinen ◽  
Johan Peränen ◽  
Pekka Lappalainen
Keyword(s):  
Tyrosine Kinase ◽  
Binding Protein ◽  
Small Gtpases ◽  
Small Gtpase ◽  
Dominant Negative ◽  
Actin Dynamics ◽  
Actin Binding ◽  
Cell Cortex ◽  
Actin Monomer

ABSTRACT In our database searches, we have identified mammalian homologues of yeast actin-binding protein, twinfilin. Previous studies suggested that these mammalian proteins were tyrosine kinases, and therefore they were named A6 protein tyrosine kinase. In contrast to these earlier studies, we did not find any tyrosine kinase activity in our recombinant protein. However, biochemical analysis showed that mouse A6/twinfilin forms a complex with actin monomer and prevents actin filament assembly in vitro. A6/twinfilin mRNA is expressed in most adult tissues but not in skeletal muscle and spleen. In mouse cells, A6/twinfilin protein is concentrated to the areas at the cell cortex which overlap with G-actin-rich actin structures. A6/twinfilin also colocalizes with the activated forms of small GTPases Rac1 and Cdc42 to membrane ruffles and to cell-cell contacts, respectively. Furthermore, expression of the activated Rac1(V12) in NIH 3T3 cells leads to an increased A6/twinfilin localization to nucleus and cell cortex, whereas a dominant negative form of Rac1(V12,N17) induces A6/twinfilin localization to cytoplasm. Taken together, these studies show that mouse A6/twinfilin is an actin monomer-binding protein whose localization to cortical G-actin-rich structures may be regulated by the small GTPase Rac1.

scholarly journals Systematic Structure-Function Analysis of the Small GTPase Arf1 in Yeast

2002 ◽  
Vol 13 (5) ◽  
pp. 1652-1664 ◽  
Author(s):  
Eleanor S. Click ◽  
Tim Stearns ◽  
David Botstein
Keyword(s):  
Structure Function ◽  
Secretory Pathway ◽  
Synthetic Lethality ◽  
Function Analysis ◽  
Small Gtpases ◽  
Small Gtpase ◽  
Vesicle Traffic ◽  
Systematic Structure ◽  
Guanine Nucleotide Binding ◽  
High Or Low Temperature

Members of the ADP-ribosylation factor (Arf) family of small GTPases are implicated in vesicle traffic in the secretory pathway, although their precise function remains unclear. We generated a series of 23 clustered charge-to-alanine mutations in the Arf1 protein ofSaccharomyces cerevisiae to determine the portions of this protein important for its function in cells. These mutants display a number of phenotypes, including conditional lethality at high or low temperature, defects in glycosylation of invertase, dominant lethality, fluoride sensitivity, and synthetic lethality with thearf2 null mutation. All mutations were mapped onto the available crystal structures for Arf1p: Arf1p bound to GDP, to GTP, and complexed with the regulatory proteins ArfGEF and ArfGAP. From this systematic structure-function analysis we demonstrate that all essential mutations studied map to one hemisphere of the protein and provide strong evidence in support of the proposed ArfGEF contact site on Arf1p but minimal evidence in support of the proposed ArfGAP-binding site. In addition, we describe the isolation of a spatially distant intragenic suppressor of a dominant lethal mutation in the guanine nucleotide-binding region of Arf1p.

scholarly journals S-Palmitoylation-Dependent Regulation of Cardiomyocyte Rac1 Signaling Activity and Cardiac Hypertrophy

2021 ◽  
Author(s):  
Matthew J Brody ◽  
Tanya A. Baldwin ◽  
Arasakumar Subramani ◽  
Onur Kanisicak ◽  
Ronald J Vagnozzi ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Transgenic Mice ◽  
Cardiac Disease ◽  
Small Gtpases ◽  
Small Gtpase ◽  
Transferase Activity ◽  
Related Enzyme ◽  
Rho Family ◽  
Novel Therapeutic Strategies

S-palmitoylation is a reversible lipid modification that regulates trafficking, localization, activity, and/or stability of protein substrates by serving as a fatty acid anchor to cell membranes. However, S-palmitoylation-dependent control of signal transduction in cardiomyocytes and its effects on cardiac physiology are not well understood. We performed an in vivo gain-of-function screen of zinc finger Asp-His-His-Cys (zDHHC) family S-acyl transferases that catalyze S-palmitoylation and identified the Golgi-localized enzyme zDHHC3 as a critical regulator of cardiac maladaptation. The closely-related enzyme, zDHHC7, also induced severe cardiomyopathy but this effect was not observed with overexpression of plasma membrane enzyme zDHHC5, endoplasmic reticulum enzyme zDHHC6, or Golgi enzyme zDHHC13. To identify effectors that may underlie zDHHC3-induced cardiomyopathy we performed quantitative site-specific S-acyl proteomics in zDHHC3-overexpressing cells that revealed the small GTPase Rac1 as a novel substrate. We generated cardiomyocyte-specific transgenic mice overexpressing zDHHC3, which develop severe cardiac disease. Cardiomyopathy and congestive heart failure in zDHHC3 transgenic mice are preceded by enhanced S-palmitoylation of Rac1 and induction of additional Rho family small GTPases including RhoA, Cdc42, and the Rho family-specific chaperone RhoGDI. In contrast, transgenic mice overexpressing an enzymatically-dead mutant of zDHHC3 do not exhibit this profound induction of RhoGTPase signaling or develop cardiac disease. Rac1 S-palmitoylation, plasma membrane localization, activity, and downstream hypertrophic signaling were substantially increased in zDHHC3 overexpressing hearts. Taken together, these data suggest inhibition of zDHHC3/7 S-acyl transferase activity at the cardiomyocyte Golgi or disruption of Rac1 S-palmitoylation as novel therapeutic strategies to treat cardiac disease or other diseases associated with enhanced RhoGTPase signaling.

scholarly journals An enzymatic cascade of Rab5 effectors regulates phosphoinositide turnover in the endocytic pathway

2005 ◽  
Vol 170 (4) ◽  
pp. 607-618 ◽  
Author(s):  
Hye-Won Shin ◽  
Mitsuko Hayashi ◽  
Savvas Christoforidis ◽  
Sandra Lacas-Gervais ◽  
Sebastian Hoepfner ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Dual Role ◽  
Small Gtpase ◽  
Endocytic Pathway ◽  
Cell Cortex ◽  
Rab Gtpase ◽  
Functional Importance ◽  
Dual Mechanism ◽  
Transferrin Uptake

Generation and turnover of phosphoinositides (PIs) must be coordinated in a spatial- and temporal-restricted manner. The small GTPase Rab5 interacts with two PI 3-kinases, Vps34 and PI3Kβ, suggesting that it regulates the production of 3-PIs at various stages of the early endocytic pathway. Here, we discovered that Rab5 also interacts directly with PI 5- and PI 4-phosphatases and stimulates their activity. Rab5 regulates the production of phosphatidylinositol 3-phosphate (PtdIns[3]P) through a dual mechanism, by directly phosphorylating phosphatidylinositol via Vps34 and by a hierarchical enzymatic cascade of phosphoinositide-3-kinaseβ (PI3Kβ), PI 5-, and PI 4-phosphatases. The functional importance of such an enzymatic pathway is demonstrated by the inhibition of transferrin uptake upon silencing of PI 4-phosphatase and studies in weeble mutant mice, where deficiency of PI 4-phosphatase causes an increase of PtdIns(3,4)P2 and a reduction in PtdIns(3)P. Activation of PI 3-kinase at the plasma membrane is accompanied by the recruitment of Rab5, PI 4-, and PI 5-phosphatases to the cell cortex. Our data provide the first evidence for a dual role of a Rab GTPase in regulating both generation and turnover of PIs via PI kinases and phosphatases to coordinate signaling functions with organelle homeostasis.

scholarly journals Nd6p, a Novel Protein with RCC1-Like Domains Involved in Exocytosis in Paramecium tetraurelia

2005 ◽  
Vol 4 (12) ◽  
pp. 2129-2139 ◽  
Author(s):  
Delphine Gogendeau ◽  
Anne-Marie Keller ◽  
Akira Yanagi ◽  
Jean Cohen ◽  
France Koll
Keyword(s):  
Plasma Membrane ◽  
Membrane Fusion ◽  
Secretory Pathway ◽  
Small Gtpase ◽  
Paramecium Tetraurelia ◽  
Acid Protein ◽  
Nuclear Envelope Assembly ◽  
Regulated Secretory Pathway ◽  
Dense Core Granules ◽  
Intracellular Membrane Fusion

ABSTRACT In Paramecium tetraurelia, the regulated secretory pathway of dense core granules called trichocysts can be altered by mutation and genetically studied. Seventeen nondischarge (ND) genes controlling exocytosis have already been identified by a genetic approach. The site of action of the studied mutations is one of the three compartments, the cytosol, trichocyst, or plasma membrane. The only ND genes cloned to date correspond to mutants affected in the cytosol or in the trichocyst compartment. In this work, we investigated a representative of the third compartment, the plasma membrane, by cloning the ND6 gene. This gene encodes a 1,925-amino-acid protein containing two domains homologous to the regulator of chromosome condensation 1 (RCC1). In parallel, 10 new alleles of the ND6 gene were isolated. Nine of the 12 available mutations mapped in the RCC1-like domains, showing their importance for the Nd6 protein (Nd6p) function. The RCC1 protein is well known for its guanine exchange factor activity towards the small GTPase Ran but also for its involvement in membrane fusion during nuclear envelope assembly. Other proteins with RCC1-like domains are also involved in intracellular membrane fusion, but none has been described yet as involved in exocytosis. The case of Nd6p is thus the first report of such a protein with a documented role in exocytosis.

Translocation of cortactin to the cell periphery is mediated by the small GTPase Rac1

1998 ◽  
Vol 111 (16) ◽  
pp. 2433-2443 ◽  
Author(s):  
S.A. Weed ◽  
Y. Du ◽  
J.T. Parsons
Keyword(s):  
Actin Polymerization ◽  
Intracellular Localization ◽  
Adhesion Formation ◽  
Small Gtpases ◽  
Small Gtpase ◽  
Dominant Negative ◽  
Actin Binding ◽  
Cell Cortex ◽  
Cell Periphery ◽  
Membrane Ruffling

Small GTPases of the Rho family regulate signaling pathways that control actin cytoskeletal structures. In Swiss 3T3 cells, RhoA activation leads to stress fiber and focal adhesion formation, Rac1 to lamellipoda and membrane ruffles, and Cdc42 to microspikes and filopodia. Several downstream molecules mediating these effects have been recently identified. In this report we provide evidence that the intracellular localization of the actin binding protein cortactin, a Src kinase substrate, is regulated by the activation of Rac1. Cortactin redistributes from the cytoplasm into membrane ruffles as a result of growth factor-induced Rac1 activation, and this translocation is blocked by expression of dominant negative Rac1N17. Expression of constitutively active Rac1L61 evoked the translocation of cortactin from cytoplasmic pools into peripheral membrane ruffles. Expression of mutant forms of the serine/threonine kinase PAK1, a downstream effector of Rac1 and Cdc42 recently demonstrated to trigger cortical actin polymerization and membrane ruffling, also led to the translocation of cortactin to the cell cortex, although this was effectively blocked by coexpression of Rac1N17. Collectively these data provide evidence for cortactin as a putative target of Rac1-induced signal transduction events involved in membrane ruffling and lamellipodia formation.

Sign in / Sign up

Export Citation Format

Share Document