scholarly journals Roles for a lipid phosphatase in the activation of its opposing lipid kinase

2020 ◽  
Vol 31 (17) ◽  
pp. 1835-1845
Author(s):  
Bethany S. Strunk ◽  
Noah Steinfeld ◽  
Sora Lee ◽  
Natsuko Jin ◽  
Cecilia Muñoz-Rivera ◽  
...  
Keyword(s):  
Protein Complex ◽  
Dynamic Regulation ◽  
Lipid Kinase ◽  
Lipid Phosphatase ◽  
Phosphoinositide Phosphatase ◽  
Turn Over

The phosphoinositide phosphatase Fig4 is predicted to turn over the signaling lipid PI3,5P2. It is shown that a major role of Fig4 is to elevate PI3,5P2 via dynamic regulation of the protein complex that activates its opposing lipid kinase, Fab1.

scholarly journals Assembly of a Fab1 Phosphoinositide Kinase Signaling Complex Requires the Fig4 Phosphoinositide Phosphatase

2008 ◽  
Vol 19 (10) ◽  
pp. 4273-4286 ◽  
Author(s):  
Roberto J. Botelho ◽  
Jem A. Efe ◽  
David Teis ◽  
Scott D. Emr
Keyword(s):  
Protein Complex ◽  
Functional Unit ◽  
Dual Function ◽  
Dual Roles ◽  
Lipid Kinase ◽  
Unknown Mechanism ◽  
Signaling Complex ◽  
Lipid Phosphatase ◽  
Phosphoinositide Phosphatase ◽  
Phosphoinositide Kinase

Phosphatidylinositol-3,5-bisphosphate [PtdIns(3,5)P2] regulates several vacuolar functions, including acidification, morphology, and membrane traffic. The lipid kinase Fab1 converts phosphatidylinositol-3-phosphate [PtdIns(3)P] to PtdIns(3,5)P2. PtdIns(3,5)P2levels are controlled by the adaptor-like protein Vac14 and the Fig4 PtdIns(3,5)P2-specific 5-phosphatase. Interestingly, Vac14 and Fig4 serve a dual function: they are both implicated in the synthesis and turnover of PtdIns(3,5)P2by an unknown mechanism. We now show that Fab1, through its chaperonin-like domain, binds to Vac14 and Fig4 and forms a vacuole-associated signaling complex. The Fab1 complex is tethered to the vacuole via an interaction between the FYVE domain in Fab1 and PtdIns(3)P on the vacuole. Moreover, Vac14 and Fig4 bind to each other directly and are mutually dependent for interaction with the Fab1 kinase. Our observations identify a protein complex that incorporates the antagonizing Fab1 lipid kinase and Fig4 lipid phosphatase into a common functional unit. We propose a model explaining the dual roles of Vac14 and Fig4 in the synthesis and turnover of PtdIns(3,5)P2.

The photoreceptor cytoskeleton visualized

1992 ◽  
Vol 50 (1) ◽  
pp. 480-481
Author(s):  
Beth Burnside
Keyword(s):  
Outer Segment ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Cell Polarization ◽  
Synaptic Proteins ◽  
Cell Functions ◽  
Vertebrate Photoreceptor ◽  
Numerous Cell ◽  
Turn Over

The vertebrate photoreceptor provides a drammatic example of cell polarization. Specialized to carry out phototransduction at its distal end and to synapse with retinal interneurons at its proximal end, this long slender cell has a uniquely polarized morphology which is reflected in a similarly polarized cytoskeleton. Membranes bearing photopigment are localized in the outer segment, a modified sensory cilium. Sodium pumps which maintain the dark current critical to photosensory transduction are anchored along the inner segment plasma membrane between the outer segment and the nucleus.Proximal to the nucleus is a slender axon terminating in specialized invaginating synapses with other neurons of the retina. Though photoreceptor diameter is only 3-8u, its length from the tip of the outer segment to the synapse may be as great as 200μ. This peculiar linear cell morphology poses special logistical problems and has evoked interesting solutions for numerous cell functions. For example, the outer segment membranes turn over by means of a unique mechanism in which new disks are continuously added at the proximal base of the outer segment, while effete disks are discarded at the tip and phagocytosed by the retinal pigment epithelium. Outer segment proteins are synthesized in the Golgi near the nucleus and must be transported north through the inner segment to their sites of assembly into the outer segment, while synaptic proteins must be transported south through the axon to the synapse.The role of the cytoskeleton in photoreceptor motile processes is being intensely investigated in several laboratories.

scholarly journals Screening Assay for Small-Molecule Inhibitors of Synaptojanin 1, a Synaptic Phosphoinositide Phosphatase

2013 ◽  
Vol 19 (4) ◽  
pp. 585-594 ◽  
Author(s):  
Laura Beth J. McIntire ◽  
Kyu-In Lee ◽  
Belle Chang-Ileto ◽  
Gilbert Di Paolo ◽  
Tae-Wan Kim
Keyword(s):  
Amyloid Β ◽  
Receptor Trafficking ◽  
Water Soluble ◽  
Amyloid Β Peptide ◽  
Screening Assay ◽  
Vesicle Recycling ◽  
Lipid Phosphatase ◽  
Phosphoinositide Phosphatase ◽  
Synaptojanin 1 ◽  
Behavioral Impairments

Elevation of amyloid β-peptide (Aβ) is critically associated with Alzheimer disease (AD) pathogenesis. Aβ-induced synaptic abnormalities, including altered receptor trafficking and synapse loss, have been linked to cognitive deficits in AD. Recent work implicates a lipid critical for neuronal function, phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2], in Aβ-induced synaptic and behavioral impairments. Synaptojanin 1 (Synj1), a lipid phosphatase mediating the breakdown of PI(4,5)P2, has been shown to play a role in synaptic vesicle recycling and receptor trafficking in neurons. Heterozygous deletion of Synj1 protected neurons from Aβ-induced synaptic loss and restored learning and memory in a mouse model of AD. Thus, inhibition of Synj1 may ameliorate Aβ-associated impairments, suggesting Synj1 as a potential therapeutic target. To this end, we developed a screening assay for Synj1 based on detection of inorganic phosphate liberation from a water-soluble, short-chain PI(4,5)P2. The assay displayed saturable kinetics and detected Synj1’s substrate preference for PI(4,5)P2 over PI(3,4,5)P3. The assay will enable identification of novel Synj1 inhibitors that have potential utility as chemical probes to dissect the cellular role of Synj1 as well as potential to prevent or reverse AD-associated synaptic abnormalities.

Comparative phytohormone profiles, lipid kinase and lipid phosphatase activities in barley aleurone, coleoptile, and root tissues

2012 ◽  
Vol 58 ◽  
pp. 83-88 ◽  
Author(s):  
Maria V. Meringer ◽  
Ana L. Villasuso ◽  
Susana J. Pasquaré ◽  
Norma M. Giusto ◽  
Estela E. Machado ◽  
...  
Keyword(s):  
Lipid Kinase ◽  
Phosphatase Activities ◽  
Lipid Phosphatase ◽  
Barley Aleurone ◽  
Root Tissues

scholarly journals Genetic disruption of calpain correlates with loss of membrane blebbing and differential expression of RhoGDI-1, cofilin and tropomyosin

2008 ◽  
Vol 411 (3) ◽  
pp. 657-666 ◽  
Author(s):  
Anna K. Larsen ◽  
René Lametsch ◽  
John S. Elce ◽  
Jørgen K. Larsen ◽  
Bo Thomsen ◽  
...  
Keyword(s):  
Membrane Surface ◽  
Proteome Analysis ◽  
Time Lapse ◽  
Wild Type ◽  
Genetic Rescue ◽  
Dynamic Regulation ◽  
Membrane Blebbing ◽  
Signalling Molecules ◽  
Membrane Blebs

Dynamic regulation of the actin cytoskeleton is important for cell motility, spreading and the formation of membrane surface extensions such as lamellipodia, ruffles and blebs. The ubiquitous calpains contribute to integrin-mediated cytoskeletal remodelling during cell migration and spreading, by cleavage of focal adhesion components and signalling molecules. In the present study, the live-cell morphology of calpain-knockout and wild-type cells was examined by time-lapse fluorescence microscopy, and a role of calpain in mediating the formation of sporadic membrane blebs was established. Membrane blebbing was significantly reduced in calpain-knockout cells, and genetic rescue fully restored the wild-type phenotype in knockout cells. Proteomic comparison of wild-type and knockout cells identified decreased levels of RhoGDI-1 (Rho GDP-dissociation inhibitor) and cofilin 1, and increased levels of tropomyosin in calpain-knockout cells, suggesting a role of calpain in regulating membrane extensions involving these proteins. RhoGDI, cofilin and tropomyosin are known regulators of actin filament dynamics and membrane extensions. The reduced levels of RhoGDI-1 in calpain-knockout cells observed by proteome analysis were confirmed by immunoblotting. Genetic rescue of the calpain-knockout cells enhanced RhoGDI-1-expression 2-fold above that normally present in wild-type cells. These results suggest a regulatory connection between calpain and RhoGDI-1 in promoting formation of membrane blebs.

scholarly journals Differential Role of PTEN Phosphatase in Chemotactic Growth Cone Guidance

2013 ◽  
Vol 288 (29) ◽  
pp. 20837-20842 ◽  
Author(s):  
Steven J. Henle ◽  
Lucas P. Carlstrom ◽  
Thomas R. Cheever ◽  
John R. Henley
Keyword(s):  
Growth Cone ◽  
Essential Feature ◽  
Pten Expression ◽  
Spinal Neurons ◽  
Phosphoinositide Phosphatase ◽  
Integrin Clustering ◽  
Myelin Associated Glycoprotein ◽  
Phosphatase And Tensin Homologue ◽  
Regenerative Therapies

Negatively targeting the tumor suppressor and phosphoinositide phosphatase PTEN (phosphatase and tensin homologue) promotes axon regrowth after injury. How PTEN functions in axon guidance has remained unknown. Here we report the differential role of PTEN in chemotactic guidance of axonal growth cones. Down-regulating PTEN expression in Xenopus laevis spinal neurons selectively abolished growth cone chemorepulsion but permitted chemoattraction. These findings persisted during cAMP-dependent switching of turning behaviors. Live cell imaging using a GFP biosensor revealed rapid PTEN-dependent depression of phosphatidylinositol 3,4,5-trisphosphate levels in the growth cone induced by the repellent myelin-associated glycoprotein. Moreover, down-regulating PTEN expression blocked negative remodeling of β1-integrin adhesions triggered by myelin-associated glycoprotein, yet permitted integrin clustering by a positive chemotropic treatment. Thus, PTEN negatively regulates growth cone phosphatidylinositol 3,4,5-trisphosphate levels and mediates chemorepulsion, whereas chemoattraction is PTEN-independent. Regenerative therapies targeting PTEN may therefore suppress growth cone repulsion to soluble cues while permitting attractive guidance, an essential feature for re-forming functional neural circuits.

scholarly journals Retromer subunit, VPS29, regulates synaptic transmission and is required for endolysosomal function in the aging brain

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Hui Ye ◽  
Shamsideen A Ojelade ◽  
David Li-Kroeger ◽  
Zhongyuan Zuo ◽  
Liping Wang ◽  
...  
Keyword(s):  
Synaptic Transmission ◽  
Protein Complex ◽  
Adult Brain ◽  
Aging Brain ◽  
Gtpase Activating Protein ◽  
Ultrastructural Evidence ◽  
Aging Adults ◽  
And Function ◽  
Brain Homeostasis

Retromer, including Vps35, Vps26, and Vps29, is a protein complex responsible for recycling proteins within the endolysosomal pathway. Although implicated in both Parkinson’s and Alzheimer’s disease, our understanding of retromer function in the adult brain remains limited, in part because Vps35 and Vps26 are essential for development. In Drosophila, we find that Vps29 is dispensable for embryogenesis but required for retromer function in aging adults, including for synaptic transmission, survival, and locomotion. Unexpectedly, in Vps29 mutants, Vps35 and Vps26 proteins are normally expressed and associated, but retromer is mislocalized from neuropil to soma with the Rab7 GTPase. Further, Vps29 phenotypes are suppressed by reducing Rab7 or overexpressing the GTPase activating protein, TBC1D5. With aging, retromer insufficiency triggers progressive endolysosomal dysfunction, with ultrastructural evidence of impaired substrate clearance and lysosomal stress. Our results reveal the role of Vps29 in retromer localization and function, highlighting requirements for brain homeostasis in aging.

pVHL-mediated SMAD3 degradation suppresses TGF-β signaling

2021 ◽  
Vol 221 (1) ◽  
Author(s):  
Jun Zhou ◽  
Yasamin Dabiri ◽  
Rodrigo A. Gama-Brambila ◽  
Shahrouz Ghafoory ◽  
Mukaddes Altinbay ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Transforming Growth Factor ◽  
Transforming Growth Factor Β ◽  
Tissue Homeostasis ◽  
Wing Development ◽  
Dynamic Regulation ◽  
Drosophila Wing ◽  
Wing Growth ◽  
Expression And Activity

Transforming growth factor β (TGF-β) signaling plays a fundamental role in metazoan development and tissue homeostasis. However, the molecular mechanisms concerning the ubiquitin-related dynamic regulation of TGF-β signaling are not thoroughly understood. Using a combination of proteomics and an siRNA screen, we identify pVHL as an E3 ligase for SMAD3 ubiquitination. We show that pVHL directly interacts with conserved lysine and proline residues in the MH2 domain of SMAD3, triggering degradation. As a result, the level of pVHL expression negatively correlates with the expression and activity of SMAD3 in cells, Drosophila wing, and patient tissues. In Drosophila, loss of pVHL leads to the up-regulation of TGF-β targets visible in a downward wing blade phenotype, which is rescued by inhibition of SMAD activity. Drosophila pVHL expression exhibited ectopic veinlets and reduced wing growth in a similar manner as upon loss of TGF-β/SMAD signaling. Thus, our study demonstrates a conserved role of pVHL in the regulation of TGF-β/SMAD3 signaling in human cells and Drosophila wing development.

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