scholarly journals Dynamic association of the PI3P-interacting Mon1-Ccz1 GEF with vacuoles is controlled through its phosphorylation by the type 1 casein kinase Yck3

2014 ◽  
Vol 25 (10) ◽  
pp. 1608-1619 ◽  
Author(s):  
Gus Lawrence ◽  
Christopher C. Brown ◽  
Blake A. Flood ◽  
Surya Karunakaran ◽  
Margarita Cabrera ◽  
...  
Keyword(s):  
Fusion Reaction ◽  
Casein Kinase ◽  
Nucleotide Exchange ◽  
Wild Type ◽  
Phosphatidylinositol 3 Kinase ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Phosphatidic Acid Phosphatase ◽  
Phosphatidylinositol 3

Maturation of organelles in the endolysosomal pathway requires exchange of the early endosomal GTPase Rab5/Vps21 for the late endosomal Rab7/Ypt7. The Rab exchange depends on the guanine nucleotide exchange factor activity of the Mon1-Ccz1 heterodimer for Ypt7. Here we investigate vacuole binding and recycling of Mon1-Ccz1. We find that Mon1-Ccz1 is absent on vacuoles lacking the phosphatidic acid phosphatase Pah1, which also lack Ypt7, the phosphatidylinositol 3-kinase Vps34, and the lipid phosphatidylinositol 3-phosphate (PI3P). Interaction of Mon1-Ccz1 with wild-type vacuoles requires PI3P, as shown in competition experiments. We also find that Mon1 is released from vacuoles during the fusion reaction and its release requires its phosphorylation by the type 1 casein kinase Yck3. In contrast, Mon1 is retained on vacuoles lacking Yck3 or when Mon1 phosphorylation sites are mutated. Phosphorylation and release of Mon1 is restored with addition of recombinant Yck3. Together the results show that Mon1 is recruited to endosomes and vacuoles by PI3P and, likely after activating Ypt7, is phosphorylated and released from vacuoles for recycling.

scholarly journals Par3 integrates Tiam1 and phosphatidylinositol 3-kinase signaling to change apical membrane identity

2017 ◽  
Vol 28 (2) ◽  
pp. 252-260 ◽  
Author(s):  
Travis R. Ruch ◽  
David M. Bryant ◽  
Keith E. Mostov ◽  
Joanne N. Engel
Keyword(s):  
Apical Membrane ◽  
Protein Localization ◽  
Apical Surface ◽  
Nucleotide Exchange ◽  
Phosphatidylinositol 3 Kinase ◽  
Signaling Mechanism ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Chemically Induced Dimerization ◽  
Phosphatidylinositol 3

Pathogens can alter epithelial polarity by recruiting polarity proteins to the apical membrane, but how a change in protein localization is linked to polarity disruption is not clear. In this study, we used chemically induced dimerization to rapidly relocalize proteins from the cytosol to the apical surface. We demonstrate that forced apical localization of Par3, which is normally restricted to tight junctions, is sufficient to alter apical membrane identity through its interactions with phosphatidylinositol 3-kinase (PI3K) and the Rac1 guanine nucleotide exchange factor Tiam1. We further show that PI3K activity is required upstream of Rac1, and that simultaneously targeting PI3K and Tiam1 to the apical membrane has a synergistic effect on membrane remodeling. Thus, Par3 coordinates the action of PI3K and Tiam1 to define membrane identity, revealing a signaling mechanism that can be exploited by human mucosal pathogens.

scholarly journals Sbf/MTMR13 coordinates PI(3)P and Rab21 regulation in endocytic control of cellular remodeling

2012 ◽  
Vol 23 (14) ◽  
pp. 2723-2740 ◽  
Author(s):  
Steve Jean ◽  
Sarah Cox ◽  
Eric J. Schmidt ◽  
Fred L. Robinson ◽  
Amy Kiger
Keyword(s):  
Endosomal Trafficking ◽  
Rab Gtpases ◽  
Nucleotide Exchange ◽  
Phosphatidylinositol 3 Kinase ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Membrane Compartment ◽  
Endosomal Pathway ◽  
Gtpase Activation ◽  
Phosphatidylinositol 3

Cells rely on the coordinated regulation of lipid phosphoinositides and Rab GTPases to define membrane compartment fates along distinct trafficking routes. The family of disease-related myotubularin (MTM) phosphoinositide phosphatases includes catalytically inactive members, or pseudophosphatases, with poorly understood functions. We found that Drosophila MTM pseudophosphatase Sbf coordinates both phosphatidylinositol 3-phosphate (PI(3)P) turnover and Rab21 GTPase activation in an endosomal pathway that controls macrophage remodeling. Sbf dynamically interacts with class II phosphatidylinositol 3-kinase and stably recruits Mtm to promote turnover of a PI(3)P subpool essential for endosomal trafficking. Sbf also functions as a guanine nucleotide exchange factor that promotes Rab21 GTPase activation associated with PI(3)P endosomes. Of importance, Sbf, Mtm, and Rab21 function together, along with Rab11-mediated endosomal trafficking, to control macrophage protrusion formation. This identifies Sbf as a critical coordinator of PI(3)P and Rab21 regulation, which specifies an endosomal pathway and cortical control.

scholarly journals αPIX nucleotide exchange factor is activated by interaction with phosphatidylinositol 3-kinase

Oncogene ◽  
1999 ◽  
Vol 18 (41) ◽  
pp. 5680-5690 ◽  
Author(s):  
Shigeto Yoshii ◽  
Masamitsu Tanaka ◽  
Yoshirou Otsuki ◽  
Dong-Yu Wang ◽  
Rong-Jun Guo ◽  
...  
Keyword(s):  
Nucleotide Exchange ◽  
Phosphatidylinositol 3 Kinase ◽  
Exchange Factor ◽  
Nucleotide Exchange Factor ◽  
Phosphatidylinositol 3

scholarly journals The RAC1 activator Tiam1 regulates centriole duplication through controlling PLK4 levels

2020 ◽  
Author(s):  
Andrew P. Porter ◽  
Gavin R. M. White ◽  
Erinn-Lee Ogg ◽  
Helen J. Whalley ◽  
Angeliki Malliri
Keyword(s):  
Cell Cycle ◽  
Guanine Nucleotide Exchange Factor ◽  
S Phase ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Wild Type ◽  
Centriole Duplication ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
F Box Protein

SummaryCentriole duplication is tightly controlled to maintain correct centriole number through the cell cycle. A key component of this control is the regulated degradation of PLK4, the master regulator of centriole duplication. Here we show that the Rac1 guanine nucleotide exchange factor (GEF) Tiam1 localises to centrosomes during S-phase, where it is required for maintenance of normal centriole number. Depletion of Tiam1 leads to an increase in centrosomal PLK4, centriole overduplication and ultimately to lagging chromosomes at anaphase and aneuploidy. The effects of Tiam1 depletion can be rescued by re-expression of wild-type Tiam1 and catalytically inactive (GEF*) Tiam1, but not by Tiam1 mutants unable to bind to the F-box protein βTRCP, implying that Tiam1 regulates PLK4 levels through promoting βTRCP-mediated degradation.

scholarly journals The Rac activator Tiam1 controls tight junction biogenesis in keratinocytes through binding to and activation of the Par polarity complex

2005 ◽  
Vol 170 (7) ◽  
pp. 1029-1037 ◽  
Author(s):  
Alexander E.E. Mertens ◽  
Tomasz P. Rygiel ◽  
Cristina Olivo ◽  
Rob van der Kammen ◽  
John G. Collard
Keyword(s):  
Cell Polarity ◽  
Epidermal Keratinocytes ◽  
Nucleotide Exchange ◽  
Wild Type ◽  
Invasion And Metastasis ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
T Lymphoma ◽  
Maturation Defect ◽  
Membrane Sealing

The GTPases Rac and Cdc42 play a pivotal role in the establishment of cell polarity by stimulating biogenesis of tight junctions (TJs). In this study, we show that the Rac-specific guanine nucleotide exchange factor Tiam1 (T-lymphoma invasion and metastasis) controls the cell polarity of epidermal keratinocytes. Similar to wild-type (WT) keratinocytes, Tiam1-deficient cells establish primordial E-cadherin–based adhesions, but subsequent junction maturation and membrane sealing are severely impaired. Tiam1 and V12Rac1 can rescue the TJ maturation defect in Tiam1-deficient cells, indicating that this defect is the result of impaired Tiam1–Rac signaling. Tiam1 interacts with Par3 and aPKCζ, which are two components of the conserved Par3–Par6–aPKC polarity complex, and triggers biogenesis of the TJ through the activation of Rac and aPKCζ, which is independent of Cdc42. Rac is activated upon the formation of primordial adhesions (PAs) in WT but not in Tiam1-deficient cells. Our data indicate that Tiam1-mediated activation of Rac in PAs controls TJ biogenesis and polarity in epithelial cells by association with and activation of the Par3–Par6–aPKC polarity complex.

scholarly journals Rab5-family guanine nucleotide exchange factors bind retromer and promote its recruitment to endosomes

2015 ◽  
Vol 26 (6) ◽  
pp. 1119-1128 ◽  
Author(s):  
Bjorn D. M. Bean ◽  
Michael Davey ◽  
Jamie Snider ◽  
Matthew Jessulat ◽  
Viktor Deineko ◽  
...  
Keyword(s):  
Mammalian Cells ◽  
Guanine Nucleotide Exchange Factors ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Phosphatidylinositol 3 Kinase ◽  
Endosomal Membrane ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factors ◽  
New Yeast ◽  
Phosphatidylinositol 3

The retromer complex facilitates the sorting of integral membrane proteins from the endosome to the late Golgi. In mammalian cells, the efficient recruitment of retromer to endosomes requires the lipid phosphatidylinositol 3-phosphate (PI3P) as well as Rab5 and Rab7 GTPases. However, in yeast, the role of Rabs in recruiting retromer to endosomes is less clear. We identified novel physical interactions between retromer and the Saccharomyces cerevisiae VPS9-domain Rab5-family guanine nucleotide exchange factors (GEFs) Muk1 and Vps9. Furthermore, we identified a new yeast VPS9 domain-containing protein, VARP-like 1 (Vrl1), which is related to the human VARP protein. All three VPS9 domain–containing proteins show localization to endosomes, and the presence of any one of them is necessary for the endosomal recruitment of retromer. We find that expression of an active VPS9-domain protein is required for correct localization of the phosphatidylinositol 3-kinase Vps34 and the production of endosomal PI3P. These results suggest that VPS9 GEFs promote retromer recruitment by establishing PI3P-enriched domains at the endosomal membrane. The interaction of retromer with distinct VPS9 GEFs could thus link GEF-dependent regulatory inputs to the temporal or spatial coordination of retromer assembly or function.

scholarly journals Depletion of Ric-8B leads to reduced mTORC2 activity

2019 ◽  
Author(s):  
Maíra H. Nagai ◽  
Luciana M. Gutiyama ◽  
Victor P. S. Xavier ◽  
Cleiton F. Machado ◽  
Alice H. Reis ◽  
...  
Keyword(s):  
Signaling Pathways ◽  
Neural Tube ◽  
Adult Brain ◽  
Nucleotide Exchange ◽  
Wild Type ◽  
Hypomorphic Mutation ◽  
Downstream Target ◽  
Cellular Processes ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor

AbstractmTOR, a serine/threonine protein kinase that is involved in a series of critical cellular processes, can be found in two functionally distinct complexes, mTORC1 and mTORC2. In contrast to mTORC1, little is known about the mechanisms that regulate mTORC2. Here we show that mTORC2 activity is reduced in mice with a hypomorphic mutation of the Ric-8B gene. Ric-8B is a highly conserved protein that acts as a non-canonical guanine nucleotide exchange factor (GEF) for heterotrimeric Gαs/olf type subunits. We found that Ric-8B hypomorph embryos are smaller than their wild type littermates, fail to close the neural tube in the cephalic region and die during mid-embryogenesis. Comparative transcriptome analysis revealed that signaling pathways involving GPCRs and G proteins are dysregulated in the Ric-8B mutant embryos. Interestingly, this analysis also revealed an unexpected impairment of the mTOR signaling pathway.Phosphorylation of Akt at Ser 473 is downregulated in the Ric-8B mutant embryos, indicating a decreased activity of mTORC2. In contrast, phosphorylation of S6, a downstream target of mTORC1, is unaltered. Knockdown of the endogenous Ric-8B gene in HEK293T cells leads to reduced phosphorylation levels of Akt at Ser 473, but not of S6, further supporting the selective involvement of Ric-8B in mTORC2 activity. Our results reveal a crucial role for Ric-8B in development and provide novel insights into the signals that regulate mTORC2 activity.Author SummaryGene inactivation in mice can be used to identify genes that are involved in important biological processes and that may contribute to disease. By using this approach, we found that the Ric-8B gene is essential for embryogenesis and for the normal development of the nervous system. Ric-8B mutant mouse embryos are smaller than their wild type littermates and show neural tube defects at the cranial region. This approach also allowed us to identify the biological pathways that are involved in the observed phenotypes, the G protein and mTORC2 signaling pathways. mTORC2 plays particular important roles also in the adult brain, and has been implicated in neurological disorders. Ric-8B is highly conserved in mammals, including humans. Our mutant mice provide a model to study the complex molecular and cellular processes underlying the interplay between Ric-8B and mTORC2 in neuronal function.

scholarly journals The RAC1 activator Tiam1 regulates centriole duplication through controlling PLK4 levels

2021 ◽  
pp. jcs.252502
Author(s):  
Andrew P. Porter ◽  
Hannah Reed ◽  
Gavin R. M. White ◽  
Erinn-Lee Ogg ◽  
Helen J. Whalley ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Guanine Nucleotide Exchange Factor ◽  
S Phase ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Wild Type ◽  
Centriole Duplication ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
F Box Protein

Centriole duplication is tightly controlled to maintain correct centriole number through the cell cycle. Key to this is the regulated degradation of PLK4, the master regulator of centriole duplication. Here we show that the Rac1 guanine nucleotide exchange factor (GEF) Tiam1 localises to centrosomes during S-phase, where it is required for maintenance of normal centriole number. Depletion of Tiam1 leads to an increase in centrosomal PLK4 and centriole overduplication, whereas overexpression of Tiam1 can restrict centriole overduplication. Ultimately Tiam1 depletion leads to lagging chromosomes at anaphase and aneuploidy, potential drivers of malignant progression. The effects of Tiam1 depletion on centrosomal PLK4 levels and centriole overduplication can be rescued by re-expression of both wild-type Tiam1 and catalytically inactive (GEF*) Tiam1, but not by Tiam1 mutants unable to bind to the F-box protein βTRCP, implying that Tiam1 regulates PLK4 levels through promoting βTRCP-mediated degradation independently of Rac1 activation.

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