Regulation of RabGAPs involved in insulin action

2018 ◽  
Vol 46 (3) ◽  
pp. 683-690 ◽  
Author(s):  
Samaneh Mafakheri ◽  
Alexandra Chadt ◽  
Hadi Al-Hasani
Keyword(s):  
Insulin Action ◽  
Glucose Transporter ◽  
Rab Gtpase ◽  
Rab Proteins ◽  
Rab Gtpases ◽  
Gtp Hydrolysis ◽  
Gtpase Activating Proteins ◽  
Glucose Transporter Glut4 ◽  
Related Proteins

Rab (Ras-related proteins in brain) GTPases are key proteins responsible for a multiplicity of cellular trafficking processes. Belonging to the family of monomeric GTPases, they are regulated by cycling between their active GTP-bound and inactive GDP-bound conformations. Despite possessing a slow intrinsic GTP hydrolysis activity, Rab proteins rely on RabGAPs (Rab GTPase-activating proteins) that catalyze GTP hydrolysis and consequently inactivate the respective Rab GTPases. Two related RabGAPs, TBC1D1 and TBC1D4 (=AS160) have been described to be associated with obesity-related traits and type 2 diabetes in both mice and humans. Inactivating mutations of TBC1D1 and TBC1D4 lead to substantial changes in trafficking and subcellular distribution of the insulin-responsive glucose transporter GLUT4, and to subsequent alterations in energy substrate metabolism. The activity of the RabGAPs is controlled through complex phosphorylation events mediated by protein kinases including AKT and AMPK, and by putative regulatory interaction partners. However, the dynamics and downstream events following phosphorylation are not well understood. This review focuses on the specific role and regulation of TBC1D1 and TBC1D4 in insulin action.

scholarly journals Emerging role for AS160/TBC1D4 and TBC1D1 in the regulation of GLUT4 traffic

2008 ◽  
Vol 295 (1) ◽  
pp. E29-E37 ◽  
Author(s):  
Kei Sakamoto ◽  
Geoffrey D. Holman
Keyword(s):  
Glucose Transporter ◽  
Cell Types ◽  
Small Gtpase ◽  
Rab Gtpase ◽  
Rab Proteins ◽  
Energy Status ◽  
Vesicle Traffic ◽  
Vesicular Traffic ◽  
Gtpase Activating Proteins ◽  
Glucose Transporter Glut4

Vesicular traffic of the glucose transporter GLUT4 occurs in response to insulin, muscle contraction, and metabolic stimuli that lead to changes in the energy status of the cell. These stimuli are associated with linked kinase cascades that lead to changes in glucose uptake that meet the energy challenges imposed on the highly regulated cell types in insulin-responsive tissues. The need to mechanistically link these kinase-associated stimuli to identifiable intermediates in vesicular traffic has long been known but has been difficult to fulfill. The Rab-GTPase-activating proteins AS160 and TBC1D1 have now emerged as strong candidates to fill this void. Here we review the initial discovery of these proteins as phosphorylated substrates for Akt and the more recent emerging data that indicate that these proteins are substrates for additional kinases that are downstream of contraction and energy status signaling. The mechanism of coupling these phosphorylated proteins to vesicle traffic appears to be dependent on linking to small GTPase of the Rab family. We examine the current state of a hypothesis that suggests that phosphorylation of the Rab-GTPase-activating proteins leads to increased GTP loading of Rab proteins on GLUT4 vesicles and subsequently to increased interaction with Rab effectors that control GLUT4 vesicle translocation.

A model for Rab GTPase localization

2005 ◽  
Vol 33 (4) ◽  
pp. 627-630 ◽  
Author(s):  
S. Pfeffer
Keyword(s):  
Steady State ◽  
Cellular Localization ◽  
Rab Gtpase ◽  
Rab Proteins ◽  
Rab Gtpases ◽  
Macromolecular Assemblies ◽  
Complex Interactions ◽  
Membrane Compartment ◽  
Membrane Bound ◽  
Distinct Membrane

The human genome encodes almost 70 Rab GTPases. These proteins are C-terminally geranylgeranylated and are localized to the surfaces of distinct membrane-bound compartments in eukaryotic cells. This mini review presents a working model for how Rabs achieve and maintain their steady-state localizations. Data from a number of laboratories suggest that Rabs participate in the generation of macromolecular assemblies that generate functional microdomains within a given membrane compartment. Our data suggest that these complex interactions are important for the cellular localization of Rab proteins at steady state.

scholarly journals Rab GTPases: Emerging Oncogenes and Tumor Suppressive Regulators for the Editing of Survival Pathways in Cancer

Cancers ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 259 ◽  
Author(s):  
Priya D. Gopal Krishnan ◽  
Emily Golden ◽  
Eleanor A. Woodward ◽  
Nathan J. Pavlos ◽  
Pilar Blancafort
Keyword(s):  
Membrane Trafficking ◽  
Molecular Mechanisms ◽  
Intracellular Localization ◽  
Cellular Migration ◽  
Rab Gtpase ◽  
Rab Proteins ◽  
Rab Gtpases ◽  
Aberrant Expression ◽  
Post Translational Modifications ◽  
Survival Pathways

The Rab GTPase family of proteins are mediators of membrane trafficking, conferring identity to the cell membranes. Recently, Rab and Rab-associated factors have been recognized as major regulators of the intracellular positioning and activity of signaling pathways regulating cell growth, survival and programmed cell death or apoptosis. Membrane trafficking mediated by Rab proteins is controlled by intracellular localization of Rab proteins, Rab-membrane interactions and GTP-activation processes. Aberrant expression of Rab proteins has been reported in multiple cancers such as lung, brain and breast malignancies. Mutations in Rab-coding genes and/or post-translational modifications in their protein products disrupt the cellular vesicle trafficking network modulating tumorigenic potential, cellular migration and metastatic behavior. Conversely, Rabs also act as tumor suppressive factors inducing apoptosis and inhibiting angiogenesis. Deconstructing the signaling mechanisms modulated by Rab proteins during apoptosis could unveil underlying molecular mechanisms that may be exploited therapeutically to selectively target malignant cells.

scholarly journals AS160, the Akt substrate regulating GLUT4 translocation, has a functional Rab GTPase-activating protein domain

2005 ◽  
Vol 391 (1) ◽  
pp. 87-93 ◽  
Author(s):  
Cristinel P. Mîinea ◽  
Hiroyuki Sano ◽  
Susan Kane ◽  
Eiko Sano ◽  
Mitsunori Fukuda ◽  
...  
Keyword(s):  
Glucose Transporter ◽  
Protein Domain ◽  
Rab Gtpase ◽  
Significant Activity ◽  
Glut4 Translocation ◽  
Gtpase Activating Protein ◽  
Akt Phosphorylation ◽  
Intracellular Vesicles ◽  
Glucose Transporter Glut4 ◽  
Protein Kinase Akt

Recently, we described a 160 kDa protein (designated AS160, for Akt substrate of 160 kDa) with a predicted Rab GAP (GTPase-activating protein) domain that is phosphorylated on multiple sites by the protein kinase Akt. Phosphorylation of AS160 in adipocytes is required for insulin-stimulated translocation of the glucose transporter GLUT4 to the plasma membrane. The aim of the present study was to determine whether AS160 is in fact a GAP for Rabs, and, if so, what its specificity is. We first identified a group of 16 Rabs in a preparation of intracellular vesicles containing GLUT4 by MS. We then prepared the recombinant GAP domain of AS160 and examined its activity against many of these Rabs, as well as several others. The GAP domain was active against Rabs 2A, 8A, 10 and 14. There was no significant activity against 14 other Rabs. GAP activity was further validated by the finding that the recombinant GAP domain with the predicted catalytic arginine residue replaced by lysine was inactive. Finally, it was found by immunoblotting that Rabs 2A, 8A and 14 are present in GLUT4 vesicles. These results indicate that AS160 is a Rab GAP, and suggest novel Rabs that may participate in GLUT4 translocation.

scholarly journals Deciphering the LRRK code: LRRK1 and LRRK2 phosphorylate distinct Rab proteins and are regulated by diverse mechanisms

2020 ◽  
Author(s):  
Asad U. Malik ◽  
Athanasios Karapetsas ◽  
Raja S. Nirujogi ◽  
Sebastian Mathea ◽  
Prosenjit Pal ◽  
...  
Keyword(s):  
Kinase Inhibitor ◽  
Growth Factor Receptor ◽  
Binding Motif ◽  
Rab Proteins ◽  
Rab Gtpases ◽  
Missense Mutations ◽  
Knock Out ◽  
Equivalent Site ◽  
Effector Binding

AbstractMuch attention has focused on LRRK2, as autosomal dominant missense mutations that enhance its kinase activity cause inherited Parkinson’s disease. LRRK2 regulates biology by phosphorylating a subset of Rab GTPases including Rab8A and Rab10 within its effector binding motif. In this study we explore whether LRRK1, a less studied homologue of LRRK2 that regulates growth factor receptor trafficking and osteoclast biology might also phosphorylate Rab proteins. Using mass spectrometry, we found that the endogenous Rab7A protein, phosphorylated at Ser72 was most impacted by LRRK1 knock-out. This residue is not phosphorylated by LRRK2 but lies at the equivalent site targeted by LRRK2 on Rab8A and Rab10. Accordingly, recombinant LRRK1 efficiently phosphorylated Rab7A at Ser72, but not Rab8A or Rab10. Employing a novel phospho-specific antibody, we found that phorbol ester stimulation of mouse embryonic fibroblasts markedly enhanced phosphorylation of Rab7A at Ser72 via LRRK1. We identify two LRRK1 mutations (K746G and I1412T), equivalent to the LRRK2 R1441G and I2020T Parkinson’s mutations, that enhance LRRK1 mediated phosphorylation of Rab7A. We demonstrate that two regulators of LRRK2 namely Rab29 and VPS35[D620N], do not influence LRRK1. Widely used LRRK2 inhibitors do not inhibit LRRK1, but we identify a promiscuous Type-2 tyrosine kinase inhibitor termed GZD-824 that inhibits both LRRK1 and LRRK2. Finally, we show that interaction of Rab7A with its effector RILP is not affected by high stoichiometry LRRK1 phosphorylation. Altogether, these finding reinforce the idea that the LRRK enzymes have evolved as major regulators of Rab biology.

Muscle cells engage Rab8A and myosin Vb in insulin-dependent GLUT4 translocation

2008 ◽  
Vol 295 (4) ◽  
pp. C1016-C1025 ◽  
Author(s):  
Shuhei Ishikura ◽  
Amira Klip
Keyword(s):  
Glucose Transporter ◽  
Muscle Cells ◽  
Rab Gtpase ◽  
Glut4 Translocation ◽  
Interacting Protein ◽  
Akt Activation ◽  
Gtpase Activating Proteins ◽  
Insulin Dependent ◽  
Myosin Vb

Insulin causes translocation of glucose transporter 4 (GLUT4) to the membrane of muscle and fat cells, a process requiring Akt activation. Two Rab-GTPase-activating proteins (Rab-GAP), AS160 and TBC1D1, were identified as Akt substrates. AS160 phosphorylation is required for insulin-stimulated GLUT4 translocation, but the participation of TBC1D1 on muscle cell GLUT4 is unknown. Moreover, there is controversy as to the AS160/TBC1D1 target Rabs in fat and muscle cells, and Rab effectors are unknown. Here we examined the effect of knockdown of AS160, TBC1D1, and Rabs 8A, 8B, 10, and 14 (in vitro substrates of AS160 and TBC1D1 Rab-GAP activities) on insulin-induced GLUT4 translocation in L6 muscle cells. Silencing AS160 or TBC1D1 increased surface GLUT4 in unstimulated cells but did not prevent insulin-induced GLUT4 translocation. Knockdown of Rab8A and Rab14, but not of Rab8B or Rab10, inhibited insulin-induced GLUT4 translocation. Furthermore, silencing Rab8A or Rab14 but not Rab8B or Rab10 restored the basal-state intracellular retention of GLUT4 impaired by AS160 or TBC1D1 knockdown. Lastly, overexpression of a fragment of myosin Vb, a recently identified Rab8A-interacting protein, inhibited insulin-induced GLUT4 translocation and altered the subcellular distribution of GTP-loaded Rab8A. These results support a model whereby AS160, Rab8A, and myosin Vb are required for insulin-induced GLUT4 translocation in muscle cells, potentially as part of a linear signaling cascade.

scholarly journals Rab GTPases: master regulators that establish the secretory and endocytic pathways

2017 ◽  
Vol 28 (6) ◽  
pp. 712-715 ◽  
Author(s):  
Suzanne R. Pfeffer
Keyword(s):  
Membrane Trafficking ◽  
Membrane Microdomains ◽  
Rab Gtpase ◽  
Rab Proteins ◽  
Rab Gtpases ◽  
Nucleotide Exchange ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factors ◽  
Open Questions ◽  
Endocytic Pathways

Several of the most important discoveries in the field of membrane traffic have come from studies of Rab GTPases by Marino Zerial and Peter Novick and their colleagues. Zerial was the first to discover that Rab GTPases represent identity markers for different membrane-bound compartments, and each Rab organizes a collection of specific effectors into function-specifying membrane microdomains to carry out receptor trafficking. Novick discovered that the order (and thus polarity) of Rab GTPases along the secretory and endocytic pathways are established by their specific, cognate guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs), which partner with one Rab to regulate the subsequent- and prior-acting Rabs. Such so-called Rab cascades have evolved to establish domains that contain unique Rab proteins and their cognate effectors, which drive all steps of membrane trafficking. These findings deserve much broader recognition by the biomedical research community and are highlighted here, along with open questions that require serious attention for full understanding of the molecular basis of Rab GTPase-regulated membrane trafficking in eukaryotic cells.

scholarly journals Substrate specificity and effect on GLUT4 translocation of the Rab GTPase-activating protein Tbc1d1

2007 ◽  
Vol 403 (2) ◽  
pp. 353-358 ◽  
Author(s):  
William G. Roach ◽  
Jose A. Chavez ◽  
Cristinel P. Mîinea ◽  
Gustav E. Lienhard
Keyword(s):  
Plasma Membrane ◽  
Glucose Transporter ◽  
Insulin Treatment ◽  
Ectopic Expression ◽  
Rab Gtpase ◽  
Glut4 Translocation ◽  
Gtpase Activating Protein ◽  
Insulin Stimulation ◽  
Glucose Transporter Glut4 ◽  
Stimulation Of

Insulin stimulation of the trafficking of the glucose transporter GLUT4 to the plasma membrane is controlled in part by the phosphorylation of the Rab GAP (GTPase-activating protein) AS160 (also known as Tbc1d4). Considerable evidence indicates that the phosphorylation of this protein by Akt (protein kinase B) leads to suppression of its GAP activity and results in the elevation of the GTP form of a critical Rab. The present study examines a similar Rab GAP, Tbc1d1, about which very little is known. We found that the Rab specificity of the Tbc1d1 GAP domain is identical with that of AS160. Ectopic expression of Tbc1d1 in 3T3-L1 adipocytes blocked insulin-stimulated GLUT4 translocation to the plasma membrane, whereas a point mutant with an inactive GAP domain had no effect. Insulin treatment led to the phosphorylation of Tbc1d1 on an Akt site that is conserved between Tbc1d1 and AS160. These results show that Tbc1d1 regulates GLUT4 translocation through its GAP activity, and is a likely Akt substrate. An allele of Tbc1d1 in which Arg125 is replaced by tryptophan has very recently been implicated in susceptibility to obesity by genetic analysis. We found that this form of Tbc1d1 also inhibited GLUT4 translocation and that this effect also required a functional GAP domain.

Transcriptional regulation of the insulin-responsive glucose transporter GLUT4 gene: from physiology to pathology

2008 ◽  
Vol 295 (1) ◽  
pp. E38-E45 ◽  
Author(s):  
Eddy Karnieli ◽  
Michal Armoni
Keyword(s):  
Gene Expression ◽  
Glucose Metabolism ◽  
Glucose Transporter ◽  
Metabolic Demand ◽  
Protein Levels ◽  
Rate Limiting Step ◽  
Glucose Transporter Glut4 ◽  
And Function ◽  
Glut4 Gene Expression

The insulin-responsive glucose transporter 4 (GLUT4) plays a key role in glucose uptake and metabolism in insulin target tissues. Being a rate-limiting step in glucose metabolism, the expression and function of the GLUT4 isoform has been extensively studied and found to be tightly regulated at both mRNA and protein levels. Adaptation to states of enhanced metabolic demand is associated with increased glucose metabolism and GLUT4 gene expression, whereas states of insulin resistance such as type 2 diabetes mellitus (DM2), obesity, and aging are associated with impaired regulation of GLUT4 gene expression and function. The present review focuses on the interplay among hormonal, nutritional, and transcription factors in the regulation of GLUT4 transcription in health and sickness.

scholarly journals Diversity and plasticity in Rab GTPase nucleotide release mechanism has consequences for Rab activation and inactivation

eLife ◽  
2014 ◽  
Vol 3 ◽  
Author(s):  
Lars Langemeyer ◽  
Ricardo Nunes Bastos ◽  
Yiying Cai ◽  
Aymelt Itzen ◽  
Karin M Reinisch ◽  
...  
Keyword(s):  
Active Site ◽  
Free Form ◽  
Release Mechanism ◽  
Rab Gtpase ◽  
Rab Gtpases ◽  
Nucleotide Exchange ◽  
Active Site Residues ◽  
Gtp Hydrolysis ◽  
Activation Mechanisms ◽  
Gtpase Activation

Ras superfamily GTPase activation and inactivation occur by canonical nucleotide exchange and GTP hydrolysis mechanisms. Despite conservation of active-site residues, the Ras-related Rab GTPase activation pathway differs from Ras and between different Rabs. Analysis of DENND1-Rab35, Rabex-Rab5, TRAPP-Rab1 and DrrA-Rab1 suggests Rabs have the potential for activation by distinct GDP-release pathways. Conserved active-site residues in the Rab switch II region stabilising the nucleotide-free form differentiate these pathways. For DENND1-Rab35 and DrrA-Rab1 the Rab active-site glutamine, often mutated to create constitutively active forms, is involved in GEF mediated GDP-release. By contrast, in Rab5 the switch II aspartate is required for Rabex mediated GDP-release. Furthermore, Rab1 switch II glutamine mutants refractory to activation by DrrA can be activated by TRAPP, showing that a single Rab can be activated by more than one mechanistically distinct GDP-release pathway. These findings highlight plasticity in the activation mechanisms of closely related Rab GTPases.

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