Pontus Aspenström Group
The Ras-like family of Rho GTPases are key regulators of the actin filament system and thereby they control vital cellular processes such as cell morphogenesis, cell polarity and cell migration. The work in our group is aimed to elucidate the Rho-dependent signalling mechanisms in health and disease.
We have characterised the little known members of the Rho GTPases and evaluated their impact on the organisation of the actin filament system. Currently, we want to identify the mechanism that determines the signalling specificity of the Rho GTPases and we have focused on the cellular roles of the atypical Rho GTPases (RhoBTB, RhoH, Rnd1-3, Chp and Wrch-1).
We recently identified a new family of Ras-like proteins, the Miro GTPases. These proteins bind mitochondria and link them to the kinesin motor proteins. This way, Miro functions as a regulator of mitochondrial transport along microtubules. We want to examine the potential involvement of Miro GTPases in diseases caused by deregulated mitochondrial function.
Finally, we are studying regulators and effectors of Rho GTPases, since many of them have profound effects on the cytoskeletal organisation. We are particularly interested in proteins that can function as links actin regulation and membrane dynamics. We have a specific interest in F-BAR domain-containing proteins (such as CIP4 and Toca-1) and WASP-interacting proteins (such as WIP and WIRE). Our goal is to identify how signalling involving Rho GTPases contribute to processes such as cell migration, cell growth and tumour progression.
The research activities in our group are aimed to elucidate various aspects of cell signalling mediated by Rho GTPases. This group of proteins has emerged as key regulators of cell morphogenesis, cell migration and cell polarity but they also participate in signalling pathways that control cell growth, cell cycle progression and cell survival. We have previously shown that this family of proteins consists of 20 members and that their effect on the organization of the actin filament system is more intricate and complex than recognised before. Our goal is to identify how signalling involving Rho GTPases contribute to processes such as cell migration, cell growth and tumour progression. A key challenge for the near future will be to identify the precise mechanisms by which a multitude of extracellular and intracellular signals, via the activity of the Rho GTPases and the Rho-regulated proteins, is transformed into highly specific physiological responses.
The Rho GTPases
The Rho GTPases can be divided into two main categories the classical Rho GTPases and the atypical Rho GTPases. We have put efforts into the identification of the atypical Rho GTPases (RhoBTB1-3, Rnd1-3, RhoH, Rac1B, Chp and Wrch-1). RhoBTB binds cullin 3 and it is a subunit in the cullin 3-based ubiquitin ligase complex, which ubiquitinylates specific substrate proteins and targets them for proteasomal degradation. Wrch-1 is involved in the regulation of cell adhesion and cell morphology. We used a yeast two hybrid approach to identify Wrch-1 targets and found the non receptor tyrosine kinases Pyk2 and FAK. Pyk2 is needed for the Wrch1-dependent reorganisation of the actin filament system and formation of filopodia. Wrch1 also have a role in the regulation of cell growth and it is transforming cells in vitro cell transformation assays. We are currently in the process to identify novel binding partners for all members of the atypical Rho GTPases.
The Miro proteins have unique characteristics since they are markedly bigger compared to the classical Rho GTPases. Miro contains two putative GTP-binding domains. The N-terminal GTPase domain is highly related to the RhoGTPases but the C-terminal domain is only distantly related to known GTPases. Two potential calcium-binding sites, so-called EF hands, reside in a linker region between the two GTPase domains. We have shown that Miro-1 and Miro-2 bind to the mitochondria and that Miro GTPases are building blocks of the mitochondrial transport machinery by linking to the kinesin-binding proteins GRIF1 and OIP106. We are currently evaluating the role of Miro GTPases in neuropathological conditions as well as diseases caused by deregulated mitochondrial function.
Regulators and effectors of Rho GTPases
We have previously identified several proteins, which bind to the activated Rho GTPases and affect their biological activities. One such protein, the Cdc42-binding protein 4 (CIP4) have a role in the Cdc42-dependent regulation of the actin filament system. CIP4 has an F-BAR domain, which is binding to lipid bilayers and induces membrane deformation, a process occurring in vesicle formation and endocytosis. F-BAR has important roles in linking cytoskeletal regulation and membrane dynamics and we have found a role for CIP4-like proteins in the regulation of trafficking of tyrosine kinase receptors. We are currently studying the involvement of CIP4 and other F-BAR proteins in receptor activation and trafficking in health and disease.
The verprolins are pivotal modulators of signalling mediated by the WASP family of proteins. The Cdc42-binding protein WASP was originally identified as the gene defective in the severe X-linked immunodeficiency disorder Wiskott-Aldrich syndrome (WAS). The mammalian verprolin family consists of 3 genes: WIP, WIRE and CR16. The verprolins bind actin and the actin-regulating protein profilin via an N-terminal domain. Multiple proline-rich motifs confer binding to SH3 domain-containing proteins, such as Nck and cortactin, whereas the WASP-binding motif resides in the C-terminus of the verprolins. Recently, we have focused our studies to the identification of additional binding partners for the mammalian verprolins and their role in the regulation of cytoskeletal dynamics.
Deciphering the Molecular and Functional Basis of RHOGAP Family Proteins: A SYSTEMATIC APPROACH TOWARD SELECTIVE INACTIVATION OF RHO FAMILY PROTEINS.
J. Biol. Chem. 2016 Sep;291(39):20353-71
Profilin connects actin assembly with microtubule dynamics.
Mol. Biol. Cell 2016 Aug;27(15):2381-93
Mitotic redistribution of the mitochondrial network by Miro and Cenp-F.
Nat Commun 2015 Aug;6():8015
RhoD is a Golgi component with a role in anterograde protein transport from the ER to the plasma membrane.
Exp. Cell Res. 2015 May;333(2):208-19
BAR domain proteins regulate Rho GTPase signaling.
Small GTPases 2014 ;5(2):7
Atypical Rho GTPases RhoD and Rif integrate cytoskeletal dynamics and membrane trafficking.
Biol. Chem. 2014 May;395(5):477-84
Oncogenes induce a vimentin filament collapse mediated by HDAC6 that is linked to cell stiffness.
Proc. Natl. Acad. Sci. U.S.A. 2014 Jan;111(4):1515-20
Analysis of Rho GTPase-induced localization of nanoscale adhesions using fluorescence nanoscopy.
Methods Mol. Biol. 2014 ;1120():339-57
RhoD binds the Rab5 effector Rabankyrin-5 and has a role in trafficking of the platelet-derived growth factor receptor.
Traffic 2013 Dec;14(12):1242-54
Spatial organization of proteins in metastasizing cells.
Cytometry A 2013 Sep;83(9):855-65
Interaction of RhoD and ZIP kinase modulates actin filament assembly and focal adhesion dynamics.
Biochem. Biophys. Res. Commun. 2013 Apr;433(2):163-9
RhoD regulates cytoskeletal dynamics via the actin nucleation-promoting factor WASp homologue associated with actin Golgi membranes and microtubules.
Mol. Biol. Cell 2012 Dec;23(24):4807-19
Rho GTPases link cellular contractile force to the density and distribution of nanoscale adhesions.
FASEB J. 2012 Jun;26(6):2374-82
ARHGAP30 is a Wrch-1-interacting protein involved in actin dynamics and cell adhesion.
Biochem. Biophys. Res. Commun. 2011 May;409(1):96-102
Rif proteins take to the RhoD: Rho GTPases at the crossroads of actin dynamics and membrane trafficking.
Cell. Signal. 2010 Feb;22(2):183-9
Novel role of pleckstrin homology domain of the Bcr-Abl protein: analysis of protein-protein and protein-lipid interactions.
Exp. Cell Res. 2010 Feb;316(4):530-42
Formin-binding proteins: modulators of formin-dependent actin polymerization.
Biochim. Biophys. Acta 2010 Feb;1803(2):174-82
The Miro GTPases: at the heart of the mitochondrial transport machinery.
FEBS Lett. 2009 May;583(9):1391-8
Miro1 is a calcium sensor for glutamate receptor-dependent localization of mitochondria at synapses.
Neuron 2009 Feb;61(4):541-55
Roles of F-BAR/PCH proteins in the regulation of membrane dynamics and actin reorganization.
Int Rev Cell Mol Biol 2009 ;272():1-31
The atypical Rho GTPase Wrch1 collaborates with the nonreceptor tyrosine kinases Pyk2 and Src in regulating cytoskeletal dynamics.
Mol. Cell. Biol. 2008 Mar;28(5):1802-14
Nck adapters are involved in the formation of dorsal ruffles, cell migration, and Rho signaling downstream of the platelet-derived growth factor beta receptor.
J. Biol. Chem. 2008 Oct;283(44):30034-44
Characterization of RhoBTB-dependent Cul3 ubiquitin ligase complexes--evidence for an autoregulatory mechanism.
Exp. Cell Res. 2008 Nov;314(19):3453-65
Bidirectional Ca2+-dependent control of mitochondrial dynamics by the Miro GTPase.
Proc. Natl. Acad. Sci. U.S.A. 2008 Dec;105(52):20728-33
Taking Rho GTPases to the next level: the cellular functions of atypical Rho GTPases.
Exp. Cell Res. 2007 Oct;313(17):3673-9