Mechanisms of human cell division & organelle identity
Co-workers: Ricardo Nunes Bastos, Michael Cundell, Sapan Gandhi, Ryan Baron
Ekaterina Lamber, Andreas Gerondopoulos
Cancer Research UK funded post available - contact details at bottom of page
The Barr group is interested in how the polarization & division of human cells is regulated. Their work addresses a number of major questions about the processes needed for cell growth and division, and the consequences of dysregulation of these pathways in human cancers and other diseases.
Mitosis & cytokinesis in human cancers
To maintain a genetically stable diploid cell population mitosis and cytokinesis must be carried out with high fidelity. Accordingly, failure of these cell division processes can give rise to aneuploid cells, chromosome instability, and altered centrosome copy-number – all hallmarks of tumours. One aim of my current and planned research is to describe the molecular mechanisms human cells use to regulate cell division and coordinate the processes of chromosome segregation and cytokinesis, with particular focus paid to the role of protein phosphorylation and dephosphorylation. The results of this research will provide a foundation for new strategies for targeting tumours with dysregulated Aurora and Polo family mitotic kinases. In addition to segregation of chromosomes, the essential internal organelles of the cell such as endoplasmic reticulum, Golgi, endosomes and mitochondria have to be shared out to the two daughter cells. A second research aim is therefore to identify the molecular mechanisms used to create and maintain the internal membrane organelles of the cells, with a specific focus on the Rab GTPases and their regulators.
Figure 1. Cell shape changes during the cell cycle (Actin & DNA).
Ongoing projects examine the regulation of protein phosphatases in dividing cells, and how PP1 and PP2A phosphatases contribute important timing properties to the metaphase to anaphase transition. A major focus is on the mitotic kinase Aurora A & its control by protein phosphatase 6 (PP6). Recent work from the Barr group has shown this pathway is dysregulated in human cancers, and drives genome instability and DNA damage. One future aim is to exploit this pathway to specifically target and selectively kill tumours with amplified Aurora A kinase. Another priority in the group is the understanding of cell shape control in mitosis. These projects focus on the interplay between Rho and Rac1 GTPase regulators, and how this gives rise to the complex shape changes needed for cell division (Figure 1). Alterations in these pathways are observed in human cancers, yet how they promote genome instability and tumorigenesis is only poorly understood and the Barr group aims to change this.
Molecular machinery of organelle identity
Eukaryotic cells are characterised by the complex internal membrane organelles of the secretory and endocytic pathways. These organelles allow the compartmentalisation of the cell, so that different chemical environments can exist simultaneously within one cell. For this system to function, it is essential that each membrane compartment, or organelle, can establish and maintain a unique identity. This is achieved by the action of selective vesicle transport reactions. Coat protein complexes assemble on one organelle, select the protein and lipid cargo to be transferred, and then pinch off a small vesicle structure. This vesicle then moves in a vectorial fashion towards the target organelle. A complex recognition process then ensues mediated by the Rab GTPases that act as molecular switches or timers cycling between a GDP- (off) and GTP-bound (on) states. If this is recognition event is successful the vesicle becomes tethered to its target, and then fuses due to the action of the SNARE membrane fusion proteins and their cofactors. A growing number of human diseases are caused by mutations in genes encoding components of this membrane trafficking machinery. It is the failure to transport proteins and lipids to the correct destination, and correctly maintain the identity of cellular organelles that explains these diseases.
The Barr group is particularly interested in Rab functions during cell polarisation and migration events, and the formation of complex sensory structures such as the primary cilium. A crucial determinant of the Rab GTPase system is the need to specifically activate a unique set of Rabs on a target membrane. This is a complex problem due to the large number (>60) Rab GTPases encoded in the human genome, and requires a combination of animal cell biology and biochemistry, mass spectrometry and protein structure determination to identify and characterise the underlying molecular machinery. Current projects focus on a large family of Rab guanine nucleotide exchange factors that we have recently identified containing DENN and DENN-related domains, with diverse roles in trafficking at the endoplasmic reticulum, Golgi and endosomes, and in the formation of specialised organelles such as pigment granules (Figure 2).
Figure 2: Pigmentation & blood clotting defects in Hermansky-Pudlak Syndrome due to loss of Rab32 regulation by Hps1 (Rab32 &Tyrp1).
Our latest work explains how altered regulation of Rab18 at the endoplasmic reitculum occurs in the human neurological disorder Warburg Micro Syndrome. This work links WMS to the wider family of hereditary spastic paraplegias, many of which are also caused by altered regulation of the endoplasmic reticulum.
These projects are only possible through the continued funding and support of Cancer Research UK and the Wellcome Trust.
Recent Selected Publications
Mitosis & Cancer
- Cundell, M., Nunes Bastos, R., Zhang, T., Holder, J., Gruneberg, U., Novak, B., and Barr, F.A. “The BEG (PP2A-B55/ENSA/Greatwall) pathway ensures cytokinesis follows chromosome separation”. Molecular Cell 52 (2013) 393-405.
- Nunes Bastos, R., Gandhi, S.R., Baron, R.D., Gruneberg, U., Nigg, E.A., and Barr, F.A. “Aurora B suppresses microtubule dynamics and limits central spindle size by locally activating KIF4A”. Journal of Cell Biology 202 (2013) 605-621. Subject of In Focus Article in same issue.
- Hammond D., Zeng K., Espert A., Bastos R.N., Baron R.D., Gruneberg U., Barr F.A. “Melanoma-associated mutations in protein phosphatase 6 cause chromosome instability and DNA damage due to dysregulated Aurora A” Journal of Cell Science 126 (2013) 3429-3440. Subject of Comment Article in same issue.
- Dunsch, A.K., Hammond, D., Lloyd, J., Schermelleh, L., Gruneberg, U., and Barr, F.A. “Asymmetric cortical localisation of dynein during spindle orientation requires dynein light chain 1 and a spindle-associated adaptor complex” Journal of Cell Biology 198 (2012) 1039-1054.
- Nunes-Bastos, R., Penate, X., Bates, M., Hammond, D., and Barr, F.A. “CYK4 inhibits Rac1-dependent PAK1 and ARHGEF7 effector pathways during cytokinesis” Journal of Cell Biology 198 (2012) 865-880. Subject of Comment Article in same issue.
- Zeng, K., Nunes-Bastos, R. Barr, F.A., and Gruneberg, U. “Protein phosphatase 6 regulates mitotic spindle formation by controlling the T-loop phosphorylation state of Aurora A bound to its activator TPX2” Journal of Cell Biology 191 (2010) 1315-1332. Subject of In Focus Article in same issue.
- Nunes-Bastos, R., and Barr, F.A. “Plk1 negatively regulates Cep55 recruitment to the midbody to ensure orderly assembly of abscission complexes” Journal of Cell Biology 191 (2010) 751-760.
- Barr, F.A. and Gruneberg, U. "Cytokinesis: placing and making the final cut" Cell 131 (2007) 847-860.
Rab GTPases & Organelle identity
- Gerondopoulos, A., Nunes Bastos, R., Yoshimura, S., Anderson, R., Carpanini, S., Aligianis, I., Handley, M.T., and Barr, F.A. “Rab18 and a Rab18 GEF complex are required for normal ER structure” Journal of Cell Biology 205 (2014) 707-720. Subject of biosights video podcast in the same issue.
- Barr F.A. "Rab GTPases and membrane identity: causal or inconsequential" Journal of Cell Biology 202 (2013) 191-199.
- Levine T.P., Daniels R.D., Wong L.H., Gatta A.T., Gerondopoulos A., Barr F.A. “Discovery of new Longin and Roadblock domains that form platforms for small GTPases in Ragulator and TRAPP-II” Small GTPases 2013 Mar 19;4(2).
- Gerondopoulos, A., Langemeyer, L., Liang, J.R., Linford, A., and Barr, F.A. “BLOC-3 mutated in Hermansky-Pudlak syndrome is a Rab32/38 guanine nucleotide exchange factor” Current Biology 22 (2012) 2135-2139. Subject of Dispatch Article in same issue.
- Linford, A., Yoshimura, S., Langemeyer, L., Nunes-Bastos, R., Gerondopoulos, A., Rigden, D.J., and Barr, F.A. “Rab14 and its guanine nucleotide exchange factor FAM116A act in an endocytic recycling pathway controlling adherens junctions during cell migration” Developmental Cell 22 (2012) 952-966. Subject of Review Article in same issue.
- Longatti, A., Lamb, C.A., Razi, M., Yoshimura, S.I., Barr, F.A., and Tooze, S.A. “TBC1D14 regulates autophagosome formation via Rab11- and ULK1-positive recycling endosomes” Journal of Cell Biology 197 (2012) 659-675.
- Wu, X., Bradley, M., Cai, Y., De La Cruz, E., Barr, F.A., and Reinisch, K.M. “Insights regarding guanine nucleotide exchange from the structure of a DENN-domain protein complexed with its Rab GTPase substrate” Proc. Natl. Acad. Sci. 108 (2011) 18672-18677.
- Bem, D., Yoshimura, S., Nunes-Bastos, R., Bond, F., Straatman-Iwanowska, A., Cullinane, A.R., Pasha, S., Massood, I., Ceverny, K., Hadzhiev, Y., Morton, J.E., Graham, J.D., Burglen, L., Ahmed, Z., Gissen, P., Müller, F., Maher, E.R., Barr, F.A., and Aligianis, I.A. “Loss of function mutations in Rab18 cause Warburg Micro Syndrome” American Journal of Human Genetics 88 (2011) 499-507.
- Yoshimura, S., Gerondopoulos, A., Linford, A., Rigden, D.J., and Barr, F.A. “Family-wide characterization of the DENN domain Rab GDP-GTP exchange factors” Journal of Cell Biology 191 (2010) 367-381.
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