EP Abraham Professor of Mechanistic Cell Biology
Co-workers: Elena Poser, Michela Serena, Marina Demetriades, Josip Ahel, James Holder
Ekaterina Lamber, Andreas Gerondopoulos, Tatiana Alfonso Perez
My group is interested in how the polarization & division of human cells is regulated. Our 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.
These projects are only possible through the continued funding and support of Cancer Research UK, the Wellcome Trust and the BBSRC.
Mitosis & cytokinesis in human cancers
To maintain a genetically stable diploid cell population mitosis and cytokinesis must be carried out with high fidelity (Figure 1). 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 Ras superfamily of GTPases and their regulators.
Figure 1. The cell division cycle (Actin & DNA).
Ongoing projects in my group examine the regulation of PP1 and PP2A family protein phosphatases in dividing cells. Most recently we have explained how regulation of the PP2A-B55 phosphatases contribute important timing properties to the metaphase to anaphase transition, and identified and modelled the behaviour of key substrate proteins in the cell. A further major focus is on the mitotic kinase Aurora A & its control by protein phosphatase 6 (PP6). We have shown that this pathway is dysregulated in human cancers, and drives genome instability and DNA damage in melanoma. One future aim is to exploit this pathway to specifically target and selectively kill tumours with amplified Aurora A kinase.
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.
We are 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 reticulum occurs in the severe human neurological disorder Warburg Micro Syndrome (WMS). This work links WMS to the wider family of human hereditary spastic paraplegias, many of which are also caused by altered regulation of the endoplasmic reticulum. By understanding the molecular basis of these disorders we hope to contribute to the identification of targets that can be exploited therapeutically.
Recent Selected Publications
Mitosis & Cancer
Cundell, MJ, Hutter, LH, Nunes Bastos, R., Poser, E., Holder, J., Mohammed, S., Novak, B, and Barr, F.A. “A PP2A-B55 recognition signal controls substrate dephosphorylation kinetics during mitotic exit” Journal of Cell Biology 214 (2016) 539-54. Subject of Comment Article in same issue.
- Nunes Bastos, R., Cundell, M.J. and Barr, F.A. “KIF4A and PP2A-B56 form a spatially restricted feedback loop opposing Aurora B at the anaphase central spindle” Journal of Cell Biology (2014) In press. Research Highlight in same issue.
- 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.
- Langemeyer, L., Nunes Bastos, R., Itzen, A., Reinisch, K., and Barr, F.A. “Plasticity in nucleotide release mechanism results in coupling of Rab GTPase activation and inactivation” Elife (2014) Feb 11;3:e01623. doi: 10.7554/eLife.01623
- 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.
Graduate Student and Postdoctoral Positions: Enquiries with CV and a letter explaining your research interests are always welcome
Biochemistry Part II Students 2016-17: Iona Manley, Vanessa Vu