In this new paper, we have used a novel chemical biology approach to identify a small molecule targeting the transmembrane domain of death receptor p75NTR that induces melanoma cell death and reduces tumor growth
Small molecules offer powerful ways to alter protein function. However, most proteins in the human proteome lack small-molecule probes, including the large class of non-catalytic transmembrane receptors, such as death receptors. We hypothesized that small molecules targeting the interfaces between transmembrane domains (TMDs) in receptor complexes may induce conformational changes that alter receptor function. Applying this concept in a screening assay, we identified a compound targeting the TMD of death receptor p75<sup>NTR</sup> that induced profound conformational changes and receptor activity. The compound triggered apoptotic cell death dependent on p75<sup>NTR</sup> and JNK activity in neurons and melanoma cells, and inhibited tumor growth in a melanoma mouse model. Due to their small size and crucial role in receptor activation, TMDs represent attractive targets for small-molecule manipulation of receptor function.
The paper has just been published in Cell Chemical Biology.
Read the full paper HERE.
UPDATE: The positions have been filled.
We are seeking talented and enthusiastic researchers with expertise in cell signaling, cell biology and mouse genetics to advance investigations on the functions and mechanisms of growth factor receptor signaling and physiology. The research entails studies of different receptor systems, including death receptor p75NTR, TGFbeta superfamily receptor ALK7 and neurotrophin receptor TrkB, using molecular methods, cell culture models and mutant mice carrying specific mutations in these receptors. Please refer to our recent list of publications in this areas.
Candidates will be accepted at the postdoctoral level with a PhD awarded preferably within the last 5 years. Strong and documented expertise in cellular, molecular and histological methods as applied to studies of mouse models in the areas of either neurobiology, metabolic regulation or cancer is a requirement for consideration. The successful candidate is expected to be sufficiently independent to formulate questions, design experiments and perform research.
We are recruiting fellows for our laboratories at the National University of Singapore and the Karolinska Institute in Stockholm, Sweden. Interested applicants can apply to both locations or just one. Work at the two laboratories is seamlessly integrated through joint lab meetings, common reagent and protocol records, and other cloud-based tools. Both sites provide exciting environments to pursue biomedical research at the highest level and a great opportunity to advance a career in science in exciting locations in Europe and Asia.
Applications, including CV, list of publications and statement of research interests should be sent to Prof. Carlos Ibanez ( or ). Applicants should arrange to have at least two confidential letters of reference sent independently by referees to either email address.
Applications will be considered as they arrive until the positions are filled. Interested applicants are strongly recommended to submit their applications as soon as possible. Funding is available for an initial period of 3 to 4 years, starting any time during 2018 or early 2019.
In this new paper, we show how intracellular effectors RIP2 and TRAF6 compete for binding to the p75NTR intracellular domain to regulate cell death of cerebellar granule neurons.
Cerebellar granule neurons (CGNs) undergo programmed cell death during the first postnatal week of mouse development, coincident with sustained expression of the death receptor p75NTR. Although ablation of p75NTR did not affect CGN cell death, deletion of the downstream effector RIP2 significantly increased CGN apoptosis, resulting in reduced adult CGN number and impaired behaviors associated with cerebellar function. Remarkably, CGN death was restored to basal levels when p75NTR is deleted in RIP2-deficient mice. We found that RIP2 gates the signaling output of p75NTR by competing with TRAF6 for binding to the receptor intracellular domain. In CGNs lacking RIP2, more TRAF6 was associated with p75NTR, leading to increased JNK-dependent apoptosis. In agreement with this, pharmacological inhibition or genetic ablation of TRAF6 restored cell death levels in CGNs lacking RIP2. These results revealed an unexpected mechanism controlling CGN number and highlight how competitive interactions govern the logic of death receptor function.
The paper has just been published in Cell Reports.
Read the full paper HERE.
In this new paper, we show how the GDNF receptor GFRα1 functions cell-autonomously in subpopulations of olfactory bulb interneuron precursors to regulate their generation and allocation in the mammalian olfactory bulb.
GFRα1, a receptor for glial cell line-derived neurotrophic factor (GDNF), is critical for the development of the main olfactory system. The olfactory bulb (OB) of Gfra1 knockout mice showed significant reductions in the number of olfactory sensory neurons, mitral and tufted cells, as well as all major classes of OB GABAergic interneurons. However, the latter did not express significant levels of GFRα1, leaving the mechanism of action of GFRα1 in OB interneuron development unexplained. We have found that GFRα1 is highly expressed in the precursor cells that give rise to all major classes of OB interneurons, but is downregulated as these neurons mature. Conditional ablation of GFRα1 in embryonic GABAergic cells recapitulated the cell losses observed in global Gfra1 knockouts at birth. GFRα1 was also required for the sustained generation and allocation of OB interneurons in adulthood. Conditional loss of GFRα1 altered the migratory behaviour of neuroblasts along the rostral migratory stream (RMS) as well as RMS glial tunnel formation. Together, these data indicate that GFRα1 functions cell-autonomously in subpopulations of OB interneuron precursors to regulate their generation and allocation in the mammalian OB.
The paper has just been published in Biology Open.
Read the full paper HERE.
Jason has successfully defended his thesis today titled “Understanding The Influence Of TDP-43 Loss-Of-Function On Neurotrophin Signalling”. Committee members Soong Tuck Wah, Garrie Arumugam and John Chua had a closed door session with him after the presentation, but we hear that it all went well. Congratulations to Dr. Jason!
Presentation Speech by Professor Carlos Ibáñez, Member of the Nobel Assembly at the Karolinska Institute, Member of the Nobel Committee for Physiology or Medicine, at the award ceremony of the Nobel Prize, 10 December 2017.
Vanessa Rodrigues holds a PhD in Pathology and Molecular Genetics from ICBAS, University of Porto, Portugal, with a thesis work entitled “Understanding P-glycoprotein mediated multidrug resistance in cancer: new potential targets, biomarkers and molecular inhibitors”. Vanessa joins the NUS group to lead a drug discovery program to identify novel chemical probes targeting p75NTR, TrkB and ALK7 receptors.
Ajeena Ramanujan holds a PhD from the Jawaharlal Nehru University, India, for work on the interaction between FZR1 and the Retinoblastoma protein in the control of cell-cycle regulation, under the direction of A/Prof Swati Tiwari. Ajeena is joining the NUS group to lead investigations on p75NTR signaling mechanisms involving RhoGDI and RhoA proteins and their actions on the cell cytoskeleton and neurite outgrowth control.
In this new paper, we show how the GDNF regulates survival of molecular layer interneurons in the cerebellum to control normal cerebellar motor learning. The paper has just been published in Cell Reports.
The role of neurotrophic factors as endogenous survival proteins for brain neurons remains contentious. In the cerebellum, the signals controlling survival of molecular layer interneurons (MLIs) are unknown, and direct evidence for the requirement of a full complement of MLIs for normal cerebellar function and motor learning has been lacking. Here, we show that Purkinje cells (PCs), the target of MLIs, express the neurotrophic factor GDNF during MLI development and survival of MLIs depends on GDNF receptors GFRα1 and RET. Conditional mutant mice lacking either receptor lose a quarter of their MLIs, resulting in compromised synaptic inhibition of PCs, increased PC firing frequency, and abnormal acquisition of eyeblink conditioning and vestibulo-ocular reflex performance, but not overall motor activity or coordination. These results identify an endogenous survival mechanism for MLIs and reveal the unexpected vulnerability and selective requirement of MLIs in the control of cerebellar-dependent motor learning.
Read the full paper HERE.
Fellows from the KI lab flew to Singapore for a 2 day retreat with the NUS group on 16th and 17th of January 2017. After 4 years of joint lab meetings over Skype, fellows of both groups enjoyed an opportunity to discuss common projects and ideas face to face. We were joined by the NUS and UCSD groups of Prof. Ed Koo and had joint plenary and also parallel sessions, as well as group building activities, as shown in the photo below.
UPDATE 2017-05-29: The positions have been filled.
Postdoc/Research Fellows are being recruited to our NUS laboratory. We are seeking talented, innovative and enthusiastic researchers with a PhD awarded within the last 5 years.
Cell signaling
The successful candidate will have a strong background in studies of cell signaling using molecular, cellular and biochemical methods. The aim of the project is to elucidate mechanisms of differential signaling by death receptors through the NFkB, c-Jun kinase and RhoA GTPase pathways, among others, taking advantage of recent knowledge on structure-function relationships in this class of receptors as well as a large collection of mutants developed at our laboratory. Strong expertise in cell and molecular biology techniques is essential. Additional expertise in live cell imaging will also be an asset to the project.
Drug Discovery
The successful candidate will have a strong background in studies of intracellular signaling involving biochemical assays, gene reporter assays and microscopy techniques. The aim of the project is the identification and characterisation of novel small molecule modulators (inhibitors and activators) of growth factor receptor signaling taking advantage of a novel screening strategy developed in the laboratory based on recent knowledge on the mechanisms of activation and downstream signal propagation of death receptors and receptors of the TGFb superfamily. Strong expertise in cell and molecular biology techniques is essential. Additional expertise in small molecule screening and/or chemistry will also be an asset to the project.
Applications, including CV, list of publications and statement of future interests should be sent to Prof. Carlos Ibanez  . Applicants should arrange to have at least two confidential letters of reference sent independently by referees to this email address.
Funding is available for an initial period of 2 to 3 years, starting any time during 2017.
Deadline for the application is March 07, 2017.
In this new paper, we show how the GFRα1 receptor regulates Purkinje cell migration independently of GDNF or RET, by limiting the function of NCAM. The paper has just been published in Cell Reports.
During embryonic development of the cerebellum, Purkinje cells (PCs) migrate away from the ventricular zone to form the PC plate. The mechanisms that regulate PC migration are incompletely understood. Here, we report that the neurotrophic receptor GFRα1 is transiently expressed in developing PCs and loss of GFRα1 delays PC migration. Neither GDNF nor RET, the canonical GFRα1 ligand and co-receptor, respectively, contribute to this process. Instead, we found that the neural cell adhesion molecule NCAM is co-expressed and directly interacts with GFRα1 in embryonic PCs. Genetic reduction of NCAM expression enhances wild-type PC migration and restores migration in Gfra1 mutants, indicating that NCAM restricts PC migration in the embryonic cerebellum. In vitro experiments indicated that GFRα1 can function both in cis and trans to counteract NCAM and promote PC migration. Collectively, our studies show that GFRα1 contributes to PC migration by limiting NCAM function.
Read the full paper HERE.
In our latest paper, we show how thalamo-cortical axons regulate the radial dispersion of neocortical GABAergic interneurons. The paper has just been published in eLife.
Neocortical GABAergic interneuron migration and thalamo-cortical axon (TCA) pathfinding follow similar trajectories and timing, suggesting they may be interdependent. The mechanisms that regulate the radial dispersion of neocortical interneurons are incompletely understood. In this new study we report that disruption of TCA innervation, or TCA-derived glutamate, affected the laminar distribution of GABAergic interneurons in mouse neocortex, resulting in abnormal accumulation in deep layers of interneurons that failed to switch from tangential to radial orientation. Expression of the KCC2 cotransporter was elevated in interneurons of denervated cortex, and KCC2 deletion restored normal interneuron lamination in the absence of TCAs. Disruption of interneuron NMDA receptors or pharmacological inhibition of calpain also led to increased KCC2 expression and defective radial dispersion of interneurons. Thus, although TCAs are not required to guide the tangential migration of GABAergic interneurons, they provide crucial signals that restrict interneuron KCC2 levels, allowing coordinated neocortical invasion of TCAs and interneurons.
Read the full paper HERE. (Supplemental information 31.6MB)
Shuhailah Salim holds a Bachelor in Science from Nanyang Technological University. She did a research internship at the Institute of Molecular and Cell biology (IMCB, A*STAR). She joins our NUS group to support biochemical, tissue culture and drug screening studies.
New Chih Sheng holds a Bachelor in Science from the University of Toronto. He did a research internship at the Institute of Molecular and Cell biology (IMCB, A*STAR). She joins our NUS group to support our metabolism research projects with mouse genotyping and tissue culture.
Yi Chenju holds a Bachelor in Clinical Medicine from Tongji Medical College, Huazhong University of Science and Technology, China, a PhD in Neurology form the same institution and an MD from the Institute of Brain Research, University of Tübingen, Germany. She performed postdoctoral studies at College de France under the direction of Drs. Christian Gaume and Annette Koulakoff. Chenju is joining the NUS group to lead investigations on p75NTR-mediated mechanisms of neurodegeneration in mouse models of Alzheimer’s disease.
In our latest paper, we show how dimers of the p75NTR neurotrophin receptor are indipensable for p75NTR-mediated cell death in the central nervous system. The paper has justg been published in the Journal of Neuroscience.
The oligomeric state and activation mechanism that enable p75 NTR to mediate these effects have recently been called into question. In this new study, we have investigated mutant mice lacking the p75NTR death domain (DD) or a highly conserved transmembrane (TM) cysteine residue (Cys 259) implicated in receptor dimerization and activation. Neuronal death induced by proneurotrophins or epileptic seizures was assessed and compared with responses in p75NTR knock-out mice and wild-type animals. Proneurotrophins induced apoptosis of culturedhippocampalandcorticalneuronsfromwild-typemice,butmutantneuronslackingp75NTR,onlythep75NTR DD,orjustCys259 were all equally resistant to proneurotrophin-induced neuronal death. Homo-FRET anisotropy experiments demonstrated that both NGF and proNGF induce conformational changes in p75 NTR that are dependent on the TM cysteine. In vivo, neuronal death induced by pilocarpine-mediated seizures was significantly reduced in the hippocampus and somatosensory, piriform, and entorhinal cortices of all three strains of p75 NTR mutant mice. Interestingly, the levels of protection observed in mice lacking the DD or only Cys 259 were identical to those of p75 NTR knock-out mice even though the Cys 259 mutant differed from the wild-type receptor in only one amino acid residue. We conclude that,bothinvitroandinvivo,neuronaldeathinducedbyp75NTR requirestheDDandTMCys259,supportingthephysiological relevance of DD signaling by disulfide-linked dimers of p75NTR in the CNS.
Read the full paper HERE.
UPDATE 01-06-2016: The position has been filled.
A Research Assistant/Associate is currently being recruited to our laboratory in the Centre for Life Sciences, National University of Singapore, Kent Ridge campus.
The successful candidate will be a dynamic, service-minded person, with a solid research background in molecular biology, tissue culture, histological techniques and/or mouse genetics methods. He/she will have a strong presence in the laboratory by assisting the group with experimental lab routines as well as conducting research together with other lab members or independently, including:
maintenance of mouse colonies and genotypinghistological studiesmolecular biology studiestissue culture studies
Applications including CV and names plus email addresses of three referees should be sent by email to Prof. Carlos Ibanez
Deadline: MAY 21st, 2016
UPDATE 2016-04-11: The position has been filled.
As part of a University-wide initiative on mechanisms of neuronal and synaptic injury in aging and neurodegenerative diseases, we are seeking talented and enthusiastic individuals to join our laboratory.
Carlos Ibanez is Professor at the Department of Physiology, Yong Loo Lin School of Medicine, National Univeristy of Singapore, and Department of Neuroscience, Karolinska Institute, Stockholm, Sweden.
Under the direction of Prof. Carlos Ibanez, this project will focus on studies of the role of neurotrophin signaling in neurodegenerative diseases, with afocus on Alzheimer’s disease and dementias. This is an exciting opportunity for individuals who have received a doctoral degree within the past five years and with a strong background in cellular neurobiology. Other requirements include i) experience on mouse models, i i) experience in neurohistological methods, and iii) ability to work independently with precision and good organizational skills. Located on the Medical School campus of the National University of Singapore, there is close integration among the core laboratories of this strategic initiative. This provides for an exciting environment to pursue neuroscience research and a great opportunity in one of the most developed and exciting countries in the region.
Applications including CV and names plus email addresses of three referees should be sent by email to Prof. Carlos Ibanez .
Deadline: MARCH 31, 2016
A targeted effort to identify novel neurotrophic factors for midbrain dopaminergic neurons resulted in the isolation of GDNF (glial cell line-derived neurotrophic factor) from the supernatant of a rat glial cell line in 1993. Over two decades and 1200 papers later, the GDNF ligand family and their different receptor systems are now recognized as one of the major neurotrophic networks in the nervous system, important for the devel- opment, maintenance and function of a variety of neurons and glial cells. The many ways in which the four mem- bers of the GDNF ligand family can signal and function allow these factors to take part in the control of multiple types of processes, from neuronal survival to axon guidance and synapse formation in the developing nervous system, to synaptic function and regenerative responses in the adult. In this review, recently published in Neurobiology Of Disease, basic aspects of GDNF signaling mechanisms and receptor systems are first summarized followed by a review of current knowledge on the physiology of GDNF activities in the central nervous system, with an eye to its relevance for neurodegenerative and neuropsychiatric diseases. Read the full paper HERE.
The National Medical Research Council of Singapore has awarded a Collaborative Basic Research Grant (CBRG) to Carlos Ibanez for investigations into novel pathways controlling metabolic functions in adipose tissue. The award includes collaborative projects with Han Weiping, from the Singapore Bioimaging Consortium at ASTAR, Neerja Karnani, from the Singapore Institue for Clinical Sciences, and Asim Shabbir, from the National University Hospital of Singapore.
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