Johnny K. Ngsee, PhD
jngsee@ohri.ca
Senior Scientist, Neuroscience, Ottawa Hospital Research Institute
Associate Professor, Department of Medicine and Cellular & Molecular Medicine, University of OttawaResearch Interests
Amyotrophic Lateral Sclerosis
Molecular Basis of Synaptic Transmission
Intracellular Membrane Trafficking
Neurite Formation and Outgrowth
Parkinson's Disease
Major Research Activities
Research in my laboratory is focused on elucidating the mechanisms of protein sorting and vesicle trafficking. The endoplasmic reticulum (ER) is the first entry point for proteins destined for secretion and other intracellular compartments. The ER exerts a quality control on proteins to ensure that only properly folded proteins are allowed to progress to the Golgi complex, while misfolded proteins are subjected to re-folding or degradation. Properly folded proteins are sorted and sequestered into ER exit sites prior to their eventual incorporation as cargoes of transport vesicles. Regulatory proteins that mediate subsequent vesicle fusion with the target organelle are also incorporated into the transport vesicles. We have previously identified a novel protein named prenylated Rab Acceptor (PRA) that recruits a class of molecular switches that control vesicle docking called Rab GTPases to the membrane. In the process, we also identified a protein called VAMP-associated protein (VAP) that plays a gatekeeper role in limiting diffusion and incorporation of membrane protein cargoes into transport vesicles. There are two VAP genes in human, designated VAPA and VAPB. Recently, a single amino acid substitution (P56S) in VAPB has been linked to a late-onset form of Amyotrophic Lateral Sclerosis (commonly referred to as Lou Gehrig's Disease). The P56S mutation in VAPB causes the ER to expand and form large vacuole-like structures that trap membrane proteins. Our current research focuses on the molecular mechanisms that generate the ER aggregates, their cellular consequences and how to resolve them once formed.
A second area of research focuses on dendritic spine formation and macropinocytosis. Dendritic spines are actin-rich protrusions emanating from shafts of dendrites that can form functional synapse with axons under the right conditions. Macropinocytosis is a form of bulk fluid and solid cargo uptake. It is the preferred route of entry into the cell by large viruses (e.g. vaccinia), pathogenic microorganisms (e.g. Salmonella), coated nanoparticles used in gene delivery, and by TAT peptide-mediated protein transduction. Both processes depend on RhoG GTPase regulated actin polymerization. We discovered that a family of proteins called the sorting nexins (SNX) recruits RhoG along with its activator protein to the membrane. Modulating this step has implication during regeneration of synaptic contacts, in microbial infection, and drug delivery by nanoparticles. In neurones, activity-dependent modulation of dendritic spine formation plays a key role in synaptic remodelling during learning and memory acquisition, and in regeneration.
Recent Publications
Venderova, K. et al. Leucine-Rich Repeat Kinase 2 interacts with Parkin, DJ-1 and PINK-1 in a Drosophila melanogaster model of Parkinson's disease. Hum. Mol. Genet. 18, 4390-4404 (2009).
Prosser, D.C., Tran, D., Gougeon, P.Y., Verly, C. & Ngsee, J.K. FFAT rescues VAPA-mediated inhibition of ER-to-Golgi transport and VAPB-mediated ER aggregation. J. Cell Sci. 121, 3052-3061 (2008).
Ridsdale, A. et al. Cholesterol is required for efficient endoplasmic reticulum-to-Golgi transport of secretory membrane proteins. Mol. Biol. Cell 17, 1593-1605 (2006).
Abdul-Ghani, M., Hartman, K.L. & Ngsee, J.K. Abstrakt interacts with and regulates the expression of sorting nexin-2. J. Cell. Physiol. 204, 210-218 (2005).
Gougeon, P.Y. & Ngsee, J.K. Purification and functional properties of prenylated Rab acceptor 2. Methods Enzymol. 403, 799-807 (2005).
Hutt, D.M., Baltz, J.M. & Ngsee, J.K. Synaptotagmin VI and VIII and syntaxin 2 are essential for the mouse sperm acrosome reaction. J. Biol. Chem. 280, 20197-20203 (2005).
Mooney, D.M. et al. Distinct forms of cholinergic modulation in parallel thalamic sensory pathways. Proc. Natl. Acad. Sci. U. S. A. 101, 320-324 (2004).
Zhang, H. et al. Localization of low density lipoprotein receptor-related protein 1 to caveolae in 3T3-L1 adipocytes in response to insulin treatment. J. Biol. Chem. 279, 2221-2230 (2004).
