The laboratory of Peter S. McPherson, Ph.D., FRSC, James McGill Professor uses biochemical, molecular, structural, genetic and cellular approaches to identify and functionally characterize proteins that operate in the formation of clathrin-coated vesicles (CCVs). CCVs are the major vehicles for endocytic uptake of multiple protein and lipid cargo including nutrient and signaling receptors. Following endocytosis, cargo is delivered to endosomes from where it either recycles back to the cell surface or is targeted to lysosomes for degradation. These sorting decisions control the localization and levels of proteins and are altered in cancer and neurological disease. For example, current projects in the lab reveal how disruption in transport of selective cargo from endosomes to the cell surface contributes to the development of glioblastoma and breast cancer.
Dr. McPherson's laboratory previously used subcellular proteomics (subcellular fractionation coupled to high throughput mass spectrometry) to identify the full complement of proteins that define CCVs from several tissues. A significant number of the proteins identified were uncharacterized open-reading frames. Dr. McPherson's laboratory has characterized the function of a number of these novel proteins although a significant number remain unstudied. One recently identified protein contains a module called a DENN domain. Dr. McPherson and his colleagues have demonstrated that DENN domains function enzymatically as guanine-nucleotide exchange factor to activate small GTPase of the Rab family. There are minimally 26 DENN domain proteins in the human genome and an important area of study in the laboratory involves the relationship of these proteins to the ~70 Rabs that function in membrane traffic. One particularly striking example is C9orf72, a DENN domain protein of unknown function. A mutation in C9orf72 is the most common cause of genetic forms of amyotrophic lateral sclerosis (ALS), and the laboratory is working to understand the relationship between endosomal membrane trafficking and disease pathogenesis.
Other proteins identified and or studied in the McPherson laboratory have been linked to other neurological diseases including Huntington disease, autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS), and Parkinson disease (PD). For example, we recently demonstrated that the major PD gene LRRK2 binds to clathrin and functions in endosomal membrane trafficking. Moreover, we showed that ARSACS shares pathophysiology with PD. In fact, alterations in the regulation of membrane trafficking is emerging as a central theme in neurodegenerative diseases. Most recently, we demonstrated that mutations in the DENN domain protein DENND5A cause epileptic encephalopathy, a devastating form of intellectual disability. Understanding the cell biological basis of neurological disease is a new focus of the laboratory.