James Dennis

Dr. Dennis began his independent career as an Assistant professor at Queens University, and moved to the Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital as a founding member in 1985.

Dr. Dennis’ major research program focuses on the structure and functions of protein Asn (N)-glycosylation in development and disease using genetic and biochemical methods with mice, C. elegans and human experimental models. N-glycans on receptor kinases and nutrient transporters are required for proper folding of these glycoproteins in the endoplasmic reticulum, and subsequently, modification to the N-glycans in the Golgi regulate their activities at the cell surface. 

Dr. Dennis has made seminal contribution on the role of protein N-glycosylation in development, cancer, immunity and metabolism. More recently, he pioneered a unifying model of growth factor receptor regulation based on metabolic input to Golgi-dependent modification of their N-glycans. The model has been used to search for and explain heritable genetic and metabolic susceptibility to autoimmune disease, cancer, and metabolic syndrome. The liver glucagon receptor which regulates gluconeogenesis and serum glucose levels is regulated by metabolic feedback to Golgi-dependent modification. 

Dr. Dennis was first to identify Polo like kinase-4 (Plk4), and its requirement in cell cycle progression. Dr. Dennis’ group identified SUP-46/MYEF2, an RNA binding protein with low complexity sequences that promotes phase-transition to form microscopy visible granules. 

Ongoing studies indicate that SUP46 regulates the hexosamine biosynthesis pathway, and is required for spermatogenesis and stress tolerance. Further studies are planned with the human homologue, MYEF2, to examine normal and pathological phase-transitions exemplified inAlzheimer's  disease.

Dr. Dennis is a Canada Research Chair in Glycobiology, a fellow of the Royal Society of Canada, and has been awarded the Friesen-Rygiel and Lloyd Fogler Prizes. Dr. Dennis was a co-founder of a Canadian Biotechnology company, GlycoDesign. He initiated the design of 2 clinical trials to test the compound swainsonine in cancer patients approved by Health and Welfare, and has 19 patients

Research Synopsis

Dr. Dennis has been studying metastasis for decades. One of his current projects focuses on cancer cell metabolism, and how cancer cells consume more energy, grow aberrantly, and spread throughout the body.

Dennis laboratory is at Lunenfeld- Tanenbaum Research Institute (LTRI), Mount Sinai Hospital on the 9th floor, room for ~12-15 people, as well as a dedicated mass spectrometry room on the 8th floor.  Core facility include microscopy, FACS, robotics, computing and massively parallel sequencing.  

Cancer Metabolism Studies

Mutations in oncogenes and tumor suppressors are often synergistic for the changes in signaling, gene expression, and metabolism that ultimately drive cancer progression. Metabolic reprogramming in cancer cells supports proliferation by increasing nutrient uptake and redirecting the resources into biosynthesis of proteins, lipids, nucleic acids and glycoconjugates, while limiting oxidative respiration.

Activated Ras and Akt-mTor up-regulate glucose transporter activity while increased c-myc or loss of p53 relieves suppression of genes that support glutamine metabolism. Solute (nutrient) transporters are critical gate-keepers of metabolite entry into the cell.

As integral membrane proteins, most transporters are N-glycosylated in the ER, and the N-glycans are remodeled in the Golgi.

The remodeled N-glycans are ligands for a super-family of lectins (ie. carbohydrate-binding proteins) that regulate receptor and transporter levels at the cell surface. The lectin-glycan interactions are dependent on Golgi branching enzymes N-acetylglucosaminyltransferases I, II, IV, V (encoded by Mgat1, Mgat2, Mgat4 and Mgat5, respectively); each catalyzes the addition of N-acetylglucosamine (GlcNAc) from the donor UDPGlcNAc to specific positions on the N-glycans.

Glucose and glutamine are substrates of the de novo hexosamine biosynthesis pathway (HBP) to UDP-GlcNAc. GlcNAc is also salvaged by conversion to GlcNAc-6P then UDP-GlcNAc.

Tumors are often poorly vascularized, and we have recently shown that in low glucose/glutamine conditions, GlcNAc salvage and up-regulation of Mgat gene expression increases glutamine transport, metabolite levels and cell growth.

We have also shown that intracellular glutamine or GlcNAc salvage increases N-glycan branching at the cell surface. Candidate transporters include SLC1A5, the high affinity glutamine transporter, which is required to support SLC7A5/SLC3A2, a bidirectional transporter that mediates glutamine efflux in exchange for the import of branched-chain essential amino acids (BCAA). BCAA from both uptake and autophagy are required for mTOR/S6K activation, protein synthesis and anabolic metabolism.

Unlike BCAA, external sources of glutamine and GlcNAc are not essential, but de novo synthesis appears to be tuned such that salvage is required under extreme conditions (rapid growth or starvation). mTOR complex is activated by BCAA interaction with RAG GTPase, growth factors signaling via GTP-binding protein RHEB, and energy charge/AMPK ratio. Here we will test the hypothesis that UDP-GlcNAc levels and N-glycan branching on glutamine and BCAA transporters promote their surface residency and thereby positive feedback via mTor signaling to metabolic reprogramming in cancer cells.

1. Our specific aims are: to determine the contribution of de novo HBP and salvage pathways to metabolic reprogramming in cancer cells under replete and depleted nutrient conditions. We are use cells with and without p53, and assess metabolism by multiple-reaction-monitoring mass spectrometry.
2. We are testing the hypothesis that HBP and N-glycan branching regulate glutamine (SLC1A5) and essential amino acid transport (SLC7A5/SLC3A2) transporters as well as the BCAA requirement for mTor activation in mammary human tumor cells.
3. We have identified additional downstream effectors of UDP-GlcNAc and N-glycan branching in cancer cells and are targeting these genes by CISPR/CAS9 to study possible synergy. (4) We are testing the vulnerabilities in cancer metabolism discovered herein as potential therapeutic targets in a human tumor cells xenograft model.

Plk4 and Cancer progression

Dr. Carol Swallow is a clinician-scientist working with Dr. Dennis in his lab on Polo family kinase Plk4, which is required for mitotic progression, centrosome replication, as well as cancer cell invasion. Plk4 is haploinsufficient for tumor suppression, and timely hepatocyte polarization in regenerating liver. Plk4 expression may also play a role in clinical cancer progression.

The gene expression pattern and functional assays incate that Plk4 cell promotes polarity, cell spreading, migration and invasion. PLK4 is often lost in human liver cancers, and in mice this event strongly promotes genome instability and liver cancer. However, up-regulation of Plk4 in late stages of cancer development promote invasion and tumor progression.

Selected Publications

J.W. Dennis and CF Brewer. Density Dependent Lectin-Glycan Interactions as a Paradigm for Conditional Regulation by Post-Translational Modifications (2013) Mol. Cell.  Proteomics 12:913-920.

Y. Zheng, C. Zhang, M.A. Soliman, R. Bagshaw, A. Pasculescu, L. Taylor, S. Tate, R.W. Hardy, R. Williams, J.W. Dennis, O. Rocks, A.Y. Dai, D.R. Croucher, R. J. Daly, T. Pawson. Temporal regulation of EGF signaling networks by the scaffold protein Shc1. (2013) Nature 499(7457):166-171.

A.A.Rahman, M. Ryczko, J. Pawling and J.W. Dennis.  Probing the hexosamine biosynthetic pathway in human tumor cells by multi-targeted tandem mass spectrometry.  (2013)  ACS Chemical Biology 8(9):2053-2062.

R. Williams, X. Ma, R.K. Schott, N. Mohammad, C.Y.Ho, C.F. Li, M. Demetriou and J.W. Dennis. Encoding asymmetry of the N-glycosylation motif facilitates glycoprotein evolution. (2014) PLoS One. 2014 Jan 24;9(1):e86088

M.A Soliman., A.M. Abdel Rahman, D.A. Lamming, K. Birsoy, J. Pawling, M.E. Frigolet, H. Lu, I.G. Fantus, A. Pasculescu, Y. Zheng, D.M. Sabatini, J.W. Dennis, T. Pawson. The Adaptor Protein p66Shc Inhibits mTOR-Dependent Anabolic Metabolism. (2014) Sci Signal. 7(313):ra17.

CO Rosario, K Kazazian, FS Zih, O Brashavitskaya, Y Haffani, RS Xu, A George, JW Dennis, CJ Swallow.  A novel role for Plk4 in regulating cell spreading and motility. (2014) Oncogene Sep 1. doi: 10.1038/onc.2014.275. [Epub ahead of print].

A Johswich, C. Longuet, J. Pawling, A. Abdel Rahman, M. Ryczko, DJ Drucker, J.W. Dennis. N-glycan Remodeling on Glucagon Receptor is an Effector of Nutrient-sensing by the Hexosamine Biosynthesis Pathway. (2014) J. Biol. Chem. 289; 15927-41.

A.M. Abdel Rahman, J. Pawling, M. Ryczko, A.A. Caudy, and J.W. Dennis. Targeted metabolomics in cultured cells and tissues by mass spectrometry: method development and validation (2014) Analytica Chimica Acta, 845:53-61.

A.M. Abdel Rahman, M. Ryczko, M. Nakano,  J. Pawling, T. Rodrigues, A. Johswich, N. Taniguchi, and J.W. Dennis. (2015) Golgi N-Glycan Branching N- Acetylglucosaminyltransferases I, V and VI Promote Nutrient Uptake and Metabolism. Glycobiology 25(2):225-240.

J. So, A. Pasculescu, A.Y. Dai, K. Williton, A. James, V. Nguyen, P. Creixell, E.M. Schoof, J. Sinclair, M. Barrios-Rodiles, J. Gu, A. Krizus, R. Williams, M. Olhovsky, J. W. Dennis, J.L Wrana, R. Linding, C. Jorgensen, T. Pawson, K. Colwill (2015)  Integrative analysis of kinase networks in TRAIL-induced apoptosis provides a source of potential targets for combination therapy. Sci. Signal. 8(371):rs3.