New Scholar Award in Global Infectious Disease
Kristin M. Hager, Ph.D.
University of Notre Dame

Analysis of membrane trafficking events in the regulation of organelle biogenesis and stability in Apicomplexan parasites

Toxoplasma gondii is an opportunistic protozoan infecting one-third of world's population. Normally asymptomatic in immune-competent individuals, it induces severe pathology in children in utero and immune compromised individuals such as AIDS patients. The alarming spread of HIV has increased the focus of the world research community on opportunistic pathogens. We believe the "success" of T. gondii as a parasite is due to its ability to infect virtually any nucleated cell. Contact with the host cell triggers a sequential release of protein from three highly specialized secretory organelles. These secreted proteins enable the parasite to invade and establish a vacuole. Therefore, proper packaging and vesicular targeting (membrane trafficking) of secretory proteins to these organelles is critical for the parasite's survival.  

My laboratory is interested in membrane trafficking mechanisms that ensure accurate targeting or "proof-reading" of essential parasite proteins. A Golgi receptor, TgERD2, was identified in my lab. TgERD2 is involved in retrieval of missorted proteins and its expression appears cell cycle regulated. This is important because the Golgi is one of the first structures to duplicate during cell division and identifies TgERD2 as a potent drug target for disrupting parasite division. Importantly, we observe Golgi collapse upon increasing TgERD2 expression and hence upregulation of retrograde trafficking. My studies show that uncoupling ER to Golgi trafficking by overexpression of TgERD2 results in disruption of membrane trafficking and impinge on organelle biogenesis and/or structural integrity. My project will determine the role of TgERD2 in "proof-reading" of proteins in T. gondii. First, we assess the role of certain amino acids in function, localization and protein-protein interactions by introducing point mutations into TgERD2-GFP. We then assess the targeting of proteins to specific organelles and overall organelle integrity. Secondly, we will determine if expression of the receptor is (or is not) cell cycle dependent. Thirdly, we will determine if TgERD2 is essential to cell viability by using antisense RNA approaches to modulate TgERD2 expression levels. 

While Toxoplasma is not a ‘tropical disease’, certain extrapolations can be made from this research to other members of its phyla which contains some of the most medically virulent parasitic protozoa (e.g. the causative agent of malaria). Toxoplasma is amenable to genetic manipulation (possessing no codon bias and high transfection efficiencies) and is readily cultured in-vitro. These features (and others) allow my lab the ability to do the types of cell biology experiments that are simply not feasible in other globally infectious protozoa where the Golgi apparatus is either not present or exists as a primitive collection of tubules.

Contact Dr. Hager.