Norma W. Andrews, Ph.D.

Professor of Microbial Pathogenesis and Cell Biology
Andrews lab website Phone: (203) 737-2410 Fax: (203) 737-2630 Lab: (203) 737-2411 e-mail: norma.andrews@yale.edu		Section of Microbial Pathogenesis Yale University School of Medicine 295 Congress Avenue PO Box 9812 New Haven, CT 06536-0812 <Courier Address> 295 Congress Avenue BCMM 354D (Lab: BCMM 341) New Haven, CT 06519-1418

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We are currently pursuing two interconnected lines of investigation. One is focused on molecular strategies utilized by intracellular pathogens to interact with their host cells, and fundamental cell biological processes that are subverted by pathogens during infection. The second is a study of mechanisms regulating calcium-dependent exocytosis of lysosomes, and the role of this process in plasma membrane repair and in specialized cells of the immune system.

Invasion and intracellular survival of protozoan parasites
Our studies of the cell invasion mechanism of Trypanosoma cruzi uncovered a previously unrecognized, ubiquitous process of calcium-triggered recruitment and fusion of lysosomes with the plasma membrane. This pathway is subverted by the parasites as a strategy to form a vacuole, through which they gain entry to host cells. Current projects include the study of signaling pathways involved in trypanosome entry, and molecular mechanisms of intracellular survival of the related trypanosomatid parasite Leishmania.

Regulation of lysosomal exocytosis and membrane repair
We found that a ubiquitously expressed member of the synaptotagmin family of calcium sensors, Syt VII, is localized on the membrane of lysosomes in many cell types. Experiments using inhibitory reagents and Syt VII-deficient mice demonstrated that this protein is required for lysosomal exocytosis and for the normal resealing of plasma membrane wounds, in addition to modulating the killing activity of cytotoxic lymphocytes and providing additional membrane to phagosomes in macrophages. We are now focusing on mechanisms used by mammalian cells to repair plasma membrane wounds caused by bacterial pathogens. Injury inflicted by bacteria was probably one of the earliest threats to the integrity of eukaryotic cell membranes, and is likely to have played an important role in the evolution of repair mechanisms. We are interested in elucidating how mammalian cells repair lesions induced by bacterial agents (pore-forming toxins, specialized secretion systems), and in determining whether this mechanism, similar to what occurs in response to mechanical wounds, involves lysosomal exocytosis. Invasion and intracellular replication of bacterial mutants lacking specific membrane-damaging agents are being compared in wild type and resealing-defective mouse cells.

Selected Publications:

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Huynh, C, Sacks, D.L. and Andrews, N.W. (2006) A Leishmania amazonensis ZIP family iron transporter is essential for parasite replication within macrophage phagolysosomes. J. Exp. Med.203: 2363-2375.

Czibener, C., Sherer, N.M., Mothes, W. and Andrews, N.W. (2006) Ca2+ and Synaptotagmin VII-dependent delivery of lysosomal membrane to nascent phagosomes. J. Cell Biol.174:997-1007.

Arantes, R.M.E. and Andrews, N.W. (2006) A role for synaptotagmin VII-regulated exocytosis in neurite outgrowth from primary sympathetic neurons. J. Neurosci. 26: 4630-4637.

Andrews, N. W. (2005) Membrane Repair and Immunological Danger. EMBO reports 6: 826-830.

Andrade, L. O. and Andrews, N. W. (2005) The Trypanosoma cruzi-host cell interplay: Location, invasion, retention. Nature Reviews Microbiology 3: 819-823.

Andrews, N. W and Chakrabarti, S. (2005) There’s more to life than neurotransmission: The regulation of exocytosis by synaptotagmin VII.  Trends in Cell Biology 11: 626-631.

Roy D, Liston DR, Idone VJ, Di A, Nelson DJ, Pujol C, Bliska JB, Chakrabarti S, Andrews NW. (2004)  A process for controlling intracellular bacterial infections induced by membrane injury. Science 304: 1515-1518. 

Andrade LO and Andrews NW. (2004)  Lysosomal fusion is essential for the retention of Trypanosoma cruzi inside host cells. J Exp Med, 200: 1135-1143. 

Huynh C, Roth D, Ward DM, Kaplan J, Andrews NW. (2004)  Defective lysosomal exocytosis and plasma membrane repair in Chediak-Higashi cells. Proc Natl Acad Sci. 101: 16795-16800. 

Chakrabarti S, Kobayashi K, Flavell RA, Miyak, K, Liston D, Fowler K, Gorelick FS, Andrews NW. (2003)  Impaired membrane resealing and autoimmune myositis in synaptotagmin VII-deficient mice. J Cell Biol. 162(4): 543-549. 

 

Figure 1: Scanning electron micrographs of Trypanosoma cruzi attached (left image) and invading (right image) a mammalian cell. Invasion occurs by formation of a tight vacuole, derived from intracellular lysosomal membranes.

Figure 2: Lysosomes fuse with the plasma membrane of injured cells. Cells were wounded by scratching in the presence of membrane-impermeable fluorescent dextran, which penetrates into the cytosol of wounded cells (red). The lysosomal glycoprotein Lamp-1 is exposed on the surface of wounded cells (green), but not on intact cells (nuclei are stained in blue).