Microbiology and Immunology : Microbiology and Immunology Faculty

Ken Fields, Ph.D.

Assistant Professor of Microbiology and Immunology

(305) 243-6711 (office)

(305) 243-4623 (fax)

Room 3033 (office) / 3084 (lab), Rosenstiel Medical Sciences Building

kfields@med.miami.edu

Curriculum Vitae

BS, Biochemistry and Molecular Biology, 1991

PhD, Microbial Pathogenesis, 1999

Postdoctoral, Laboratory of Intracellular Parasites, NIAID, 1999-2004

Assistant Professor, University of Miami Miller School of Medicine, 2004-present

Research Interests

The Gram-negative bacterium Chlamydiatrachomatisis an obligate intracellular, medically significant human pathogen capable of colonizing genital or ocular mucosal epithelia. Infections by genital-specificC.trachomatisserovars represent the most common reportable sexually transmitted disease in the United States with an average of 4 million new cases reported annually. Ocular-specific serovars potentially affect 400 million people worldwide. Infections result in progressive corneal scarring that can lead to trachoma, the most prevalent form of preventable blindness worldwide. Disease pathology most likely results from the significant inflammatory response provoked by chlamydial infection and not by specific toxins per se. Pathology is exacerbated and in some cases may depend on repeated or chronic infection. The fact that most chlamydial genital infections are asymptomatic until serious, irreversible pathology develops makes this a particularly insidious and costly pathogen. Significantly, infections fail to elicit solid, long-term protective immunity, and there is currently no efficacious vaccine available. Chlamydiaspp. develop entirely within a parasitophorous vacuole termed an inclusion (Figure 1), which remains non-fusogenic with the host endocytic pathway. Although chlamydiae certainly stimulate and are susceptible to inactivation by mediators of both cellular and humoral immunity, their ability to persist is likely related to an ability to exploit the privileged intracellular niche afforded by the inclusion. The focus of my lab is to understand how Chlamydia, while sequestered within a membrane-bound vacuole, are able to directly modulate host-cell functions and thereby create and maintain a pathogen-permissive environment.

Figure 1. The C. trachomatis inclusion. A. Electron micrograph of an inclusion containing actively growing reticulate bodies. Indirect immunofluorescence (B) and corresponding Nomarski image (C) of an inclusion containing both reticulate and elementary bodies. The secreted T3SS protein CopB is shown in Red while chlamydiae are shown in green. Bars = 1 mM.

Specifically, the lab studies contributions of a type III secretion mechanism to chlamydial pathogenesis. The type III mechanism has been described in a diverse array of medically and commercially significant bacterial pathogens (see pages of Drs. Greg Plano and Kurt Schesser) and represents a sophisticated secretion system used to deploy anti-host proteins termed effectors that disrupt the host’s ability to effectively combat infection. Type III systems are essential for full virulence, and although the secretory apparatus is somewhat conserved among pathogenic bacteria, the complement of effectors varies depending on the needs of the specific pathogen. Chlamydiagenomes contain genes encoding a functional type III apparatus but consistent with Chlamydia’s unique niche, lack coding sequences for effectors homologous to recognized effectors in other systems. Since there is currently no tractable genetic system for Chlamydia, a screen for chlamydial type III effectors has been developed using the heterologous Yersiniatype III system. The identification and elucidation of the functional contributions of these effectors to chlamydial pathogenesis are a primary research focus.

Current projects include:

• Identification of host targets for currently identified Chlamydiatype III effectors that likely function during crucial stages of chlamydial development.

• Study of the in vitro and in vivo consequences of these interactions on chlamydial pathogenesis and development.

• Elucidation of additional Chlamydiaeffectors that are unique to a given chlamydial species and possible confer to observed differences in pathogenesis.

The investigation of the type III system as a target for disrupting normal chlamydial development represents a secondary focus of the lab. Given the importance of this secretion system to pathogenesis and the exposure of functionally important components of the apparatus on infectious particles, we hypothesize that interference with T3S activity will result in non-productive growth and therefore the ability to cause disease. We are specifically targeting antigen specific antibodies as well as treatments that disrupt essential protein-protein interactions as a means to prevent chlamydial infection.

Current projects include:

• Identification of surface-exposed components of the Chlamydiatype III apparatus.

• Studies designed to identify direct interactions of apparatus components with host cells and evaluate functional consequences of those interactions.

• Assessment of surface-exposed type III components as targets for neutralizing antibodies.

Recent Publications

Hower, S., Wolf, K., and Fields K.A. 2009. Evidence that CT694 is a novel Chlamydia trachomatis T3S substrate capable of functioning during invasion or early cycle development. Mol Microbiol. 72:1423-1437.

Wolf, K., Plano, G.V., and Fields K.A. 2009. CP0236 is a C. pneumoniae-specific Inc which impairs IL-17 signaling via interaction with Act1. Cell Microbiol. 11:769-779.

Betts, H.J., Twiggs, L.E., Sal, M.S., Wyrick, P.B., and Fields, K.A. 2008. Bioinformatic and biochemical evidence for the identification of the type III secretion system needle protein of Chlamydia trachomatis. J. Bacteriol. 190:1680-1690.

Chellas-Gery, B., Linton, C.N., and Fields, K.A.2007. Human GCIP interacts with CT847, a novel Chlamydia trachomatistype III secretion substrate, and is degraded in a tissue-culture infection model. Cell Microbiol. 9:2417-2430.

Wolf, K., Betts, H.J., Chellas-Gery, B., Hower, S., Linton, C.N., and Fields K.A. 2006. Treatment of Chlamydia trachomatiswith a small molecule inhibitor of the Yersiniatype III secretion system disrupts progression of the chlamydial developmental cycle. Mol Microbiol. 61:1543-1555.

Clifton, D.R., Fields, K.A., Grieshaber, S.S., Dooley, C.A., Fischer, E.R., Mead, D.J., Carabeo, R.A., and Hackstadt, T. (2004) A chlamydial type III translocated protein is tyrosine-phosphorylated at the site of entry and associated with recruitment of actin. Proc Natl Acad Sci U S A 101: 10166-10171.

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