Tom Huxford
Assistant Professor
Biochemistry
Office: CSL 325A
Office Phone: 619-594-1606
e-mail: thuxford_at_sciences.sdsu.edu
Curriculum Vita
- B.S. Biochemistry, Brigham Young University, Provo, Utah, 1995
- Ph.D. Chemistry, University of California San Diego, La Jolla, California, 2001, Advisor: Dr. Gourisankar Ghosh
- Postdoc Structural Biology, University of California San Diego, La Jolla, California, 2005, Fellow of the University of California University-wide AIDS Research Program
- Assistant Professor, Department of Chemistry & Biochemistry, San Diego State University, 2005-present
- Assistant Professor, Molecular Biology Institute, San Diego State University, 2005-present
Research Interests
NF-kappaB is an inducible transcription factor that regulates the expression of genes involved in inflammation, immunity, cell adhesion, growth, development, and death. NF-kappaB is present in most resting cells as an inactive complex with a member of the IkappaB family of transcription factor inhibitor proteins. In response to inducing stimuli, such as cytokines and growth factors, viral and bacterial products, physical or environmental stresses, and chemotherapeutic drugs, the complex-associated IkappaB molecule becomes degraded. Removal of IkappaB converts NF-kappaB to its active form. Active NF-kappaB rapidly accumulates in the nucleus where it binds to specific DNA sequences present in the promoter regions of target genes and activates their expression. Some of the genes that are activated by NF-kappaB include cytokines, immunoreceptors, and other mediators of innate and adaptive immunity, cell adhesion molecules, transcription factors, and anti-apoptotic genes.
Because NF-kappaB responds to so many different stimuli and is capable of activating the expression of so many important genes, its regulation is paramount for proper cellular function. During the past decade, multiple layers of NF-kappaB regulation have been proposed to function in various cell types and states. While proper NF-kappaB function is required for robust immune response, proper healing of tissues, and protection against massive apoptotic cell death, too much NF-kappaB has been implicated to contribute to inflammatory diseases such as rheumatoid arthritis, asthma, and irritable bowel diseases. Due to its ability to help protect cells against apoptosis, NF-kappaB has become an important general target for treatment of cancerous tumors.
In my lab, we use a combination of structural biology and protein biochemistry techniques to study the molecular mechanisms of NF-kappaB signaling and regulation. By understanding the structures and chemistries behind NF-kappaB regulation, it is hoped that we might contribute to an improved ability to control the activity of this master transcription factor.
Some specific areas of interest:
Classical IkappaB structure- Stucture-based biochemical anaylsis of IkappaBalpha and IkappaBbeta proteins bound to NF-kappaB dimers has revealed significant differences in the mechanisms used by these otherwise homologous proteins in regulating NF-kappaB. For example, we now understand that NF-kappaB/IkappaBalpha complexes shuttle between the nucleus and cytoplasm in resting cells while inactive NF-kappaB/IkappaBbeta complexes reside exclusively in the cell cytosol. The newest member of the class of "professional IkappaB" is IkappaBepsilon. While it shares many functional characteristics of IkappaBalpha, it shows some differences including a longer amino-terminal domain, a consensus sixth ankyrin repeat, and the absence of a true C-terminal PEST domain.
Nuclear IkappaB structure and function- Not all NF-kappaB dimers are capable of activating gene transcription. The NF-kappaB p50 homodimer contains the nuclear localization and DNA binding functions, but acts as a repressor of reporter gene transcription in vitro. A subclass of nuclear IkappaB proteins is thought to recognize NF-kappaB p50 homodimers on target gene promoters and convert the repressor to an activator of transcription. This mechanism has been proposed to account for the delayed NF-kappaB-dependent expression of genes such as the inflammatory cytokine interleukin-6 (IL-6).
NF-kappaB as an activator of HIV transcription- The human immunodeficiency virus-1 (HIV) genome encodes for a pair of NF-kappaB binding sites within its long terminal repeat (LTR) promoter element. As a consequence, activation of NF-kappaB in cells harboring the virus leads to activated viral transcription. Recently, a small protein known as Murr1 was found to interfere with NF-kappaB signaling at the level of IkappaBalpha degradation. This results in inhibition of gene transcription from the HIV LTR promoter in T cells.
Microbial factors that interfere with NF-kappaB signaling- The open reading frame A238L, contained in the double-stranded DNA virus African Swine Fever Virus (ASFV), is an inhibitor of multiple immune signaling pathways. A238L has been shown to interfere with NF-kappaB signalling in host cell macrophages by binding and inhibiting NF-kappaB. The same protein has also been shown to inhibit the phosphatase calcineurin, which functions in the signaling pathway of another immune system transcription factor called nuclear factor of activated T cells (NF-AT). Thus, the versatile A238L protein serves to knock out two vital lines of communication in immune signaling and helps this virus escape immune detection.
Full Publication list
Selected Publications
- "Thermodynamics reveal that helix four in the NLS of NF-kappa B p65 anchors I kappa B alpha, forming a very stable complex," Bergqvist S, Croy CH, Kjaergaard M, Huxford T, Ghosh G, Komives EA, Journal of Molecular Biology 360 421-434 2006.
- "Structures of Aplysia AChBP complexes with nicotinic agonists and antagonists reveal distinctive binding interfaces and conformations," Hansen SB, Sulzenbacher G, Huxford T, Marchot P, Taylor P, Bourne Y, Embo Journal 24 3635-3646 2005.
- "Biophysical characterization of the free I kappa B alpha ankyrin repeat domain in solution," Croy CH, Bergqvist S, Huxford T, Ghosh G, Komives EA, Protein Science 13 1767-1777 2004.
- "X-ray crystal structure of an I kappa B beta center dot NF-kappa B p65 homodimer complex," Malek S, Huang DB, Huxford T, Ghosh S, Ghosh G, Journal of Biological Chemistry 278 23094-23100 2003.
MS Theses and Ph.D. Dissertations
- Danny Trinh, M.S. Thesis 2007. Biochemical characterization of IkappaBzeta interactions with NF-kappaB/DNA complexes.