Core Faculty

Nigel Bunnett, Ph.D.

Research Description

The nervous system plays an essential role in inflammation and pain. Sensory nerves detect inflammatory and noxious stimuli in peripheral tissues that activate G-protein coupled receptors, receptor tyrosine kinases and ligand-gated ion channels. These stimuli cause the secretion of neuropeptides from sensory fibers in peripheral tissues and the spinal cord. In peripheral tissues, sensory neuropeptides cause inflammation, characterized by edema and granulocyte infiltration. In the spinal cord, sensory neuropeptides activate receptors on spinal neurons resulting in pain transmission. Although inflammation protects against infection, and pain sensations allow organisms to avoid damaging stimuli, these processes must be tightly controlled, since dysregulated inflammation and pain cause disease.

We study the mechanisms that switch-on and switch-off inflammation and pain. Our work focuses on the role of proteolytic enzymes as “molecular switches” that initiate and terminate signal transduction by mediators of inflammation and pain. Proteases that act at the cell-surface, in endosomes, lysosomes and proteasomes cleave neuropeptides, G-protein coupled receptors and ion channels and thereby control signaling by major mediators of inflammation and pain.

Serine proteases from the circulation, inflammatory cells, epithelial tissues and neurons, which are generated and released during injury and inflammation, signal to nerves by cleaving protease-activated receptors. Proteases from invading pathogens, such as bacteria and fungi, can also cleave these receptors. Once cleaved, protease-activated receptors exert multiple proinflammatory and nociceptive effects. They also cause sustained hyperexcitability of neurons, in part by sensitizing ion channels, including members of the large family of transient receptor potential channels.

Cell-surface metalloendopeptidases, such as  neprilysin, degrade neuropeptides in the extracellular fluid and thereby terminate inflammatory and nociceptive signaling. Once activated at the plasma membrane, many G-protein coupled receptors desensitize and traffic to endosomes by well-defined processes. Far less is known about the post-endocytic sorting of receptors to the plasma membrane, which mediates resensitization of signaling, or to lysosomes or proteasomes, which irrevocably terminates signaling. Metalloendopeptidases that have been recently discovered in endosomes control post-endocytic trafficking and signaling of G-protein coupled receptors. For instance, endothelin converting enzyme cleaves endocytosed neuropeptides in acidified early endosomes and thereby disrupts endocytic signaling complexes, comprising peptides/receptors/arrestins and mitogenic kinases. This mechanism terminates mitogenic signaling of endocytosed receptors and promotes receptor recycling and resensitization.

Proteases in lysosomes and proteasomes degrade receptors and ion channels to irrevocably terminate their ability to signal. Ubiquitin ligases covalently modify receptors and channels and thereby direct proteins to lysosomes and proteasomes, where proteolysis terminates signaling. Deubiquitinating proteases in endosomes remove ubiquitin, a necessary step in trafficking to degradatory pathways.

We seek to discover the mechanisms that switch inflammation and pain on and off through studies at the molecular, cellular and organismal level. An understanding of the mechanisms that initiate and terminate inflammation and pain will provide insights into new therapies for prevalent and debilitating human diseases.

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Current Projects

Characterization of the molecular mechanisms that regulate the trafficking of G-protein coupled receptors and transient receptor potential ion channels to and from the plasma membrane.

Investigation of the roles of metalloendopeptidases and deubiquitinating proteases in endosomes in controlling the post-endocytic trafficking and signaling of G-protein coupled receptors and ion channels.

Discovery of the mechanisms by which proteases and protease-activated receptors sensitize ion channels to induce sustained hyperexcitability of neurons.

Characterization of mechanisms by which microbial proteases cleave protease-activated receptors on sensory nerves and thereby regulate the activity and function of sensory nerves.

Evaluation of the roles of proteases, neuropeptides and transient receptor potential ion channels in inflammatory diseases of the intestine and pancreas.

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Selected Publications

Roosterman, D., Cottrell, G.S., Padilla, B.E., Muller, L., Cottrell, G.S., Bunnett, N.W., Steinhoff, M. Endothelin-converting enzyme-1 degrades substance P in endosomes to regulate resensitization of the neurokinin 1 receptor. PNAS, 2007.

Cottrell, G.S., Amadesi, S., Pikios, S., Camerer, E., Willardsen, A., Murphy, B., Caughey, G., Wolters, P.J., Coughlin, S.R., Pothoulakis, C., Bunnett, N.W., Grady, E.F. Protease-activated receptor 2, dipeptidyl peptidase I and tryptic proteases mediate Clostridium difficile toxin A-induced ileitis in mice. Gastroenterology, 2007.

Grant, A.D., Cottrell, G.S., Amadesi, S., Trevisani, M., Nicoletti, P., Materazzi, S., Altier, C., Cenac, N., Zamponi, G.W., Bautista-Cruz, F., Lopez, C.B., Joseph, E.K., Levine, J.D., Liedtke, W., Vanner, S., Vergnolle, N., Geppetti, P. and Bunnett, N.W. Protease-activated receptor 2 sensitizes the transient receptor potential vanilloid 4 ion channel to cause mechanical hyperalgesia in mice. J Physiol 578, 715-733, 2007.

Cenac, N., Andrews, C.N., Holzhausen, M., Chapman, K., Cottrell, G., Andrade-Gordon, P., Steinhoff, M., Barbara, G., Beck, P., Bunnett, N.W., Sharkey, K.A., Ferraz, J.G., Shaffer, E. and Vergnolle, N. Role for protease activity in visceral pain in irritable bowel syndrome. J Clin Invest 117, 636-647, 2007.

Jacob, C., Yang, P.C., Darmoul, D., Amadesi, S., Saito, T., Cottrell, G.A., Coelho, A.M., Singh, P., Grady, E.F., Perdue, M., and Bunnett, N.W. Mast cell tryptase controls paracellular permeability of the intestine: Role of protease-activated receptor 2 and beta -arrestins. J Biol Chem 280: 31936-31948, 2005.

Amadesi, S., Nie, J., Vergnolle, N., Cottrell, G.S., Grady. E.F., Trevisani, M., Manni, C., Geppetti, P., McRoberts, J.A., Ennes, H., Davis, J.B., Mayer, E.A. and Bunnett, N.W. Protease-activated receptor 2 sensitizes the capsaicin receptor TRPV1 to cause thermal hyperalgesia. J Neurosci 24: 4300-4012, 2004.

Steinhoff, M., Vergnolle, N., Young, S. H., Tognetto, M., Amadesi, S., Ennes, H. S., Trevisani, M., Hollenberg, M. D., Wallace, J. L., Caughey, G. H., Mitchell, S. E., Williams, L. M., Geppetti, P., Mayer, E. A. and Bunnett, N. W. Agonists of proteinase-activated receptor 2 induce inflammation by a neurogenic mechanism. Nat Med 6: 151-158, 2000.

DeFea, K. A., Zalevsky, J., Thoma, M. S., Dery, O., Mullins, R. D. and Bunnett, N. W. beta-arrestin-dependent endocytosis of proteinase-activated receptor 2 is required for intracellular targeting of activated ERK1/2. J Cell Biol 148: 1267-1281, 2000.

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Contact Information

Email: nigel.bunnett@ucsf.edu
Phone: 415-476-0489
Mailing Address:
Nigel W. Bunnett Ph.D.
Room S1268
University of California San Francisco
521 Parnassus Avenue
San Francisco, CA 94143-0660, USA

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