William E. Courchesne, Ph.D.
Associate
Professor
Department
of Microbiology and Immunology
School of Medicine, MS 320
University of Nevada
Reno, NV 89557-0197
Office Phone: (775)
784-4113
Fax: (775) 327-2332
E-mail: wcourchesne@medicine.nevada.edu
Research Interests:
Our research focuses on calcium metabolism in the yeast Saccharomyces cerevisiae and on the molecular mechanism of amiodarone, a novel antifungal that we have identified.
Calcium signaling is involved in myriad cellular processes such as mating morphogenesis. Mating in yeast induces changes in cell morphology with a concomitant increase in calcium uptake that is dependent on the MID1 and CCH1 genes. Mid1p and Cch1p are believed to function in a capacitative-calcium entry (CCE)-like process.
We have shown that amiodarone causes a dramatic increase in the free cytoplasmic
calcium concentration ([Ca2+]cyt) in S. cerevisiae. About 90%
of this increase is dependent on extracellular Ca2+, while 10% of the
increase in [Ca2+]cyt is due to release from intracellular stores. The
influx of extracellular Ca2+ may be a direct effect of amiodarone on a
membrane transporter or may be by a capacitative-calcium entry mechanism.
Uptake of the extracellular Ca2+ is inhibited by caffeine and reduced
in strains deleted for the mid1 gene but not in cells deleted
for cch1. Our data are the first demonstrating control of yeast
calcium channels by amiodarone and caffeine.
Novel
Antifungal. Fungal infections are common in patients with acquired
immunodeficiency syndrome and pose a major health management problem.
There is a need for identification of new antifungals to complement the
limited current repertoire and to combat newly arising resistant fungal
strains. We have identified a novel antifungal activity for the antiarrhythmic
drug amiodarone. Extensive characterization of this activity shows that
amiodarone exhibits a growth inhibition for several diverse fungi, including
species of Cryptococcus, Saccharomyces, Aspergillus, Candida, and
Fusarium. The antifungal activity was shown to be fungicidal;
Cryptococcus neoformans treated with amiodarone
lost viability within hours of drug exposure. Growth inhibition could
be suppressed by addition of very high concentrations (10 mM) of Ca2+
to the medium, suggesting that disruption of calcium homeostasis was involved
in the antifungal activity. In conclusion, amiodarone displays broad-based
fungicidal activity and may be acting in part by perturbing the calcium
balance.
Recent Publications:
Courchesne, W.E. 2002. Characterization of a novel, broad-based fungicidal activity for the antiarrhythmic drug amiodarone. J.Pharm.Exp.Therap., 300: 1-5.
Cao, H., W.E. Courchesne, and C.C. Mastick. 2002. A phosphotyrosine-dependent protein interaction screen reveals a role for phosphorylation of caveolin-1 on tyrosine 14: recruitment of C-terminal Src kinase. J. Biol. Chem. 277: 8771-8774.
Courchesne, W.E. and S. Ozturk. 2003. Amiodarone induces a caffeine-inhibited, MID1-dependent rise in free cytoplasmic calcium in Saccharomyces cerevisiae. Mol. Microbiol. 47: 223-234.
Courchesne, W.E., M. Tunc, S. Liao. 2009. Amiodarone induces stress responses and calcium flux mediated by the cell wall in S. cerevisiae. Ca. J. Microbiology 55:288-303.