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Christian Paumi, Ph.D.

Assistant Professor
Graduate Center for Toxicology

Mailing Address:
Graduate Center for Toxicology
1095 V.A. Drive
306 Health Sciences Research Building
Lexington, KY  40536-0305
Office: 212 Combs
Phone: (859) 323-6086
Fax: (859) 323-6086
Web site:

Research Interests

Determining the biological role of multidrug resistance proteins (MRPs) in cellular metabolism and detoxification

The multidurug resistance-associated protein (MRP, also called the ABCC) subfamily of the ATP-binding cassette (ABC) transporters promote multidrug resistance and the detoxification of exogenous toxins such as heavy metals (Cd+2, As+3, Hg+2, and Pb+2). In mammalian cells the MRPs promote the efflux of leukotrienes and glutathione conjugated prostaglandins, and in yeast the MRPs are required for the formation of the red pigment of ade2 mutants, suggesting that they may also play a key role in protecting cells from endogenous toxins or the over accumulation of metabolic pathway intermediates.

The goal of my research is to answer important, unsolved questions about how MRP proteins perform their physiological roles in drug disposition and metabolism and to determine how and to what extent is MRP function regulated. To answer these questions I have used the yeast, Saccharomyces cerevisiae, as a model system to study the physiological function of the MRPs. Recently, I have used the genetic and biochemical versatility of yeast to identify and characterize genes that regulate MRP function. Ultimately, I intend to extend my studies into a mammalian cell system where I will determine if human homologues of the newly identified regulators of MRP function have similar roles for the human MRPs. By combining the genetic power available in yeast with in vitro biochemical assays and in vivo cellular assays I have been able to ask questions about MRP physiological function that previously could not be tested. The skills I have developed during my postdoc in yeast in combination with the skills I developed as a graduate student in mammalian cell culture will provide me with the tools necessary to answer questions that would be difficult to answer in either a yeast or mammalian model system alone.

The current approaches that I am using to examine the physiological role of the MRPs in drug detoxification and metabolism, and dissect cellular mechanisms of MRP regulation are to: 1) Carry out genetic and protein-interactor (yeast two-hybrid) screens, in Saccharomyces cerevisiae, to identify proteins that regulate MRP function in vivo and 2) determine the mechanism by which these genetic and protein-interactors regulate MRP function by a combination of in vivo cellular based assays and in vitro biochemical assays. Yeast are amenable to genetic and biochemical manipulation and therefore are an excellent tool in which to study MRP function and regulation. Further, with the recent addition of iMYTH, a membrane based yeast two-hybrid assay designed to identify protein interactors for membrane proteins, yeast are an extremely attractive model organism in which to study the membrane tethered MRPs. As a postdoctoral fellow in the lab of Dr. Susan Michaelis I compiled an extensive set of yeast tools which I have used to study the yeast MRP, Ycf1p. In collaboration with Dr. Igor Stagljar, I used iMYTH to identify protein-interactors of Ycf1p. Through a series of genetic and biochemical studies I have showed that one Ycf1p-protein interactor, Tus1p (A GEF for the small GTPase Rho1p), promotes Ycf1p transport activity via the small GTPase, Rho1p. Our studies suggest that Tus1p tethers Ycf1p and Rho1p together and via an as of yet undefined mechanism, activated Rho1p increases Ycf1p function. These studies have established that iMYTH is a robust technology which I can use to dissect MRP function and that we have identified a novel role for GEFs in regulating MRP function in vivo.

In the immediate future I will continue using yeast as a model to study the role of phosphorylation as a mechanism to posttranslationally regulate MRP function. I am currently interested in the mechanism by which the yeast CKII, cka1p, regulates Ycf1p cellular function and determining if the human cka1p homologue, CKIIalpha, regulates human MRP cellular function.

For a list of Dr. Paumi's publications, please visit the PubMed web site.

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