Anna Radominska-Pandya, Ph.D.

Professor

Ph.D., Institute of Biochemistry and Biophysics,

Polish Academy of Sciences, Warsaw, Poland

  Our laboratory is extensively involved in structure-function relationship studies of human UGTs.  UGTs are a class of enzymes that are involved in the detoxification of a variety of toxic and endogenous compounds.  Our goal is to identify critical amino acids within the active sites of these enzymes using photoaffinity labeling.  To do this, we use UGT substrates or inhibitors that have been modified with a photolabile group, which upon photoactivation of this probe in situ covalently bind to the active site of the UGT protein.

Photoaffinity labeling allows membrane bound UGTs to be labeled in their native state, and valuable information on the structure, architecture and orientation of the active sites of UGTs has been obtained in our lab using this technique.  A recent development in the identification of active site amino acids has been the generation of recombinant human UGTs containing a C-terminal His-tag that are expressed in baculovirus infected Sf9 insect cells.  This system results in high levels of expressed proteins that are post-transcriptionally modified by glycosylation.  Now that sufficient amounts of catalytically-active UGT protein are available, our probes are indispensable for the identification of both the co-substrate and substrate-binding sites of the UGTs.  As a result, we have generated the first comprehensive data in this area identifying the phenol binding site of UGT1A10. 

Information generated from these studies will lead to the identification of more UGT binding sites and will eventually result in the elucidation of the molecular mechanisms of the important detoxification processes carried out by UGTs.  This information can then be directly applied to pharmacological and clinical settings, resulting in the design of safer and more efficient medications.  

Regulation of Human UGTs.  Our research in this area is focused on the transcriptional regulation of UGTs from the UGT1A and UGT2B families.  Our research builds on our findings that: 1) UGT1A isoforms are target genes for two human nuclear receptors, hPXR and hCAR. 2) UGT2B7, which glucuronidates a variety of endogenous compounds recognized as ligands for NRs, is down-regulated by bile acids and retinoic acid.  3) Two human isoforms from the UGT1A family, UGT1A3 and 1A4, are targets for AhR.  Characterization of the mechanism by which endogenous and exogenous compounds regulate UGT expression can lead to: 1) understanding of UGTs function in a normal state and in various diseases, such as cancer, and 2) it will also allow for the development of NR-targeted genes that will be able to increase or decrease UGTs activity.

Suppression of Human UGTs in Cancer Cells.  It is recognized that UGTs can metabolize a wide range of toxins and carcinogens and, therefore, play a critical role in detoxification of these compounds.  We and others have observed a correlation between the absence of UGT expression and cell proliferation. Comparisons of UGT expression levels in normal and cancer cells demonstrated a significant reduction in UGT mRNA in a number of tumor samples.  It is hypothesized that down regulation of UGTs could be one of the basic events in neoplastic transformation.  We have demonstrated that the levels of UGTs in cancer cells, as compared to corresponding normal cells, are significantly reduced or totally absent. Our study with ovarian cancer cells, which are lacking UGT2B7, demonstrated that stable expression of UGT2B7 in these cells resulted in colony formation, cell growth arrest, and decreased cell proliferation.  Similar studies are also being done with breast cancer tissue.  These data allows us to propose a role for UGTs in preventing hormone-induced and/or chemical carcinogenesis.

Selected Publications:

Starlard-Davenport, A., Xiong, Y., Bratton, S., Gallus-Zawada, A., Finel, M., and Radominska-Pandya, A.  (2006) Phenylalanine90 and Phenylalanine93 are crucial amino acids within the estrogen binding site of the human UDP-glucuronosyltransferase 1A10. Steroids, IN PRESS.

Xiong, Y., Bernardi, D., Bratton, S., Ward, M. D., Battagia, E., Finel, M., Drake, R., and Radominska-Pandya, A. (2006) Phenylalanine90 and 93 are amino acids localized within the phenol binding site of human UDP-glucuronosyltransferase 1A10 as determined by photoaffinity labeling, mass spectrometry, and site-directed mutagenesis. Biochemistry 21, 322-32. [Abstract]

Lu, Y., Heydel, J. M., Li, X., Bratton, S., Lindblom, T., and Radominska-Pandya, A. (2005) Lithocholic acid decreases expression of UGT2B7 in Caco-2 cells: a potential role for a negative farnesoid X receptor response element. Drug Metab Dispos 33, 937-46. [Abstract]

Gardner-Stephen, D., Heydel, J. M., Goyal, A., Lu, Y., Xie, W., Lindblom, T., Mackenzie, P., and Radominska-Pandya, A. (2004) Human PXR variants and their differential effects on the regulation of human UDP-glucuronosyltransferase gene expression. Drug Metab Dispos 32, 340-7. [Abstract]

Xie, W., Yeuh, M. F., Radominska-Pandya, A., Saini, S. P., Negishi, Y., Bottroff, B. S., Cabrera, G. Y., Tukey, R. H., and Evans, R. M. (2003) Control of steroid, heme, and carcinogen metabolism by nuclear pregnane X receptor and constitutive androstane receptor. Proc Natl Acad Sci U S A 100, 4150-5. [Abstract]

Radominska-Pandya, A., and Chen, G. (2002) Photoaffinity labeling of human retinoid X receptor beta (RXRbeta) with 9-cis-retinoic acid: identification of phytanic acid, docosahexaenoic acid, and lithocholic acid as ligands for RXRbeta. Biochemistry 41, 4883-90. [Abstract]

Xie, W., Radominska-Pandya, A., Shi, Y., Simon, C. M., Nelson, M. C., Ong, E. S., Waxman, D. J., and Evans, R. M. (2001) An essential role for nuclear receptors SXR/PXR in detoxification of cholestatic bile acids. Proc Natl Acad Sci U S A 98, 3375-80. [Abstract]

Radominska-Pandya, A., Chen, G., Czernik, P. J., Little, J. M., Samokyszyn, V. M., Carter, C. A., and Nowak, G. (2000) Direct interaction of all-trans-retinoic acid with protein kinase C (PKC). Implications for PKC signaling and cancer therapy. J Biol Chem 275, 22324-30. [Abstract]