Research Interests:

The aldo-keto reductase (AKR) superfamily role in steroid hormone action and chemical carcinogenesis.

Key Words:

Aldo-keto reductase, steroid hormones, chemical carcinogenesis.

Research Summary:

The aldo-keto reductase (AKR) superfamily are monomeric (37 kDa), NAD(P)(H)-linked oxidoreductases that play pivotal roles in steroid hormone, prostaglandin and xenobiotic metabolism (drugs and carcinogens). Their broad-based specificity suggests that like the CYP450 superfamily, isoforms will exist with polymorphism that will effect, steroid hormone and drug response, and susceptibility to carcinogen exposure. For a full-description of the AKR superfamily go to www.med.upenn.edu/akr.

Dr. Penning's laboratory conducts structure-function studies on steroid-hormone transforming AKRs known as hydroxysteroid dehydrogenases (HSDs). For each steroid hormone there are pairs of HSDs that either convert a potent steroid hormone into its cognate inactive metabolite or catalyze the reverse reaction. In steroid target tissues HSDs regulate the amount of steroid ligand available for the receptor and hence its trans-activation. This pre-receptor regulation of steroid hormone action may have profound consequences for the normal and abnormal growth of the prostate and breast. Dr. Penning's group is conducting x-ray crystallography, site-directed mutagenesis, transient and steady state kinetics, and inhibitor design on the human AKRs that regulate occupancy of the androgen, estrogen and progesterone receptors.

AKRs are also implicated in the metabolic activation of polycyclic aromatic hydrocarbons (PAH). PAH are ubiquitous environmental pollutants, they are tobacco carcinogens, and are implicated as the causative agents in human lung cancer. Human AKR isoforms are over expressed in human lung cells where they convert trans -dihydrodiol (proximate carcinogens) to reactive and redox active o -quinones. The hypothesis being tested is that electrophilic quinones and the reactive-oxygen species they generate may lesion DNA (initiate cancer). Further they may cause changes in protein kinase C activation that can lead to loss of cell-cycle control (promote cancer). Thus metabolic activation of PAH via AKRs may account for the complete carcinigenicity of the parent hydrocarbon. Dr. Penning' group is using AKR transfection strategies to measure their contribution to PAH-activation, DNA-adduct formation, and mutation of p53 and K- Ras in lung cells.

Lab Rotation Projects:

Dissection of microscopic steps in AKR catalysis (methods: site-directed mutagenesis, transient kinetics, kinetic isotope effects)

Design, synthesis and evaluation of inhibitors for steroid hormone transforming AKRs (methods: recombinant enzyme purification, chemical synthesis, steady state kinetics)

AKRs and trans -activation of steroid hormone receptors (methods: mammalian cell transfection, steroid metabolism and reporter gene assays)

Formation of PAH o -quinone and ROS-derived DNA adducts: detection in AKR transfectants (methods: synthesis of DNA-adduct standards, transfection, analytical chemistry)

Competing roles of CYP450 and AKRs in PAH Metabolism (expression of recombinant proteins, RP-HPLC and radiochemistry)

Key References:

Ma, H, and Penning, T.M.: Conversion of mammalian 3-alpha-hydroxysteroid

dehydrogenase   to 20-alpha-hydroxysteroid dehydrogenase using loop chimeras: changing specificity from androgens to progestins. Proc. Natl. Acad. Sci. USA, 96: 11161-11166, 1999.

Jin, Y., Stayrook, S.E., Albert, R.H., Palackal, N.T., Penning, T.M. and Lewis, M.: Crystal structure of human type III 3-alpha-hydroxysteroid dehydrogenase/bile-acid binding protein complexed with NADP + and ursodeoxycholate. Biochemistry, 40: 10161-10168, 2001.

Yu, D., Berlin , J.A., Penning, T.M., and Field, J.M.: Reactive oxygen species generated by PAH o-quinones cause change-in-function mutations in p53. Chemical Res. Toxicol., 15: 832-842, 2002. (Profiled on the Front Cover)

Palackal, N.T., Lee, S-H., Harvey , R.G., Blair, I.A. and Penning, T.M.: Activation of polycyclic aromatic hydrocarbon trans-dihydrodiol proximate carcinogens by human aldo-keto reductase (AKR1C) enzymes and their functional overexpression in human lung carcinoma (A549) cells. J. Biol. Chem. 277: 24799-24808, 2002

Lab Personnel:

Dr. Yi Jin (Research Associate)
Dr. Sridhar Gopishetty (Postdoctoral Researcher)
Dr. William B. Cooper (Postdoctoral Researcher)
Dr. Stephan Steckelbroeck (Postdoctoral Researcher)
Dr. Hao Jiang (Postdoctoral Researcher)
Dr. Hum-Kim Park (Postdoctoral Researcher)
Ms. Valdi Heredia (Predoctoral Fellow, BMB)
Mr. Larry Szewczuk ( Predoctoral Fellow, BMB)
Mr. David Bauman (Predoctoral Fellow, PHARM)
Ms. Amy Quinn (Predoctoral Fellow, PHARM)
Mr. Yumin Shen (Research Specialist)
Ms. Busola Oyenami (Laboratory Technician )