Richard Pollenz
Richard Pollenz
Professor
Contact
Office: BSF 206
Phone: 813/974-1596
Email:
Links
Research
Environmental molecular toxicology with focus on signal transduction mechanisms.
Our overall focus is to better understand the response of organisms to environmental stress at the molecular level. The stresses of interest are chemical contaminants (halogenated aromatic hydrocarbons, typified by 2,3,7,8-tetrachlorodibenzo-p-dioxin, TCDD) and low oxygen (hypoxia). The models of interest include both aquatic and mammalian species.
TCDD and its related congeners are persistent environmental contaminants that have very high stability and have been detected in nearly all aquatic, avian and mammalian species evaluated. Exposure to these compounds results in a wide range of responses that include carcinogenesis, immune suppression and reproductive dysfunction. However, TCDD has the most sensitive and profound affect during development. The reason for this is explained by the fact that TCDD stimulates a receptor-mediated signaling pathway that can directly affect gene regulation. TCDD is a ligand for the aryl hydrocarbon receptor (AHR), a ubiquitous protein found in every cell. Once TCDD binds the AHR, the protein dimerizes with a second protein termed ARNT to form a deterodimeric transcription factor with specificity for DNA sequences termed Xenobiotic Response Elements (XREs). The binding of the AHRlARNT complex can repress or stimulate various genes, and it is hypothesized that changes in the regulated genes are responsible for the biological effects associated with TCDD and other halogenated hydrocargons. (See Figure) The AHR and ARNT protein are members of the basic-helix-loop-helix/PAS (bHHL/PAS) family of transcription factors that also included the proteins SIM, PER and hypoxia factor 1a (HIF-1a). Interestingly, the HIF-1a protein is induced in cells by reduced O2, and forms a heterodimeric transcription factor with ARNT that binds Hypoxia Response Elements (HREs) to induce genes such as VEGF, erythropoietin and various glycolytic enzymes. ARNT also can dimerize with SIM and itself. Thus, the overall function of bHLH/PAS proteins appear to be related to stress response and the analysis of the pathways initiated by these proteins will be key in unraveling the complexity of the biological outcomes to chemical and environmental exposure.
The laboratory is interested in AHR-mediated signaling at many levels. A current area of interest in the level of AHR protein expression in cells and the control of its turnover. We have recently determined that the AHR is degraded following ligand binding and thus, understanding the mechanism of degradation and consequence of reductions in AHR may provide key insight into the physiological role of this signaling cascade. Another area of research includes the ARNT dimerization partner and its interaction with non-AHR proteins. We have isolated two isoforms of ARNT from rainbow trout that have divergent functions and can act as positive or negative regulator of AHR-mediated signaling. Another aspect of research in the lab focus on the expression of the AHR and ARNT at key points in development. Our lab has developed sensitive techniques that allow the analysis of AHR and ARNT protein as early as gestation day 15 in the mouse. Central questions include: Is the AHR down regulated at early time points? Is the down regulation tissue specific? Does the level of AHR or ARNT change with age? These questions are intimately tied to understanding the pathway of AHR down regulation, ratios to other bHLH proteins and analysis of AHR activation during development.
Finally, we have projects to apply some of our research models to analysis of contamination within the environment. By use of cell culture models, we have established precise dose response relationships between induction of genes and the level of contaminant applied to aquatic or mammalian cells. Thus, ongoing studies are designed to use changes in these genes to assess levels of bioremediation of specific sites and as models to predict the level of contamination that might exist.
The Pollenz lab utilizes state-of the art molecular and cellular techniques for many of the studies. The lab is equipped with cell culture facilities, CO2 incubators, shaking bacterial incubators, microcentrigufes, PCR equipment, spectrophotometer, Western blotting modules, sonication equipment and DNA analysis equipment. The lab also houses an Olympus IX70 inverted fluorescence microscope in a separate darkroom that is linked via an Optronics digital camera to a G4 Macintosh computer with a CD burner and scanner. In addition, the microscope is integrated with a Femtojet microinjection system for delivery of purified protein to various cellular compartments of living cells.
Current Courses
Recent Publications
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