Figure 1. Simplified version of the mechanism of cellular response to TCDD, a model receptor-ligand interaction. See text for details

ERDC TN-DOER-C19

December 2000

significant alterations in biochemistry between generations, they are ideal for toxicity testing as the

lack of change in cell characteristics provides consistent results. Cell cultures provide the basis for a

wide variety of rapid screening assays ranging from fairly nonspecific responses (cell death) to

highly specific responses (enzyme induction). Recent advancements in molecular biology such as

cloning and transgene insertions have allowed the development of highly sensitive cell-based assays

for extremely specific endpoints, as discussed in the following example.

P450RGS - A Model Cell-Based Assay. An excellent example of a cell-based screening assay

is P450RGS, which is used for the detection of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) equiv-

alents in sample extracts (Ang et al. 2000; McFarland et al. 1999; U.S. Environmental Protection

Agency 1999). The system relies on the interaction of TCDD and TCDD-like compounds

(polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and coplanar polychlorinated

biphenyls) with a specific receptor, as depicted in Figure 1. In the figure, TCDD diffuses across the

cell membrane and interacts with a specific receptor in the cytosol. The TCDD-receptor complex is

then translocated into the cell nucleus where it binds to a specific region (dioxin-responsive element,

CELL MEMBRANE

TCDD

AH Receptor

Receptor

binding

NUCLEUS

Dioxin-

Responsive

DNA

Element

translocation

mRNA

DRE gene battery products

(e.g., Cyp1A1)

Protein synthesis

Figure 1. Simplified version of the mechanism of cellular response to TCDD, a model receptor-ligand

interaction. See text for details