PARENT SESSION

PM10 Mechanisms of Toxic Action
Exhibit Hall
8:00 AM - Monday

(PM163) Lack of p53 induction in fish cells by model chemotherapeutics.

Rau, M¹, Billiard, S¹, Di Giulio, R¹, ¹ Duke University Nicholas School of the Environment and Earth Sciences, Durham, NC, USA

ABSTRACT- The p53 tumor suppressor gene is the most commonly mutated gene in human cancers. Although this gene has been extensively studied in mammalian models, relatively little is known about its specific function in lower vertebrates. It has long been assumed, based on high sequence homology in five conserved functional regions, that p53 pathways characterized in mammals apply to other vertebrates as well. Fish provide a particularly useful model for the study of environmental carcinogenesis, and populations of fish inhabiting highly polluted environments provide information on the etiology of pollutant-mediated cancer. In this study, we investigated p53 protein and apoptosis induction in PLHC-1 (desert topminnow hepatocellular carcinoma), RTL-W1 (rainbow trout normal liver), and primary rainbow trout hepatocytes exposed to model chemotherapeutics. All of the chemicals used in these studies have been demonstrated to increase p53 protein levels and induce apoptosis in mammalian cell lines. In contrast, PLHC-1 p53 protein was not induced in response to any model mammalian p53 inducers, including cisplatin (0-100M), camptothecin (0-20M), etoposide (0-200M), 5-fluorouracil (0-25M), mitomycin C (0-25M) and bleomycin (0-100g/ml) following 24 hour exposures. Additionally, both trout cell types demonstrated this same lack of p53 induction upon exposure to cisplatin (RTL-W1, 0-400M), camptothecin (primaries, 0-20M), and bleomycin (primaries, 0-100M). PLHC-1 cells demonstrated an induction of apoptosis as measured by caspase-3 activation following exposure to all of the chemotherapeutics tested. Due to the induction of apoptosis in fish cells by etoposide, a p53-dependent apoptosis inducer in mammalian systems, we hypothesize that p53 is activated in these cells despite a lack of protein induction, although it is also possible that the etoposide-induced apoptotic pathways in fish are entirely p53-independent. Our results suggest that fish p53 may be activated differently from that of their mammalian counterparts, and that important differences may exist between phyla in the function and regulation of p53 as well as other mechanisms involved in environmental carcinogenesis. Additional studies are necessary to further characterize the regulation of p53 in lower vertebrate species.

Key words: PLHC-1, p53, rainbow trout, apoptosis