| The most commonly mutated gene in human malignancies, p53 is a tumor suppressor gene mutated in 50% of all human cancers, and the study of this gene provides valuable insight into the etiology of environmentally-induced cancers. Although this gene has been extensively studied in mammalian models, relatively little is known about this gene in lower vertebrate species, such as fish. It has long been assumed that p53 would function in these species in the same manner as in mammalian systems. The results of our studies in fish models suggest that this may not be true in all systems.;In the first study, I sequenced the full-length p53 gene in the cancer-sensitive brown bullhead catfish (Ameriurus nebulosus) and the partial p53 sequence from the cancer-resistant channel catfish (Ictalurus punctatus). No major differences were found between the overlapping regions of the gene in these two species. Phylogenetic analysis of these p53 sequences and current genbank p53 submissions suggests the possibility that two copies of the p53 gene exist in the brown bullhead and the channel catfish, and possibly other fish species as well.;The second and third studies investigated the activation of p53 in response to model chemotherapeutic chemicals and prooxidants in several fish cell lines. I show that fish p53 protein is not induced in response to model chemotherapeutics, although apoptosis induction does occur. I also demonstrate that fish p53 protein is induced in response to tert-butylhydroquinone (t-BHQ) and nitrofurantoin (NF), but is not induced in response to CuSO4, Fenton reagents (FeSO4 + H2O2), CdCl2, tert-butylhydroperoxide (t-BOOH), cumene hydroperoxide (COOH), or diquat exposure. Apoptosis was induced in response to several, but not all, of the prooxidants tested. Additionally, a novel 29 kilodalton protein that cross-reacts with a p53 polyclonal antibody was found to be highly-inducible upon exposure to t-BHQ, CdCl2, Fenton reagents, and CuSO4, but none of the other prooxidants tested. Initial protein identification techniques were utilized to obtain de novo protein sequence.;Taken together, this data indicates that fish species may contain multiple copies of the p53 gene. In addition, the activation and function of p53 in fish species may differ from that of other vertebrates, certain p53-response pathways may be more highly conserved than others, and other as yet unidentified proteins could play important roles in the activation of p53 in fish. |
