MP7 Toxicogenomics in Environmental Studies
Monday, 14 November 2005: 8:00 AM - 5:30 PM in Exhibit Hall

(CRA-1117-834750) Are all p53s created equal? Uncovering the function of soft-shell clam (Mya arenaria) p53.

Crawford, Lauren¹, Butler, Rondi¹, Van Beneden, Rebecca¹, ¹ University of Maine, School of Marine Sciences, Orono, ME, 04469

ABSTRACT- The presence of gonadal tumors in the soft-shell clam, Mya arenaria, has been observed in certain eastern Maine populations. The etiology of the tumors is unknown, but environmental factors including cell cycle disrupting contaminants are likely involved. We are particularly interested in the tumor suppressor protein p53, which functions as a transcription factor in cell cycle regulation. In response to DNA damage, stabilized p53 protein can activate pathways leading to either cell cycle arrest or apoptosis, thereby preventing the perpetuation of damaged DNA. If mutated, p53 loses its protective function, potentially leading to tumor formation. Mya arenaria p53 (Map53) has been identified through sequence similarity to known vertebrate and invertebrate p53s. Earlier histological and gene expression studies linked an undifferentiated cell state in clam gonadal tissue with altered p53 protein levels. These cells were noted in both field-collected tumor-bearing clams and clams exposed in the laboratory to 2,4-D. Map53 shows sequence homology to H. sapiens p53 (Hsp53) in key functional domains. In order to assess functional similarity, vectors having a constituitive promoter were constructed using Map53 or wild-type Hsp53 cDNA, and transfected into the p53 null cell line H1299. The expression of p53, p21^WAF1/CIP1, and actin was determined by western blot analysis. p21^WAF1/CIP1, when upregulated by p53, is known to lead to growth arrest. The ability of Map53 to induce apoptosis was evaluated by caspase-3 activation. Preliminary results show an increase in cellular p21^WAF1/CIP1 protein levels in both human and clam p53-expressing H1299 cells and no activation of caspase-3. This suggests that both human and clam p53 are functioning in a similar manner to lead the H1299 cells into growth arrest. Uncovering Map53 function will contribute to the understanding of its role in clam gonadal tumorigenesis.

Key words: Mya arenaria, p53