BOETTGER, Stefanie A; RICKETTS, Bryon F; SAHLER, Christopher S; WALKER, Charles W; Univ. New Hampshire, Durham; Univ. New Hampshire, Durham; Univ. New Hampshire, Durham; Univ. New Hampshire, Durham: Cytoplasmic sequestration of p53 family member proteins by heat shock protein family member mortalin II in leukemic clam hemocytes.

Mechanisms causing cytoplasmic sequestration and inactivation of the tumor suppressor p53 are currently investigated only in vertebrate models, which are expensive to maintain and highly regulated. We use leukemic hemocytes from the softshell clam, Mya arenaria, both in vivo and in vitro, to investigate cytoplasmic anchoring of p53 family member proteins by mortalin (mot-2). Clam mot-2 displays a high degree of sequence conservation with human mot-2 and co-localizes with cytoplasmically sequestered clam p53 and p63/73 proteins. Etoposide was administered in vitro and leukemic clam hemocytes were examined for the cellular localization of p53, p63/73 and mot-2 prior to and following drug exposure. Immunocytochemistry indicated translocation of both p53 and p63/73 proteins from the cytoplasm into the nucleus followed by an increase in apoptotic cells and a subsequent decrease in viable cells/ml hemolymph. Following drug treatment, mot-2 distribution in the cytoplasm switched from perinuclear to pan-cytoplasmic. Changes in mot-2 distribution indicate that etoposide treatment may lead to cleavage of the bond between mortalin and p53 and p63/73 followed by movement of these transcription factors into the nucleus and apoptosis of tumor cells. (Supported by NCI CA88883 to CWW)