Multiple protein differences distinguish clam leukemia cells from normal hemocytes: evidence for the involvement of p53 homologues

In coastal locations, marine invertebrates, primarily molluscs, develop fat al leukemias in their blood or hemolymph. In the clam Mya arenaria, non-adh esive, mitotic, spherical leukemia cells replace adhesive, motile, normal h emocytes as leukemia progresses. End-stage leukemia cells express a unique antigen, IE10, while normal cells express the 2A4 marker. The goals of this work were to further differentiate the normal and leukemia specific antige ns relative to protein structure, determine if other protein distinctions e xist, and examine p53 gene family expression in both cell types. Recognized by the monoclonal antibody 2A4, normal cells express a 185-kDa glycoprotei n that may have multiple forms. Detected by the monoclonal antibody IE10, l eukemic cells express a very hydrophobic 252-kDa glycoprotein that is likel y to be a transmembrane protein with spectrin/dystrophin-like characteristi cs. After normalization to the major cytoskeletal protein actin, sodium dod ecyl sulfate-polyacrylamide gel electrophoresis reveals major distinguishin g protein and glycoprotein differences between the two cell types. Most obv ious is the near-absence of tubulin in the non-mitotic normal hemocytes. We have also characterized the expression of p53 gene family members in norma l and end-stage leukemia cells, finding shifts in expression of the p53 gen e homologues p73 and p97 coincident with leukemia-specific protein synthesi s. (C) 2001 Elsevier Science Inc. All rights reserved.