Single-chain antibody against the common epitope of mutant p53: isolation and intracytosolic expression in mammalian cells

The peptide epitope FRHSVV is cryptic in wild-type p53 and is exposed in ma ny types of mutant p53 molecules isolated from various tumors. Mutant p53 m arked by this epitope abrogates a tumor-suppressor function of wild-type p5 3 and possibly contributes to the transforming potential of other oncogenic processes. We report here the construction of a single-chain scFv antibody gene library derived from the mRNA of a mouse immunized with the epitope p eptide FRHSVV which mimics the common epitope in p53 mutant protein molecul es. The scFv was presented by phage display. The selected antibody gene, na med MEI, was found to bind to the mutant p53 protein but not to the wild-ty pe p53 protein. Preliminary studies show that the MEI gene is expressed in the cytosol of mammalian cells. These findings suggest that the MEI single- chain antibody may be useful as a tool for clarifying the role of mutant p5 3 in tumor transformation, especially in cells heterozygous in p53, and pos sibly for gene therapy of tumors. (C) 2001 Elsevier Science B.V. All rights reserved.