Rejection Antigen Peptides on BALB/c RL ♂ 1 Leukemia Recognized by Cytotoxic T Lymphocytes: Derivation from the Normally Untranslated 5′ Region of the c-Akt Proto-Oncogene Activated by Long Terminal Repeat

Abstract

Tumor antigen peptides on BALB/c leukemia RL♂1 that were recognized by cytotoxic T lymphocytes were shown to be derived from a normally unstranslated region of the akt proto-oncogene (Uenaka, A. et al., J. Exp. Med., 180: 1599, 1994). We show here that the murine leukemia virus (MuLV) long terminal repeat (LTR) was inserted directly into the exon of c-akt in RL♂1 leukemia and that transcription started from the cap site of the LTR. Translation appeared to start from the ATG codon created in the six nucleotides of unknown origin, which were inserted into the LTR/akt junction. The deduced molecular size is approximately M_r 59,000 due to the addition of 33 amino acid residues to the normally expressed c-AKT protein. Western blot analysis demonstrated the presence of M_r 59,000 molecules in an RL♂1 lysate, and their expression at about ten times the level of normal AKT molecules of M_r 56,000, which is consistent with the increased expression of akt mRNA demonstrated by Northern blot analysis. The findings show that the molecular alteration of AKT protein by insertion of MuLV LTR is the mechanism for creating rejection antigen peptides derived from the untranslated region of akt.