Cross-reactivity of the monoclonal antibody 9E10 with murine c-MYC

The C-terminal regions of the human and the murine c-MYC consist of a commo n conserved sequence, the amino acids (a.a.) 418-439 with one terminal exch ange (C438G). The pre-C-terminal region of both proteins, a.a. 408-417, exh ibit four exchanges. A commercially available monoclonal antibody, 9E10, ra ised against the C-terminal a.a. 408-439 of human c-MYC, is declared to rec ognize specifically and exclusively human c-MYC. However, in an immunofluor escence assay we observed, in addition to the reaction with a human cell li ne (SV80), reactivity with the murine cell line L929. In analogy, a rabbit polyclonal antiserum raised against a peptide which corresponds to the muri ne pre-C-terminus of c-MYC, a.a. 408-417, showed also cross-reactivity in i mmunofluorescence. The immunostaining with both antibodies in the human and the murine cell line was competed by the peptide, corresponding to the mur ine pre-C-terminal a.a. 408-417, whereas the staining of both cell lines wi th an antiserum raised against the conserved N-terminal region of c-MYC was not competed by this peptide. The cross-reactivity of 9E10 with murine c-M YC was confirmed by Western blot using two additional cell lines. In conclu sion, our findings indicate that 9E10 which is generally regarded as specif ic for human c-MYC cross-reacts with denaturated murine c-MYC.