Rearranged c-mos locus in a MOPC 21 murine myeloma cell line and its persistence in hybridomas.

Studies of a number of normal and carcinogen-transformed murine cell lines, and a variety of murine tissues, have indicated that, in contrast to several other cellular oncogenes, the oncogene c-mos gene is usually transcriptionally silent. The recent report by Rechavi et al. indicating that in the mouse myeloma XRPC24 originally induced by pristane (2,6,10-14-tetramethylpentadecane) the c-mos gene is rearranged and transcriptionally active, and that it can transform murine fibroblasts in a transfection assay, is therefore of considerable interest. Here we show that the c-mos locus has undergone a similar rearrangement, and is also transcriptionally active, in the cell line P3-X63-Ag8-653, a derivative of the mouse myeloma MOPC 21 which was induced by mineral oil. This line is widely used for making hybridomas that synthesize monoclonal antibodies. We also demonstrate that the rearranged c-mos sequence is maintained in three different hybridomas derived by fusion of this cell line with normal murine spleen lymphocytes, suggesting that it may play a role in the continuous growth and/or constitutive immunoglobulin production by these hybridomas.