Dysregulation of c-myc in multiple myeloma.

Translocation of c-myc to IgH switch regions, or less frequently to one of the IgL loci, is essentially an invariant event in murine plasmacytomas. This results in dysregulation of c-myc, manifested by selective expression of the translocated allele. Human multiple myeloma (MM) has a similarly high incidence of translocations involving IgH switch regions, but c-myc is infrequently involved as a partner in these translocations. However, in screening a panel of 20 MM cell lines, we identified six lines containing two genetically distinguishable c-myc alleles. For these six informative lines (and the corresponding tumor for one line) there is selective expression of one c-myc allele despite the apparent absence of translocation, DNA rearrangement, or amplification involving c-myc. This result suggests frequent tumor specific cis-dysregulation of c-myc in MM by a presently unknown mechanism.