Expression of myc ‐family genes in established human multiple myeloma cell lines: L‐ myc but not c‐ myc gene expression in the U‐266 myeloma cell line

Deregulated c‐ myc expression, as a consequence of translocation of the c‐ myc gene to one of the immunoglobulin loci, appears to play an important role in the pathogenesis of several B‐cell tumors, including Burkitt's lymphoma, mouse plasmacytoma and rat immunocytoma. This study investigated the expression of c‐ myc and 2 other members of the myc gene family, L‐ and N‐ myc , at the mRNA and protein level, and analyzed for possible rearrangements of these genes in the human counterpart to the mouse plasmacytoma—multiple myeloma (MM). Nine well‐characterized MM cell lines were examined by using Northern‐ and Southern‐blot analysis and immunoprecipitation. The c‐ myc gene was found to be highly expressed in most MM cell lines. The level of expression was comparable to that observed in the COLO 320 and HL‐60 cell lines, carrying amplified c‐ myc genes, and to that of B‐cell lines with a higher proliferative activity than the MM cell lines. In the U‐266 MM cell line, L‐ myc , but no c‐ myc mRNA or protein, was found. The L‐ myc gene was expressed in both early‐ and late‐passage U‐266 cells, suggesting that the L‐ myc expression was not the result of the in vitro cultivation. N‐ myc was not expressed in any of the MM cell lines. No rearrangements of c‐ myc or L‐ myc genes were found. We thus conclude that (a) in contrast to the corresponding mouse and rat B‐cell tumors, c‐ myc is not frequently rearranged in MM; (b) c‐ myc is highly expressed in most MM lines; and (c) L‐ myc but not c‐ myc is expressed in the U‐266 MM cell line.