DIFFERENTIAL GENE-EXPRESSION OF THE NEURAL CELL-ADHESION MOLECULE (N-CAM) IN A PANEL OF MULTIPLE-MYELOMA CELL-LINES

A striking feature of myeloma plasma cells concerns their expression o f the neural cell adhesion molecule (N-CAM). The regulation of this pa rticular expression is, however, not known. In this study, the N-CAM ( CD56) gene regulation was examined in a panel of multiple myeloma (MM) cell lines. In this panel, both N-CAM-positive and -negative cells we re analysed, reflecting the in vivo situation where a minority of MM p atients have CD56-negative plasma cells at diagnosis or where in cases of extramedullary involvement CD56 expression decreases. At least two N-CAM mRNAs were found in the cell lines expressing the 140 kDa isofo rm. With one exception, no N-CAM transcripts could be detected in the N-CAM-negative cell lines. No structural differences could be found in the genomic organization of the N-CAM gene, or in the regulatory prom oter region when CD56-positive and -negative cell lines were compared. In transfection studies, however, transcriptional activity of the N-C AM promoter was observed in N-CAM-negative cells, leading us to conclu de that the up-regulation of N-CAM in MM cannot be explained by a simp le transcriptional gene activation.