NEOPLASIA Role of NF - k B in the Rescue of Multiple Myeloma Cells From Glucocorticoid - Induced Apoptosis by Bcl - 2

The molecular mechanisms by which multiple myeloma (MM) cells evade glucocorticoid-induced apoptosis have not been delineated. Using a human IgAk MM cell line (ARP-1), we found that dexamethasone (Dex)-induced apoptosis is associated with decreased NF-kB DNA binding and kBdependent transcription. Both nuclear p50:p50 and p50:p65 NF-kB complexes are detected in ARP-1 cells by supershift electrophoretic mobility shift assay (EMSA). Dex-mediated inhibition of NF-kB DNA binding precedes a notable increase in annexin V binding, thereby indicating that diminished NF-kB activity is an early event in Dex-induced apoptosis. Overexpression of bcl-2 in ARP-1 cells prevents Dexmediated repression of NF-kB activity and apoptosis. Sustained NF-kB DNA binding is also observed in two previously characterized Dex-resistant MM cell lines (RPMI8226 and ARH-77) that express moderate levels of endogenous bcl-2 and IkBa proteins. In addition, enforced bcl-2 expression in ARP-1 cells did not prevent the augmentation of IkBa protein by Dex. We also noted a possible association between Dex-mediated downregulation of NF-kB in freshly obtained primary myeloma cells and the patients’ responsiveness to glucocorticoid-based chemotherapy. Collectively, our data suggest that the protective effects of bcl-2 in MM cells act upstream in the NF-kB activation–signaling pathway and the potential use of NF-kB as a biomarker in progressive MM. r 1999 by The American Society of Hematology.