Role of NF-kappa 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 glucoco rticoid-induced apoptosis have not been delineated. Using a human IgA kappa MM cell line (ARP-1), we found that dexamethasone (Dex)-induced apoptosis is associated with decreased NF-kappa B DNA binding and kappa B-dependent t ranscription. Both nuclear p50:p50 and p50:p65 NF-kappa B complexes are det ected in ARP-1 cells by supershift electrophoretic mobility shift assay (EM SA). Dex-mediated inhibition of NF-kappa B DNA binding precedes a notable i ncrease in annexin V binding, thereby indicating that diminished NF-kappa B activity is an early event in Dex-induced apoptosis, Overexpression of bcl -2 in ARP-1 cells prevents Dex-mediated repression of NF-kappa B activity a nd apoptosis. Sustained NF-kappa B DNA binding is also observed in two prev iously characterized Dex-resistant MM cell lines (RPMI8226 and ARH-77) that express moderate levels of endogenous bcl-2 and I kappa B alpha proteins. In addition, enforced bcl-2 expression in ARP-1 cells did not prevent the a ugmentation of I kappa B alpha protein by Dex. We also noted a possible ass ociation between Dex-mediated downregulation of NF-kappa B in freshly obtai ned primary myeloma cells and the patients' responsiveness to glucocorticoi d-based chemotherapy. Collectively, our data suggest that the protective ef fects of bcl-2 in MM cells act upstream in the NF-kappa B activation-signal ing pathway and the potential use of NF-kappa B as a biomarker in progressi ve MM. (C) 1999 by The American Society of Hematology.