Dexamethasone-induced apoptotic mechanisms in myeloma cells investigated by analysis of mutant glucocorticoid receptors.
The mechanism by which the glucocorticoid (GC) dexamethasone induces apoptosis in multiple myeloma (MM) cells is unknown, although previous work suggests that either transactivation through the glucocorticoid response element (GRE), transrepression of NF-kappaB, phosphorylation of RAFTK (Pyk2), or induction of Bim is important. We studied this question by ectopically expressing mutant glucocorticoid receptors (GRs) in the dexamethasone-resistant MM1R cell line, which has lost its GR. Lentiviral-mediated reexpression of wild-type GR restored GRE transactivation, NF-kappaB transrepression, RAFTK phosphorylation, Bim induction, and dexamethasone-induced apoptosis. We then reexpressed 4 GR mutants, each possessing various molecular effects, into MM1R cells. A perfect correlation was present between induction of GRE transactivation and induction of apoptosis. In contrast, NF-kappaB transrepression and RAFTK phosphorylation were not required for apoptosis. Although not required for dexamethasone-mediated apoptosis, NF-kappaB inhibition achieved by gene transfer suggested that NF-kappaB transrepression could contribute to apoptosis in dexamethasone-treated cells. Dexamethasone treatment of MM1R cells expressing a mutant incapable of inducing apoptosis successfully resulted in RAFTK (Pyk2) phosphorylation and Bim induction indicating the latter GR-mediated events were not sufficient to induce apoptosis. MM1R cells expressing mutant GRs will be helpful in defining the molecular mechanisms of dexamethasone-induced apoptosis of myeloma cells.
Department of Hematology Oncology, Division of Hematology Oncology, UCLA West Los Angeles, VA Medical Center, Los Angeles, CA 90073, USA. sasharma@mednet.ucla.edu
Sanjai
S
Sharma
Alan
A
Lichtenstein
D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D051017:Apoptosis Regulatory Proteins / Q000096:biosynthesis; D000072224:Bcl-2-Like Protein 11; D045744:Cell Line, Tumor; D003907:Dexamethasone / Q000494:pharmacology*; D051418:Focal Adhesion Kinase 2 / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000096:biosynthesis; D009101:Multiple Myeloma / Q000188:drug therapy* / Q000473:pathology; D009154:Mutation; D016328:NF-kappa B; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis; D011965:Receptors, Glucocorticoid / Q000235:genetics* / Q000502:physiology; D020218:Response Elements; D015533:Transcriptional Activation
D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; D008565:Membrane Proteins; D016328:NF-kappa B; D011518:Proto-Oncogene Proteins; D011965:Receptors, Glucocorticoid; D003907:Dexamethasone; D051418:Focal Adhesion Kinase 2