title: Dexamethasone induces caspase activation in murine osteoblastic MC3T3-E1 cells.
abstract: Glucocorticoids are widely used as anti-inflammatory and chemotherapeutic agents. However, prolonged use of glucocorticoids leads to osteoporosis. This study was designed to examine the mechanism of dexamethasone (DEX)-induced apoptosis in murine osteoblastic MC3T3-E1 cells. Total RNA was extracted from MC3T3-E1 cells treated with 10(-7) M DEX for 6 h. DEX exerted a variety of effects on apoptotic gene expression in osteoblasts. Ribonuclease protection assays (RPA) revealed that DEX upregulated mRNA levels of caspases-1, -3, -6, -8, -11, -12, and bcl-XL. Western blot analysis showed enhanced processing of these caspases, with the appearance of their activated enzymes 8 h after DEX treatment. In addition, DEX also induced the activation of caspase-9. DEX elevated the levels of cleaved poly(ADP-ribose) polymerase and lamin A, a caspase-3 and a caspase-6 substrate, respectively. Expression of bcl-XL protein level was upregulated by DEX. Cytochrome c release was detected in the cytosol of DEX-treated cells. Furthermore, caspase-3 enzyme activity was elevated by 2-fold after DEX treatment for 7 h. Finally, early apoptotic cells were detected in cells treated with DEX for 3 h. Our results demonstrate that DEX-induced apoptosis involves gene activation of a number of caspases.
authors.affiliation: Osteoporosis Center, James H. Quillen College of Medicine, East Tennessee State University, and Veterans Affairs Medical Center, Box 70432, Johnson City, TN 37614, USA. chua.chu@med.va.gov
authors.forename: Chu Chang
authors.initials: CC
authors.lastname: Chua
authors.forename: Balvin H L
authors.initials: BH
authors.lastname: Chua
authors.forename: Zhongyi
authors.initials: Z
authors.lastname: Chen
authors.forename: Cathy
authors.initials: C
authors.lastname: Landy
authors.forename: Ronald C
authors.initials: RC
authors.lastname: Hamdy
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D020169:Caspases / Q000235:genetics*; D003574:Cytochrome c Group / Q000187:drug effects / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology*; D004790:Enzyme Induction / Q000187:drug effects*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000235:genetics; D034904:Lamin Type A / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D010006:Osteoblasts / Q000187:drug effects* / Q000201:enzymology; D010024:Osteoporosis / Q000139:chemically induced / Q000201:enzymology / Q000235:genetics; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; D011506:Proteins / Q000187:drug effects / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D015533:Transcriptional Activation; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics; D051020:bcl-X Protein
chemical_list: C494812:Bcl2l1 protein, mouse; D003574:Cytochrome c Group; D034904:Lamin Type A; D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D051020:bcl-X Protein; D003907:Dexamethasone; C499321:Parp1 protein, mouse; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; D020169:Caspases