Gene expression during terminal differentiation: dexamethasone suppression of inducer-mediated alpha 1- and beta maj-globin gene expression.
Previous studies demonstrated that hexamethylenebisacetamide (HMBA)-mediated murine erythroleukemia cell (MELC) commitment to terminal division could be suppressed by dexamethasone. A rapid (less than 2 hr) increase (step-up) in commitment to terminal cell division was observed if, after 60-70 hr in culture with inducer and steroid, MELC were transferred to medium with HMBA alone. This step-up commitment was not inhibited by actinomycin or cordycepin but was blocked by cycloheximide. In this study, we show that dexamethasone blocks HMBA-mediated activation of alpha 1- and beta maj-globin gene transcription but not the induced chromatin change characterized by appearance of DNase I-hypersensitive regions upstream from the 5' cap sites of the alpha 1- and beta maj-globin genes. A rapid (less than 2 hr) activation (step-up) of alpha 1-globin gene transcription was observed if, after 48-60 hr in culture with HMBA and dexamethasone, MELC were transferred to medium with HMBA alone. Activation of transcription of the beta maj-globin gene requires 12-24 hr of further culture. Cycloheximide inhibits step-up transcription of both globin genes. Thus, dexamethasone blocks HMBA-mediated modulation of transcription of several nonlinked genes whose expression is altered in a coordinated manner during induced MELC terminal differentiation. Further, the steroid blocks at a late step, a step after that which is rate-limiting to HMBA-mediated MELC differentiation.
D000081:Acetamides / Q000037:antagonists & inhibitors; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects*; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002843:Chromatin / Q000502:physiology / Q000648:ultrastructure; D003907:Dexamethasone / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects*; D005914:Globins / Q000235:genetics*; D004915:Leukemia, Erythroblastic, Acute / Q000473:pathology; D051379:Mice; D014158:Transcription, Genetic / Q000187:drug effects
D000081:Acetamides; D002843:Chromatin; D003907:Dexamethasone; D005914:Globins; C014026:hexamethylene bisacetamide