Constitutive gene expression in myeloid leukemia and cell competence for induction of differentiation by the steroid dexamethasone.

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Regulation of the cytoplasmic protein changes during myeloid cell differentiation has been analyzed with two-dimensional gel electrophoresis and differentiation-defective cell mutants. The cells studied include a clone of myeloid leukemia cells (clone 11) that can be induced to differentiate to macrophages by the protein inducer MGI and the steroid dexamethasone (Dex) and mutant clones that were inducible for differentiation to macrophages by MGI but not by Dex. The mutants were not defective in the specific binding of [3H]Dex to cytoplasmic receptors or in the transport and nuclear binding of the receptor--steroid complex. The protein patterns in the mutants showed both specific constitutive protein changes and nonresponding proteins. Twenty-one percent of the Dex-induced protein changes and 2% of the MGI-induced protein changes in clone 11 were constitutively expressed in the mutants. In addition, 28% of the proteins that responded to Dex in clone 11 did not respond to Dex in the mutants, whereas only 4% of the proteins that responded to MGI in clone 11 did not respond to MGI. The higher percentage of constitutive changes was thus associated with a larger defect in induction. The proteins with an abnormal response to Dex still showed a normal response to MGI, and the constitutive changes and nonresponding proteins were different for the two inducers. It is suggested that specific constitutive protein changes expressed by the mutants produced an asynchrony in the developmental program, resulting in a defective response to Dex and to MGI, and that this may apply to other inducers and developmental programs.

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