Specificity of the cAMP-induced gene exposure reaction in CHO cells

Previous studies demonstrated that in the transformed CHO (Chinese hamster ovary) cell a substantial part of the genome behaves as though its genes are sequestered from effective contact with soluble constituents of the intracellular fluid. The reverse transformation reaction, initiated by cAMP derivatives, causes this cell to regain the morphology, growth regulation, surface characteristics, and sensitivity of its DNA to digestion by DNase I that are characteristic of normal fibroblasts. In this paper we show that this action of cAMP is gene specific. In examination of 47 different genetic loci, some, like ribosomal RNA genes, are found to be sensitive to DNase I hydrolysis both in the absence and in the presence of cAMP; some are resistant under both conditions; and some are resistant in the untreated cell but become sensitive after cAMP treatment. Unlike other gene exposure reactions, which are irreversible and connected with differentiation phenomena, that produced by cAMP is readily reversed when the reagent is removed. A sequence of events is observed after cAMP treatment, the first of which is reorganization of the cytoskeleton. Afterwards, metabolic changes occur over periods as long as 72 hr. The cAMP-induced cytoskeleton-mediated gene exposure reaction appears to be an important genetic regulatory mechanism in mammalian cells and to have special implications for cancer.