DNA replication, chromatin structure, and histone phosphorylation altered by theophylline in synchronized HeLa S3 cells.
The onset of DNA replication normally is coincident with an increase in histone 1 phosphorylation and a relaxation in chromatin structure. In this paper we show that 5 mM theophylline, added 2 h after selective detachment to synchronized HeLa-S-3 cells, delays the onset and reduces the rate of DNA synthesis while theophylline treatment beginning at 8 h has no effect on subsequent DNA synthesis. These actions of theophylline are accompanied by an inhibition of histone 1 phosphorylation and a prevention of the normal relaxation in chromatin structure between G1 and S phases as revealed by image analysis of Feulgen-stained nuclei. The time courses of intracellular cyclic AMP levels, nonhistone protein phosphorylation, and [3H]lysine incorporation are also compared in the same treated and untreated synchronized HeLa cells. Comparison with experiments using 1-beta-D-arabinofuranosylcytosine (Ara-C) shows that the above phenomena are not a direct result of inhibition of DNA synthesis. We interpret our results as evidence that the associations between histone 1 phosphorylation, chromatin relaxation, and the onset of DNA synthesis are temporally and causally related.
D002453:Cell Cycle / Q000187:drug effects; D002843:Chromatin / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D004261:DNA Replication / Q000187:drug effects*; D004273:DNA, Neoplasm / Q000096:biosynthesis; D006367:HeLa Cells / Q000187:drug effects / Q000378:metabolism; D006657:Histones / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D010766:Phosphorylation; D013806:Theophylline / Q000494:pharmacology*
D002843:Chromatin; D004273:DNA, Neoplasm; D006657:Histones; D013806:Theophylline