5-azacytidine-induced alterations in the GH12C1 cells: effects on cellular morphology, chromosome structure, DNA and...

Growth hormone-producing rat pituitary tumor cells (GH12C1) were cultivated in the presence of 5-azacytidine (5-AC). After cessation of treatment the cells were allowed to recover in normal cell culture medium prior to subcultivation. Within hours after the subcultivation the cells underwent several morphological alterations, later followed by changes in growth pattern: (1) cell shape was irreversibly changed from round or spindle shape to different clones of fibroblast-like cells; (2) some of these clones later formed foci; and (3) an extensive generation of multinucleated cells was seen. The demethylation was maximal approximately one week after the first subcultivation in the absence of 5-AC. Severe alterations of the chromosome structure were seen after the first subcultivation. During the following weeks the 5-AC-treated cells showed impaired chromosome condensation, and homogeneous staining with quinacrine mustard. During this period the DNA synthesis is doubled when compared to control cell DNA synthesis. The core histone synthesis increases in parallel with the DNA synthesis, but the majority of nuclear proteins, including the linker histones, remain at the control level. This results in a ratio of linker histone to core histone synthesis at approximately half the control cell level. The altered ratio of synthesis slowly decreased to control levels during a period of five weeks of continuous cultivation in the absence of the drug, and the under-condensed chromosomes could no longer be seen. The induced novel phenotypes with their pleiomorphic appearances were conserved. The growth hormone synthesis remained constant during all phases of the experiment and prolactin synthesis was not induced.