Induction of G2 arrest and gene expression by 2-aminopurine in human U937 promonocyte-macrophage cells.

The adenine analogue, 2-aminopurine (2-AP), induces G2 arrest in the human promonocyte-macrophage cell line, U937. The arrest is reversible and cells enter mitosis to resume normal logarithmic growth upon removal of the drug. These physiological changes are accompanied by markedly stimulated expression of eukaryotic gene constructs stably integrated in the chromosomes or introduced into the cells by transient transfection. Induction by 2-AP has two components: one involves increased transcription of the introduced genes as shown by run-on transcription experiments. The other involves markedly increased mRNA half-life that affects mRNA transcribed from transiently transfected DNA but apparently does not affect mRNA transcribed from the same chromosomally integrated sequences. Together, these two components could account for the 100- to 1000-fold inductions observed with various transfected gene constructs reported here and elsewhere. Maximum induction by 2-AP is promiscuous with respect to eukaryotic promoter origins or sequences, but appears to require a minimum of two such promoter elements. Thus, G2 cell cycle arrest induced by 2-AP is also associated with transcriptional and post-transcriptional alterations in gene expression. The data also suggest that transiently transfected DNAs may enter spatial or biochemical compartments of the nucleus that are different from those of normal genes in their native locations. These differences may affect the abundance and fate of the transcribed mRNA and, in some circumstances, introduce serious discordances into studies of gene regulation.