CALCIUM IONOPHORE-A23187 INDUCES EXPRESSION OF THE GROWTH ARREST AND DNA DAMAGE INDUCIBLE CCAAT ENHANCER-BINDING PROTEIN (C/EBP)-RELATED GENE, GADD153 - CA2+ INCREASES TRANSCRIPTIONAL ACTIVITY AND MESSENGER-RNA STABILITY

gadd153 is a CCAAT/enhancer-binding protein (C/EBP)-related gene whose expression is induced in response to growth arrest and DNA damage. This investigation explored the possibility that Ca2+ might play a role in regulating expression of gadd153. We have demonstrated that treatment of HeLa cells with the calcium ionophores A23187 and ionomycin leads to the induction of gadd153 mRNA. The induction was rapid; increases in mRNA were detected by 90 min of treatment, and near maximum levels were achieved within 5-h exposure to A23187. Elevated mRNA levels resulted from both an increase in the rate of gadd153 transcription and an increase in the stability of the gadd153 mRNA. The response was not dependent on protein kinase C nor was it coupled to c-fos expression. Buffering intracellular and extracellular Ca2+ by combined treatment with BAPTA-AM (acetoxymethyl ester form of bis(aminophenoxy)ethane N,N'-tetraacetic acid) and EGTA prevented the induction of gadd153 mRNA by A23187. In addition, these treatments prevented the induction of gadd153 mRNA in response to the DNA damaging agent methyl methanesulfonate. We conclude that intracellular Ca2+ plays a role in regulating gadd153 expression. More specifically, Ca2+ likely plays a role in the induction of gadd153 mRNA following DNA damage.