Antagonism of p53-dependent apoptosis by mitogen signals.

p53-mediated apoptosis is antagonized by growth factor stimulation. Here, we show that p53-dependent cell death induced by DNA damage was effectively prevented by mitogen activation. The levels of Bcl-2, Bcl-xL, and Bax were not altered by cisplatin treatment and mitogen rescue. Instead, the protection against p53-regulated apoptosis was mediated by at least three distinct signaling pathways. Either phosphatidylinositol (PI) 3-kinase or mitogen-activated protein kinase kinase (MEK) antagonized p53-induced apoptosis, and an additive preventive effect was observed when both kinases were activated. However, the combination of PI 3-kinase and MEK was not sufficient to completely prevent apoptosis induced by DNA damage. Mitogen activation further suppressed cisplatin-induced p53 expression, and the inhibition was mainly dependent on the Ca2+ pathway. Our results demonstrate that effective antagonism of p53-dependent apoptosis by mitogenic activation requires the presence of multiple signal pathways, including PI 3-kinase, MEK, and Ca2+.