PGA₂-induced HO-1 attenuates G₂M arrest by modulating GADD45α expression

Prostaglandin (PG) A₂, a cyclopentenone PG, arrested the growth of U2OS cells in the G₂M phase. While inducing G₂M arrest, PGA₂ increased the expression of heme oxygenase-1 (HO-1) at the level of transcription along with the accumulation of ROS and the activation of MAPKs including JNK, p38MAPK, and ERK1/2. Among the MAPKs, the inhibition of p38MAPK by a specific chemical inhibitor SB203580, or by RNA interference, but not JNK or ERK1/2, attenuated the PGA₂-induced transcription of HO-1. N-acetylcysteine (NAC), a ROS scavenger, prevented PGA₂-induced G₂M arrest, p38MAPK activation and transcriptional induction of HO-1. PGA₂ also stimulated GADD45α expression at the level of transcription, and the knockdown of GADD45α repressed PGA₂-induced G₂M arrest. Finally, the knockdown of the HO-1 protein elevated PGA₂-induced GADD45α expression as well as G₂M arrest. Collectively, these results suggest that PGA₂ causes an increase in ROS accumulation which initiates both HO-1 transcription via p38MAPK, and G₂M arrest via GADD45α transcription, and HO-1 attenuates G₂M arrest by modulating the expression of GADD45α.