Abstract
Redox regulation of cell cycle progression during nitric oxide (NO) mediated cytostasis is not well‐understood. In this study, we investigated the role of the intracellular antioxidant glutathione (GSH) in regulating specific signaling events that are associated with NO‐mediated cell cycle arrest. Manipulation of intracellular GSH content through pharmacological inhibition of glutamate‐cysteine ligase (GCL) indicated that GSH depletion potentiated nitrosative stress, DNA damage, phosphorylation of the tumor suppressor p53 (Ser‐18) and upregulation of p21^cip1/waf1^ upon NO stimulation. However, we found that neither overexpression of a dominant negative p53 nor pharmacological inhibition of p53 with cyclic pifithrin‐α (cPFT‐α) was sufficient to reverse NO‐mediated cell cycle arrest or hypophosphorylation of retinoblastoma protein (Rb). We found that the decrease in cyclin D1 levels induced by NO was GSH‐sensitive implying that the redox regulation of NO‐mediated cytostasis was a multifaceted process and that both p53/p21^cip1/waf1^ and p53 independent cyclin D1 pathways were involved. Together, our results demonstrate that GSH serves as an important component of cellular protective mechanisms against NO‐derived nitrosative stress to regulate DNA damage checkpoint. J. Cell. Physiol. 212:827–839, 2007. © 2007 Wiley‐Liss, Inc.