In this study, we examined the posttranscriptional regulation of p21(CIP1/WAF1) after Fe depletion and demonstrated that its down-regulation was due to 2 mechanisms: (1) inhibited translocation of p21(CIP1/WAF1) mRNA from the nucleus to cytosolic translational machinery.     ///    "We observed that Fe depletion increased the mRNA of the universal cyclin-dependent kinase inhibitor, p21(CIP1/WAF1), while its protein level was not elevated. "    ///    "In Fe-replete cells, p21(CIP1/WAF1) was degraded in an ubiquitin-dependent manner, while after Fe depletion, ubiquitin-independent proteasomal degradation occurred. "    ///    Iron chelation significantly (P < .01) decreased p21(CIP1/WAF1) protein half-life from 61 (+/- 4 minutes.     ///    "Proteasomal inhibitors rescued the chelator-mediated decrease in p21(CIP1/WAF1) protein, while lysosomotropic agents were not effective. "    ///    "This observation is unique to the G(1)/S arrest seen after Fe deprivation, as increased p21(CIP1/WAF1) mRNA and protein are usually found when arrest is induced by other stimuli. "