All-trans-retinoic acid induces manganese superoxide dismutase in human neuroblastoma through NF-kappaB

Retinoids are signaling molecules that are involved in proliferation, differentiation, and apoptosis during development. Retinoids exert their effects, in part, by binding to nuclear receptors, thereby altering gene expression. Clinical use of retinoids in the treatment of neuroblastoma is of interest due to their success in management of acute promyelocytic leukemia. Using the SK-N-SH human neuroblastoma cell line we investigated the effects of the differentiation agent all-trans-retinoic acid (ATRA) on the expression of manganese superoxide dismutase (MnSOD), an enzyme previously shown to enhance differentiation in vitro. Manganese superoxide dismutase mRNA, protein, and activity levels increased in a time-dependent manner upon treatment with ATRA. Nuclear levels of the NF-kappaB proteins p50 and p65 increased within 24 h of ATRA administration. This increase paralleled the degradation of the cytoplasmic inhibitor IkappaB-beta. Furthermore an increase in DNA binding to a NF-kappaB element occurred within a 342-bp enhancer (I2E) of the SOD2 gene with 10 microM ATRA treatment. Reporter analysis showed that ATRA-mediated I2E-dependent luciferase expression was attenuated upon mutation of the NF-kappaB element, suggesting a contribution of this transcription factor to retinoid-mediated upregulation of MnSOD. This study identifies SOD2 as a retinoid-responsive gene and demonstrates activation of the NF-kappaB pathway in response to ATRA treatment of SK-N-SH cells. These results suggest that signaling events involving NF-kappaB and SOD2 may contribute to the effects of retinoids used in cancer therapy.