The chemopreventive effect of retinoids on cellular NF-kappaB activity induced by NMU and NEU in human malignant keratinocytes.
OBJECTIVE
Retinoids have been shown to be effective in suppressing tumor development when chemical carcinogens such as N-nitroso-N-methylurea (NMU) and N-nitroso-N-ethylurea (NEU) were used to induce mammary tumors in a variety of animal models. However, the molecular mechanisms associated with the retinoid-mediated chemopreventive process, as linked to transcription factor NF-kappaB activation, for chemoprevention have not been elucidated. The purpose of this study was to determine the implications of NF-kappaB activation on the chemopreventive role of retinoids and their effect on cellular NF-kappaB activity that's induced by known alkylating chemical carcinogens such as NMU and NEU in human transfectant squamous cell carcinoma (SCC-13) cells.


METHODS
The activity of NF-kappaB, as regulated by chemical carcinogens and retinoids, was determined in cultured human SCC-13 keratinocytes that were transfected with the pNF-kappaB-SEAP-NPT plasmid; this permitted the expression of the secretory alkaline phosphatase (SEAP) reporter gene in response to the NF-kappaB activity, and the plasmid contained the neomycin phosphotransferase (NPT) gene, which confers resistance to geneticin. The reporter enzyme activity was measured using a fluorescence detection assay method.


RESULTS
All-trans retinoic acid and 13-cis retinoic acid induced a reduction of NF-kappaB activity up to 64% and 65%, respectively, compared to the control. For the treatment of the human transfectant cells with chemical carcinogens, all-trans retinoic acid (5 mM) and 13-cis retinoic acid (5 mM) downregulated the cellular NF-kappaB activation up to 83% and 85% compared to the NF-kappaB activity that was upregulated by NMU (5microM) and NEU (5microM), respectively.


CONCLUSIONS
These results suggest that the chemopreventive effect of retinoids may be mediated by the downregulated activation of NF-kappaB and that retinoids are implicated in the activation of NF-kappaB in human skin cells.
Moon
Ki-Young
KY
Department of Clinical Pathology, Bioindustry and Technology Research Institute, Gwangju Health College, Gwangju, Korea. kmoon@ghc.ac.kr