Inositol hexaphosphate inhibits ultraviolet B-induced signal transduction

Inositol hexaphosphate (InsP₆) has an effective anticancer action in many experimental models in vivo and in vitro. Ultraviolet B (UVB) radiation is believed to be responsible for many of the carcinogenic effects related to sun exposure, and alteration in UVB-induced signal transduction is associated with UVB-induced carcinogenesis. Here we report the effects of InsP₆ on UVB-induced signal transduction. InsP₆ strongly blocked UVB-induced activator protein-1 (AP-1) and NF-κB transcriptional activities in a dose-dependent manner. InsP₆ also suppressed UVB-induced AP-1 and nuclear factor κB (NF-κB) DNA binding activities and inhibited UVB-induced phosphorylation of extracellular signal-regulated protein kinases (Erks) and c-Jun NH2-terminal kinases (JNKs). Phosphorylation of p38 kinases was not affected. InsP₆ also blocked UVB-induced phosphorylation of IκB-α, which is known to result in the inhibition of NF-κB transcriptional activity. InsP₆ does not block UVB-induced phosphotidylinositol-3′ (PI-3) kinase activity, suggesting that the inhibition of UVB-induced AP-1 and NF-κB activities by InsP₆ is not mediated through PI-3 kinase. Because AP-1 and NF-κB are important nuclear transcription factors that are related to tumor promotion, our work suggests that InsP₆ prevents UVB-induced carcinogenesis by inhibiting AP-1 and NF-κB transcription activities.