INTERLEUKIN-1-INDUCED GROWTH-INHIBITION OF HUMAN-MELANOMA CELLS - INTERLEUKIN-1-INDUCED ANTIZYME EXPRESSION IS RESPONSIBLE FOR ORNITHINE DECARBOXYLASE ACTIVITY DOWN-REGULATION

Interleukin (IL)-1 is a multi-functional cytokine and regulates cell g rowth either positively or negatively. Previous studies have shown tha t IL-1-induced ornithine decarboxylase (ODC) activity down-regulation is involved in the anti-proliferative effect of IL-1 on human A375 mel anoma cells. In this study, we examined the IL-1 alpha-induced molecul ar events resulting in ODC activity down-regulation in C2-1, a A375 ce ll. Line stably transfected with human type I IL-1 receptor, Recombina nt human (rh) IL-1 alpha inhibited the growth and down-regulated the O DC activity of C2-1 cells in a dose-dependent manner. Kinetics studies showed that both the DNA synthesis and ODC activity of C2-1 cells pro gressively decreased horn 12 h after IL-1 addition, Northern hybridiza tion showed that IL-1 had no influence on ODC mRNA level. However, rhI L-1 induced both a decrease of ODC protein and an ODC-inhibiting activ ity in IL-1-treated C2-1 cells. IL-1 specifically up-modulated the mRN A level of antizyme, a protein essential for ODC regulation, but had l ittle effect on its stability. IL-1-induced antizyme up-modulation pre ceded IL-1-induced down-regulation of ODC protein, ODC activity, and D NA synthesis in C2-1 cells. Run-on transcription analysis confirmed th at the increased antizyme mRNA expression was due to elevated antizyme gene transcription. Furthermore, the action of IL-1 to inhibit the OD C activity and growth of C2-1 cells was blocked by expressing the anti sense RNA of human antizyme in C2-1 cells. These results suggest that IL-1-induced antizyme expression is responsible for IL-1-induced ODC a ctivity down-regulation in human melanoma cells.