ONE AND 2-LEVEL REGULATION PATTERNS AFFECTING NF-KAPPA-B MESSENGER-RNA AND NUCLEAR NF-KAPPA-B ACTIVITY AFTER TREATMENT WITH TNF-ALPHA, IFN-GAMMA AND IL-4

The transactivating nuclear factor NF-kappaB is believed to be importa nt in the pathophysiology of many cellular systems and mainly during H IV infection. KappaB activation has also been implicated in the proces s of differentiation as a cell progresses to a more mature and functio nal stage. As induction of differentiation equals growth retardation w e undertook this study in order to establish the role of NF-kappaB in cell growth and maturity. Thus we employed the well described HL-60 ce llular system that expresses constitutively basal amounts of NF-kappaB and is susceptible to NF-kappaB induction by various biological or ch emical agents. We also used known inducers of differentiation like TNF -alpha, IFN-gamma and IL-4 that interact via their corresponding surfa ce receptors found on HL-60 cells. We first studied by Northern analys is the possible correlation between c-myc and NF-kappaB precursor (p10 5) mRNA. We witnessed that all three cytokines were able to confer pro liferative senescence and down-regulate concomitantly c-myc and NF-kap paB mRNA levels, events chronologically in accord with induction of di fferentiation as assessed by the induction of HLA-DR surface antigens. It is known that TNF-alpha is capable of inducing nuclear kappaB acti vity in HL-60 as the cells progress to a more mature stage. Therefore we examined whether the other two cytokines could do the same during t he time they lead the cells to a differentiated phenotype. If this was the case, nuclear activation of NF-kappaB should be obtained by the s ame factors. Electrophoretic mobility nuclear shift assays (EMSA) show ed however, that in contrast to TNF-alpha, neither IFN-gamma nor IL-4 were able to activate NF-kappaB indicating a complicated regulatory ne twork governing the processes of proliferation and differentiation. Th ese findings indicate that the transition of a cell to a more differen tiated state is not necessarily kappaB-dependent. They also point to a multi-step and compartmentalised action of each cytokine influencing different cellular functions at the nuclear or cytoplasmic level.