1,25-Dihydroxyvitamin D{sub 3} induces biphasic NF-{kappa}B responses during HL-60 leukemia cells differentiation through protein induction and PI3K/Akt-dependent phosphorylation/degradation of I{kappa}B

1,25-Dihydroxyvitamin D{sub 3} (VD{sub 3}) induces differentiation in a number of leukemia cell lines and under various conditions is able to either stimulate or inhibit nuclear factor kappa B (NF-{kappa}B) activity. Here we report a time-dependent biphasic regulation of NF-{kappa}B in VD{sub 3}-treated HL-60 leukemia cells. After VD{sub 3} treatment there was an early {approx} 4 h suppression and a late 8-72 h prolonged reactivation of NF-{kappa}B. The reactivation of NF-{kappa}B was concomitant with increased IKK activities, IKK-mediated I{kappa}B{alpha} phosphorylation, p65 phosphorylation at residues S276 and S536, p65 nuclear translocation and p65 recruitment to the NF-{kappa}B/vitamin D responsive element promoters. In parallel with NF-{kappa}B stimulation, there was an up-regulation of NF-{kappa}B controlled inflammatory and anti-apoptotic genes such as TNF{alpha}, IL-1{beta} and Bcl-xL. VD{sub 3}-triggered reactivation of NF-{kappa}B was associated with PI3K/Akt phosphorylation. PI3K/Akt antagonists suppressed VD{sub 3}-stimulated I{kappa}B{alpha} phosphorylation as well as NF-{kappa}B-controlled gene expression. The early {approx} 4 h VD{sub 3}-mediated NF-{kappa}B suppression coincided with a prolonged increase of I{kappa}B{alpha} protein which require de novo protein synthesis, lasted for as least 72 h and was insensitive to MAPK, IKK or PI3K/Akt inhibitors. Our data suggest a novel biphasic regulation of NF-{kappa}B in VD{sub 3}-treated leukemia cells and our results may have provided the first molecular explanation for the contradictory observations reported on VD{sub 3}-mediated immune-regulation.