1,25-Dihydroxyvitamin D3 induces biphasic NF-κB responses during HL-60 leukemia cells differentiation through protein induction and PI3K/Akt-dependent phosphorylation/degradation of IκB

1,25-Dihydroxyvitamin D-3 (VD3) 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 VD3-treated HL-60 leukemia cells. After VD3 treatment there was an early similar to 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. VD3-triggered reactivation of NF-kappa B was associated with PI3K/Akt phosphorylation. PI3K/Akt antagonists suppressed VD3-stimulated I kappa B alpha phosphorylation as well as NF-kappa B-controlled gene expression. The early similar to 4 h VD3-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 VD3-treated leukemia cells and our results may have provided the first molecular explanation for the contradictory observations reported on VD3-mediated immune-regulation. (c) 2007 Elsevier Inc. All rights reserved.