The direct role of NF-κB signalling in Tax2-mediated CC-chemokine secretion in PBMCs was then examined using a potent NF-κB canonical pathway inhibitor, pyrrolidine dithiocarbamate (PDTC), which inhibits the IκB-ubiquitin ligase activity blocking the degradation of IκB; as a consequence, the IκB-p65/RelA-p50 complex remains sequestered in the cytoplasm [35, 36]. We investigated whether the inhibition of the canonical NF-κB pathway could restrain the secretion
of CC-chemokines by Tax2A-treated Doxorubicin PBMCs. Thus, cells were pretreated or not with PDTC at 30 μM for 1 h, prior to the addition of extracellular Tax1, Tax2A, Tax2A/1–198, Tax2A/135–331, PHA/PMA (5 μg/ml and 50 ng/ml, respectively) or mock control, then cell-free supernatants were taken after 3 h of incubation, a time-point shown to have significant measurable levels of CC-chemokines (Fig. 1). PBMCs pretreated with PDTC resulted in a two- to threefold reduction of MIP-1α and RANTES production (P < 0·01; Fig. 4a,c) and a four- to sevenfold inhibition of MIP-1β release (P < 0·01) using all Tax proteins tested (Fig. 4b). As a test control, PDTC pretreated PBMCs stimulated with PHA/PMA showed a statistically significant reduction of all CC-chemokines compared with the PHA/PMA-stimulated PMBCs (P < 0·05, Fig. 4a–c). These results PI3K Inhibitor Library were confirmed using a NF-κB super-repressor (NF-κB/SR) at a MOI of 25 to pretreat PBMCs for
20 h before adding Tax proteins, and harvesting cell-free supernatants after 3 h of culture. The data showed that the NF-κB/SR pretreatment significantly reduced the expression of MIP-1α, MIP-1β and RANTES when PBMCs were treated
with Tax1, the entire Tax2A protein and the Tax2A/135–331 fragment (P < 0·05, Fig. 4d–f). NF-κB/SR reduced the expression of MIP-1α significantly (P < 0·05) (Fig. 4d), but there was only a trend towards reduced levels of MIP-1β and RANTES expression in Tax2A/1–198-treated PBMCs (Fig. 4e,f). The inhibition of CC-chemokine induction by the NF-κB/SR was also examined Sclareol co-transducing PBMCs with the adenovirus expressing NF-κB/SR and Ad-Tax2B (subtype Tax2B). Tax2B expressed via the recombinant adenoviral vector retained the ability to initiate viral transcription, as determined by HTLV pLTR-Luc reporter assay in Jurkat cells (data not shown) and reported to induce high levels of all three CC-chemokines in monocyte-derived macrophages (MDMs) . PBMCs transduced with Ad-Tax2B produced significant levels of MIP-1α, MIP-1β and RANTES in supernatants harvested at 24 h compared to transfected Ad-GFP-PBMCs or untreated PBMC controls (P < 0·01) (Fig. 5a). The production of MIP-1α and MIP-1β was suppressed significantly after co-transducing PBMCs with NF-κB/SR and Ad-Tax2B (P < 0·01; Fig. 5b). A slight trend towards lower RANTES production was observed when PBMCs were co-transduced with NF-κB/SR and Ad-Tax2B; however, a high background limited interpretation of these results (Fig. 5b).