In activated T cells, NF-κB transcription

factors, by co-operating with a number of transcriptional learn more regulators, enhance the expression of several genes, including those for the mitogenic cytokine interleukin (IL)-2 and its high-affinity receptor IL-2RA.17,18 Upon interacting with its receptor, IL-2 elicits the co-ordinated activation of several intracellular signalling pathways that promote entry of T cells into the cell cycle, and clonal expansion. For this reason, CD28 costimulation was proposed to trigger T-cell proliferation through accumulation of IL-2, and subsequent activation of its signalling pathway.19 However, a number of observations in CD28-,20 IL-2-21 and cytotoxic T-lymphocyte antigen 4 (CTLA4)-deficient22 mice, as well as in human primary T cells,3 suggest that in CD28-costimulated T cells additional IL-2-independent cell cycle regulatory mechanisms are required for cell proliferation. Recent studies have shown that the duration

of the TCR/CD28 engagement appears to be a critical factor determining the IL-2 requirement for T-cell proliferation: while a short (20–24 hr) engagement of the TCR and CD28 programmes T cells to proliferate in response to autocrine IL-2, a prolonged (72–96 hr) TCR/CD28 engagement circumvents the need for autocrine IL-2 and supports IL-2-independent lymphocyte proliferation.3,23,24 In this study we aimed to determine if, in human naïve CD4+ T cells, PLX4032 stimulated through a short engagement of the TCR and the CD28 co-receptor, signals from IKK promote T-cell proliferation through IL-2-independent cell-cycle regulatory mechanisms. The effects of a neutralizing anti-human IL-2 antibody on the expression of cell-cycle regulatory proteins involved in the G0/G1 transition

and S phase entry of CD28-costimulated human naïve CD4+ T cells were compared with the effects of two selective, structurally unrelated, cell-permeable IKK inhibitors, BMS-34554125 and PS-1145.26 Our results demonstrate that, in addition to having a pivotal role in the up-regulation of Hydroxychloroquine IL-2 and IL-2RA gene expression, proliferative signals from IKK control the expression of the cell-cycle regulatory proteins cyclin D3, cyclin E and CDK2, and the stability of the F-box protein SKP2 and its co-factor CKS1B, through mechanisms independent of IL-2. BMS-345541[4(2′-aminoethyl)amino-1,8-dimethylimidazol [1,2-a]quinoxaline] (B9935) and PS-1145[N-(6-chloro-9H-pyrido[3,4-b]indol-8-yl)-3-pyridinecarboxamide] (P6624), protease inhibitor cocktail (P8340), antibiotic-antimycotic solution (A5955), Laemmli 2× sample buffer (S3401), phosphate-buffered saline (PBS) (P5493), and β-actin monoclonal antibody (A-5441) were from Sigma-Aldrich (Milan, Italy).