IL-15 increases c-Myc transcription and c-Myc binding to the KIR distal promoter element. (A) KIR-negative NK cells were isolated from adult peripheral blood and cultured in the presence of 10 ng/mL IL-15 for 4, 24, or 48 hours. Cells were harvested at each time point, and c-myc transcript levels were determined by quantitative RT-PCR (n = 3). Samples are normalized to unstimulated peripheral blood NK-cell controls. (B) ChIP analysis of c-Myc binding to freshly isolated KIR-negative NK cells or NK cells stimulated with 10 ng/mL IL-15 for 48 hours. Input sample represents the total input DNA contained in the chromatin aliquot used for each ChIP. Rabbit antibodies used for the IP were purified rabbit IgG (as a negative control), histone H3 (as a positive control), anti-Myc, and anti-USF. Results from a 35-cycle PCR are shown.