Lytic reactivation of KSHV leads to down-regulation of p27^KIP1 in PEL cells. (A) BC-3, BC-1, and JOK-1 (a KSHV-negative control cell line) cells were either treated with TPA or with DMSO (noninduced control) for 24 hours. Whole-cell extracts were resolved by 12% SDS-PAGE and analyzed by immunoblotting with antibodies against p-p27 (Thr187), p27^KIP1, and actin (loading control). (B) BC-3 and BC-1 cells were induced to viral replication with TPA for 48 hours. The p27^KIP1 down-regulation in anti-ORF59-positive cells was determined by double-label immunofluorescence experiment after cytocentrifugation. Arrowheads point to ORF59-positive cells with down-regulated p27^KIP1.