Down-regulation of JAB1 increases p27 levels and induces cell cycle arrest. A, knockdown of JAB1 with siRNA enhanced p27 stability. Cells were transfected with siRNA targeting either JAB1 or a scrambled sequence (control); 48 hours later, proteins were isolated and immunoblotted with anti-JAB1 and anti-p27 antibodies. Anti-β-actin antibodies were used as loading controls. The specific JAB1 bands (filled arrow)and nonspecific bands (n.s., white arrow) are indicated. B, siRNA ablation of JAB1 induced G1 arrest. Mia PaCa-2 and Panc-28 cells were transfected as described in (A); 48 hours later, BrdUrd (BRdU)was added and the cells were stained with FITC-anti-BrdUrd antibodies. Cells that stained positively for BrdUrd were then analyzed by flow cytometry. Columns, percentage of BrdUrd-positive (i.e., S-phase)cells.