Figure 4.

SSA, a SF3b inhibitor, induces P27* and reduces p-cdk2/cyclinE expression. A, HeLa cells were treated with SSA (100 ng/ml) for 0,1,6, and 24 hours. P27Kip1 and its splicing variant P27* were detected by Western blotting using anti-P27Kip1 antibody. P27* expression was higher than authentic P27 following SSA treatment. Schematic constructs of P27 and P27* are shown. SSA inhibited P27 pre-mRNA alternative splicing, and P27* was generated using a stop codon within intron 1 (between exon 1 and exon 2). B, the expression of c-Myc, total cdk2, phosphorylated cdk2 (Phos-cdk2), cyclinE, and cyclinB1 were examined after SSA treatment. β-Actin served as an internal control.