FIGURE 5.

Pim-1 is required for Skp2 to signal cell cycle S phase entry. A, HeLa cells were treated with a double-thymidine block and released into fresh medium. Cells were then harvested at the indicated time points and subjected to FACS (left panel) and immunoblot analysis (right panel). The arrow denotes the Pim-1 signal. * indicates a nonspecific signal. B, Rat1 cells were transduced with a lentivirus carrying the indicated cDNAs. Cells were maintained in low serum conditions (0.2%) for 48 h before harvested for FACS (upper panel) and immunoblot (lower panel) analyses. Percent of S phase cells was compared with vector control, except where indicated by a bracket. C, the experiment was performed as in B except that SMI-4a (5 μm) was added 3 h before a 20% FBS stimulation (16 h). S phase induction was also determined by BrdU incorporation assay. Brackets indicate comparison of with and without SMI-4a treatment.