FIG. 5.

NS1 expression and MVMp infection induce accumulation of cyclin A and the Cdk inhibitor p21^cip1 and inhibitory phosphorylation of the p34^cdc2 kinase. Cyclins A, B, and E, the kinase p34^cdc2, and the Cdk inhibitors p21^cip1 and p27^kip1 were detected by immunoblotting in rat fibroblasts after infection with MVMp or induction of NS1 expression with dexamethasone. FRNS1.25, FRNS1.25EJ1, and FRNS1.25MT4.1 rat fibroblasts contain the LTR-NS1 construct. The former is not transformed. The two latter are transformed with the Ha-ras oncogene and the polyomavirus middle T antigen, respectively. Control cell lines without the LTR-NS1 construct were used to distinguish either effects of NS1 or dexamethasone treatment. FR3T3 cells are nontransformed rat fibroblasts. FREJ4 and FRMT4 are transformed rat fibroblasts. The former is transformed with the Ha-ras oncogene, and the latter is transformed with the polyomavirus middle T antigen. The cells were harvested 24 h after infection or dexamethasone treatment. Proteins were purified on p9 beads from cellular extracts before detection by Western blotting, except for cyclin B.