Fig. 4.

Constitutive Cyclin A-Cdk2 activity drives aberrant S-phase responses to replication stress. (A) Cdk2^+/+ and Cdk2^AF/AF cells were treated with HU for 6 h and Roscovitine as indicated, and γH2AX staining was analyzed by flow cytometry. (B, Upper) Cdk2^AF/AF cells transfected with either control or two Cdk2 siRNAs were treated with 0.5 mM HU for 24 h, and percent proliferation relative to untreated controls was measured by Alamar Blue 3 d after HU release. (B, Lower) Cdk2 abundance after siRNA transfection. (C) Cdk2^AF/AF cells transduced with control or lentiviruses expressing cyclin E or cyclin A shRNAs were grown asynchronously or treated with HU, and γH2AX abundance was assayed by flow cytometry. (D) Cyclin E and cyclin A abundance in samples from C.