Cellular DNA damage triggers the DNA damage response pathway and leads to enforcement of cell cycle checkpoints, which are essential for the maintenance of genomic integrity and are activated in early stages of tumorigenesis. A special feature of prostate cancer is its high incidence and multifocality. To address the functionality of DNA damage checkpoints in the prostate, we analyzed the responses of human primary prostate epithelial cells (HPECs) and freshly isolated human prostate tissues to ␥-irradiation. We find that ␥-irradiation activates the ataxia telangiectasia mutated-associated DNA damage response pathway in the HPECs but that the clearance of phosphorylated histone H2AX (␥H2AX) foci is delayed. Surprisingly, ␥-irradiated HPECs were unable to enforce cell cycle checkpoint arrest and had sustained cyclin-dependent kinase 2 (Cdk2)-associated kinase activity because of a lack of inhibitory Cdk phosphorylation by Wee1A tyrosine kinase. We further show that HPECs express low levels of Wee1A and that ectopic Wee1A efficiently rescues the checkpoints. We recapitulate the absence of checkpoint responses in epithelium of ex vivo irradiated human prostate tissue despite robust induction of ␥H2AX. The findings show that prostate epithelium has a surprising inability to control checkpoint arrest, the lack of which may predispose to accrual of DNA lesions.p53 ͉ irradiation ͉ cyclin-dependent kinase

Transforming growth factor-L L (TGF-L L) signaling relies on Smad-signaling pathway controlled in part by the proteasome. Here we demonstrate that inhibition of the proteasome function in mink epithelial cells accumulates both positive and negative modulators of TGF-L L signaling, phospho-Smad2 and SnoN. Inhibition of the proteasome led to abrogation of TGF-L L target gene regulation in a gene-speci¢c manner. While regulation of p15Ink4b and myc by TGF-L L are lost, PAI-1 induction, previously shown to occur in a Smad3-dependent manner, was not a¡ected by treatment of the cells with the proteasomal inhibitor MG132. The results suggest that proteasomal activity is required for TGF-L L signaling in a gene-speci¢c manner. ß