Induction of apoptosis by an inhibitor of the mitotic kinesin KSP requires both activation of the spindle assembly checkpoint and mitotic slippage.

The inhibition of KSP causes mitotic arrest by activating the spindle assembly checkpoint. While transient inhibition of KSP leads to reversible mitotic arrest, prolonged exposure to a KSP inhibitor induces apoptosis. Induction of apoptosis by the KSP inhibitor couples with mitotic slippage. Slippage-refractory cells show resistance to KSP inhibitor-mediated lethality, whereas promotion of slippage after mitotic arrest enhances apoptosis. However, attenuation of the spindle checkpoint confers resistance to KSP inhibitor-induced apoptosis. Furthermore, sustained KSP inhibition activates the proapoptotic protein, Bax, and both activation of the spindle checkpoint and subsequent mitotic slippage are required for Bax activation. These studies indicate that in response to KSP inhibition, activation of the spindle checkpoint followed by mitotic slippage initiates apoptosis by activating Bax.

A new approach to a site radiological control manual.

The Pantex Plant significantly revised its Radiological Control Manual to improve its usability, streamline plant procedures, and clarify conflicting guidance. This article overviews the process used to develop the new Radiological Control Manual.

Examination of the pRb-dependent and pRb-independent functions of E7 in vivo.

High-risk human papillomaviruses encode two oncogenes, E6 and E7, expressed in nearly all cervical cancers. Although E7 protein is best known for its ability to inactivate the retinoblastoma tumor suppressor protein, pRb, many other activities for E7 have been proposed in in vitro studies. Herein, we describe studies that allowed us to define unambiguously the pRb-dependent and -independent activities of E7 for the first time in vivo. In these studies, we crossed mice transgenic for human papillomavirus 16 E7 to knock-in mice genetically engineered to express a mutant form of pRb (pRb(DeltaLXCXE)) that is selectively defective for binding E7. pRb inactivation was necessary for E7 to induce DNA synthesis and to overcome differentiation-dependent cell cycle withdrawal and DNA damage-induced cell cycle arrest. While most of E7's effects on epidermal differentiation were found to require pRb inactivation, a modest delay in terminal differentiation with resulting hyperplasia was observed in E7 mice on the Rb(DeltaLXCXE) mutant background. E7-induced p21 upregulation was also pRb dependent, and genetic Rb inactivation was sufficient to reproduce this effect. While E7-mediated p21 induction was partially p53 dependent, neither p53 nor p21 induction by E7 required p19(ARF). These data show that E7 upregulates the expression of p53 and p21 via pRb-dependent mechanisms distinct from the proposed p19-Mdm2 pathway. These results extend our appreciation of the importance of pRb as a relevant target for high-risk E7 oncoproteins.

Protection against human papillomavirus type 16-E7 oncogene-induced tumorigenesis by in vivo expression of dominant-negative c-jun.

Expression of the human papillomavirus (HPV) type 16 E6 and E7 gene products is a risk factor for human cervical carcinogenesis as well as skin and oral carcinogenesis. Expression of the HPV-16 E7 gene in mouse skin induces hyperplasia and enhances tumor promotion. Expression of dominant-negative c-jun (TAM67) in the mouse skin protects mice from 7,12-dimethylbenz[a]anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA)-induced papillomagenesis without blocking mitogen-induced hyperproliferation. To determine the role of activator protein-1 (AP-1) in HPV-induced cancer, we crossed HPV-16 E7 mice with TAM67 mice and analyzed the effects of DMBA/TPA on tumor promotion. We showed that expression of TAM67 protected mice from HPV-16 E7-enhanced tumorigenesis, suggesting AP-1 as a target for prevention of HPV-induced cancer.