The atypical E2F family member E2F7 couples the p53 and RB pathways during cellular senescence

Oncogene-induced senescence is an anti-proliferative stress response program that acts as a fail-safe mechanism to limit oncogenic transformation and is regulated by the retinoblastoma protein (RB) and p53 tumor suppressor pathways. We identify the atypical E2F family member E2F7 as the only E2F transcription factor potently up-regulated during oncogene-induced senescence, a setting where it acts in response to p53 as a direct transcriptional target. Once induced, E2F7 binds and represses a series of E2F target genes and cooperates with RB to efficiently promote cell cycle arrest and limit oncogenic transformation. Disruption of RB triggers a further increase in E2F7, which induces a second cell cycle checkpoint that prevents unconstrained cell division despite aberrant DNA replication. Mechanistically, E2F7 compensates for the loss of RB in repressing mitotic E2F target genes. Together, our results identify a causal role for E2F7 in cellular senescence and uncover a novel link between the RB and p53 pathways

Oncogene-dependent apoptosis in extracts from drug-resistant cells

Many genotoxic agents kill tumor cells by inducing apoptosis; hence, mutations that suppress apoptosis produce resistance to chemotherapy. Although directly activating the apoptotic machinery may bypass these mutations, how to achieve this activation in cancer cells selectively is not clear. In this study, we show that the drug-resistant 293 cell line is unable to activate components of the apoptotic machinery-the ICE-like proteases (caspases)-following treatment with an anticancer drug. Remarkably, extracts from untreated cells spontaneously activate caspases and induce apoptosis in a cell-free system, indicating that drug-resistant cells have not only the apoptotic machinery but also its activator. Comparing extracts from cells with defined genetic differences, we show that this activator is generated by the adenovirus E1A oncogene and is absent from normal cells. We provide preliminary characterization of this oncogene generated activity (OGA) and show that partially purified OGA activates caspases when added to extracts from untransformed cells. We suggest that agents that link OGA to caspases in cells would kill tumor cells otherwise resistant to conventional cancer therapy. As this killing relies on an activity generated by an oncogene, the effect of these agents should be selective for transformed cells

PERP, an apoptosis-associated target of p53, is a novel member of the PMP-22/gas3 family

The p53 tumor suppressor activates either cell cycle arrest or apoptosis in response to cellular stress. Mouse embryo fibroblasts (MEFs) provide a powerful primary cell system to study both p53-dependent pathways. Specifically, in response to DNA damage, MEFs undergo p53-dependent G(1) arrest, whereas MEFs expressing the adenovirus E1A oncoprotein undergo p53-dependent apoptosis. As the p53-dependent apoptosis pathway is not well understood, we sought to identify apoptosis-specific p53 target genes using a subtractive cloning strategy. Here, we describe the characterization of a gene identified in this screen, PERP, which is expressed in a p53-dependent manner and at high levels in apoptotic cells compared with G(1)-arrested cells. PERP induction is linked to p53-dependent apoptosis, including in response to E2F-1-driven hyperproliferation. Furthermore, analysis of the PERP promoter suggests that PERP is directly activated by p53. PERP shows sequence similarity to the PMP-22/gas3 tetraspan membrane protein implicated in hereditary human neuropathies such as Charcot-Marie-Tooth, Like PMP-22/gas3, PERP is a plasma membrane protein, and importantly, its expression causes cell death in fibroblasts. Taken together, these data suggest that PERP is a novel effector of p59-dependent apoptosis

bax-deficiency promotes drug resistance and oncogenic transformation by attenuating p53-dependent apoptosis

Inactivation of p53-dependent apoptosis promotes oncogenic transformation, tumor development, and resistance to many cytotoxic anticancer agents. p53 can transcriptionally activate bax, a bcl-2 family member that promotes apoptosis. To determine whether bax is required for p53-dependent apoptosis, the effects of bax deficiency were examined in primary fibroblasts expressing the E1A oncogene, a setting where apoptosis is dependent on endogenous p53. We demonstrate that bax can function as an effector of p53 in chemotherapy-induced apoptosis and contributes to a p53 pathway to suppress oncogenic transformation. Furthermore, we show that additional p53 effectors participate in these processes. These p53-controlled factors act synergistically with Bax to promote a full apoptotic response, and their action is suppressed by the Bcl-2 and E1B 19K oncoproteins. These studies demonstrate that Bax is a determinant of p53-dependent chemosensitivity and illustrate how p53 can promote apoptosis by coordinating the activities of multiple effectors

E1A signaling to p53 involves the p19(ARF) tumor suppressor

The adenovirus E1A oncogene activates p53 through a signaling pathway involving the retinoblastoma protein and the tumor suppressor p19(ARF). The ability of E1A to induce p53 and its transcriptional targets is severely compromised in ARF-null cells, which remain resistant to apoptosis following serum depletion or adriamycin treatment. Reintroduction of p19(ARF) restores p53 accumulation and resensitizes ARF-null cells to apoptotic signals. Therefore, p19(ARF) functions as part of a p53-dependent failsafe mechanism to counter uncontrolled proliferation. Synergistic effects between the p19(ARF) and DNA damage pathways in inducing p53 may contribute to E1A's ability to enhance radio- and chemosensitivity

Stepped-wedge randomised trial of laparoscopic ventral mesh rectopexy in adults with chronic constipation: Study protocol for a randomized controlled trial

BACKGROUND: Laparoscopic ventral mesh rectopexy (LVMR) is an established treatment for external full-thickness rectal prolapse. However, its clinical efficacy in patients with internal prolapse is uncertain due to the lack of high-quality evidence. METHODS: An individual level, stepped-wedge randomised trial has been designed to allow observer-blinded data comparisons between patients awaiting LVMR with those who have undergone surgery. Adults with symptomatic internal rectal prolapse, unresponsive to prior conservative management, will be eligible to participate. They will be randomised to three arms with different delays before surgery (0, 12 and 24 weeks). Efficacy outcome data will be collected at equally stepped time points (12, 24, 36 and 48 weeks). The primary objective is to determine clinical efficacy of LVMR compared to controls with reduction in the Patient Assessment of Constipation Quality of Life (PAC-QOL) at 24 weeks serving as the primary outcome. Secondary objectives are to determine: (1) the clinical effectiveness of LVMR to 48 weeks to a maximum of 72 weeks; (2) pre-operative determinants of outcome; (3) relevant health economics for LVMR; (4) qualitative evaluation of patient and health professional experience of LVMR and (5) 30-day morbidity and mortality rates. DISCUSSION: An individual-level, stepped-wedge, randomised trial serves the purpose of providing an untreated comparison for the active treatment group, while at the same time allowing the waiting-listed participants an opportunity to obtain the intervention at a later date. In keeping with the basic ethical tenets of this design, the average waiting time for LVMR (12 weeks) will be shorter than that for routine services (24 weeks)

The Base Excision Repair Pathway Is Required for Efficient Lentivirus Integration

An siRNA screen has identified several proteins throughout the base excision repair (BER) pathway of oxidative DNA damage as important for efficient HIV infection. The proteins identified included early repair factors such as the base damage recognition glycosylases OGG1 and MYH and the late repair factor POLß, implicating the entire BER pathway. Murine cells with deletions of the genes Ogg1, Myh, Neil1 and Polß recapitulate the defect of HIV infection in the absence of BER. Defective infection in the absence of BER proteins was also seen with the lentivirus FIV, but not the gammaretrovirus MMLV. BER proteins do not affect HIV infection through its accessory genes nor the central polypurine tract. HIV reverse transcription and nuclear entry appear unaffected by the absence of BER proteins. However, HIV integration to the host chromosome is reduced in the absence of BER proteins. Pre-integration complexes from BER deficient cell lines show reduced integration activity in vitro. Integration activity is restored by addition of recombinant BER protein POLß. Lentiviral infection and integration efficiency appears to depend on the presence of BER proteins