Unique epigenetic influence of H2AX phosphorylation and H3K56 acetylation on normal stem cell radioresponses.

Normal tissue injury resulting from cancer radiotherapy is often associated with diminished regenerative capacity. We examined the relative radiosensitivity of normal stem cell populations compared with non-stem cells within several radiosensitive tissue niches and culture models. We found that these stem cells are highly radiosensitive, in contrast to their isogenic differentiated progeny. Of interest, they also exhibited a uniquely attenuated DNA damage response (DDR) and muted DNA repair. Whereas stem cells exhibit reduced ATM activation and ionizing radiation-induced foci, they display apoptotic pannuclear H2AX-S139 phosphorylation (γH2AX), indicating unique radioresponses. We also observed persistent phosphorylation of H2AX-Y142 along the DNA breaks in stem cells, which promotes apoptosis while inhibiting DDR signaling. In addition, down-regulation of constitutively elevated histone-3 lysine-56 acetylation (H3K56ac) in stem cells significantly decreased their radiosensitivity, restored DDR function, and increased survival, signifying its role as a key contributor to stem cell radiosensitivity. These results establish that unique epigenetic landscapes affect cellular heterogeneity in radiosensitivity and demonstrate the nonubiquitous nature of radiation responses. We thus elucidate novel epigenetic rheostats that promote ionizing radiation hypersensitivity in various normal stem cell populations, identifying potential molecular targets for pharmacological radioprotection of stem cells and hopefully improving the efficacy of future cancer treatment.

Silencing Egr1 Attenuates Radiation-Induced Apoptosis in Normal Tissues while Killing Cancer Cells and Delaying Tumor Growth.

Normal tissue toxicity reduces the therapeutic index of radiotherapy and decreases the quality of life for cancer survivors. Apoptosis is a key element of the radiation response in normal tissues like the hippocampus and small intestine, resulting in neurocognitive disorders and intestinal malabsorption. The Early Growth Response 1 (Egr1) transcription factor mediates radiation-induced apoptosis by activating the transcription of proapoptosis genes in response to ionizing radiation (IR). Therefore, we hypothesized that the genetic abrogation of Egr1 and the pharmacologic inhibition of its transcriptional activity could attenuate radiation-induced apoptosis in normal tissues. We demonstrated that Egr1-null mice had less apoptosis in the hippocampus and intestine following irradiation as compared with their wild-type littermates. A similar result was achieved using Mithramycin A (MMA) to prevent binding of Egr1 to target promoters in the mouse intestine. Abolishing Egr1 expression using shRNA dampened apoptosis and enhanced the clonogenic survival of irradiated HT22 hippocampal neuronal cells and IEC6 intestinal epithelial cells. Mechanistically, these events involved an abrogation of p53 induction by IR and an increase in the ratio of Bcl-2/Bax expression. In contrast, targeted silencing of Egr1 in two cancer cell lines (GL261 glioma cells and HCT116 colorectal cancer cells) was not radioprotective, since it reduced their growth while also sensitizing them to radiation-induced death. Further, Egr1 depletion delayed the growth of heterotopically implanted GL261 and HCT116 tumors. These results support the potential of silencing Egr1 in order to minimize the normal tissue complications associated with radiotherapy while enhancing tumor control.

GSK-3ß: A Bifunctional Role in Cell Death Pathways.

Although glycogen synthase kinase-3 beta (GSK-3ß) was originally named for its ability to phosphorylate glycogen synthase and regulate glucose metabolism, this multifunctional kinase is presently known to be a key regulator of a wide range of cellular functions. GSK-3ß is involved in modulating a variety of functions including cell signaling, growth metabolism, and various transcription factors that determine the survival or death of the organism. Secondary to the role of GSK-3ß in various diseases including Alzheimer's disease, inflammation, diabetes, and cancer, small molecule inhibitors of GSK-3ß are gaining significant attention. This paper is primarily focused on addressing the bifunctional or conflicting roles of GSK-3ß in both the promotion of cell survival and of apoptosis. GSK-3ß has emerged as an important molecular target for drug development.

The politics of partnerships: a study of police and housing collaboration to tackle anti-social behaviour on Australian public housing estates.

This paper draws on the findings from a research project on partnership arrangements between the police and housing departments on three Australian public housing estates to tackle problems associated with illicit drug activity and anti-social behaviour (ASB). The analysis focused on the setting up of the partnerships and the interactions that followed from these institutional arrangements. The assumption that informs the paper is that when studying partnerships there is a need for a more critically framed analysis. The temptation to posit "a successful model" of what partnership entails and then to judge practices in relation to this model is considerable, but it inevitably falls into the trap of constructing a narrative of partnership success or failure in terms of individual agency (that is, the degree of commitment from individuals). The analysis undertaken in this paper has therefore sought to fathom a more complex set of organizational processes. Rather than confine the discussion to issues of success and failure, the study foregrounds the subjective accounts of individuals who work within partnership and the constraints they encounter. The paper therefore makes explicit the cultural tensions within and across agencies, contestation as to the extent of the policy "problem," and the divergent perspectives on the appropriate modes of intervention.