Lisa Minter

Hormonal control of p53 and chemoprevention

Lisa Minter et al. — Thu, 12 Jan 2012 11:11:28 PST

Improvements in the detection and treatment of breast cancer have dramatically altered its clinical course and outcome. However, prevention of breast cancer remains an elusive goal. Parity, age of menarche, and age at menopause are major risk factors drawing attention to the important role of the endocrine system in determining the risk of breast cancer, while heritable breast cancer susceptibility syndromes have implicated tumor suppressor genes as important targets. Recent work demonstrating hormonal modulation of the p53 tumor suppressor pathway draws together these established determinants of risk to provide a model of developmental susceptibility to breast cancer. In this model, the mammary epithelium is rendered susceptible due to impaired p53 activity during specific periods of mammary gland development, but specific endocrine stimuli serve to activate p53 function and to mitigate this risk. The results focus attention on p53 as a molecular target for therapies to reduce the risk of breast cancer.

Epithelial cell cycling predicts p53 - repsoniveness to gamma-irradiation during post-natal mammary gland development

Lisa Minter et al. — Thu, 12 Jan 2012 11:10:18 PST

The tumor suppressor gene, TP53, plays a major role in surveillance and repair of radiation-induced DNA damage. In multiple cell types, including mammary epithelial cells, abrogation of p53 (encoded by Trp53) function is associated with increased tumorigenesis. We examined γ-irradiated BALB/c-Trp53+/+ and -Trp53–/– female mice at five stages of post-natal mammary gland development to determine whether radiation-induced p53 activity is developmentally regulated. Our results show that p53-mediated responses are attenuated in glands from irradiated virgin and lactating mice, as measured by induction of p21/WAF1 (encoded by Cdkn1a) and apoptosis, while irradiated early- and mid-pregnancy glands exhibit robust p53 activity. There is a strong correlation between p53-mediated apoptosis and the degree of cellular proliferation, independent of the level of differentiation. In vivo, proliferation is intimately influenced by steroid hormones. To determine whether steroid hormones directly modulate p53 activity, whole organ cultures of mammary glands were induced to proliferate using estrogen plus progesterone or epidermal growth factor plus transforming growth factor-α and p53 responses to γ-irradiation were measured. Regardless of mitogens used, proliferating mammary epithelial cells show comparable p53 responses to γ-irradiation, including expression of nuclear p53 and p21/WAF1 and increased levels of apoptosis, compared to non-proliferating irradiated control cultures. Our study suggests that differences in radiation-induced p53 activity during post-natal mammary gland development are influenced by the proliferative state of the gland, and may be mediated indirectly by the mitogenic actions of steroid hormones in vivo.

Hyperbaric oxygen inhibits stimulus-induced pro-inflammatory cytokine synthesis by human blood-derived monocyte-macrophages

Lisa Minter et al. — Thu, 12 Jan 2012 11:07:50 PST

Hyperbaric oxygen (HBO) is 100% oxygen administered at elevated atmospheric pressure to patients with inflammatory diseases. We developed an in vitro model to investigate the effects of HBO on stimulus-induced proinflammatory cytokine transcription and translation. Human blood-derived monocyte-macrophages were stimulated before being transferred to an HBO chamber where they were incubated at 97·9% O2, 2·1% CO2, 2·4 atmospheres absolute, 37°C. Controls were maintained in the same warm room at normoxia at sea level, hyperoxia or increased pressure alone. A 90-min HBO exposure inhibited IL-1β synthesized in response to lipopolysaccharide by 23%, lipid A by 45%, phytohaemagglutinin A (PHA) by 68%, and tumour necrosis factor (TNF)-α by 27%. HBO suppressed lipopolysaccharide-, lipid A- and PHA-induced TNF-α by 29%, 31% and 62%, respectively. HBO transiently reduced PHA-induced steady state IL-1β mRNA levels. Hyperoxia alone and pressure alone did not affect cytokine production. The immunosuppressive effect of HBO was no longer evident in monocyte-macrophages exposed to HBO for more than 3 h. Interestingly, cells exposed to HBO for 12 h synthesized more IL-1β than cells cultured under control conditions. In summary, HBO exposure transiently suppresses stimulus-induced proinflammatory cytokine production and steady state RNA levels.

Cell Death in the Thymus - It's All a Matter of Contacts

Lisa Minter et al. — Thu, 12 Jan 2012 11:06:28 PST

Apoptosis, or programmed cell death, plays a critical role in shaping the T cell repertoire, deleting unproductive as well as potentially autoreactive T cells. Our understanding of how thymocyte apoptosis is regulated is continually evolving, as new essential modulators of this process are discovered. A conundrum that remains, however, is how signaling through essentially the same receptors and cascades evokes distinct biological responses: death by neglect, positive or negative selection. We hypothesize that the immunological synapse (IS) may be critical to transducing survival signals during thymocyte development, and suggest that factors affecting IS assembly may also influence T cell selection.

Inhibitors ofg-secretase block in vivo and in vitro T helper type 1 polarization by preventing Notch upregulation of Tbx21

Lisa Minter et al. — Thu, 12 Jan 2012 11:05:32 PST

Notch receptors are processed by bold gamma-secretase acting in synergy with T cell receptor signaling to sustain peripheral T cell activation. Activated CD4+ T cells differentiate into T helper type 1 (TH1) or TH2 subsets. Molecular cues directing TH1 differentiation include expression of the TH1-specific transcription factor T-bet, encoded by Tbx21. However, the regulation of Tbx21 remains incompletely defined. Here we report that Notch1 can directly regulate Tbx21 through complexes formed on the Tbx21 promoter. In vitro, bold gamma-secretase inhibitors extinguished expression of Notch, interferon-bold gamma and Tbx21 in TH1-polarized CD4+ cells, whereas ectopic expression of activated Notch1 restored Tbx21 transcription. In vivo, administration of bold gamma-secretase inhibitors substantially impeded TH1-mediated disease progression in the mouse experimental autoimmune encephalomyelitis model of multiple sclerosis. Thus, using bold gamma-secretase inhibitors to modulate Notch signaling may prove beneficial in treating TH1-mediated autoimmunity.

Notch-1 augments NF-B activity by facilitating its nuclear retention

Lisa Minter et al. — Thu, 12 Jan 2012 11:04:47 PST

Notch1 specifically upregulates expression of the cytokine interferon-gamma in peripheral T cells through activation of NF-kappaB. However, how Notch mediates NF-kappaB activation remains unclear. Here, we examined the temporal relationship between Notch signaling and NF-kappaB induction during T-cell activation. NF-kappaB activation occurs within minutes of T-cell receptor (TCR) engagement and this activation is sustained for at least 48 h following TCR signaling. We used gamma-secretase inhibitor (GSI) to prevent the cleavage and subsequent activation of Notch family members. We demonstrate that GSI blocked the later, sustained NF-kappaB activation, but did not affect the initial activation of NF-kappaB. Using biochemical approaches, as well as confocal microscopy, we show that the intracellular domain of Notch1 (N1IC) directly interacts with NF-kappaB and competes with IkappaBalpha, leading to retention of NF-kappaB in the nucleus. Additionally, we show that N1IC can directly regulate IFN-gamma expression through complexes formed on the IFN-gamma promoter. Taken together, these data suggest that there are two 'waves' of NF-kappaB activation: an initial, Notch-independent phase, and a later, sustained activation of NF-kappaB, which is Notch dependent.

Notch signalling during peripheral T-cell activation and differentiation

Lisa Minter et al. — Thu, 12 Jan 2012 11:02:52 PST

For many years, researchers have focused on the contribution of Notch signalling to lymphoid development. Only recently have investigators begun to ask what role, if any, Notch has during the activation and differentiation of naive CD4+ T cells in the periphery. As interest in this issue grows, it is becoming increasingly clear that the main role of Notch signalling, to regulate cell-fate decisions, might also be influential in peripheral T cells.