Epidermal Growth Factor Receptor Inhibition Modulates the Microenvironment by Vascular Normalization to Improve Chemotherapy and Radiotherapy Efficacy

Background: Epidermal growth factor receptor (EGFR) inhibitors have shown only modest clinical activity when used as single agents to treat cancers. They decrease tumor cell expression of hypoxia-inducible factor 1-a (HIF-1a) and vascular endothelial growth factor (VEGF). Hypothesizing that this might normalize tumor vasculature, we examined the effects of the EGFR inhibitor erlotinib on tumor vascular function, tumor microenvironment (TME) and chemotherapy and radiotherapy sensitivity. Methodology/Principal Findings: Erlotinib treatment of human tumor cells in vitro and mice bearing xenografts in vivo led to decreased HIF-1a and VEGF expression. Treatment altered xenograft vessel morphology assessed by confocal microscopy (following tomato lectin injection) and decreased vessel permeability (measured by Evan’s blue extravasation), suggesting vascular normalization. Erlotinib increased tumor blood flow measured by Power Doppler ultrasound and decreased hypoxia measured by EF5 immunohistochemistry and tumor O2 saturation measured by optical spectroscopy. Predictin

Spatial patterns of microbial diversity and activity in an aged creosote-contaminated site

Restoration of polluted sites via in situ bioremediation relies heavily on the indigenous microbes and their activities. Spatial heterogeneity of microbial populations, contaminants and soil chemical parameters on such sites is a major hurdle in optimizing and implementing an appropriate bioremediation regime. We performed a grid-based sampling of an aged creosote-contaminated site followed by geostatistical modelling to illustrate the spatial patterns of microbial diversity and activity and to relate these patterns to the distribution of pollutants. Spatial distribution of bacterial groups unveiled patterns of niche differentiation regulated by patchy distribution of pollutants and an east-to-west pH gradient at the studied site. Proteobacteria clearly dominated in the hot spots of creosote pollution, whereas the abundance of Actinobacteria, TM7 and Planctomycetes was considerably reduced from the hot spots. The pH preferences of proteobacterial groups dominating in pollution could be recognized by examining the order and family-level responses. Acidobacterial classes came across as generalists in hydrocarbon pollution whose spatial distribution seemed to be regulated solely by the pH gradient. Although the community evenness decreased in the heavily polluted zones, basal respiration and fluorescein diacetate hydrolysis rates were higher, indicating the adaptation of specific indigenous microbial populations to hydrocarbon pollution. Combining the information from the kriged maps of microbial and soil chemistry data provided a comprehensive understanding of the long-term impacts of creosote pollution on the subsurface microbial communities. This study also highlighted the prospect of interpreting taxa-specific spatial patterns and applying them as indicators or proxies for monitoring polluted sites

HIV Protease Inhibitors Decrease VEGF/HIF-1α Expression and Angiogenesis in Glioblastoma Cells

Glioblastomas are malignant brain tumors that are rarely curable, even with aggressive therapy (surgery, chemotherapy, and radiation). Glioblastomas frequently display loss of PTEN and/or epidermal growth factor receptor activation, both of which activate the PI3K pathway. This pathway can increase vascular endothelial growth factor (VEGF) and hypoxia-inducible factor (HIF)-1α expression. We examined the effects of two human immunodeficiency virus protease inhibitors, nelfinavir and amprenavir, which inhibit Akt signaling, on VEGF and HIF-1α expression and on angiogenesis. Nelfinavir decreased VEGF mRNA expression and VEGF secretion under normoxia. Downregulation of P-Akt decreased VEGF secretion in a manner similar to that of nelfinavir, but the combination of the two had no greater effect, consistent with the idea that nelfinavir decreases VEGF through the PI3K/Akt pathway. Nelfinavir also decreased the hypoxic induction of VEGF and the hypoxic induction of HIF-1α, which regulates VEGF promoter. The effect of nelfinavir on HIF-1α was most likely mediated by decreased protein translation. Nelfinavir's effect on VEGF expression had the functional consequence of decreasing angiogenesis in in vivo Matrigel plug assays. Similar effects on VEGFand HIF-1α expression were seen with a different protease inhibitor, amprenavir. Our results support further research into these protease inhibitors for use in future clinical trials for patients with glioblastoma multiformes

Inhibition of centrosome separation after DNA damage : a role for Nek2

DNA damage results in cell cycle arrest in G2. Centrosomes also separate in G2, raising the question of whether separation occurs during the DNA damage-induced G2 arrest. Nek2, the mammalian homologue of NIMA, is a cell cycle-regulated serine/threonine protein kinase that regulates centrosome separation during G2. Here we show that damaged cells fail to activate Nek2. Both Nek2 levels and activity are reduced after DNA damage. Radiation inhibits the premature centrosome splitting induced by overexpression of Nek2, indicating that Nek2 is involved in activation of the G2 checkpoint and is not secondary to cell cycle arrest. We confirm using siRNA that centrosome separation and cell growth are impaired in the absence of Nek2. These studies define a previously unreported DNA damage response of inhibition of centrosome separation mechanistically linked to Nek2

The HIV Protease Inhibitor Nelfinavir Downregulates Akt Phosphorylation by Inhibiting Proteasomal Activity and Inducing the Unfolded Protein Response

HIV protease inhibitors(HPIs), which have been used to treat HIV patients since the mid 1990s, have been shown to downregulate the phosphatidylinositol 3-kinase (PI3K)-Akt pathway. Because this pathway is frequently activated in human malignancies and associated with resistance to ionizing radiation, we investigated and confirmed that HPIs could radiosensitize cells. However, the mechanism underlying this downregulation was unclear, prompting the investigations in this report. In this paper we show that nelfinavir inhibits proteasome activity. Inhibition of the proteasome leads to endoplasmic reticulum-based stress with accumulation of misfolded proteins, which triggers the unfolded protein response (UPR). As part of the UPR, the alpha subunit of eukaryotic translation initiation factor 2 (eIF2α) is phosphorylated, resulting in a decrease in global protein synthesis and induction of the feedback regulator growth arrest and DNA damage-inducible protein (GADD34), which acts as a phosphatase in complex with protein phosphatase 1. This complex dephosphorylates eIF2α; however, our data also suggest that this phosphatase activity can dephosphorylate Akt. Furthermore, our data indicate that nelfinavir decreases Akt phosphorylation by triggering this response. These findings may have important implications in understanding how nelfinavir may increase radiation sensitivity and also result in downregulation of the PI3K/Akt pathway

Translational Upregulation of an Individual p21^Cip1 Transcript Variant by GCN2 Regulates Cell Proliferation and Survival under Nutrient Stress

<div><p>Multiple transcripts encode for the cell cycle inhibitor p21^Cip1. These transcripts produce identical proteins but differ in their 5’ untranslated regions (UTRs). Although several stresses that induce p21 have been characterized, the mechanisms regulating the individual transcript variants and their functional significance are unknown. Here we demonstrate through ³⁵S labeling, luciferase reporter assays, and polysome transcript profiling that activation of the Integrated Stress Response (ISR) kinase GCN2 selectively upregulates the translation of a p21 transcript variant containing 5’ upstream open reading frames (uORFs) through phosphorylation of the eukaryotic translation initiation factor eIF2α. Mutational analysis reveals that the uORFs suppress translation under basal conditions, but promote translation under stress. Functionally, ablation of p21 ameliorates G₁/S arrest and reduces cell survival in response to GCN2 activation. These findings uncover a novel mechanism of p21 post-transcriptional regulation, offer functional significance for the existence of multiple p21 transcripts, and support a key role for GCN2 in regulating the cell cycle under stress.</p></div

Polysome profiling reveals differences between the translational efficiencies of p21 variants 1 and 2 under nutrient stress.

<p>A)Polysome profiles of leucine-starved GCN2^+/+ MEFs over time. Lysates from GCN2^+/+ MEFs grown with or without leucine for 8, 12, 16, 20, and 24 hours were separated on 10 to 50% sucrose gradients. Polysome profiles of the gradients were generated by measuring absorbance at 254 nm. B) Time course of p21 translational efficiency as measured by mRNA association with polysomes. qPCR was performed on fractions pooled from sucrose gradients as indicated in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1005212#pgen.1005212.s004" target="_blank">S4A Fig</a> p21 transcript levels in each group were normalized to total transcript. C) Time course of β-actin and ATF4 translational efficiency as measured by mRNA association with polysomes. qPCR was performed on fractions pooled from sucrose gradients as indicated in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1005212#pgen.1005212.s004" target="_blank">S4A Fig</a>. Transcript levels in each group were normalized to total transcript. D) Time course of global translational efficiency in leucine-deprived GCN2^+/+ MEFs. Left: Time course of translational efficiency in leucine-deprived cells. Right: Western blot analysis of p-eIF2α in leucine-deprived GCN2^+/+ MEFs. Values below blot represent the fold change in total pixel intensity of p-eIF2α over control normalized to eIF2α.</p