Andreas Möller

Regulation of p53 activity by its interaction with homeodomain-interacting protein kinase-2

Transcriptional activity of p53, a central regulatory switch in a network controlling cell proliferation and apoptosis, is modulated by protein stability and post-translational modifications including phosphorylation and acetylation. Here we demonstrate that the human serine/threonine kinase homeodomain-interacting protein kinase-2 (HIPK2) colocalizes and interacts with p53 and CREB-binding protein (CBP) within promyelocytic leukaemia (PML) nuclear bodies. HIPK2 is activated by ultraviolet (UV) radiation and selectively phosphorylates p53 at Ser 46, thus facilitating the CBP-mediated acetylation of p53 at Lys 382, and promoting p53-dependent gene expression. Accordingly, the kinase function of HIPK2 mediates the increased expression of p53 target genes, which results in growth arrest and the enhancement of UV-induced apoptosis. Interference with HIPK2 expression by antisense oligonucleotides impairs UV-induced apoptosis. Our results imply that HIPK2 is a novel regulator of p53 effector functions involved in cell growth, proliferation and apoptosis.

Optimized exosome isolation protocol for cell culture supernatant and human plasma

Extracellular vesicles represent a rich source of novel biomarkers in the diagnosis and prognosis of disease. However, there is currently limited information elucidating the most efficient methods for obtaining high yields of pure exosomes, a subset of extracellular vesicles, from cell culture supernatant and complex biological fluids such as plasma. To this end, we comprehensively characterize a variety of exosome isolation protocols for their efficiency, yield and purity of isolated exosomes. Repeated ultracentrifugation steps can reduce the quality of exosome preparations leading to lower exosome yield. We show that concentration of cell culture conditioned media using ultrafiltration devices results in increased vesicle isolation when compared to traditional ultracentrifugation protocols. However, our data on using conditioned media isolated from the Non-Small-Cell Lung Cancer (NSCLC) SK-MES-1 cell line demonstrates that the choice of concentrating device can greatly impact the yield of isolated exosomes. We find that centrifuge-based concentrating methods are more appropriate than pressure-driven concentrating devices and allow the rapid isolation of exosomes from both NSCLC cell culture conditioned media and complex biological fluids. In fact to date, no protocol detailing exosome isolation utilizing current commercial methods from both cells and patient samples has been described. Utilizing tunable resistive pulse sensing and protein analysis, we provide a comparative analysis of 4 exosome isolation techniques, indicating their efficacy and preparation purity. Our results demonstrate that current precipitation protocols for the isolation of exosomes from cell culture conditioned media and plasma provide the least pure preparations of exosomes, whereas size exclusion isolation is comparable to density gradient purification of exosomes. We have identified current shortcomings in common extracellular vesicle isolation methods and provide a potential standardized method that is effective, reproducible and can be utilized for various starting materials. We believe this method will have extensive application in the growing field of extracellular vesicle research.

Silencing of Irf7 pathways in breast cancer cells promotes bone metastasis through immune escape

Breast cancer metastasis is a key determinant of long-term patient survival. By comparing the transcriptomes of primary and metastatic tumor cells in a mouse model of spontaneous bone metastasis, we found that a substantial number of genes suppressed in bone metastases are targets of the interferon regulatory factor Irf7. Restoration of Irf7 in tumor cells or administration of interferon led to reduced bone metastases and prolonged survival time. In mice deficient in the interferon (IFN) receptor or in natural killer (NK) and CD8+ T cell responses, metastasis was accelerated, indicating that Irf7-driven suppression of metastasis was reliant on IFN signaling to host immune cells. We confirmed the clinical relevance of these findings in over 800 patients in which high expression of Irf7-regulated genes in primary tumors was associated with prolonged bone metastasis–free survival. This gene signature may identify patients that could benefit from IFN-based therapies. Thus, we have identified an innate immune pathway intrinsic to breast cancer cells, the suppression of which restricts immunosurveillance to enable metastasis.

The pre-metastatic niche: finding common ground.

It is rapidly becoming evident that the formation of tumor-promoting pre-metastatic niches in secondary organs adds a previously unrecognized degree of complexity to the challenge of curing metastatic disease. Primary tumor cells orchestrate pre-metastatic niche formation through secretion of a variety of cytokines and growth factors that promote mobilization and recruitment of bone marrow-derived cells to future metastatic sites. Hypoxia within the primary tumor, and secretion of specific microvesicles termed exosomes, are emerging as important processes and vehicles for tumor-derived factors to modulate pre-metastatic sites. It has also come to light that reduced immune surveillance is a novel mechanism through which primary tumors create favorable niches in secondary organs. This review provides an overview of our current understanding of underlying mechanisms of pre-metastatic niche formation and highlights the common links as well as discrepancies between independent studies. Furthermore, the possible clinical implications, links to metastatic persistence and dormancy, and novel approaches for treatment of metastatic disease through reversal of pre-metastatic niche formation are identified and explored.

Primary Tumor Hypoxia Recruits CD11b+/Ly6Cmed/Ly6G+ Immune Suppressor Cells and Compromises NK Cell Cytotoxicity in the Premetastatic Niche

Hypoxia within a tumor acts as a strong selective pressure that promotes angiogenesis, invasion, and metastatic spread. In this study, we used immune competent bone marrow chimeric mice and syngeneic orthotopic mammary cancer models to show that hypoxia in the primary tumor promotes premetastatic niche formation in secondary organs. Injection of mice with cell-free conditioned medium derived from hypoxic mammary tumor cells resulted in increased bone marrow-derived cell infiltration into the lung in the absence of a primary tumor and led to increased metastatic burden in mammary and melanoma experimental metastasis models. By characterizing the composition of infiltrating bone marrow-derived cells, we identified CD11b+/Ly6Cmed/Ly6G+ myeloid and CD3-/NK1.1+ immune cell lineages as key constituents of the premetastatic niche. Furthermore, the cytotoxicity of natural killer (NK) cells was significantly decreased, resulting in a reduced antitumor response that allowed metastasis formation in secondary organs to a similar extent as ablation of NK cells. In contrast, metastatic burden was decreased when active NK cells were present in premetastatic lungs. Together, our findings suggest that primary tumor hypoxia provides cytokines and growth factors capable of creating a premetastatic niche through recruitment of CD11b+/Ly6Cmed/Ly6G+ myeloid cells and a reduction in the cytotoxic effector functions of NK cell populations.

EVpedia: a community web portal for extracellular vesicles research

MOTIVATION Extracellular vesicles (EVs) are spherical bilayered proteolipids, harboring various bioactive molecules. Due to the complexity of the vesicular nomenclatures and components, online searches for EV-related publications and vesicular components are currently challenging. RESULTS We present an improved version of EVpedia, a public database for EVs research. This community web portal contains a database of publications and vesicular components, identification of orthologous vesicular components, bioinformatic tools and a personalized function. EVpedia includes 6879 publications, 172 080 vesicular components from 263 high-throughput datasets, and has been accessed more than 65 000 times from more than 750 cities. In addition, about 350 members from 73 international research groups have participated in developing EVpedia. This free web-based database might serve as a useful resource to stimulate the emerging field of EV research. AVAILABILITY AND IMPLEMENTATION The web site was implemented in PHP, Java, MySQL and Apache, and is freely available at http://evpedia.info.

Inflammation and immune surveillance in cancer.

Chronic inflammation is a risk factor for tumor development. However, understanding the effect of the immune system on tumor development has only been significantly advanced over the past two decades. We now appreciate that the immune system, in addition to tumor-suppressive function by eliminating nascent transformed tumor cells, can also exert selection pressure on tumor cells and facilitate tumor growth by providing a favorable tumor microenvironment. Yet, the distinctions between tumor-promoting inflammation and tumor-suppressive immunity are still not clear due to the dual role of some cytokines and other molecules in the immune system. The danger signal hypothesis has shaped our view of the role of immunity in cancer development, but still little is known about the exact role of danger signal receptors in cancer progression. In this review, we introduce the processes of cancer immunoediting and inflammation-induced cancer and discuss what is currently known about the role of danger signal receptors in cancer development and progression.

An inducible autoregulatory loop between HIPK2 and Siah2 at the apex of the hypoxic response.

Oxygen deprivation (hypoxia) results in reprogrammed gene expression patterns that induce multifaceted cellular responses. Here we identify a regulated interaction between the serine/threonine kinase HIPK2 and the ubiquitin E3 ligase Siah2 as a mechanism controlling the hypoxic response. Under normoxic conditions, several mechanisms ensure HIPK2 stability: only a fraction of HIPK2 is found in association with Siah2, whereas HIPK2-mediated phosphorylation of this E3 ligase at positions 26, 28 and 68 weakens mutual binding and destabilizes its phosphorylated interaction partner. Hypoxic conditions allow a markedly increased HIPK2/Siah2 interaction and result in efficient polyubiquitylation and proteasomal degradation of the kinase. Accordingly, hypoxia-induced HIPK2 elimination is markedly reduced in Siah2-deficient cells. As HIPK2 has an important role as a negative regulator of gene expression, its elimination from promoter-associated repressor complexes allows the induction of a substantial fraction of hypoxia-induced genes.

IL-23 suppresses innate immune response independently of IL-17A during carcinogenesis and metastasis

IL-23 is an important molecular driver of Th17 cells and has strong tumor-promoting proinflammatory activity postulated to occur via adaptive immunity. Conversely, more recently it has been reported that IL-17A elicits a protective inflammation that promotes the activation of tumor-specific CD8+ T cells. Here we show the much broader impact of IL-23 in antagonizing antitumor immune responses primarily mediated by innate immunity. Furthermore, the majority of this impact was independent of IL-17A, which did not appear critical for many host responses to tumor initiation or metastases. IL-23–deficient mice were resistant to experimental tumor metastases in three models where host NK cells controlled disease. Immunotherapy with IL-2 was more effective in mice lacking IL-23, and again the protection afforded was NK cell mediated and independent of IL-17A. Further investigation revealed that loss of IL-23 promoted perforin and IFN-γ antitumor effector function in both metastasis models examined. IL-23-deficiency also strikingly protected mice from tumor formation in two distinct mouse models of carcinogenesis where the dependence on host IL-12p40 and IL-17A was quite different. Notably, in the 3′-methylcholanthrene (MCA) induction of fibrosarcoma model, this protection was completely lost in the absence of NK cells. Overall, these data indicate the general role that IL-23 plays in suppressing natural or cytokine-induced innate immunity, promoting tumor development and metastases independently of IL-17A.

Siah Proteins: Novel Drug Targets in the Ras and Hypoxia Pathways

The Siah (seven in absentia homolog) family of RING-domain proteins are components of ubiquitin ligase complexes, targeting proteins for proteasomal degradation. Siah family members have been reported to function in Ras, estrogen, DNA-damage, and hypoxia response pathways. Although earlier reports implicated Siah proteins as tumor suppressors, recent studies in mouse models have shown that Siah inhibition impairs tumor growth and metastasis. Given their central role in oncogenic and angiogenic pathways, Siah proteins are attractive novel therapeutic targets in cancer.