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Hematopoietic stem cells (HSCs) sustain blood and immune cells in the body and are therefore crucial for our survival. HSCs are at rest, but as soon as blood needs to be formed - like after blood loss or chemotherapy - they are quickly activated to compensate for this loss. After completing their mission, they must return a dormant state. A team of scientists, including Christoph Bock (CeMM) and Veronika Sexl (Vetmeduni Vienna) – lead by Manuela Baccarini (Max F. Perutz Laboratories (MFPL)) – has now shown how intracellular signal transmissions can maintain this delicate balance between activation and dormancy. 

The switch between HSC active and inactive states requires a precisely regulated balance. It was already known that HSC activation is driven in part through the phosphatidylinositol 3-kinase (PI3K)/AKT/mTORC1 signaling pathway, but less was known about the cell-intrinsic pathways that control HSC dormancy. In this study, the researchers were able to describe in detail the intracellular networks responsible for this balance. The authors show that the MEK/ERK and PI3K pathways are synchronously activated in HSCs during emergency hematopoiesis. Importantly, they show that the feedback phosphorylation of MEK1 by activated ERK counterbalances AKT/mTORC1 activation and that the MEK1 phosphorylation returns activated HSCs to quiescence. Overall, these results suggest a new role for the MEK/ERK pathway in hematopoiesis and that MEK inhibitors currently used for cancer therapy may find additional utility in controlling HSC activation.

Publication in Cell Stem Cell

Christian Baumgartner, Stefanie Toifl, Matthias Farlik, Florian Halbritter, Ruth Scheicher, Irmgard Fischer, Veronika Sexl, Christoph Bock and Manuela Baccarini

Doi: https://doi.org/10.1016/j.stem.2018.05.003

Natural killer (NK) cells are an innate weapon against cancer and virus-infected cells. The higher the NK cell activity, the higher its effect against a tumour. Researchers at Vetmeduni Vienna have now shown that the NK cell cytotoxic activity can be increased even further if the cdk8 gene is removed in these cells. This translates into an improved NK cell–mediated tumour surveillance in vivo in three independent cancer models.

For decades, researchers have been interested in how cancer cells proliferate despite the action of the immune system. In order to increase the activity of the body's immune system against the tumour, researchers at the Institute for Pharmacology and Toxicology at Vetmeduni Vienna have now shown a way to increase the killing activity of NK cells against tumour cells. In order to achieve this, the NK cells were depleted from the cdk8 gene, which codes for the cyclin-dependent kinase 8 (CDK8). This led to the significant blocking of tumour growth in mouse models. Agnieszka Witalisz-Siepracka, first author of this study, explains that: “Due to the loss of CDK8, the NK cells were activated more intensely and their ability to kill increased; therefore, the tumour shrank."

These results define a suppressive effect of CDK8 on NK-cell activity and open the exciting possibility of targeting CDK8 in cancer patients to enhance NK-cell responses against tumour cells, thus using the body’s own weapons. Such inhibitors are already being developed in a number of pre-clinical stage studies.

Publication in Cancer Immunology Research

Agnieszka Witalisz-Siepracka, Dagmar Gotthardt, Michaela Prchal-Murphy, Zrinka Didara, Ingeborg Menzl, Daniela Prinz, Leo Edlinger, Eva Maria Putz and Veronika Sexl

https://cancerimmunolres.aacrjournals.org/content/6/4/458.long

Doi: 10.1158/2326-6066.CIR-17-0183

The invitation only meeting on May 6-9, 2018 boasts an outstanding scientific programme and will take place in a beautiful location and inspiring atmosphere. We have invited international experts to complement the scientific programme of the two SFBs, including: Jacqueline Bromberg, New York; Gerard Evan, Cambridge; Thomas Graf, Barcelona; Nancy Hynes, Basel; Shai Izraeli, Tel Aviv; David Levy, New York; A. Tom Look, Harvard;  Tak Mak, Toronto

A cooperation of Ludwig Boltzmann Institute for Cancer Research, Ludwig Boltzmann Cluster Oncology, SFB-F47, and SFB-F61

Acute myeloid leukaemia (AML) is the most common type of acute cancer of the blood and bone marrow in adults. This type of cancer usually progresses quickly and only 26 percent of the patients survive longer than 5 years as resistance against established treatments arises. The most common molecular cause is FLT3 mutations, which result in hyper-activation of STAT5. An international consortium of researchers cofounded by SFB-F61 now report on an early preclinical development to target STAT5 directly, which cooperates well with existing therapies.

Publication in Leukemia:

Bettina Wingelhofer, Barbara Maurer, Elizabeth C. Heyes, Abbarna C. Cumaraswamy, Angelika Berger-Becvar, Elvin D. de Araujo, Anna Orlova, Patricia Freund, Frank Ruge, Jisung Park, Gary Tin, Siawash Ahmar, Charles-Hugues Lardeau, Irina Sadovnik, Dávid Bajusz, György Miklós Keserű, Florian Grebien, Stefan Kubicek, Peter Valent, Patrick T. Gunning and Richard Moriggl,

Pharmacologic inhibition of STAT5 in acute myeloid leukemia, Leukemia (2018), doi:10.1038/s41375-017-0005-9

Acute myeloid leukemia (AML) is the most common form of acute cancer in the blood and bone marrow in adults. The most common molecular cause are mutations in the Flt3 gene, which activate the signal transmitter and transcription factor STAT5. A new strategy has now been described to directly inhibit STAT5 with a novel compound, in the scientific journal Leukemia.

AML, as one of the most devastating white blood cells disorders, is usually very aggressive and despite considerable progress in therapeutic approaches only 26% of patients survive for more than 5 years because of resistance to treatments. This type of leukemia is often caused by mutations that overactivate intracellular signalling or gene transcription. Mutations in the receptor FLT3, which represent 30% of the driver mutations in AML, activate STAT5, an important transcription factor that is required for the transformation of blood cells. New treatment strategies to inhibit STAT5 are needed to improve the survival of patients with this disease.

Previous attempts to inhibit STAT5 transcription factors often failed due to the effectiveness or lack of specificity. Now, an international consortium of researchers from Austria, Canada and Hungary, led by Richard Moriggl, reports a new compound that directly binds and selectively inhibits STAT5. The researchers could target STAT5 at the SH2 domain, which is essential for its activity, and discovered that the new inhibitor efficiently blocks the pathological levels of STAT5 activity in AML. It does so by disrupting STAT5 activation, dimerization, nuclear translocation, and STAT5-dependent gene transcription, which leads to a substantial impair in the proliferation and clonogenic growth of human AML cells in vitro and in vivo. Collaboration with a pharmaceutical company will now be required to further develop this new class of compound to make it suitable for a clinical trial.

Publication in Leukemia

 Bettina Wingelhofer, Barbara Maurer, Elizabeth C. Heyes, Abbarna A. Cumaraswamy, Angelika Berger-Becvar, Elvin D. de Araujo, Anna Orlova, Patricia Freund, Frank Ruge, Jisung Park, Gary Tin, Siawash Ahmar, Charles-Hugues Lardeau, Irina Sadovnik, Dávid Bajusz, György Miklós Keserű, Florian Grebien, Stefan Kubicek, Peter Valent, Patrick T. Gunning and Richard Moriggl

Doi: https://doi.org/10.1038/s41375-017-0005-9