RIP1-HAT1-SirT complex identification and targeting in treatment and prevention of cancer

Purpose: Alteration in cell death is a hallmark of cancer. A functional role regulating survival, apoptosis, and necroptosis has been attributed to RIP1/3 complexes.Experimental Design: We have investigated the role of RIP1 and the effects of MC2494 in cell death induction, using different methods as flow cytometry, transcriptome analysis, immunoprecipitation, enzymatic assays, transfections, mutagenesis, and in vivo studies with different mice models.Results: Here, we show that RIP1 is highly expressed in cancer, and we define a novel RIP1/3-SIRT1/2-HAT1/4 complex. Mass spectrometry identified five acetylations in the kinase and death domain of RIP1. The novel characterized pan-SIRT inhibitor, MC2494, increases RIP1 acetylation at two additional sites in the death domain. Mutagenesis of the acetylated lysine decreases RIP1-dependent cell death, suggesting a role for acetylation of the RIP1 complex in cell death modulation. Accordingly, MC2494 displays tumor-selective potential in vitro, in leukemic blasts ex vivo, and in vivo in both xenograft and allograft cancer models. Mechanistically, MC2494 induces bona fide tumor-restricted acetylated RIP1/caspase-8-mediated apoptosis. Excitingly, MC2494 displays tumor-preventive activity by blocking 7,12-dimethylbenz(α)anthracene-induced mammary gland hyperproliferation in vivoConclusions: These preventive features might prove useful in patients who may benefit from a recurrence-preventive approach with low toxicity during follow-up phases and in cases of established cancer predisposition. Thus, targeting the newly identified RIP1 complex may represent an attractive novel paradigm in cancer treatment and prevention

Probing the interaction interface of the GADD45β/MKK7 and MKK7/DTP3 complexes by chemical cross-linking mass spectrometry

GADD45β is selectively and constitutively expressed in Multiple Myeloma cells, and this expression correlates with an unfavourable clinical outcome. GADD45β physically interacts with the JNK kinase, MKK7, inhibiting its activity to enable the survival of cancer cells. DTP3 is a small peptide inhibitor of the GADD45β/MKK7 complex and is able to restore MKK7/JNK activation, thereby promoting selective cell death of GADD45β-overexpressing cancer cells. Enzymatic MS foot-printing and diazirine-based chemical cross-linking MS (CX-MS) strategies were applied to study the interactions between GADD45β and MKK7 kinase domain (MKK7_KD) and between DTP3 and MKK7_KD. Our data show that the binding between GADD45β and MKK7 largely occurs between GADD45β loop 2 (region 103–117) and the kinase enzymatic pocket. We also show that DTP3 interferes with this GADD45β/MKK7 interaction by contacting the MKK7 peptides, 113–136 and 259–274. Accordingly, an MKK7_KD Δ(101–136) variant lacking Trp135 did not produce a fluorescence quenching effect upon the binding of DTP3. The assessment of the interaction between GADD45β and MKK7 and the elucidation of the recognition surfaces between DTP3 and MKK7 significantly advance the understanding of the mechanism underlying the inhibition of the GADD45β/MKK7 interaction by DTP3 and pave the way to the design of small-molecule DTP3 analogues

HESS J1809−-193: a halo of escaped electrons around a pulsar wind nebula?

Context. HESS J1809$-$193 is an unassociated very-high-energy $\gamma$-ray source located on the Galactic plane. While it has been connected to the nebula of the energetic pulsar PSR J1809$-$1917, supernova remnants and molecular clouds present in the vicinity also constitute possible associations. Recently, the detection of $\gamma$-ray emission up to energies of $\sim$100 TeV with the HAWC observatory has led to renewed interest in HESS J1809$-$193. Aims. We aim to understand the origin of the $\gamma$-ray emission of HESS J1809$-$193. Methods. We analysed 93.2 h of data taken on HESS J1809$-$193 above 0.27 TeV with the High Energy Stereoscopic System (H.E.S.S.), using a multi-component, three-dimensional likelihood analysis. In addition, we provide a new analysis of 12.5 yr of Fermi-LAT data above 1 GeV within the region of HESS J1809$-$193. The obtained results are interpreted in a time-dependent modelling framework. Results. For the first time, we were able to resolve the emission detected with H.E.S.S. into two components: an extended component that exhibits a spectral cut-off at $\sim$13 TeV, and a compact component that is located close to PSR J1809$-$1917 and shows no clear spectral cut-off. The Fermi-LAT analysis also revealed extended $\gamma$-ray emission, on scales similar to that of the extended H.E.S.S. component. Conclusions. Our modelling indicates that based on its spectrum and spatial extent, the extended H.E.S.S. component is likely caused by inverse Compton emission from old electrons that form a halo around the pulsar wind nebula. The compact component could be connected to either the pulsar wind nebula or the supernova remnant and molecular clouds. Due to its comparatively steep spectrum, modelling the Fermi-LAT emission together with the H.E.S.S. components is not straightforward. (abridged)Comment: 14 pages, 10 figures. Accepted for publication in A&A. Corresponding authors: Vikas Joshi, Lars Mohrman

Detection of extended gamma-ray emission around the Geminga pulsar with H.E.S.S

Geminga is an enigmatic radio-quiet gamma-ray pulsar located at a mere 250 pc distance from Earth. Extended very-high-energy gamma-ray emission around the pulsar was discovered by Milagro and later confirmed by HAWC, which are both water Cherenkov detector-based experiments. However, evidence for the Geminga pulsar wind nebula in gamma rays has long evaded detection by imaging atmospheric Cherenkov telescopes (IACTs) despite targeted observations. The detection of gamma-ray emission on angular scales > 2 deg poses a considerable challenge for the background estimation in IACT data analysis. With recent developments in understanding the complementary background estimation techniques of water Cherenkov and atmospheric Cherenkov instruments, the H.E.S.S. IACT array can now confirm the detection of highly extended gamma-ray emission around the Geminga pulsar with a radius of at least 3 deg in the energy range 0.5-40 TeV. We find no indications for statistically significant asymmetries or energy-dependent morphology. A flux normalisation of $(2.8\pm0.7)\times10^{-12}$ cm$^{-2}$s$^{-1}$TeV$^{-1}$ at 1 TeV is obtained within a 1 deg radius region around the pulsar. To investigate the particle transport within the halo of energetic leptons around the pulsar, we fitted an electron diffusion model to the data. The normalisation of the diffusion coefficient obtained of $D_0 = 7.6^{+1.5}_{-1.2} \times 10^{27}$ cm$^2$s$^{-1}$, at an electron energy of 100 TeV, is compatible with values previously reported for the pulsar halo around Geminga, which is considerably below the Galactic average.Comment: 16 pages, 15 figures, 7 tables. Accepted for publication in Astronomy & Astrophysic

Science verification of the new FlashCam-based camera in the 28m telescope of H.E.S.S

In October 2019 the central 28m telescope of the H.E.S.S. experiment has been upgraded with a new camera. The camera is based on the FlashCam design which has been developed in view of a possible future implementation in the medium-sized telescopes of the Cherenkov Telescope Array (CTA). We report here on the results of the science verification program that has been performed after commissioning of the new camera, to show that the camera and software pipelines are working up to expectations

Detection of extended TeV emission around the Geminga pulsar with H.E.S.S

Highly extended gamma-ray emission around the Geminga pulsar was discovered by Milagro and verified by HAWC. Despite many observations with Imaging Atmospheric Cherenkov Telescopes (IACTs), detection of gamma-ray emission on angular scales exceeding the IACT field-of-view has proven challenging. Recent developments in analysis techniques have enabled the detection of significant emission around Geminga in archival data with H.E.S.S.. In 2019, further data on the Geminga region were obtained with an adapted observation strategy. Following the announcement of the detection of significant TeV emission around Geminga in archival data, in this contribution we present the detection in an independent dataset. New analysis results will be presented, and emphasis given to the technical challenges involved in observations of highly extended gamma-ray emission with IACTs

Evidence of 100 TeV γ-ray emission from HESS J1702-420 : a new PeVatron candidate

The identification of active PeVatrons, hadronic particle accelerators reaching the knee of the cosmic-ray spectrum (at the energy of few PeV), is crucial to understand the origin of cosmic rays in the Galaxy. In this context, we report on new H.E.S.S. observations of the PeVatron candidate HESS J1702-420, which bring evidence for the presence of γ-rays up to 100 TeV. This is the first time in the history of H.E.S.S. that photons with such high energy are observed. Remarkably, the new deep observations allowed the discovery of a new γ-ray source component, called HESS J1702-420A, that was previously hidden under the bulk emission traditionally associated with HESS J1702-420. This new object has a power-law spectral slope < 2 and a γ-ray spectrum that, extending with no sign of curvature up to 100 TeV, makes it an excellent candidate site for the presence of PeV-energy cosmic rays. This discovery brings new information to the ongoing debate on the nature of the unidentified source HESSJ1702-420, and on the origin of Galactic cosmic rays

Search for dark matter annihilation signals from unidentified Fermi-LAT objects with H.E.S.S.

Cosmological N-body simulations show that Milky-Way-sized galaxies harbor a population of unmerged dark matter subhalos. These subhalos could shine in gamma rays and be eventually detected in gamma-ray surveys as unidentified sources. We search for very-high-energy (VHE, E $\geq$ 100~GeV) gamma-ray emission using H.E.S.S. observations carried out from a thorough selection of unidentified Fermi-LAT Objects (UFOs) as dark matter subhalo candidates. Provided that the dark matter mass is higher than a few hundred GeV, the emission of the UFOs can be well described by dark matter annihilation models. No significant VHE gamma-ray emission is detected in any UFO dataset nor in their combination. We, therefore, derive constraints on the product of the velocity-weighted annihilation cross-section \left by the J-factor on dark matter models describing the UFO emissions. Upper limits at 95% confidence level are derived on \left J in W$^{+}$W$^{-}$ and τ$^{+}$τ$^{-}$ annihilation channels for the TeV dark matter particles. Focusing on thermal WIMPs, strong constraints on the J-factors are obtained from H.E.S.S. observations. Adopting model-dependent predictions from cosmological N-body simulations on the J-factor distribution function for Milky Way (MW)-sized galaxies, only $\lesssim$ 0.3 ~TeV mass dark matter models marginally allow to explain observed UFO emission

Search for enhanced TeV gamma ray emission from Giant Molecular Clouds using H.E.S.S.

Cosmic Ray (CR) interactions with the dense gas inside Giant Molecular Clouds (GMCs) produce neutral pions, which in turn decay into gamma rays. Thus, the gamma ray emission from GMCs is a direct tracer of the cosmic ray density and the matter density inside the clouds. Detection of enhanced TeV emission from GMCs, i.e., an emission significantly larger than what is expected from the average Galactic cosmic rays illuminating the cloud, can imply a variation in the local cosmic ray density, due to, for example, the presence of a recent accelerator in proximity to the cloud. Such gamma-ray observations can be crucial in probing the cosmic ray distribution across our Galaxy, but are complicated to perform with present generation Imaging Atmospheric Cherenkov Telescopes (IACTs). These studies require differentiating between the strong cosmic-ray induced background, the large scale diffuse emission, and the emission from the clouds, which is difficult to the small field of view of present generation IACTs. In this contribution, we use H.E.S.S. data collected over 16 years to search for TeV emission from GMCs in the inner molecular galacto-centric ring of our Galaxy. We implement a 3D FoV likelihood technique, and simultaneously model the hadronic background, the galactic diffuse emission and the emission expected from known VHE sources to probe for excess TeV gamma ray emission from GMCs

Is PKS 0625-354 another variable TeV active galactic nucleus?

The majority of the active galactic nuclei (AGN) detected at very-high-energies above 100 GeV belong to the class of blazars with a small angle between the jet-axis and the line-of-sight. Only about 10 percent of the gamma-ray AGN are objects with a larger viewing angle resulting in a smaller Doppler boosting of the emission. Originally, it was believed that gamma-ray emission can only be observed from blazars and those are variable in its brightness. Instead, the last years have shown that non-blazar active galaxies also show a fascinating variability behaviour which provide important new insights into the physical processes responsible for the gamma-ray production and especially for flaring events. Here, we report on the observation of gamma-ray variability of the active galaxy PKS 0625−354 detected with the H.E.S.S. telescopes in November 2018. The classification of PKS 0625−354 is a still matter of debate. The H.E.S.S. measurements were performed as part of a flux observing program and showed in the first night of the observation a detection of the object with > 5σ. A denser observation campaign followed for the next nine nights resulting in a decrease of the gamma-ray flux. Those observations were accompanied with Swift in the X-ray and UV/optical band allowing for the reconstruction of a multi-band broad-band spectral energy distribution. We will discuss the implications of the gamma-ray variability of the object