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Onco-exaptation of an Endogenous Retroviral LTR Drives IRF5 Expression in Hodgkin Lymphoma

ABSTRACT: The transcription factor interferon regulatory factor 5 (IRF5) is upregulated in Hodgkin lymphoma (HL) and a key regulator of the aberrant transcriptome characteristic of this disease. Here we show that IRF5 upregulation in HL is driven by transcriptional activation of a normally dormant endogenous retroviral LOR1a long terminal repeat (LTR) upstream of IRF5. Specifically, through screening of RNA-seq libraries, we detected LTR-IRF5 chimeric transcripts in multiple HL cell lines but not in normal B-cell controls. In HL, the LTR was in an open and hypomethylated epigenetic state and we further show the LTR is the site of transcriptional initiation. Among HL cell lines, usage of the LTR promoter strongly correlates with overall levels of IRF5 mRNA and protein, indicating that LTR transcriptional awakening is a major contributor to IRF5 upregulation in HL. Taken together, oncogenic IRF5 overexpression in HL is the result of a specific LTR transcriptional activation. We propose that such LTR derepression is a distinct mechanism of oncogene activation (“onco-exaptation”) and that such a mechanism warrants further investigation in molecular and cancer research.

PROVIDER: EGAS00001001205 | EGA |

REPOSITORIES: EGA

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Project description:Disease relapse and resistance to chemotherapy represent challenging issues in a subset of Hodgkin Lymphoma (HL) patients. Activity and mechanism(s) of action of a novel PI3K/ERK dual inhibitor AEZS-136 (Ãterna Zentaris GmbH, Germany, EU) were examined in L-540, SUP-HD1, KM-H2 and L-428 cell lines. Despite exposure to AEZS-136 induced a significant cell growth inhibition (range, 30-80%), levels of caspase-independent cell death and mitochondrial dysfunction, were only observed in L-540 (62 Â±9 vs 14 Â±3%, P â¤.0001) and SUP-HD1 (46 Â±2% vs 15 Â±2%, P â¤.0001) cells. Gene expression profiling indicated that the effects of AEZS-136 treatment are associated with the modulation of cell cycle and cell death pathways. Exposure to AEZS-136 resulted in sustained production of reactive oxygen species (ROS) and activation of necroptotic cell death. The necroptosis inhibitor Necrostatin-1 prevented AEZS-136-induced ROS production, mitochondrial injury, activation of JNK and cell death. Knockdown experiments identified the immediate early response 3 (IER3) as a key signaling molecule that mediates AEZS-136-resistance to oxidative death of HL cells. Furthermore, in vivo xenograft studies demonstrated a 40-70% reduction in tumor burden (P < 0.0001) and a 10-fold increase in tumor necrosis in AEZS-136-treated animals compared to control mice. These data support further clinical evaluation of AEZS-136 in refractory/relapsed HL. The Hodgkin lymphoma cell lines were obtained from the DSMZ (Braunschweig, Germany, EU). Cells were routinely maintained in RPMI medium 1640 (Lonza, Basel, Switzerland) supplemented with 20% FBS (Lonza) and 2 mM glutamine (Lonza). Cells were maintained at 37Â°C in a water-saturated atmosphere of 5% CO2 in air. 4x106 HL cells were seeded in 75 cm2 flask and, after 24 hrs, cells were treated with 10 ÂµM AEZS-136 (Aeterna Zentaris, Frankfurt, Germany, EU) in culture medium for 24 hours. At the end of treatment, cells were collected and RNA extracted.

Project description:Disease relapse and resistance to chemotherapy represent challenging issues in a subset of Hodgkin Lymphoma (HL) patients. Activity and mechanism(s) of action of a novel PI3K/ERK dual inhibitor AEZS-136 (Ãterna Zentaris GmbH, Germany, EU) were examined in L-540, SUP-HD1, KM-H2 and L-428 cell lines. Despite exposure to AEZS-136 induced a significant cell growth inhibition (range, 30-80%), levels of caspase-independent cell death and mitochondrial dysfunction, were only observed in L-540 (62 Â±9 vs 14 Â±3%, P â¤.0001) and SUP-HD1 (46 Â±2% vs 15 Â±2%, P â¤.0001) cells. Gene expression profiling indicated that the effects of AEZS-136 treatment are associated with the modulation of cell cycle and cell death pathways. Exposure to AEZS-136 resulted in sustained production of reactive oxygen species (ROS) and activation of necroptotic cell death. The necroptosis inhibitor Necrostatin-1 prevented AEZS-136-induced ROS production, mitochondrial injury, activation of JNK and cell death. Knockdown experiments identified the immediate early response 3 (IER3) as a key signaling molecule that mediates AEZS-136-resistance to oxidative death of HL cells. Furthermore, in vivo xenograft studies demonstrated a 40-70% reduction in tumor burden (P < 0.0001) and a 10-fold increase in tumor necrosis in AEZS-136-treated animals compared to control mice. These data support further clinical evaluation of AEZS-136 in refractory/relapsed HL. The Hodgkin lymphoma cell lines were obtained from the DSMZ (Braunschweig, Germany, EU). Cells were routinely maintained in RPMI medium 1640 (Lonza, Basel, Switzerland) supplemented with 20% FBS (Lonza) and 2 mM glutamine (Lonza). Cells were maintained at 37Â°C in a water-saturated atmosphere of 5% CO2 in air. 4x106 HL cells were seeded in 75 cm2 flask and, after 24 hrs, cells were treated with 10 ÂµM AEZS-136 (Aeterna Zentaris, Frankfurt, Germany, EU) in culture medium for 2 hours. At the end of treatment, cells were collected and RNA extracted.

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Onco-exaptation of an Endogenous Retroviral LTR Drives IRF5 Expression in Hodgkin Lymphoma

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