Project description:To investigate the effect of PAX3-FOXO1 and B7-H3 in rhabdomyosarcoma, Rh-30 (PAX3-FOXO1 positive rhabdomyosarcoma cell line) was transfected by siPAX3-FOXO1 or siB7-H3. After knockdown, total RNA was extracted and analyzed. As a result, some genes and pathways, such as chemotaxis, differentiation, and INF-gamma production were comonnly effected by PAX3-FOXO1 and B7-H3.
Project description:PAX3-FOXO1 is a fusion transcription factor that is the main driver of tumorigenesis leading to the development of alveolar rhabdomyosarcoma (aRMS). Since aRMS cells are addicted to PAX3-FOXO1 activity, the fusion protein also represents a major target for therapeutic interference, which is however challenging as transcription factors usually cannot be inhibited directly by small molecules. Hence, characterization of the biology of PAX3-FOXO1 might lead to the discovery of new possibilities for an indirect inhibition of its activity. Here, our goal was to characterize the proteomic neighborhood of PAX3-FOXO1 and to find candidates potentially affecting its activity and tumor cell viability. Towards this aim, we expressed BirA fused versions of PAX3-FOXO1 (N- and C-terminal) in HEK293T cells under presence of biotin. In the control setup, we expressed the BirA enzyme alone. After Streptavidin purification of biotinylated proteins, we performed mass spectrometry and quantified relative abundances compared to control conditions. This enabled us to determine PAX3-FOXO1 proximal proteins, which we investigated further in orthogonal endogenous systems.
Project description:The fusion transcription factor PAX3-FOXO1 drives oncogenesis in a subset of rhabdomyosarcomas, however the mechanisms by which it remodels chromatin are unknown. We find PAX3-FOXO1 reprograms the cis-regulatory landscape by inducing super enhancers (SEs), in collaboration with master transcription factors MYOG, MYOD and MYCN. This myogenic SE circuitry is consistent across cell lines and primary tumors. Deregulation of PAX3-FOXO1 itself occurs by translocation-induced chromatin loops bringing the PAX3 promoter under the control of FOXO1 enhancers. Protein targets induced by, or bound to, PAX3-FOXO1 occupied SEs, were selectively sensitive to small molecule inhibition. PAX3-FOXO1 co-binds BRD4 at SEs, and BET bromodomains are required for PAX3-FOXO1-dependent transcription and cancer cell growth.
Project description:Hallmarks of the alveolar subclass of Rhabdomyosarcoma are chromosomal translocations that generate PAX3-FOXO1 or PAX7-FOXO1 chimeric transcription factors. Both PAX-FOXO1s drive related cell transformation in animal models, yet the two mutations are associated with distinct pathological manifestations in patients. To evaluate the mechanisms underlying these differences, we generated isogenic fibroblast lines expressing either PAX-FOXO1 paralog. Mapping their genome recruitment using CUT&Tag revealed that the two chimeric proteins have distinct DNA binding preferences. Furthermore, PAX7-FOXO1 causes stronger de novo transactivation of its bound regions than PAX3-FOXO1, resulting in greater transcriptomic dynamics involving genes regulating cell shape and cycle. Consistently, PAX3-FOXO1 accentuates fibroblast cellular traits associated with contractility and surface adhesion and limits entry to M phase. Instead, PAX7-FOXO1 pushes cells to adopt an amoeboid-like shape, reduce S phase entry and provokes more genome instabilities. Altogether, our results demonstrate that PAX7-FOXO1 has a greater chromatin remodelling and transactivating abilities and is more deleterious to cells than PAX3-FOXO1. Altogether our results argue that the diversity in rhabdomyosarcoma manifestation stems, in part, from the diverging transcriptional activity of PAX3-FOXO1 and PAX7-FOXO1. Furthermore, PAX7-FOXO1 pronounced deleterious effects provides an explanation for the low frequency of the translocation generating this factor in Rhabdomyosarcoma patients.
Project description:Alveolar rhabdomyosarcoma (aRMS) is an aggressive sarcoma of skeletal muscle characterized by expression of the PAX3-FOXO1 fusion gene. Despite its discovery over almost 20 years ago, PAX3-FOXO1 remains an enigmatic tumor driver. Previously, we reported that PAX3-FOXO1 supports aRMS initiation by enabling bypass of cellular senescence. Here, we show that bypass occurs in part by PAX3-FOXO1-mediated upregulation of RASSF4, a Ras-association domain family (RASSF) member, which then suppresses the evolutionarily conserved mammalian Hippo/Mst1 pathway. RASSF4 loss-of-function activates Hippo/Mst1 and inhibits downstream YAP, causing aRMS cell cycle arrest and senescence. This is the first evidence for an oncogenic role for RASSF4, and a novel mechanism for Hippo signaling suppression in human cancer. Human skeletal muscle myoblasts (HSMMs) were retrovirally transduced with either an empty vector (Vp, pK1) or PAX3-FOXO1 (PFp, pK1-PAX3-FOXO1) and selected on puromycin. Presenescent (presen) cells were harvested before the senescence checkpoint. Since cells expressing PAX3-FOXO1 can bypass the senescence checkpoint, postsenescent (postsen) cells expressing PAX3-FOXO1 were also harvested. the gene expression affected by the introduction of PAX3-FOXO1
Project description:The fusion transcription factor PAX3-FOXO1 drives oncogenesis in a subset of rhabdomyosarcomas, however the mechanisms by which it remodels chromatin are unknown. We find PAX3-FOXO1 reprograms the cis-regulatory landscape by inducing super enhancers (SEs), in collaboration with master transcription factors MYOG, MYOD and MYCN. This myogenic SE circuitry is consistent across cell lines and primary tumors. Deregulation of PAX3-FOXO1 itself occurs by translocation-induced chromatin loops bringing the PAX3 promoter under the control of FOXO1 enhancers. Protein targets induced by, or bound to, PAX3-FOXO1 occupied SEs, were selectively sensitive to small molecule inhibition. PAX3-FOXO1 co-binds BRD4 at SEs, and BET bromodomains are required for PAX3-FOXO1-dependent transcription and cancer cell growth.
Project description:Chimeric transcription factors drive lineage-specific oncogenesis but are notoriously difficult to target. Alveolar rhabdomyosarcoma (RMS) is an aggressive childhood soft tissue sarcoma transformed by the pathognomonic PAX3–FOXO1 fusion protein, which governs a core regulatory circuitry transcription factor (CRC TF) network. Here we show that the histone lysine demethylase KDM4B is a therapeutic vulnerability for PAX3–FOXO1+ RMS. Genetic and pharmacologic inhibition of KDM4B significantly delays tumor growth by disrupting the expression of CRC TFs caused by epigenetic alterations of PAX3–FOXO1-governed super enhancers. Combining KDM4B inhibition with cytotoxic chemotherapy leads to significant tumor regression in preclinical PAX3–FOXO1+ RMS models. In summary, we have identified a targetable mechanism required for maintenance of PAX3-FOXO1-related CRC TF network, which may translate to a novel therapeutic approach for fusion-positive RMS.
Project description:The fusion transcription factor PAX3-FOXO1 drives oncogenesis in a subset of rhabdomyosarcomas, however the mechanisms by which it remodels chromatin are unknown. We find PAX3-FOXO1 reprograms the cis-regulatory landscape by inducing super enhancers (SEs), in collaboration with master transcription factors MYOG, MYOD and MYCN. This myogenic SE circuitry is consistent across cell lines and primary tumors. Deregulation of PAX3-FOXO1 itself occurs by translocation-induced chromatin loops bringing the PAX3 promoter under the control of FOXO1 enhancers. Protein targets induced by, or bound to, PAX3-FOXO1 occupied SEs, were selectively sensitive to small molecule inhibition. PAX3-FOXO1 co-binds BRD4 at SEs, and BET bromodomains are required for PAX3-FOXO1-dependent transcription and cancer cell growth.
Project description:Chimeric transcription factors drive lineage-specific oncogenesis but are notoriously difficult to target. Alveolar rhabdomyosarcoma (RMS) is an aggressive childhood soft tissue sarcoma transformed by the pathognomonic PAX3–FOXO1 fusion protein, which governs a core regulatory circuitry transcription factor (CRC TF) network. Here we show that the histone lysine demethylase KDM4B is a therapeutic vulnerability for PAX3–FOXO1+ RMS. Genetic and pharmacologic inhibition of KDM4B significantly delays tumor growth by disrupting the expression of CRC TFs caused by epigenetic alterations of PAX3–FOXO1-governed super enhancers. Combining KDM4B inhibition with cytotoxic chemotherapy leads to significant tumor regression in preclinical PAX3–FOXO1+ RMS models. In summary, we have identified a targetable mechanism required for maintenance of PAX3-FOXO1-related CRC TF network, which may translate to a novel therapeutic approach for fusion-positive RMS.
Project description:Chimeric transcription factors drive lineage-specific oncogenesis but are notoriously difficult to target. Alveolar rhabdomyosarcoma (RMS) is an aggressive childhood soft tissue sarcoma transformed by the pathognomonic PAX3–FOXO1 fusion protein, which governs a core regulatory circuitry transcription factor (CRC TF) network. Here we show that the histone lysine demethylase KDM4B is a therapeutic vulnerability for PAX3–FOXO1+ RMS. Genetic and pharmacologic inhibition of KDM4B significantly delays tumor growth by disrupting the expression of CRC TFs caused by epigenetic alterations of PAX3–FOXO1-governed super enhancers. Combining KDM4B inhibition with cytotoxic chemotherapy leads to significant tumor regression in preclinical PAX3–FOXO1+ RMS models. In summary, we have identified a targetable mechanism required for maintenance of PAX3-FOXO1-related CRC TF network, which may translate to a novel therapeutic approach for fusion-positive RMS.