Although some studies suggested that disruption of the Hippo signaling pathway is associated with osteosarcoma progression, the molecular mechanisms by which YAP regulates primary tumor growth is not fully clarified. In addition, the validation of YAP as a therapeutic target through the use of inhibitors in a preclinical model must be demonstrated. RNA-seq analysis and Kaplan–Meier assays identified a YAP signature in osteosarcoma patients and a correlation with patients’ outcomes. Molecular and cellular analysis (RNAseq, PLA, immunoprecipitation, promoter/specific gene, proliferation, cell cycle assays) using overexpression of mutated forms of YAP able or unable to interact with TEAD, indicate that TEAD is crucial for YAP-driven cell proliferation and in vivo tumor growth. In addition, in vivo experiments using an orthotopic mice model of osteosarcoma show that two YAP/TEAD inhibitors, verteporfin and CA3, reduce primary tumor growth. In this context, in vitro experiments demonstrate that these inhibitors decrease YAP expression, YAP/TEAD transcriptional activity and cell viability mainly by their ability to induce cell apoptosis. We thus demonstrate that the YAP/TEAD signaling axis is a central actor in mediating primary tumor growth of osteosarcoma, and that the use of YAP inhibitors may be a promising therapeutic strategy against osteosarcoma tumor growth.

Osteosarcoma (OS) is the most common malignant bone tumor in children and teenagers. In many cases, such as poor response to treatment or the presence of metastases at diagnosis, the survival rate of patients remains very low. Although in the literature, more and more studies are emerging on the role of Ubiquitin-Specific Proteases (USPs) in the development of many cancers, few data exist regarding OS. In this context, RNA-sequencing analysis of OS cells and mesenchymal stem cells differentiated or not differentiated into osteoblasts reveals increased expression of four USPs in OS tumor cells: USP6, USP27x, USP41 and USP43. Tissue microarray analysis of patient biopsies demonstrates the nucleic and/or cytoplasmic expression of these four USPs at the protein level. Interestingly, Kaplan–Meyer analysis shows that the expression of two USPs, USP6 and USP41, is correlated with patient survival. In vivo experiments using a preclinical OS model, finally demonstrate that PR619, a USP inhibitor able to enhance protein ubiquitination in OS cell lines, reduces primary OS tumor growth and the development of lung metastases. In this context, in vitro experiments show that PR619 decreases the viability of OS cells, mainly by inducing a caspase3/7-dependent cell apoptosis. Overall, these results demonstrate the relevance of targeting USPs in OS.

The formation of the skeleton occurs throughout the lives of vertebrates and is achieved through the balanced activities of two kinds of specialized bone cells: the bone-forming osteoblasts and the bone-resorbing osteoclasts. Impairment in the remodeling processes dramatically hampers the proper healing of fractures and can also result in malignant bone diseases such as osteosarcoma. MicroRNAs (miRNAs) are a class of small non-coding single-strand RNAs implicated in the control of various cellular activities such as proliferation, differentiation, and apoptosis. Their post-transcriptional regulatory role confers on them inhibitory functions toward specific target mRNAs. As miRNAs are involved in the differentiation program of precursor cells, it is now well established that this class of molecules also influences bone formation by affecting osteoblastic differentiation and the fate of osteoblasts. In response to various cell signals, the tumor-suppressor protein p53 activates a huge range of genes, whose miRNAs promote genomic-integrity maintenance, cell-cycle arrest, cell senescence, and apoptosis. Here, we review the role of three p53-related miRNAs, miR-34c, -125b, and -203, in the bone-remodeling context and, in particular, in osteoblastic differentiation. The second aim of this study is to deal with the potential implication of these miRNAs in osteosarcoma development and progression.

Unintegrated retroviral DNA is transcriptionally silenced by host chromatin silencing factors. Here, we used the proteomics of isolated chromatin segments method to reveal viral and host factors associated with unintegrated HIV-1DNA involved in its silencing. By gene silencing using siRNAs, 46 factors were identified as potential repressors of unintegrated HIV-1DNA. Knockdown and knockout experiments revealed POLE3 as a transcriptional repressor of unintegrated HIV-1DNA. POLE3 maintains unintegrated HIV-1DNA in a repressive chromatin state, preventing RNAPII recruitment to the viral promoter. POLE3 and the recently identified host factors mediating unintegrated HIV-1 DNA silencing, CAF1 and SMC5/SMC6/SLF2, show specificity toward different forms of unintegrated HIV-1DNA. Loss of POLE3 impaired HIV-1 replication, suggesting that repression of unintegrated HIV-1DNA is important for optimal viral replication. POLE3 depletion reduces the integration efficiency of HIV-1. POLE3, by maintaining a repressive chromatin structure of unintegrated HIV-1DNA, ensures HIV-1 escape from innate immune sensing in primary CD4 ⁺ T cells.

Vascular calcification (V) is an independent risk factor for all-cause and cardiovascular mortality. Vascular smooth muscle cells (VSMCs) play a major role in VC as they can acquire mineralizing properties when exposed to osteogenic conditions. Despite its clinical impact, there are still no dedicated therapeutic strategies targeting VC. To address this issue, we used human calcified and non-calcified atherosclerotic arteries (ECLAGEN Biocollection) to screen and identify microRNA (miR) associated with VC. We combined non-biased miRNomic (microfluidic arrays) and transcriptomic analysis to select miR candidates and their putative target genes with expression associated with VC and ossification. We further validated miR functional regulation and function in relation to cell mineralization using primary human VSMCs. Our study identified 12 miRs associated with VC in carotid and femoral arteries. Among those, we showed that miR136, miR155, and miR183 expression were regulated during VSMC mineralization and that overexpression of these miRs promoted VSMC mineralization. Cross-analysis of this miRNomic and a transcriptomic analysis led to the identification of CD73 and Smad3 pathways as putative target genes responsible for mediating the miR155 pro-mineralizing function. These results highlight the potential benefit of miR155 inhibition in limiting VC development in peripheral atherosclerotic arteries.

Unintegrated retroviral DNA are transcriptionally silent by mechanisms involving host chromatin silencing factors1–3. Here, we applied the proteomics of isolated chromatin segments approach (PICh)4 to reveal the proteomic of the linear unintegrated HIV-1 DNA (uniHIV-1 DNA) with the aim of identifying viral and host factors involved in its chromatin-mediated silencing 1–3 . Gene invalidation using siRNAs targeting the 456 candidates selected for their specific binding to HIV-1 DNA identified 46 factors as potential repressors of uniHIV-1 DNA. Knockdown (KD) and Knockout (KO) experiments revealed POLE3, the non-essential subunit of the polymerase epsilon (POLE), as a transcriptional repressor of the linear uniHIV-1 DNA in different cell types including primary CD4 T cells. POLE3 functions by maintaining the uniHIV-1 DNA in chromatin repressed state, preventing RNAPII recruitment to the viral LTR. We found that POLE3 and the recently identified host factors silencing uniHIV-1 DNA (CAF1 and SMC5/SMC6/SLF2) show specificity towards different forms of uniHIV-1 DNA. Unexpectedly, loss of POLE3 impaired HIV-1 replication, suggesting that derepression of unintegrated linear HIV-1 DNA is detrimental to the virus. Loss of POLE3 reduces HIV-1 integration efficiency without affecting viral DNA synthesis. Remarkably, we found that POLE3, by maintaining a repressive chromatin structure of uniHIV-1 DNA, ensures HIV-1 escape from innate immune sensing in primary CD4 T cell.