Transcriptional Profiling Supports the Notochordal Origin of Chordoma and Its Dependence on a TGFB1-TBXT Network.

Chordoma is a rare malignant tumor demonstrating notochordal differentiation. It is dependent on brachyury (TBXT), a hallmark notochordal gene and transcription factor, and shares histologic features and the same anatomic location as the notochord. This study involved a molecular comparison of chordoma and notochord to identify dysregulated cellular pathways. The lack of a molecular reference from appropriate control tissue limits our understanding of chordoma and its relationship to notochord. Therefore, an unbiased comparison of chordoma, human notochord, and an atlas of normal and cancerous tissue was conducted using gene expression profiling to clarify the chordoma/notochord relationship and potentially identify novel drug targets. The study found striking consistency in gene expression profiles between chordoma and notochord, supporting the hypothesis that chordoma develops from notochordal remnants. A 12-gene diagnostic chordoma signature was identified and the TBXT/transforming growth factor beta (TGF-ß)/SOX6/SOX9 pathway was hyperactivated in the tumor, suggesting that pathways associated with chondrogenesis were a central driver of chordoma development. Experimental validation in chordoma cells confirmed these findings and emphasized the dependence of chordoma proliferation and survival on TGF-ß. The computational and experimental evidence provided the first molecular connection between notochord and chordoma and identified core members of a chordoma regulatory pathway involving TBXT. This pathway provides new therapeutic targets for this unique malignant neoplasm and highlights TGF-ß as a prime druggable candidate.

RXRα Regulates the Development of Resident Tissue Macrophages.

Resident tissue macrophages (RTMs) develop from distinct waves of embryonic progenitor cells that seed tissues before birth. Tissue-specific signals drive a differentiation program that leads to the functional specialization of RTM subsets. Genetic programs that regulate the development of RTMs are incompletely understood, as are the mechanisms that enable their maintenance in adulthood. In this study, we show that the ligand-activated nuclear hormone receptor, retinoid X receptor (RXR)α, is a key regulator of murine RTM development. Deletion of RXRα in hematopoietic precursors severely curtailed RTM populations in adult tissues, including the spleen, peritoneal cavity, lung, and liver. The deficiency could be traced to the embryonic period, and mice lacking RXRα in hematopoietic lineages had greatly reduced numbers of yolk sac and fetal liver macrophages, a paucity that persisted into the immediate postnatal period.

Cytocidal activities of topoisomerase 1 inhibitors and 5-azacytidine against pheochromocytoma/paraganglioma cells in primary human tumor cultures and mouse cell lines.

There is currently no effective treatment for metastatic pheochromocytomas and paragangliomas. A deficiency in current chemotherapy regimens is that the metastases usually grow very slowly. Drugs that target dividing tumor cells have therefore had limited success. To improve treatment, new strategies and valid experimental models are required for pre-clinical testing. However, development of models has itself been hampered by the absence of human pheochromocytoma/paraganglioma cell lines for cultures or xenografts. Topoisomerase 1 (TOP1) inhibitors are drugs that interfere with mechanisms that maintain DNA integrity during transcription in both quiescent and dividing cells. We used primary cultures of representative human tumors to establish the cytotoxicity of camptothecin, a prototypical TOP1 inhibitor, against non-dividing pheochromocytoma/paraganglioma cells, and then employed a mouse pheochromocytoma model (MPC) to show that efficacy of low concentrations of camptothecin and other TOP1 inhibitors is increased by intermittent coadministration of sub-toxic concentrations of 5-azacytidine, a DNA methylation inhibitor that modulates transcription. We then tested the same drugs against a clonal MPC derivative that expresses CMV reporter-driven luciferase and GFP, intended for in vivo drug testing. Unexpectedly, luciferase expression, bioluminescence and GFP expression were paradoxically increased by both camptothecin and SN38, the active metabolite of irinotecan, thereby masking cell death. Expression of chromogranin A, a marker for neuroendocrine secretory granules, was not increased, indicating that the drug effects on levels of luciferase and GFP are specific to the GFP-luciferase construct rather than generalized cellular responses. Our findings provide proof of principle for use of TOP1 inhibitors against pheochromocytoma/paraganglioma and suggest novel strategies for enhancing efficacy and reducing toxicity by optimizing the combination and timing of their use in conjunction with other drugs. The paradoxical effects of TOP1 inhibitors on luciferase and GFP dictate a need for caution in the use of CMV promoter-regulated constructs for cancer-related imaging studies.

Expression of an anti-RNA autoantibody in a mouse model of SLE increases neutrophil and monocyte numbers as well as IFN-I expression.

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the presence of antinucleic acid autoantibodies, high levels of circulating type I interferon (IFN-I), and an IFN-I-dependent elevated expression of activating FcγR. Increases in neutrophils and monocytes are often observed in clinical SLE, but how these contribute to autoantibody and IFN-I production is poorly understood. Here, we analyzed SLE pathogenesis in 564Igi mice, an SLE-model strain carrying gene-targeted heavy and light chain antibody genes encoding an anti-RNA autoantibody in a C57BL/6 background. Similar to human SLE patients, 564Igi mice produce anti-RNA autoantibodies and expanded neutrophil and monocyte populations. These myeloid cells produced IFN-I and exhibit increased FcγRIV expression induced via an IFN-I autocrine loop. A direct effect of IFN-I on 56 Igi BM B cells and neutrophils was supported by their upregulation of "IFN-I signature genes". In addition, 564Igi developing B cells showed upregulated TLR7 resulting in IgG2a/2b class switch recombination and autoantibody production. Our results indicate that the production of anti-RNA autoantibody is sufficient to induce an increase of BM, blood, and spleen IFN-I-producing neutrophils, and suggest a mechanism by which autoantibody and IFN-I contribute to SLE by activating B lymphocytes, neutrophils, and monocyte effector cells in vivo.