RING1B contributes to Ewing sarcoma development by repressing the NaV1.6 sodium channel and the NF-κB pathway, independently of the fusion oncoprotein

Ewing sarcoma (ES) is an aggressive tumor defined by EWSR1 gene fusions that behave as an oncogene. Here we demonstrate that RING1B is highly expressed in primary ES tumors, and its expression is independent of the fusion oncogene. RING1B-depleted ES cells display an expression profile enriched in genes functionally involved in hematological development but RING1B depletion does not induce cellular differentiation. In ES cells, RING1B directly binds the SCN8A sodium channel promoter and its depletion results in enhanced Nav1.6 expression and function. The signaling pathway most significantly modulated by RING1B is NF-κB. RING1B depletion results in enhanced p105/p50 expression, which sensitizes ES cells to apoptosis by FGFR/SHP2/STAT3 blockade. Reduced NaV1.6 function protects ES cells from apoptotic cell death by maintaining low NF-κB levels. Our findings identify RING1B as a trait of the cell-of-origin and provide a potential targetable vulnerability.

Abstract A21: The PRC1 protein RING1B contributes to Ewing sarcoma tumorigenesis by blocking the NaV1.6 sodium channel and modulating the NF-κB pathway, independently of the fusion oncoprotein

Objective: Ewing sarcoma (ES) is an aggressive and poorly differentiated tumor, commonly arising in adolescents and young adults. It is molecularly defined by a reciprocal translocation resulting in the fusion of EWS to an ETS transcription factor, being EWS-FLI the most common chimera. EWS-FLI1 up-regulates gene expression through the interaction with GGAA repeats, however, data obtained by depleting EWS-FLI1 revealed that more genes are down-regulated than up-regulated. A variety of repressive mechanisms have been described including the polycomb group (PcG) of proteins EZH2 and BMI1 that contribute to the epigenetic repressive landscape in ES. We have characterized the expression and function of the PcG RING1B in ES.

Methods: 18 ES primary tissues were evaluated. The intensity of the immunostaining was evaluated and scored for the PcG RING1B, EZH2, MEL18 and BMI1. Western blot quantification was performed using Image J densitometry software. RNA was analyzed by qRT-PCR assays using SYBR Green PCR master mix from Applied Biosystems. ES cell lines (A4573, A673, SK-ES-1, TC71) were grown in standard conditions and treated with DNZep, TSA, SU5402, NSC87877, S3I-201 and BMS-345541 for 24 hours. Mock, RING1B, BMI1, FLI1 and EZH2 shRNA and siRNAs were generated using standard methods. Microarray analysis was performed according to protocols from Ambion and Affymetrix, and hybridized to GeneChip Human Gene 2.0 ST Array (Affymetrix). Each experiment was performed in triplicate at least three times. Statistical analysis was performed using the Student's t-test with a p < 0.05 as significant.

Results: RING1B was highly and universally expressed in all primary ES tumor specimens. In ES cell lines, RING1B mRNA levels were not affected by oncogene down-regulation or treatment with differentiation agents (ATRA; BHA). When RING1B was depleted in ES cell lines by retroviral shRNA, heme biosynthesis and hematopoiesis were 2 of the canonical pathways identified and the set of genes regulated by RING1B unique. Among the most up-regulated genes upon RING1B depletion stand FGF14 and SCN8A. Repression of the 2 components of the NaV1.6 channel was proved specific for RING1B and functionally relevant in ES. Upon RING1B depletion, NF-κB was the most significantly altered pathway identified. Expression of the NF-κB protein p105 (and p50) was found enhanced and RING1B depletion sensitized specifically ES cells to apoptosis by FGFR-SHP2 and STAT3 blockade.

Conclusion: we show that RING1B is pivotal in ES cells, independent of the fusion oncogene, likely reflecting traits of the cell of origin.

Citation Format: Inmaculada Hernandez-Muñoz, Elisabeth Figuerola, Sara Sanchez-Molina, Jaume Mora. The PRC1 protein RING1B contributes to Ewing sarcoma tumorigenesis by blocking the NaV1.6 sodium channel and modulating the NF-κB pathway, independently of the fusion oncoprotein. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Pediatric Cancer Research: From Mechanisms and Models to Treatment and Survivorship; 2015 Nov 9-12; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(5 Suppl):Abstract nr A21.

Human rgr: transforming activity and alteration in T-cell malignancies

We have previously identified the oncogene rgr (ralGDS related) in DNA derived from a rabbit squamous cell carcinoma. Here we describe the identification of the human orthologue of the rabbit rgr gene termed hrgr (human ralGDS related). Four alternatively spliced full-length hrgr transcripts were isolated from normal human testes and liver libraries. Truncation of hrgr confers transforming ability to its cDNA. Using a RT-PCR assay we have been able to detect the expression of an abnormally truncated transcript in several human T-cell lymphoma lines, and in fresh tissue samples of patients with T-cell malignancies. In the DHL cell line, an Anaplastic Large Cell Lymphoma (ALCL) line, a DNA rearrangement was detected within the hrgr gene region. We propose that these T-cell lymphomas, at least in part, owe their malignant phenotypes to genetic alterations of the hrgr gene. These findings also raise the possibility that mutations in the hrgr gene are involved in other malignancies.

The Rgr oncogene (homologous to RalGDS) induces transformation and gene expression by activating Ras, Ral and Rho mediated pathways

The effects of the 5'-truncated Rgr oncogene, a previously shown specific guanine exchange factor for Ral in vitro, in stimulating proliferation, cell transformation and gene expression were investigated. We have established TetRgr cell lines in which expression of Rgr can be inhibited by the presence of tetracycline in the medium. Using this system, we show that Rgr overexpressing cells are morphologically transformed and grow in a disorganized manner. At the transcriptional level, Rgr enhances the activity of the serum response element and c-Jun. Rgr induces phosphorylation of ERKs, p38 and JNK kinases, and increases the levels of the GTP-bound forms of Ral and Ras. Ras activation could account for the broad spectra of effects displayed by Rgr. The important role of these pathways is confirmed by experiments in which the transcriptional activation events can be blocked by dominant negative versions of Ras, Ral and Rho. Among all the Rgr-induced pathways, the Ras-Raf-MEK-ERK cascade is essential for the transforming properties of Rgr. Additional analysis has shown that the activation of this pathway by Rgr is not due to a feed back mechanism mediated by the Grb2 adaptor protein. Oncogene (2000).

Diminished cytochrome b content and toxic oxygen metabolite production in circulating neutrophils from patients with Crohn's disease

Phagocytic, chemotactic, and oxidative metabolic capacity of circulating neutrophils was studied in 20 patients with Crohn's disease. In vitro tests of chemotaxis and phagocytosis of isolated neutrophils from patients did not differ from that of healthy controls. However, superoxide anion production by phorbol-myristate-acetate and formylmethionyl-leucyl-phenylalanine-stimulated neutrophils from patients with Crohn's disease was significantly diminished compared with controls. Measurement of cytochrome b559 in total membranes of neutrophils from patients showed that it was significantly lower than in controls. Disease activity did not correlate either with the production of superoxide anion or with the cytochrome b559 content. It is concluded that oxidative metabolism is impaired in neutrophils from patients with Crohn's disease and that this defect could be caused by a reduced content in membrane b-type cytochrome. Although this defective neutrophil function may contribute to granuloma formation, other factors have to be implicated in disease inflammatory activity.