Remodeling and spacing factor 1 (RSF1): a rising star in DNA repair

Transcriptional regulation and chromatin dynamics at DNA double-strand breaks

In eukaryotic cells, DNA damage can occur at any time and at any chromatin locus, including loci at which active transcription is taking place. DNA double-strand breaks affect chromatin integrity and elicit a DNA damage response to facilitate repair of the DNA lesion. Actively transcribed genes near DNA lesions are transiently suppressed by crosstalk between DNA damage response factors and polycomb repressive complexes. Epigenetic modulation of the chromatin environment also contributes to efficient DNA damage response signaling and transcriptional repression. On the other hand, RNA transcripts produced in the G1 phase, as well as the active chromatin context of the lesion, appear to drive homologous recombination repair. Here, we discuss how the ISWI family of chromatin remodeling factors coordinates the DNA damage response and transcriptional repression, especially in transcriptionally active regions, highlighting the direct modulation of the epigenetic environment.

RSF1 requires CEBP/β and hSNF2H to promote IL-1β-mediated angiogenesis: the clinical and therapeutic relevance of RSF1 overexpression and amplification in myxofibrosarcomas

Myxofibrosarcoma is genetically complex and lacks effective nonsurgical treatment strategies; thus, elucidation of novel molecular drivers is urgently needed. Reanalyzing public myxofibrosarcoma datasets, we identified mRNA upregulation and recurrent gain of RSF1 and characterized this chromatin remodeling gene. Myxofibrosarcoma cell lines were employed to elucidate the oncogenic mechanisms of RSF1 by genetic manipulation and two IL-1β-neutralizing antibodies (RD24, P2D7KK), highlighting the regulatory basis and targetability of downstream IL-1β-mediated angiogenesis. Tumor samples were assessed for RSF1, IL-1β, and microvascular density (MVD) by immunohistochemistry and for RSF1 gene status by FISH. In vivo, RSF1-silenced and P2D7KK-treated xenografts were analyzed for tumor-promoting effects and the IL-1β-linked therapeutic relevance of RSF1, respectively. In vitro, RSF1 overexpression promoted invasive and angiogenic phenotypes with a stronger proangiogenic effect. RT-PCR profiling identified IL1B as a top-ranking candidate upregulated by RSF1. RSF1 required hSNF2H and CEBP/β to cotransactivate the IL1B promoter, which increased the IL1B mRNA level, IL-1β secretion and angiogenic capacity. Angiogenesis induced by RSF1-upregulated IL-1β was counteracted by IL1B knockdown and both IL-1β-neutralizing antibodies. Clinically, RSF1 overexpression was highly associated with RSF1 amplification, IL-1β overexpression, increased MVD and higher grades (all P ≤ 0.01) and independently predicted shorter disease-specific survival (P = 0.019, hazard ratio: 4.556). In vivo, both RSF1 knockdown and anti-IL-1β P2D7KK (200 μg twice weekly) enabled significant growth inhibition and devascularization in xenografts. In conclusion, RSF1 overexpression, partly attributable to RSF1 amplification, contributes a novel proangiogenic function by partnering with CEBP/β to cotransactivate IL1B, highlighting its prognostic, pathogenetic, and therapeutic relevance in myxofibrosarcomas.

aniFOUND: analysing the associated proteome and genomic landscape of the repaired nascent non-replicative chromatin

Specific capture of chromatin fractions with distinct and well-defined features has emerged as both challenging and a key strategy towards a comprehensive understanding of genome biology. In this context, we developed aniFOUND (accelerated native isolation of factors on unscheduled nascent DNA), an antibody-free method, which can label, capture, map and characterise nascent chromatin fragments that are synthesized in response to specific cues outside S-phase. We used the 'unscheduled' DNA synthesis (UDS) that takes place during the repair of UV-induced DNA lesions and coupled the captured chromatin to high-throughput analytical technologies. By mass-spectrometry we identified several factors with no previously known role in UVC-DNA damage response (DDR) as well as known DDR proteins. We experimentally validated the repair-dependent recruitment of the chromatin remodeller RSF1 and the cohesin-loader NIPBL at sites of UVC-induced photolesions. Developing aniFOUND-seq, a protocol for mapping UDS activity with high resolution, allowed us to monitor the landscape of UVC repair-synthesis events genome wide. We further resolved repair efficacy of the rather unexplored repeated genome, in particular rDNA and telomeres. In summary, aniFOUND delineates the proteome composition and genomic landscape of chromatin loci with specific features by integrating state-of-the-art 'omics' technologies to promote a comprehensive view of their function.

gga-miR-99a targets SMARCA5 to regulate Mycoplasma gallisepticum (HS strain) infection by depressing cell proliferation in chicken

Mycoplasma gallisepticum (MG), one of the primary etiological agents of poultry chronic respiratory disease, has caused significant economic losses worldwide, and increasing evidence has recently indicated that miRNAs are involved in its microbial pathogenesis. gga-miR-99a, a member of the miR-99 family, plays an essential role in a variety of diseases. Through miRNA Solexa sequencing, we previously found that gga-miR-99a is significantly down-regulated in the lungs of MG-infected chicken embryos. In this study, we further verified that the expression of gga-miR-99 was significantly down-regulated in both MG-infected lungs and a chicken embryonic fibroblast cell line (DF-1) by qPCR. Moreover, we predicted and validated SMARCA5 as its target gene through a luciferase reporter assay, qPCR, and western blot analysis. The over-expression of gga-miR-99a significantly depressed SMARCA5 expression, whereas a gga-miR-99a inhibitor enhanced the expression of SMARCA5. Inversely, SMARCA5 was significantly up-regulated and gga-miR-99a was obviously down-regulated in MG-HS-infected chicken embryonic lungs and DF-1 cells. At 72h post-transfection, the over-expression of gga-miR-99a significantly repressed the proliferation of DF-1 cells by inhibiting the transition from the G1 phase to the S and G2 phases. This study reveals that gga-miR-99a plays a key role in MG infection through the regulation of SMARCA5 expression and provides new insights regarding the mechanisms of MG pathogenesis.

RSF1 regulates the proliferation and paclitaxel resistance via modulating NF-κB signaling pathway in nasopharyngeal carcinoma

Purpose: Aberrant expression and dysfunction of RSF1 has been reported in diverse human malignancies. However, its exact role in nasopharyngeal carcinoma (NPC) remains unclear.

Methods: The expression of RSF1 mRNA and protein were assayed by qRT-PCR and western blotting, and their correlations with clinicopathological parameters of patients with NPC were further analysed. Lentivirus mediated RSF1 shRNA and RSF1 cDNA were used to knockdown and upregulate the expression of RSF1. CCK8 assays and flow cytometry were applied to monitor the changes of proliferation and paclitaxel sensitivity caused by RSF1 modulation, inhibition of NF-κB pathway by inhibitor Bay 11-7082 and Survivin knockdown. Western blotting was used to detect protein alterations in NF-κB signaling pathway.

Results: Our present study demonstrated that both mRNA and protein expressions of RSF1 were increased and correlated with advanced NPC clinical stage. Functional analyses revealed that RSF1 inhibition or overexpression induced changes in cell cycle, apoptosis, and then led to altered proliferation and paclitaxel sensitivity in diverse NPC cells in vitro. Further mechanism investigation hinted that RSF1 overexpression in NPC CNE-2 cells activated NF-κB pathway and promoted the expression NF-κB dependent genes involved in cell cycle and apoptosis including Survivin. Importantly, inhibition of NF-κB pathway by Bay 11-7082 and knockdown its downstream Survivin reversed the paclitaxel resistance caused by RSF1 overexpression.

Conclusions: Taken together, our data indicate that RSF1 regulates the proliferation and paclitaxel resistance via activating NF-κB signaling pathway and NF-κB-dependent Survivin upregulation, suggesting that RSF1 may be used as a potential therapeutic target in NPC.